[Executive Summary]   [Introduction]   [Geographical Background]   [Upper Paraguay River]   [Environmental Impact]   [Summary]   [References]     


HYDROLOGIC AND ENVIRONMENTAL IMPACT

OF THE PARANÁ-PARAGUAY WATERWAY

ON THE PANTANAL OF MATO GROSSO, BRAZIL


A Reference Study


Victor Miguel Ponce

San Diego State University


[August 1995]

Online version August 2015

[Versão em Portugués]


EXECUTIVE SUMMARY
[Introduction]   [Geographical Background]   [Upper Paraguay River]   [Environmental Impact]   [Summary]   [References]      [Top]  

The hydrologic and environmental impacts that the proposed Hidrovia navigation project would have on the Pantanal of Mato Grosso are evaluated in this report. The Pantanal is a seasonally inundated depression, characteristically a wetland (or closely related group of wetlands), wholly contained within the Upper Paraguay river basin. It encompasses an area of 136,700 km2 in the states of Mato Grosso and Mato Grosso do Sul, in Central Western Brazil. The Hidrovia project entails navigational improvements along the existing Paraná-Paraguay Waterway, which links five countries of South America: Argentina, Bolivia, Brazil, Paraguay, and Uruguay. The project considers extensive river engineering works, including channel straightening, dredging, blasting of rocky sills, and other structural interventions to render 3,442 km of the river navigable for ocean-going vessels. The affected region would be from the downstream point at Nueva Palmira, Uruguay, to the upstream point at Cáceres, Brazil, near the headwaters of the Upper Paraguay river. At issue is the impact that extensive channel modifications will have on the Pantanal, the largest remaining wetland in the world.

The proposed navigational improvements are likely to have a substantial impact on the flood regime of the Upper Paraguay river. The degree of the impact will vary depending on the type and extent of intervention and location along the river. In particular, channel straightening upstream of Corumbá will accelerate the concentration of flood runoff and increase the flood wave peak at Ladario, a key reference point in the Pantanal, during high mean (2-yr), extraordinary (4-yr), and exceptional (10-yr) floods. The Upper Paraguay river upstream of Porto São Francisco (located 146 km upstream of Corumbá) is incapable, without extensive artificial channel deepening, of accommodating ocean-going vessels (requiring a 3-m draft) throughout the year. Currently, autodredging, the river's natural self-cleaning/deepening process, provides a minimum depth of 1.2 m, except where rock outcrops do not permit autodredging to take place.

The longitudinal profile of the Upper Paraguay river is convex when observed from above, revealing the presence of substantial geologic controls. These controls operate in the form of rock outcrops on the banks or rocky sills in the middle of the channel. The Pantanal exists largely because of these geologic controls, which influence the regional flow patterns in at least three places: Amolar, Porto da Manga and Fecho dos Morros. The rocky sills act as natural dams; if they are removed, extensive areas of Pantanal will no longer be subject to seasonal flooding. Blasting rocky sills as a means of deepening the navigation channel will have an irreversible impact on the hydrology of the Upper Paraguay river. Furthermore, the removal of one rocky sill may lead to the appearance of another rocky sill which was previously submerged. This is a distinct possibility in the Upper Paraguay river, where rock outcrops have been documented to occur every 40 km on the average, and where the prevailing channel slopes are so mild (around 1-2 cm/km) that the backwater effect of a 0.5-m flow obstruction can be felt for about 400 km upstream.

The acceleration of runoff concentration caused by navigational improvements will intensify most annual floods, may reduce the recurrence interval of multiannual droughts, and may eventually lead to regional climatic changes in the direction of greater aridity. The Pantanal exists because its climatic/geologic/geomorphologic setting conditions it to retain water, sediment, and nutrients. Increases in flood magnitude will result in increased losses of sediment and nutrients.

The annual flooding of extensive areas of Pantanal serves the dual purpose of effectively controlling overgrazing while replenishing the soil with nutrients. In addition, the seasonal flood pulse is instrumental in maintaining the extensive grasslands, since competing vegetation types, particularly the woody species, are not well adapted to extreme alternations of saturation and desiccation.

Changes in hydrologic regime resulting in increased intensity of floods and droughts will impair nutrient replenishment in the Pantanal and lead to decreases in biotic productivity. These changes will produce a succession from herbaceous to woody species, which will eventually change the dominant character of the Pantanal, from savanna woodlands to more mesic forests. The open grasslands will shrink, and the cattle raising industry will be negatively impacted.



1.  INTRODUCTION
[Geographical Background]   [Upper Paraguay River]   [Environmental Impact]   [Summary]   [References]      [Top]   [Executive Summary]  

The Pantanal of Mato Grosso is a seasonally inundated depression wholly contained within the Upper Paraguay river basin. It encompasses 136,700 km2 in the states of Mato Grosso and Mato Grosso do Sul, in Central Western Brazil. The Pantanal is an immense and biologically diverse wetland, geomorphologically and hydrologically positioned to attenuate and reduce the runoff from the Upper Paraguay river basin.

The proposed Paraná-Paraguay Waterway Project, commonly known as the Hidrovia Project, entails navigational improvements along the existing Paraná-Paraguay waterway, which links five countries in South America: Argentina, Bolivia, Brazil, Paraguay, and Uruguay. Engineering and environmental impact studies are currently (1996-97) being funded by the Inter-American Development Bank (IDB) and the United Nations Development Programme (UNDP). Funding for the construction of the project may be considered at a later date.

An economic feasibility study completed by the Brazilian company Internave serves as a reference for the ongoing studies (INTERNAVE, 1990). The Internave study considers extensive river engineering works--including channel straightening, dredging, and blasting of rock outcrops--to render 3,442 km of the river navigable for ocean-going vessels from Nueva Palmira, Uruguay, to Cáceres, Mato Grosso, Brazil. Since the port of Cáceres is located upstream of the Pantanal, it is expected that the project will have an impact on the Pantanal.

The physical aspects of the proposed Hidrovia are the source of significant concern among indigenous peoples, environmental organizations, nongovernmental organizations (NGOs), professional associations, and universities and research institutions in Mato Grosso, Mato Grosso do Sul, Brazil, the American continent, and the rest of the world. At issue is the impact that extensive channel modifications, which would include channel straightening and deepening, will have on the Pantanal, the largest remaining wetland in the world (Alho et al., 1988). The uniqueness of the Pantanal ecosystems is widely recognized, and the need for their preservation on both intrinsic and economic grounds has been amply discussed in scientific, governmental, and political forums (EMBRAPA, 1986; Brazilian Constitution, 1988).

The Pantanal of Mato Grosso is characteristically a wetland (Fig. A1). Therefore, a study of the impact of the proposed project should start with the hydrologic cycle, from which all the other cycles of nature (uplift/denudation, sediment, nutrient, and biogeochemical cycles) derive. Thus, this study focuses on the hydrologic impacts of the proposed Hidrovia project on the Pantanal of Mato Grosso. Other environmental impacts, directly or indirectly related to the hydrologic impacts, are also considered.

The complexity of the Pantanal ecosystems does not permit a definitive study, particularly since their myriad of abiotic/biotic interrelations are only now being thoroughly examined. Moreover, the main features of the project (the location, nature and extent of human interventions in the river) are still in the process of being defined. Thus, this report is subtitled:  A Reference Study. As such, it should serve as a reference for professionals in government, funding agencies, consulting firms, nongovernmental organizations, and universities, and others interested in reconciling human needs with the workings of nature in the context of the Pantanal.

Fig. A1  The Pantanal of Mato Grosso, Brazil.
 The Pantanal of Mato Grosso Please request username/password from:  ponce.sdsu.edu


2.  GEOGRAPHICAL BACKGROUND
[Upper Paraguay River]   [Environmental Impact]   [Summary]   [References]      [Top]   [Executive Summary]   [Introduction]  

This section establishes the geographical background for this study. It is divided into four subsections:

  1. The Paraná-Paraguay River Basin

  2. The Paraguay and Upper Paraguay River Basins

  3. The Pantanal of Mato Grosso

  4. The Paraná-Paraguay Waterway (Hidrovia) Project.

This study focuses on the impact of the proposed Paraná-Paraguay waterway project on the Pantanal of Mato Grosso, which lies within the Paraguay river basin, a major tributary of the Paraná-Paraguay basin system.


2.1  The Paraná-Paraguay River Basin

The Paraná-Paraguay river basin is the most important of the La Plata basin system, in terms of both discharge (75%) and catchment area (84%) (Bonetto, 1975). The La Plata system is the second largest in South America, after the Amazon.

The Paraná-Paraguay basin drains an extensive region encompassing 2,605,000 km2 in Brazil, Argentina, Paraguay, and Bolivia (Fig. 1). As its name indicates, it is composed of two major rivers: the Paraná and the Paraguay. The Paraná is the largest of the two, draining 1,510,000 km2 (58%). The Paraguay river, draining the remaining 1,095,000 km2, is the most important tributary of the Paraná.

Fig. 1  Geographical location of Paraná and Paraguay rivers.

The geographical distribution of the Paraná river basin is the following: 59% in Brazil, 37.4% in Argentina, and 3.6% in Paraguay. The geographical distribution of the Paraguay river basin is: 33.4% in Brazil, 33.3% in Paraguay, 16.7% in Argentina, and 16.7% in Bolivia (Anderson et al., 1993). The combined Paraná-Paraguay river basin drains substantial portions of these four South American countries (Fig. 1). The Paraná river is divided into three sections (Bonetto, 1975):

  1. The Upper Paraná, from the headwaters of the Paraná river in the vicinity of Brasilia, Brazil, to the confluence with the Paraguay river.

  2. The Middle Paraná, from the confluence with the Paraguay river to the port of Diamante, near Santa Fé, Argentina, a distance of nearly 700 km.

  3. The Lower Paraná, from Diamante to the estuary of the Rio de la Plata, a distance of approximately 400 km.


2.2  The Paraguay and Upper Paraguay River Basins

The headwaters of the Paraguay river basin are located in the Serra de Tapirapuã, in the proximity of Vila de Parecis, in the state of Mato Grosso, Brazil (EDIBAP, 1979). After flowing in a general southern direction for a distance of about 2,800 km, the Paraguay river reaches the Paraná at Confluencia, north of the Argentinian cities of Corrientes and Resistencia (Fig. 1).

The Paraguay river is divided into three sections (Anderson et al., 1993):

  1. The Upper Paraguay, flowing through Brazil, Bolivia, and Paraguay, from its headwaters to the confluence with the Apa river, a distance of 1,873 km.

  2. The Middle Paraguay, flowing through Paraguay and Argentina, from the confluence with the Apa river to the confluence with the Tebicuary river, a distance of 797 km.

  3. The Lower Paraguay, flowing through Paraguay and Argentina, from the confluence with the Tebicuary river to the confluence with the Paraná river, a distance of 130 km.

The Pilcomayo and Bermejo rivers, tributaries of the Middle and Lower Paraguay, respectively, descend from the Andes to the West (Fig. 1). Likewise, the eastern tributaries of the Middle and Lower Paraguay flow over hilly terrain. The rest of the Paraguay river basin comprises an immense inland plain, with extremely flat relief. This peculiar geomorphologic setting has led to the existence of the Pantanal of Mato Grosso, an extensive group of wetlands located wholly within the confines of the Upper Paraguay river basin (Tricart, 1982).

The Upper Paraguay river is the upstream section of the Paraguay river, from its headwaters to the confluence with the Apa river (Fig. A2). The latter marks the border between Brazil (to the north) and Paraguay (to the south). The Upper Paraguay river basin contains the Pantanal of Mato Grosso and its headwaters, wholly within Brazilian territory, and portions of Eastern Bolivia and Northwestern Paraguay. While the precise western limits of the basin are uncertain (the Bañados de Izogog, in Eastern Bolivia), the northern and eastern limits are delimited by mountain ranges, all within Brazil. To the East, the basin is limited by the Maracaju, Caiapó, and Saudade ranges; to the North by the Parecis range, and partly by the Azul range. The basin lies between 14° and 23°S, and 53° and 60°W (Fig. 2).

Fig. A2  Confluence of the Upper Paraguay river with the Apa river, Mato Grosso do Sul.

Fig. 2  The Upper Paraguay river basin and Pantanal of Mato Grosso
(EDIBAP, 1979; Projeto RADAMBRASIL, 1982a&b).

The Upper Paraguay river basin comprises 496,000 km2, in two distinct regions (DNOS, 1974):

  1. The area east (left margin) of the Paraguay and Jauru rivers, wholly within Brazilian territory, encompassing 336,000 km2; half of this area is above the altitude of 200 m.

  2. The area west (right margin) of the Paraguay and Jauru rivers, encompassing 160,000 km2, of which 145,000 km2 are in Bolivian and Paraguayan territory, and the remaining 15,000 km2 are in Brazil; 19% of this area (31,000 km2) is above the altitude of 200 m.

The principal tributaries of the Upper Paraguay river are the following (Fig. 2):

  • Sepotuba,

  • Cabaçal,

  • Jauru,

  • Cuiabá, and its tributaries São Lourenço and Piquiri-Itiquira,

  • Taquari, and

  • Miranda, and its tributary the Aquidauana.

Other tributaries, primarily intermittent, include the Negro, Aquidabã, Branco, Tereré, and Amonguijá. All these are left-bank tributaries, located wholly within Brazil.

For reference purposes, Table 1 shows selected hydrographic characteristics of the Upper Paraguay river. Table 2 shows selected hydrologic data at gaging stations along the Upper Paraguay river (Fig. 3). Table 3 shows valley slopes along the Upper Paraguay river and its major tributaries.

Fig. 3  Location of gaging stations along Upper Paraguay river and tributaries (DNOS, 1974).

Table 1 shows that the Upper Paraguay river is quite sinuous, particularly upstream of Corumbá, where the sinuosity, i.e., the ratio of river length to valley length, can be quite high. For instance, the reach from 40 km downstream of Porto Conceição to Refúgio das Três Bocas, where the sinuosity is: (161 km)/(55 km) = 2.92. The influence of sinuosity on proposed navigational improvements is analyzed in Section 4.1.1.

Table 1.  Selected hydrographic characteristics of the Upper Paraguay river.1
From To Length2 Length3 Width4 Adjacent flooded area5,6
(sinuous)
(km)
(straight)
(km)
(low flow)
(m)
(low flow)
(km2)
(high flow)
(km2)
(others)
(km2)
Barra do Bugres Cáceres 280 122 100 30 200 20-150
Cáceres Confluence with Rio Jauru 71 33 150 8 120 -
Confluence with Rio Jauru Curve u/s of Descalvados 35 31 200 10 100 -
Curve u/s of Descalvados Boca do Bracinho 46 28 250 10 90 -
Boca do Bracinho Barra do Bracinho 63 30 120 - - 330
Barra do Bracinho 40 km d/s of Porto Conceição 83 41 150 - - 14007
40 km d/s of Porto Conceição Refúgio das Três Bocas 161 55 80-200 - - 14007
Refúgio das Três Bocas Amolar 29 18 300-400 - - 50
Amolar Confluence with Riacho da Mandioré 46 30 300-500 280 700 600
Confluence with Riacho da Mandioré Porto São Francisco 14 8 300-500 - 50 70
Porto São Francisco Corumbá 146 71 300-400 76 280 410
Corumbá Confluence with Taquari Velho 41 35 300 15 120 50
Confluence with Taquari Velho Porto Esperança 100 63 250-400 30 390 300
Porto Esperança Confluence with Rio Negro 126 97 300-450 50 450 -
Confluence with Rio Negro Barra do Nabileque 162 92 300-500 50 400 -
Barra do Nabileque Confluence with Rio Apa 174 128 350-600 90 700 -
1 Source:  DNOS (1974) and DNAEE. 2 Along the river. 3 In a straight line. 4 Inbank flow channel width.
5 Flooded area adjacent to mainstem river, in low flow, high flow, and other neighboring areas.
6 Estimated during drought period 1966-73. 7 Shared.

Table 2 shows that the difference between maximum and minimum observed water levels along the Upper Paraguay river is smallest at Descalvados (2.61 m), remaining small (less than 3.5 m) for about 200 km downstream (at Porto Conceição it is 3.28 m; at Bela Vista do Norte it is 3.27 m). This indicates the presence of substantial channel overflows in the Upper Paraguay river between Descalvados and Bela Vista do Norte.

Table 2.  Selected hydrologic data at gaging stations along the Upper Paraguay river.1
Station Drainage area 3 Zero of gage 4 Observed water levels
(km2) (m) Minimum (m) Maximum (m) Difference (m)
Alto Paraguay 780 - 0.30 4.00 3.70
Barra dos Bugres 10,240 - 0.28 5.54 5.26
Porto Estrela 12,770 - 0.95 6.18 5.23
Cáceres 33,860 109.34 0.75 4.792 4.04
Descalvados 48,360 98.70 2.30 4.91 2.61
Porto Conceição - 91.48 2.07 5.356 3.28
Bela Vista do Norte - 87.48 2.32 5.592 3.27
Refúgio das Trés Bocas - 84.65 3.4 8.506 5.01
Amolar - 85.46 2.17 7.022 4.85
Porto São Francisco 243,0005 83.06 2.06 8.256 6.19
Ladario - 82.15 -0.61 6.62 7.23
Porto da Manga 316,0005 78.58 1.54 9.067 7.52
Porto Esperança 363,5005 79.66 -1.30 5.956 7.25
Forte Coimbra - 78.90 -1.99 4.672 6.66
Barranco Branco 453,000 72.45 0.19 7.846 7.65
Fecho dos Morros 470,000 71.75 0.03 6.372 6.34
Porto Murtinho 474,500 70.75 0.73 7.75 7.02
1 Source:  DNOS (1974) and DNAEE. 2 Source: Hidrologia S.A.(unpublished).
3 If not shown, drainage area is not precisely definable. 4 Unavailable if not shown. 5 Small portion cannot be precisely defined.
6 Maximum known (1959 flood water mark). 7 Maximum known (1905 flood water mark).

Table 3 shows that valley slopes in the Upper Paraguay river basin decrease gradually, from 15-50 cm/km close to the mountains to the north, east, and south, to 7-15 cm/km along the major tributaries, and to 0.7-6.5 cm/km along the Upper Paraguay river. This reveals that the Upper Paraguay river constitutes a regional base level for the flow of its eastern tributaries.

Table 3.  Valley slope along the Upper Paraguay river and major tributaries.1
Stream From To Valley slope
(cm/km)
Upper Paraguay Descalvados Porto São Francisco 5.0
Porto São Francisco Porto da Manga 6.5
Porto da Manga Barra do Nabileque 2.6
Barra do Nabileque Porto Murtinho 0.7
Cuiabá Retiro Biguaçal Confluence with Rio Piquiri 7
Confluence with Rio Piquiri Porto Alegre 11
Porto Alegre Confluence with Rio Paraguay 8
São Lourenço Saída do Vale São José do Borireu 45
São José do Borireu Foz do Dois Irmãos 12
Piquiri Confluence Itiquira-Correntes Confluence with Rio Pindaíval 20
Confluence with Rio Pindaíval Confluence with Rio Cuiabá 18
Taquari Coxim São Gonçalo 45
São Gonçalo Porto Rolon 32
Porto Rolon Porto da Manga 17
Aquidauana Aquidauna Porto Ciríaco 36
Porto Ciríaco Confluence with Rio Miranda 17
Miranda Estrada MT-738 Miranda 50
Miranda Tição de Fogo 32
Tição de Fogo Confluence with Rio Paraguay 15
1 Source:  DNOS (1974).


2.3  The Pantanal of Mato Grosso

The Pantanal of Mato Grosso is a seasonally inundated depression wholly contained within the Upper Paraguay river basin, encompassing approximately 136,700 km2 (Projeto RADAMBRASIL, 1982a&b). The Pantanal is geomorphologically and hydrologically positioned to attenuate and reduce the runoff from the basin. Tricart (1982) has stated that the mountains to the south of the Pantanal "strangle" the valley of the Upper Paraguay river close to the location where it exits Brazilian territory. Significantly, this geomorphic feature is referred to locally as Fecho dos Morros, literally, "closing of the hills." (Fig. A3). The Pantanal is a huge natural reservoir receiving distributed inflows from the Upper Paraguay river and its tributaries, and concentrating runoff at the basin outlet, the Apa river confluence, about 100 km downstream of Fecho dos Morros.

Fig. A3  Aerial view of the Upper Paraguay river at Fecho dos Morros, Mato Grosso do Sul (Google Earth®).

Large portions of the Pantanal are flooded only during the annual crest of the Upper Paraguay river and its tributaries, and much nonflooded terra firma is interspersed throughout the region. The mixture of permanent swamp, seasonal swamp, and nonflooded land, as well as the contiguity of the Pantanal to major South American biomes (the humid Amazon rainforest to the north and northwest, the subhumid savannas of Central Brazil to the east, the humid Atlantic forest to the southeast, and the semiarid scrub forest of neighboring Bolivia and Paraguay to the west and southwest) have conditioned the richness and variety of its vegetation and climate (Prance and Schaller, 1982). In turn, the Pantanal ecosystems support a rich and diverse fauna, including numerous species of mammals, reptiles, fish, birds, butterflies, and other invertebrates (Brown, 1986).

The name Pantanal of Mato Grosso tends to hide the fact that the depression of the Upper Paraguay basin consists of not one but several seasonally flooded regions, quite distinct from each other; thus, the Portuguese name Planícies e pantanais matogrossenses, which stands for "Plains and swamps of Mato Grosso" (Fig. A4).

The following pantanais were identified by Projeto RADAMBRASIL (1982a&b) (Fig. 4): Corixo Grande-Jauru-Paraguay, (2) Cuiabá-Bento Gomes-Paraguaizinho, (3) Itiquira-São Lourenço-Cuiabá, (4) Paiaguás, (5) Taquari, (6) Jacadigo-Nabileque, (7) Miranda-Aquidauana, (8) Negro, (9) Tarumã-Jibóia, (10) Aquibadã, (11) Branco-Amonguijá, and (12) Apa.

Alternatively, Adámoli (1981) has classified the Pantanal of Mato Grosso into ten pantanais: (1) Cáceres, (2) Poconé, (3) Barão de Melgaço, (4) Paiaguás, (5) Nhecolândia, (6) Aquidauana, (7) Paraguay, (8) Miranda, (9) Nabileque, and (10) Abobral.

Fig. 4  Plains and swamps of Mato Grosso (Planícies e pantanais Matogrossenses)
(Projeto RADAMBRASIL, 1982a&b).

Fig. A4  The Pantanal of Mato Grosso near Corumbá, Mato Grosso do Sul.

The peculiar characteristics of the pantanais have led to the use of regional terminology to describe its most salient geomorphic features, namely baías, baixadas, barreiros, salinas, córregos, capões, cordilheiras, vazantes, and corixos. A brief description of each follows.

  • The baías are low-lying areas of circular, semicircular, or irregular shape, which have standing water, sometimes saline; their linear dimensions vary from tens to hundreds of meters.

  • The baixadas are portions of the baías subject to seasonal inundation (Silva, 1990).

  • The barreiros are baías that have seasonal or periodic water (Valverde, 1972).

  • The salinas are lakes with saline water; they are covered during the dry season with salt crusts, and are for the most part unconnected from the seasonally flooded baías (Silva and Pinto-Silva, 1989) (Fig. A5).

  • The córregos are small watercourses (Carvalho, 1986).

  • The capões are vegetated earthmounds, of various sizes, and approximately circular or elliptical in shape (Ponce and Cunha, 1993).

  • The cordilheiras are slight terrain elevations located between the baías, with mean elevations about 2-3 m above the water level in the baías. While they are normally dry, they are subject to inundation during exceptional floods. They serve as high areas for the location of cattle ranches, and as refuge for livestock during extraordinary and exceptional floods.

  • The vazantes are large depressions situated between the cordilheiras, lacking a clearly defined channel (Carvalho, 1986). During the flood season, these depressions drain intermittent streams, extending for several kilometers. However, many vazantes are perennial, revealing the presence of substantial amounts of subsurface flow.

  • The corixos, unlike the vazantes, are small permanent watercourses connecting adjacent baías with narrower and much deeper channels. When the corixo is long and has a well defined cross section, it is referred to as corixão (Carvalho, 1986).

The characteristics of the several pantanais that constitute the Pantanal of Mato Grosso are described by Projeto RADAMBRASIL (1982a&b) and Silva (1986). The soils and inundation patterns (flooding levels) of the Pantanal are described by Projeto RADAMBRASIL (1982a&b) and Amaral Filho (1986).

Fig. A5  Aerial view of salinas near the Rio Negro, Mato Grosso do Sul (Google Earth®).

2.4  The Paraná-Paraguay Waterway (Hidrovia) Project

The Paraná-Paraguay river basin system is an extensive region in South America, which lies within the countries of Argentina, Bolivia, Brazil, and Paraguay. The neighboring Uruguay river drains portions of Argentina, Brazil, and Uruguay. The confluence of these two rivers is near the city of Nueva Palmira, Uruguay (Fig. 1). The Paraná-Paraguay and Uruguay rivers are the major tributaries of the La Plata basin system.

The Paraná-Paraguay basin is home to a population of almost 20 million people. For centuries, this river system has been used as a waterway for transportation. In February 1995, the IDB and the UNDP commissioned an eighteen-month series of engineering and environmental impact studies to evaluate potential navigational improvements to the exist ing waterway. This study includes the possibility of extensive engineering works to render 3,442 km of the river navigable for ocean-going vessels, from Nueva Palmira to Cáceres, Brazil. Since the port of Cáceres is located upstream of the Pantanal of Mato Grosso, the short- and long-term impacts of the proposed navigational improvements on the Pantanal should be clearly established prior to project implementation.

The project is commonly referred to as the Hidrovia project, since "Hidrovia" means waterway in both Spanish and Portuguese. The stated purposes of the Hidrovia project are to enhance current river transport via improvements to existing port, channel, and navigation facilities and to construct a year-round navigable waterway along the 3,442 km. These efforts are being planned in two stages:

Phase 1 (Module A): Short-term intervention

This phase entails the improvement in navigational aids and the required river engineering, including dredging and related works, along 80% of the proposed project's length. The affected region extends from the downstream port of Nueva Palmira, upstream to the port of Corumbá/Ladario, in Brazil, and neighboring Puerto Quijarro, in Bolivia.

Phase 2 (Module B): Medium- and long-term intervention

This phase entails the improvement in navigational aids and the required river engineering, including dredging, channel modification, and other major river interventions, along the entire length of the proposed project (3,442 km), from Nueva Palmira to Cáceres.

The executive agency for the Hidrovia project is the Comité Intergubernamental de la Hidrovia (CIH) (Intergovernmental Committee of the Waterway), established in 1989 by the Ministers of Public Works and Transport of Argentina, Bolivia, Brazil, Paraguay, and Uruguay. The headquarters of the CIH is in Buenos Aires, Argentina.

To date (1995), the only comprehensive document with enough detail on the Hidrovia project is the Internave report, commissioned by the extinct Empresa de Portos do Brasil (PORTOBRAS), and completed in 1990 by the Brazilian company of the same name (INTERNAVE, 1990). This report is basically an economic feasibility study of the Hidrovia project. As such, it uses projections of economic benefits to justify the costs involved in project implementation.

The Internave report has been criticized for its overly optimistic projections of benefits (CEBRAC/ICV/WWF, 1994). The IDB has formally rejected the Internave study and will use the Phase 2 feasibility study, currently under execution, to recalculate cost and benefits (Lammers et al., 1994). However, the physical descriptions contained in the Internave report, which include channel straightening, dredging, blasting of rock outcrops and other structural interventions in the river, some of them irreversible, have remained the cause for significant concern among diverse segments of the local, national and international communities. These include environmental organizations, nongovernmental organizations (NGO's), professional associations, and universities and scientific research institutions in Brazil, the American continent, and the rest of the world.

Channel straightening by realignment and cutoffs, dredging, and blasting of rocky sills are being considered to improve navigational conditions along the waterway. In particular, the Terms of Reference of the Phase 2 (Module B-1) engineering study, under Section 1-Purpose, states the following task (No. 4), among seven others (IDB, 1995, p. 2):

"The development of a preliminary project of alternatives to improve the conditions of the waterway, including dredging, blasting of rocky sills, channel straightening, stabilization of the navigation channel, regularization of the water resources, and any navigational structure that is considered pertinent."

The extent of these interventions and their possible impact on the hydrologic regime of the Pantanal of Mato Grosso will be better known by the second half of 1996, once the ongoing studies are completed. The IDB has asserted that it may not fund the Hidrovia project through the Pantanal if serious environmental impacts are anticipated (Lammers et al., 1994). Thus, the present study is a contribution to the proper assessment and evaluation of these impacts.

The Internave report lists the various geographic locations along the Hidrovia project, starting from the port of Buenos Aires (km 0), progressing upstream to the port of Cáceres (km 3,442). For reference purposes, an abstracted list of locations relevant to this study is shown in Table 4. Minor discrepancies between river distances in Tables 1 and 4 reflect the different sources for these tables: DNOS (1974) and INTERNAVE (1990).

Table 4.  List of locations along the Paraná-Paraguay Waterway relevant to this study.1
Location 2 Km
Downstream of Upper Paraguay River
Buenos Aires, Argentina, port of 0
Diamante, Argentina, port of 533
Santa Fé, Argentina, port of 592
Corrientes, Argentina, port of 1,208
Confluencia (confluence of Paraná and Paraguay rivers) 1,240
Bermejo river, on the Lower Paraguay river, mouth of 1,321
Tebicuary river (the boundary between Lower and Middle Paraguay rivers), mouth of 1,381
Pilcomayo river, on the Middle Paraguay river (the boundary between Argentina and Paraguay), mouth of 1,619
Asunción, Paraguay, port of 1,630
Along Upper Paraguay River
Apa river, the boundary between Paraguay and Brazil, mouth of 2,172
Porto Murtinho 2,235
Tarumã, Passo 2,251-52
Fecho dos Morros 2,271-73
Barranco Branco 2,322
Nabileque river, inferior mouth 2,344
Rebojo Grande, Passo 2,538-40
Coimbra, Passo 2,553-54
Forte Coimbra 2,561
Piuvas Inferior, Passo 2,573-74
Piuvas Superior, Passo 2,577-78
Conselho, Passo do, beginning 2,607
Nabileque river, superior mouth 2,607
Conselho, Passo do, end 2,609
Porto Esperança 2,628
Eurico Dutra Bridge 2,630
Figueirinha, Passo 2,633-35
Miranda river, mouth of 2,662
Porto da Manga 2,686
Miguel Henrique, Passo 2,712-15
Formigueiro, Passo, beginning 2,722
Old Taquari river, mouth of 2,723
Formigueiro, Passo, end 2,724
Rabicho, port of 2,740
Ladario 2,755
Corumbá, port of 2,762
Canal Tamengo, mouth of 2,762
Faia, Passo 2,803-04
São Francisco, Passo 2,906-07
São Francisco 2,908
Rufino, Passo 2,937
Piuva Inferior, Passo 2,952
Piuva Superior, Passo 2,954-56
Amolar Pass, beginning 2,961
Mandioré Lake, mouth of 2,963
Amolar, Passo, end 2,963
Amolar 2,96
Cuiabá river, mouth of 2,988
Refúgio das Três Bocas 2,994
Ponta do Morro (exit of Gaíba Lake) 3,030
Gaíba Lake, entrance to 3,034
Bela Vista do Norte 3,047
Porto Conceição 3,182
Japuira, Passo 3,267-68
Descalvados, Passo 3,301-02
Descalvados 3,303
Paratudal, Passo 3,310
Presidente, Passo 3,320
Morro Pelado, Passo 3,322-24
Baia das Eguas, Passo 3,332-33
Corichão, Passo 3,335-36
Baiazinha, Passo 3,340-43
Beicudo, Passo 3,345-46
Barranco Vermelho, Passo 3,349
Soldado, Passo do 3,350-52
Tucum, Passo 3,356-57
Bote, Passo 3,359-60
Cambara, Passo 3,360-62
Jauru Pass, beginning 3,363
Old Jauru River, mouth of 3,365
Jauru, Passo, end 3,366
Acuri, Passo 3,366-68
Simão Nunes Inferior, Passo 3,372-73
Simão Nunes Superior, Passo 3,375-77
Passagem Velha, Passo 3,403-06
Retiro Velho, Passo 3,411-12
Cáceres 3,441
Cáceres, port of 3,442
1 Source:  INTERNAVE (1990). 2 Bolded entries correspond to gaging stations listed in Table 2.

Fig. A6  Dawn at the Pantanal of Mato Grosso near Rio Cassanges, Mato Grosso.


3.  THE UPPER PARAGUAY RIVER AND PANTANAL OF MATO GROSSO
[Environmental Impact]   [Summary]   [References]      [Top]   [Executive Summary]   [Introduction]   [Geographical Background]  

This section describes the physiographic and hydrologic characteristics of the Upper Paraguay River and the adjoining Pantanal of Mato Grosso. It is divided into four subsections:

  1. Geological setting

  2. Geomorphological setting

  3. Hydrological setting

  4. Ecological setting.

The information of this section serves as the basis for the analysis of Section 4.


3.1  Geological Setting

The geology of the Upper Paraguay river and environs is described in Almeida (1945), Projeto Bodoquena (1979), Projecto RADAMBRASIL (1982a&b), and Godoi Filho (1986), among others. The predominantly Upper Precambrian formations underlie extensive Quaternary deposits, but with significant rock outcrops. Geomorphologic evidence reveals the presence of substantial tectonic activity in the form of subsidence and uplift (Freitas, 1951; DNOS, 1974; Orellana, 1979; Ab'Sáber, 1988).

Table 5 shows the stratigraphic units that are present in the Upper Paraguay river. The Upper Precambrian is represented by the groups Alto Paraguay, Corumbá, and Jacadigo, and their respective formations; the Paleozoic by the Coimbra formation; the Mesozoic by the Alkaline Fecho dos Morros formation; and the Cenozoic by the Xaraiés and Pantanal formations. Table 6 lists primary rock types, including sandstones, silt stones, limestones, conglomerates, dolomites, calcareous dolomites, syenites, trachytes, calcareous tufa, and travertines. Table 7 shows the general location of rock outcrops in the vicinity of the Upper Paraguay river.

Table 5.  Stratigraphic units in the vicinity of the Upper Paraguay river.1
Era Period Epoch Group Formations
Precambrian Upper - Alto Paraguay Moenda
Araras
Raizama
Sepotuba
- Corumbá Puga
Cerradinho
Bocaína
Tamengo
- Jacadigo Urucum
Santa Cruz
Paleozoic Silurian - - Coimbra
Mesozoic Triassic - - Alkaline Fecho dos Morros
Cenozoic Quaternary Pleistocene - Xaraiés
- Pantanal
Holocene - Pantanal
1 Source:  Projeto RADAMBRASIL (1982a&b).

Table 6.  Lithology of formations in the vicinity of the Upper Paraguay river.1
Formation Description
Moenda Conglomerates or tillites, with sandstone, marl, and calcareous rocks.
Araras Limestones, siltstones, marl.
Raizama Quartz sandstones, quartz/feldspar sandstones.
Sepotuba Siltstones, micaceous sandstones.
Puga Conglomerates or tillites, with quartzites, granites, and schists.
Cerradinho Sandstones, siltstones, limestones, dolomites, marl, metaconglomerates.
Bocaína Calcareous dolomites, dolomites, calcareous sandstones.
Tamengo Black limestone, with fine siltstones and sandstones.
Urucum Arkosic sandstones, quartz/feldspar sandstones, metasandstones feldspar-rich metasandstones, conglomerates, siltstones.
Santa Cruz Jaspelitic arkosic sandstones.
Coimbra Thin-bedded sandstones.
Alkaline Fecho dos Morros syenites, trachytes, porphyritic trachytes.
Xaraiés Calcareous tufa, travertines, conglomerates with calcareous cement.
Pantanal Sandy sediments, silty/clayey and sandy conglomerates, unconsolidated and semiconsolidated; fluvial and lacustrine deposits in seasonally flooded areas.
1 Source:  Projeto RADAMBRASIL (1982a&b).

Table 7.  Rock outcrops in the Upper Paraguay river and environs.1
Formation Location 2
Moenda Limited areas of Serrana Province, east and southeast of Cáceres, north of Descalvados.
Araras Limited areas in Serrana Province, east and southeast of Cáceres, north of Descalvados.
Raizama Extensive areas in Serrana Province, east and southeast of Cáceres, north of Descalvados.
Sepotuba Limited areas of Serrana Province, east and southeast of Cáceres, north of Descalvados.
Puga Morro da Puga, on right bank of Paraguay river, 5 km downstream of Porto Esperança.
Cerradinho Morro da Puga, on right bank of Paraguay river, 5 km downstream of Porto Esperança.
Bocaína 1. Western limit of Morraria 2 da Ínsua, south of Lagoa Uberaba, in the proximity of Bela Vista do Norte.
2. In the hills surrounding Corumbá.
3. In Morro do Conselho, 20 km downstream of Porto Esperança.
4. In Morro de Coimbra, at Forte Coimbra.
Tamengo 1. Right bank of Upper Paraguay river, between Corumbá and Ladario.
2. In Canal Tamengo, which links the Upper Paraguay river with Lagoa Cáceres (Bolivia).
Urucum 1. In the Morraria da Ínsua, adjacent to Bela Vista do Norte.
2. In the Serra do Amolar, adjacent to Amolar.
3. In the Serra de Bonfim (in the proximity of Porto São Francisco).
4. On the right bank of Upper Paraguay river, in the Morraria do Rabichão (15 km downstream of Ladario) and adjacent hills.
Santa Cruz 1. Right bank of Upper Paraguay river, in the Morraria do Rabichão (15 km downstream of Ladario) and adjacent hills.
2. Left bank of Upper Paraguay river, in the Morraria Santa Rosa, on the right bank of Paraguai-Mirim river, at 3 km from its mouth.
Coimbra In the hills around Forte Coimbra.
Alkaline Fecho dos Morros Left bank of Upper Paraguay river, on the group of hills referred to as Fecho dos Morros.
Xaraiés 1. In the Serrana Province, close to Cáceres, associated with calcareous Araras formation.
2. Right bank of Upper Paraguay river, close to port of Corumbá.
3. South of Corumbá, in areas adjacent to outcrops of calcareous rocks from Bocaína and Tamengo formations.
4. South of Morraria do Zanetti, about 20 km northeast of Porto Esperança.
1 Source:  Projeto RADAMBRASIL (1982a&b).
2 Morraria means "group of hills" in Portuguese.

Navigation charts confirm the existence of numerous rock outcrops on or along the Upper Paraguay river (Marinha do Brasil, 1974; and later dates). A list of these outcrops is shown in Table 8, and their possible rock types in Table 9. Significantly, four of these outcrops are located in the middle of the channel, such as Passo Simão Nunes Inferior, Córrego Bonfim, Farolete Balduíno (Fig. A7), and Passo Mucunã, effectively functioning as grade controls. The existence of rock outcrops have been recognized for more than a century (Leverger, 1862a&b). Some of them have been documented in the Internave report (INTERNAVE, 1990).

Table 8.  Documented rock outcrops along Upper Paraguay river,
from Cáceres to Apa river confluence.1

No. Location Km 2 Km 3 Chart No. Description
1. Passo Simão Nunes Inferior 3,373 2,132.9 99 In the middle of the channel.
2. Ilha Barranco Vermelho 3,348 2,108 94 On the left bank, encroaching into the channel.
3. Ilha do Beiçudo 3,344 2,104 93 On the left bank, encroaching into the channel (0.6 km long).
4. Morro Pelado 3,332-34 2,082-84 89-90 On the left bank (1.5 km long).
5. Passo Papagaio 3,318 2,078 88 On the right bank, encroaching into the channel.
6. Riacho D. Pedro II 3,030 1,790 0 On the left bank, three occurrences, one of them encroaching into the channel.
7. Ponta do Morro 3,030 1,790 48 On the right bank, encroaching into the channel.
8. Fazenda Acurizal 3,004 1,764.3 44 On the right bank, encroaching into the channel.
9. Corixo da Penha 2,967 1,727.2 37 On the right bank.
10. Amolar 2,965 1,725 36-37 On the right bank, encroaching into the channel (0.5 km long).
11. Passo Amolar 2,960 1,720 36 On the right bank, encroaching into the channel.
12. Fazenda Dourados 2,957-58 1,717-18 35-36 On the right bank (1.2 km long).
13. Morro Dourados 2,956 1,716.5 35 On the right bank, encroaching into the channel (0.4 km long).
14. Passo Piuva Superior 2,956 1,715.9 35 On the left bank, encroaching into the channel.
15. Ilha do Rufino 2,935 1,695.4 31 On the left bank.
16. Córrego Bonfim 2,929 1,688.6 29 In the center right of channel.
17. Porto Santa Luzia 2,856 1,616 16 Encroaching into channel on both sides (0.6 km long).
18. Fazenda Faia 2,804 1,564.4 08 On the left bank.
19. Retiro Uberlandia 2,778 1,538.5 04 On the left bank (0.5 km long).
20. Estirão de Agua Branca 2,769 1,529.4 02 On the right bank, encroaching into the channel.
21. Farolete Balduíno 2,762 1,521.1 3,230 In the middle of the channel.
22. Barranca Limpa 2,714 1,473-74 3,231 B On the left bank, two occurrences, encroaching into the channel.
23. Volta Grande 2,705-07 1,465-07 3,231 B On the left bank, three occurrences, encroaching into the channel.
24. Passo Mucunã 2,693-94 1,453-55 3,231 B On the left bank and middle of channel, three occurrences.
25. Saladeiro Otília 2,689 1,449 3,231 B On the right bank, encroaching into the channel.
26. Morro da Onça 2,569 1,329 3,233 B On the right bank, encroaching into the channel.
27. Estirão de Baía Verde 2,549 1,309 3,234 A On the left bank.
28. Fuerte Olimpo 2,329 1,089 3,237 B On the right bank, on mouth of Riacho Barrero.
29. Passo Cambá Nupá 2,281 1,041 3,238 A On the right bank, encroaching into the channel.
30. Morro Pão de Açúcar 2,275-76 1,035-36 3,238 A On the left bank, encroaching twice into the channel.
31. Fecho dos Morros 2,268-71 1,028-31 3,238 A Hills on both sides of channel, three locations on left bank, within 3 km.
32. Passo Tarumã 2,251 1,011 3,238 B On the left bank, encroaching into the channel.
1 Source:  Marinha do Brasil, Croquis (two-digit numbers) e Cartas (four-digit numbers) de Navegação, Rio Paraguay, de Corumbá a Cáceres.
2 Km of Hidrovia, with reference to Buenos Aires as Km 0.
3 Km of Hidrovia, with reference to mouth of Rio Paraguay (Confluencia) as Km 0.

Table 9.  Stratigraphy and lithology of documented rock outcrops
along Upper Paraguay river.1

No. Location Km 2 Km 3 Formation Primary rock types 4
1. Passo Simão Nunes Inferior 3,373 2,132.9 Raizama Quartz and quartz/feldspar sandstones, siltstones.
2. Ilha Barranco Vermelho 3,348 2,108 Raizama Quartz and quartz/feldspar sandstones, siltstones.
3. Ilha do Beiçudo 3,344 2,104 Raizama Quartz and quartz/feldspar sandstones, siltstones.
4. Morro Pelado 3,332-34 2,082-84 Raizama Quartz and quartz/feldspar sandstones, siltstones.
5. Passo Papagaio 3,318 2,078 Raizama Quartz and quartz/feldspar sandstones, siltstones.
6. Riacho D. Pedro II 3,030 1,790 Urucum Arkose, quartz sandstones, conglomerates.
7. Ponta do Morro 3,030 1,790 Urucum Arkose, quartz sandstones, conglomerates.
8. Fazenda Acurizal 3,004 1,764.3 Urucum Quartz sandstones, metaconglomerates, schists.
9. Boca do Corixo da Penha 2,967 1,727.2 Urucum Quartz sandstones, metaconglomerates, schists.
10. Amolar 2,965 1,725 Urucum Quartz sandstones, metaconglomerates, schists.
11. Passo Amolar 2,960 1,720 Urucum Quartz sandstones, metaconglomerates, schists.
12. Fazenda Dourados 2,957-58 1,717-18 Urucum Quartz sandstones, metaconglomerates, schists.
13. Morro Dourados 2,956 1,716.5 Urucum Quartz sandstones, metaconglomerates, schists.
14. Passo Piuva Superior 2,956 1,715.9 Urucum Quartz sandstones, metaconglomerates, schists.
15. Ilha do Rufino 2,935 1,695.4 Urucum Quartz sandstones, metaconglomerates, schists.
16. Córrego de Bonfim 2,929 1,688.6 Bocaína Calcareous dolomites, calcareous sandstones.
17. Porto Santa Luzia 2,856 1,616 Bocaína Calcareous dolomites, calcareous sandstones.
18. Fazenda Faia 2,804 1,564.4 Bocaína Calcareous dolomites, calcareous sandstones.
19. Retiro Uberlandia 2,778 1,538.5 Bocaína Calcareous dolomites, calcareous sandstones.
20. Estirão de Agua Branca 2,769 1,529.4 Bocaína Calcareous dolomites, calcareous sandstones.
21. Farolete Balduíno 2,762 1,521.1 Urucum Arkose, quartz sandstones, conglomerates.
22. Barranca Limpa 2,714 1,473-74 - Unable to determine.5
23. Volta Grande 2,707 1,467 - Unable to determine.5
24. Passo Mucunã 2,693-94 1,453-55 - Unable to determine.5
25. Saladeiro Otília 2,689 1,449 - Unable to determine.5
26. Morro da Onça 2,569 1,329 Coimbra Layered sandstones.
27. Estirão de Baía Verde 2,549 1,309 - Unable to determine.5
28. Fuerte Olimpo 2,329 1,089 - Unable to determine.5
29. Passo Cambá Nupá 2,281 1,041 - Unable to determine.5
30. Morro Pão de Açúcar 2,275-76 1,035-36 A. Fecho dos Morros Syenites, trachytes, prophyritic trachytes.
31. Fecho dos Morros 2,268-71 1,028-31 A. Fecho dos Morros Syenites, trachytes, prophyritic trachytes.
32. Passo Tarumã 2,251 1,011 - Unable to determine.5
1 Source:  Projecto RADAMBRASIL (1982a&b). 2 Km of Hidrovia, with reference to Buenos Aires as Km 0.
3 Km of Hidrovia, with reference to mouth of Rio Paraguay (Confluencia) as Km 0.
4 Actual rock type(s) may differ from those listed.
5 Field reconnaisance may be required for precise determination.

Fig. A7  Farolete Balduíno, near Corumbá, Mato Grosso do Sul.

These facts confirm that the Upper Paraguay river is substantially controlled by the prevailing geology. While the Quaternary sediments of the Pantanal formation are the most obvious surficial feature of the landscape, the longitudinal slope of the river is controlled more by the rock outcrops than by the alluvium. As shown in Table 8, there are thirty-two (32) rock outcrops within 1,270 km of river, an average of one every 40 km.

Other outcrops along the river, particularly that of canga, may have been less thoroughly documented. According to Dorr (1945), canga is colluvium or talus, composed in large part of fragments of iron-rich rock, which has been recemented into a coherent mass by limonite. In the vicinity of the Morro de Urucum, these outcrops tend to have a linear distribution, suggesting the possibility of a fault (Dorr, 1945; Almeida, 1945). Moreover, it is noted that the Internave report mentions the occurrence of canga in several places along the river, including Porto Rabicho (km 2,740), entrance to Passo do Conselho (km 2,607), and upstream of Passo Piuva Inferior (km 2,573) (INTERNAVE, 1990).

Table 10 describes three geologic faults in the vicinity of the Upper Paraguay river (Projeto RADAMBRASIL, 1982a). The Falha da Lagoa, which crosses Lagoa Gaíba (Section 3.3.1), may have a significant effect on the flow of the Upper Paraguay river. Likewise, the Falha da Penha, which also crosses Lagoa Gaíba, is strategically located in close proximity to the river (Fig. 5). According to DNOS (1974), it appears that the northern portion of the Pantanal has subsided in relation to the Serra do Amolar (Section 3.2). This would explain the elevated position of the older rocks in the Serra do Amolar.

Table 10.  Geologic faults in the vicinity of the Upper Paraguay river.1
Name Formation(s) Location Description
Falha da Penha2 Urucum From Serra do Amolar to Ilha de Ínsua On the right bank of Upper Paraguay river, from Fazenda da Penha(north of Amolar) to Ilha de Ínsua (north of Lagoa Gaíba); partly buried near Ilha de Ínsua by sediments of Pantanal sandstones of the Urucum formation: 60 km long; arkosic sandstones of the Urucum formaion.
Falha da Lagoa2 Urucum, Bocaína From Serra do Amolar to Lagoa Gaíba On the right bank of Upper Paraguay river, in a direction parallel to Falha da Penha, west of Serra do Amolar and Ilha de Ínsua; partly covered by waters of Lagoa Gaíba; may prolong to southeast reaching Morraria de Novos Dourados; 55 km long; arkosic sandstones and calcareous dolomites of the Urucum and Bocaína Formations, respectively.
Falhas do Urucum3 Urucum, Santa Cruz Along the valley of Córrego Band'Alta Between Morro do Urucum and Morraria do Rabichão; mostly buried by sediments of Pantanal formation.
1Source:  Projeto RADAMBRASIL (1982a&b), Volume 27. 2 Falha means fault, in Portuguese.
3 System of faults, the best known of which is that along the valley of Córrego Band'Alta.

Fig. 5  Geographic location of Falha da Lagoa and Falha da Penha
(Projeto RADAMBRASIL, 1982a&b).

The tectonic character of the Upper Paraguay river basin has been admirably described by Freitas (1951). Orellana (1979) has stated that active faults in a direction contrary to the regional runoff have created local sills (soleiras) that act to impede runoff. More recently, Ab'Sáber (1988) has attributed the genesis of the Pantanal to "a tectonic character dominated by a system of faults which are geomorphologically contrary..."

A historical note regarding rock outcrops in the Upper Paraguay: In describing his passage through Lagoa Gaíba almost 150 years ago (1846), Captain Augusto Leverger of the Brazilian Navy cautioned against the rocky sills which protrude onto the lake as follows (Leverger, 1862a, p. 317):

"...Virando a Norte, tive de circumdar um como promontorio da margem do poente da lagoa o qual é terminado por um cabeço pedregoso e coberto de mato, ao cual devese dar resguardo a fim de evitar as muitas pedras que o cercam, umas submergidas, outras a flor de agua ou pouco elevadas..."


3.2  Geomorphological Setting

The geomorphology of the Upper Paraguay river basin is described in Projecto RADAMBRASIL (1982a&b) and Silva (1986). The geomorphic units in the vicinity of the Upper Paraguay river are:

  • Serras of Urucum-Amolar

  • Serrana Province

  • Depression of the Paraguay River

  • Plains and Swamps of Mato Grosso.

The Serras of Urucum-Amolar comprise two groups of serras (residual hills or mountain ranges) located to the right (west) of the Upper Paraguay river, close to the Bolivian border. These serras are important because of their strategic location, on the right bank, and often next to the river. The Serra do Urucum, southeast of Corumbá, comprises the morrarias (group of residual hills) of Urucum, Santa Cruz, São Domingos, Grande, Rabichão, and Tromba dos Macacos; further south, about 40-50 km, are the morrarias of Zanetti, Albuquerque, Mato Grande, Saiutã, and Pelada.

The Serra do Amolar, about 60-160 km north of Corumbá, comprises the Serra do Amolar proper and the morrarias of Ínsua, Novos Dourados, Santa Tereza, Castelo, and others of smaller size. The elevation of these mountains varies from 300 to 900 m, the highest point being at Morro Grande (1,065 m). The contact between the Serra of Urucum-Amolar and adjacent geomorphic units is often sudden, revealing the presence of faults of probable Cenozoic age (Projeto RADAMBRASIL, 1982a).

The Serrana Province consists of a group of serras of roughly parallel crest alignment, located east of Cáceres, trending in a predominantly SW-NE direction. From SW to NE, these serras are: (1) Simão Nunes, (2) Colonia, (3) Acorizal, (4) Facão, (5) Primavera, (6) Ponta do Morro, (7) Quilombo, (8) Morro Grande, (9) Jacobina, (10) Barreiro Preto, (11) Chapola, (12) Boi Morto, (13) Bocainão, (14) Campina, and (15) Retiro (Projeto RADAMBRASIL, 1982a). The Serra Simão Nunes, the most southwestern of the group, comes in direct contact with the Upper Paraguay river in several locations along 45 km of river, on the left bank, from Passo Acuri, at km 2,128 (km 3,368 of the Hidrovia), to Passo Morro Pelado, at km 2,083 (km 3,323 of the Hidrovia) (Table 20). The elevations in the Serrana Province vary from 300 to 700 m. The rock formations are those of the Alto Paraguay group (Table 5).

The Depression of the Paraguay River comprises extensive plain surfaces which surround the Serrana province, and to a lesser extent, the Serra of Urucum-Amolar. The relief is mild, slightly undular, with elevations varying between 150 to 250 m, and has underlying Precambrian and Cambrian formations, which often outcrop through the Quaternary deposits.

The Plains and Swamps of Mato Grosso (Planícies e Pantanais Matogrossenses) resemble an amphitheater of roughly semicircular shape, with its approximate center at Corumbá, comprising 28% of the Upper Paraguay river basin (Fig. 2). The plains are a series of mutually coalescing alluvial fans, surrounded by the Depression of the Paraguay River almost continuously to the east, and discontinuously to the north and south. They comprise an extensive surface of accumulation, of extremely flat relief, with elevations varying from 80 to 150 m, and subject to seasonal flooding by the Upper Paraguay river and its tributaries (Fig. A8).

Fig. A8  Campo Jofre, in the Pantanal of Mato Grosso.

Valley slopes are about an order of magnitude greater along the tributaries than along the main channel. The tributaries cross the plains in a predominantly east-west direction, with a slight orientation towards the center of the amphiteather, with valley slopes of 12 to 50 cm/km. The high sediment production of the tributaries has forced the main channel of the Upper Paraguay, which runs predominantly from north to south, to closely parallel the western edge of the plains (Schumm, 1977). Moreover, its unusually mild slope (0.7-6.5 cm/km) causes it to regularly overflow its banks during the wet season.

Sánchez (1978) has identified ten geomorphic subunits within the plains and swamps of Mato Grosso (Table 11). The Pantanal is seen to be a complex mosaic of geomorphic features or subunits, with a regional base level at the Upper Paraguay river, along the western edge of the plains. In turn, the base level of the Upper Paraguay river is at its mouth, at the confluence with the Apa river.

Table 11.  Geomorphic subunits of the Pantanal of Mato Grosso.1
Subunit Description
Cordones2, or small ranges (cordilheiras3) Positive relief forms, narrow and elongated, protruding slightly above the level of the surrounding terrain. Their shape and location suggests that they may be relics of a much more active geodynamical past.
Channels with permanent runoff Negative relief forms of sizable depth, with permanent or quasi-permanent runoff, such as the major and minor rivers of the Pantanal.
Channels with temporary runoff (corregos, or corixos3 Negative relief forms, shallow and more or less narrow, with temporary (intermittent) runoff.
Streambeds with temporary runoff (vazantes3) Negative forms of relief, slightly concave and quite wide and shallow, with relatively mild longitudinal slopes.
Depressed plains Generally flat and of negligible relief, typically occupying interfluvial locations and subject to more-or-less seasonal inundation.
Flooded plains Positive forms of relief which are subject to seasonal inundation from neighboring channels.
Diffuse flooded plains Flooded plains where runoff lacks a clear direction.
Composite flooded plains Flooded plains where runoff may or may not have a clear direction. Typical of this subunit is the runoff of the lower courses of the Cassange, Alegre, Caracará, and Cuiabá rivers, right-bank tributaries of the Upper Paraguay river (downstream of Bela Vista do Norte and upstream of Amolar).
Lagoons (baías3) Negative forms of relief, sometimes of sharp concavity, which may be permanently or temporarily filled with water; saline at times. The greatest density of this subunit is found in the area of Nhecôlandia.
Isolated hills (inselberg, or island hills) Extremely positive relief forms, associated with underlying Precambrian and Cambrian rocks, and occupying relatively small areas within the Pantanal depression. Examples are the Ilha de Ínsua, Morro do Conselho, Morro de Coimbra, and Fecho dos Morros.
1Source:  Sánchez (1978). 2 Spanish. 3 Portuguese.

The sequence of events leading to the formation of the Pantanal has been described by Projeto Bodoquena (1979) and Ab'Sáber (1988). During the Jurassic period, the prevailing arid climate led to substantial sediment deposition, mostly in the form of sand dunes. The Cretaceous period that followed saw a change to a more humid climate, which transformed the desert into a flood plain with numerous lakes and swamps. The end of the Mesozoic era signaled the end of sedimentation and the beginning of slow epeirogenic movements, which were generally upwards.

The subsidence of the Pantanal occurred later, probably in the Pleistocene (Tricart, 1982). A clear evidence of subsidence is the great depth of the Quaternary deposits, which at Fazenda Piquiri reaches beyond 320 m, and at Fazenda São Bento, beyond 420 m (320 m below sea level). The maximum depth of the Pantanal sediments has been estimated at 500 m at the Pantanal's center, on the alluvial fan of the Taquari river (Godoi Filho, 1986). Tectonic uplift to the south strangled the exit of the depression. In the last 6 million years, under the effects of subsidence and uplift, the Upper Paraguay river has been forced to carve an exit through the basal rocks to the south, a situation which explains its unusually mild slopes.


3.3  Hydrological Setting

The hydrology of the Upper Paraguay river is described in DNOS (1974) and EDIBAP (1979). The Upper Paraguay river flows from its headwaters in the Serra de Tapirapuã, in Mato Grosso, to its mouth at the confluence with the Apa river, in Mato Grosso do Sul. At Cáceres, where it meets the first human settlement of importance, the river drains an area of 33,860 km2; at the Apa river confluence, downstream of Porto Murtinho, it drains an area of 496,000 km2 (Fig. A9).

Fig. A9  The Upper Paraguay river at Cáceres, Mato Grosso.

The distance along the river, from Cáceres to the Apa river confluence is 1,270 km. Throughout most of this distance, the Upper Paraguay river crosses the Pantanal of Mato Grosso, flooding the Pantanal typically from March to August, and draining it from September to February. Thus, the hydrology of the Upper Paraguay river is effectively connected to and interdependent with that of the Pantanal. This blurs the distinction between surface water and groundwater, significantly increasing the complexity of hydrologic analysis. In fact, the peculiar geologic and geomorphologic setting of the Upper Paraguay river and the adjoining Pantanal results in a unique hydrologic behavior, unmatched in the American continent.

The prevailing climate is dry subhumid, grading to wet subhumid along a narrow strip paralleling the mountain ranges that delimit the basin to the north, east, and south, and humid in limited northernmost areas bordering with the Amazon basin (EDIBAP, 1979). The spatially averaged, mean annual rainfall in the Upper Paraguay basin ranges from 1,180 mm (Projeto RADAMBRASIL, 1984) to 1,380 mm (EDIBAP, 1979), depending on the data source. This fact alone would dictate that the mean runoff coefficient (the ratio of mean annual runoff to mean annual rainfall) should be relatively high, perhaps somewhat less than the global average, estimated at 0.39 for peripheral continental areas by L'vovich (1979) or 0.46 by Berner and Berner (1987). Instead, the mean runoff coefficient of the Upper Paraguay is quite low, varying in the range 0.07-0.10, depending on which data is used in the calculation (Section 3.3.4).

The abnormally low runoff coefficient of the Upper Paraguay river is a direct result of its hydrologic interaction with the Pantanal. The latter functions as an immense surface/subsurface reservoir which stores water annually and multiannually. In the annual time frame, the Pantanal stores water during the wet season and releases it back to the main channel during the subsequent dry season. In the multiannual timeframe, the Pantanal stores water in a wet year and releases it back to the main channel in a dry year. In this process, the slowness of which is compounded by the unusually mild relief, large amounts of would-be runoff are instead returned to the atmosphere through evaporation and evapotranspiration. The latter helps to sustain a series of closely related ecosystems, characteristically marshes or wetlands, their biotic productivity closely linked to the annual flood pulse (Junk et al., 1989).


3.3.1  Hydrography

The hydrography of the Upper Paraguay river, from Cáceres to the Apa river confluence, is shown in schematic form in Fig. 6. At Cáceres, the Paraguay river has already received the contributions of two of its most important right-bank tributaries: Sepotuba and Cabaçal. From Cáceres, the river flows south towards Descalvados, a distance of 139 km along the river. At a point 71 km downstream of Cáceres, the Paraguay receives the contribution of its third important right-bank tributary, the Jauru.

Fig. 6  Schematic of the hydrography of the Upper Paraguay river.

From Descalvados, the river flows first southeast and then turns south towards Porto Conceição, a distance of 121 km. At a point 46 km downstream of Descalvados, the river branches into two channels: the Paraguay proper (to the right) and the Bracinho (to the left). This bifurcation marks the beginning of the Pantanal proper; from this point on, as far downstream as Amolar, the Paraguay river crosses extensive areas of lakes (baías or lagoas) and adjoining permanently flooded plains. The two branches delimit the island of Taiamã, and rejoin 43 km downstream, measured along the main channel.

From Porto Conceição, the river first flows south and then turns southwest towards (Fazenda) Bela Vista do Norte, a distance of 135 km. At a point 40 km downstream of Porto Conceição, the river again branches into two channels: the Paraguay proper (to the right) and the Caracará (to the left). The two branches form the great island of Caracará and rejoin further south, near Refúgio das Três Bocas. The main channel of the Paraguay flows southwest towards Bela Vista do Norte, at the base of Morraria da Ínsua (Fig. 7). The Caracará branch flows south towards Refúgio das Três Bocas, in the vicinity of the Serra do Amolar.

Fig. 7  Detail of Lagoa Gaíba.

The island of Caracará constitutes a veritable inland delta, with its apex at the bifurcation (40 km downstream of Porto Conceição), and its base the Paraguay river itself, which turns from Bela Vista do Norte southeast to Refúgio das Três Bocas, flowing for a distance of 53 km. During extraordinary and exceptional floods, most of the island of Caracará is completely submerged.

In the vicinity of the Morraria da Ínsua and the Serra do Amolar, the Paraguay river interacts with three large lakes: Uberaba, Gaíba, and Mandioré (Figs. 3 and 6). The larger of the three, Lagoa Uberaba, located north of Morraria da Ínsua, receives over flows from the Paraguay as well as runoff from local streams and from Corixa Grande, the last significant right-bank tributary of the Paraguay.

Lagoa Gaíba is located between Morraria da Ínsua and Serra do Amolar. It consists of three smaller lakes:

  1. Gaíba, surrounded by mountains to the east and west.

  2. Gaíba-Mirim, surrounded by mountains to the east, west, and south, and connected to Gaíba during extremely high flows.

  3. Pre-Gaíba, a continuation of Gaíba to the northeast.


The link between the Upper Paraguay river and Lagoa Gaíba is the Riacho da Gaíba. However, a branch of the Paraguay drains into Pre-Gaíba. The Riacho da Gaíba is generally as deep as the Paraguay, excluding the exit of Lagoa Gaíba, where it is extremely shallow, with a depth of 0.1-0.6 m and a width of 2,000 m (DNOS, 1974). Judging by the unmixed colors of its waters, the Riacho da Gaíba appears to drain Lagoa Gaíba to the right (reddish color, iron-rich dissolved solids), Lagoa Uberaba to the center (dark color, humic colloids), and the main channel of the Paraguay river to the left (light brown color, suspended sediments) (Fig. 7). The link between Lagoa Gaíba and Lagoa Uberaba is the Canal Pedro II, with a length of about 100 km. The direction of the current in the Canal Pedro II is normally from Lagoa Uberaba to Gaíba, but it can change seasonally if the flow is considerably reduced (DNOS, 1974).

From Refúgio das Três Bocas, the river flows south towards Amolar, a distance of 28 km. Shortly before reaching Refúgio das Três Bocas, the river branches into two channels: the Paraguay to the left, and the Moquém to the right. Before rejoining the Paraguay, the Moquém river branches into the Ingazal, which joins together with the São Jorge, another branch of the Paraguay. In turn, the São Jorge rejoins the Paraguay immediately upstream of Amolar. These bifurcations reveal the extremely small gradient in this section of the Paraguay river.

From Amolar, the river flows south towards Porto São Francisco, a distance of 58 km. At a point 46 km downstream of Amolar, the river flows past Riacho da Mandioré, the inlet to Lagoa Mandioré. The Paraguay river flows into Lagoa Mandioré during high flows, and out during low flows.

From Porto São Francisco, the river flows in a general southwestern direction towards Corumbá, a distance of 146 km, and then turns east to Ladario, a distance of 7 km from Corumbá (Fig. A10). At a point 16 km downstream of Porto São Francisco, the Paraguay river branches again into two channels, the Paraguay to the right, and the Paraguai-Mirim to the left. The latter crosses the eastern plains and rejoins the Paraguay river 20 km downstream of Ladario. Between Porto São Francisco and Corumbá, the river can overflow (to the right) into the Lagoa Conceição, Lagoa do Castelo, and Lagoa Cáceres. The connection between Lagoa Cáceres, in Bolivia, and the Paraguay river is the Canal Tamengo, with its mouth in the vicinity of Corumbá.

Fig. A10  Upper Paraguay river near Corumbá, Mato Grosso do Sul.

From Ladario, the river flows first east and then southeast to Porto da Manga, a distance of 69 km. At a point 32 km downstream of Ladario, the Paraguay river receives the contribution of the Taquari Velho (an ancient channel of the Taquari river) to the left. About 2 km upstream of Porto da Manga, the Paraguay river receives the contribution of the Taquari river to the left. The Negro river, a tributary of the Taquari, flows into the latter right upstream of its confluence with the Paraguay.

From Porto da Manga, the river flows southwest to Porto Esperança, a distance of 58 km. At a point 24 km downstream of Porto da Manga, the Paraguay river receives the contribution of the Miranda river (Fig. A11). Together with the Aquidauana river, its principal tributary, the Miranda river drains extensive areas of Pantanal and Upper Paraguay river basin to the southeast.

Fig. A11  The Miranda river, Mato Grosso do Sul.

From Porto Esperança, the river continues to flow southwest to Forte Coimbra, a distance of 67 km (Fig. A12). Between 2 and 40 km downstream of Porto Esperança, the Paraguay river overflows to the left during floods to feed its branch, the Nabileque. The latter crosses the plains east of the Paraguay river in a general southern direction for about 250 km, eventually rejoining the Paraguay river at a point located 217 km downstream of Forte Coimbra.

Fig. A12  Upper Paraguay river at Forte Coimbra, Mato Grosso do Sul.

From Forte Coimbra, the river flows in a general southern direction for 239 km towards Barranco Branco; then an additional 51 km to Fecho dos Morros, and from there, 36 km to Porto Murtinho (Fig. A13). From Forte Coimbra to Porto Murtinho, the Paraguay river receives the contribution of several left-bank tributaries, including the Aquidabã, Branco, Tereré, and Amonguijá rivers (Fig 2), as well as small surface contributions from the Paraguayan Chaco on the right bank. At Fecho dos Morros (Closing of the Hills), 36 km upstream of Porto Murtinho, the Paraguay river passes through a group of hills, which effectively constitutes a grade control. This control has been referred to as a syenite sill (DNOS, 1974).

Fig. A13  Upper Paraguay river near Porto Murtinho, Mato Grosso do Sul.

From Porto Murtinho, the Upper Paraguay river flows south for another 63 km to reach its mouth at the confluence with the Apa river.

Table 12 shows selected hydrologic data at gaging stations along the Upper Paraguay river: drainage area, channel length, channel slope, and mean annual discharge. The following observations are made:

  • The subbasin drainage areas are not precisely defined in several points, particularly between Descalvados and Amolar. This is due to the extreme complexity of the drainage patterns, including channel bifurcations and endorheic drainages.

  • There is a slight reduction in channel slope and mean annual discharge from Descalvados to Porto Conceição, as the Paraguay river enters the Pantanal proper. This is where the Paraguay river begins to flood the Pantanal extensively.

  • There is a marked reduction in channel slope and mean annual discharge from Porto Conceição to Bela Vista do Norte, as the Paraguay river flows through and around the island of Caracará.

  • At Refúgio das Três Bocas-Amolar, the channel slope is further reduced to a mere 1.82 cm/km, while the mean annual discharge at Amolar increases sharply (to 943 m3/s). This indicates the substantial contributions of surface and subsurface runoff immediately upstream of this point.

  • Downstream of Amolar, the channel slope increases somewhat to Porto Esperança, while the mean annual discharge continues to increase gradually all the way to Porto Murtinho, near the basin's mouth.

  • Downstream of Porto Esperança, the channel slope decreases again, reaching a value of only 0.83 cm/km in the reach between Fecho dos Morros and Porto Murtinho.

  • The mean annual discharge of the Upper Paraguay river at its mouth is estimated to be 1,565 m3/s, based on measurements at Fecho dos Morros and Porto Murtinho.

Table 12.   Selected hydrologic data at gaging stations along Upper Paraguay river.1
Station Drainage area1,6
(km2)
Channel length2,4
(km)
Minimum observed water level1
(m)
Channel slope5
(cm/km)
Mean annual discharge3,6
(m3/s)
Cáceres 33,860 - 110.09 - 382
Descalvados 48,360 139 101.00 6.54 437
Porto Conceição - 121 93.55 6.16 341
Bela Vista do Norte - 135 89.80 2.78 144
Refúgio das Três Bocas - 53 88.14 3.13 -
Amolar - 28 87.63 1.82 943
Porto São Francisco 243,0007 58 85.12 4.33 1,046
Ladario - 153 81.54 2.34 1,261
Porto da Manga 316,0007 69 80.12 2.06 1,340
Porto Esperança 363,5007 58 78.36 3.03 1,412
Forte Coimbra - 67 76.91 2.16 1,467
Barranco Branco 453,000 239 72.64 1.79 1,505
Fecho dos Morros 470,000 51 71.78 1.69 1,549
Porto Murtinho 474,500 36 71.48 0.83 1,555
Confluence with Apa River 496,000 63 - - 1,5658
1Source:  DNOS (1974) and DNAEE. 2 Source: INTERNAVE (1989). 3 Source: EDIBAP (1979).
4 Measured from upstream station. 5 Based on channel length and minimum observed water levels, calculated from Table 2.
6 If not shown, not precisely definable. 7 Small portion cannot be precisely defined.
8 Estimated by linear extrapolation from measured values at Porto Murtinho and Fecho dos Morros.

The average channel slope along the Upper Paraguay river, from Cáceres to Porto Murtinho, is 3.2 cm/km. As shown in Table 12, the channel slope varies between 0.83 cm/km (Fecho dos Morros-Porto Murtinho) to 6.54 cm/km (Cáceres-Descalvados), and the bed profile alternates between convex and concave.

According to principles of fluvial geomorphology, a river that is free to move its bed eventually carves a concave upwards bed profile (Leopold et al., 1964; Leopold, 1994; Christofolleti, 1980). Thus, the documented convexities in bed elevation of the Upper Paraguay river reveal the presence of substantial geologic controls. These controls are operating in at least three reaches:

  1. Refúgio das Três Bocas-Amolar, with 1.82 cm/km

  2. Ladario-Porto da Manga, with 2.06 cm/km

  3. Fecho dos Morros-Porto Murtinho, with 0.83 cm/km.


The extent of the geologic control can be assessed by calculating the size of the hump at locations where its presence is suspected. For instance, from Table 12, the average channel slope from Refúgio das Três Bocas to Porto São Francisco can be calculated to be 3.51 cm/km. Therefore, a measure of the hump at Amolar is:

(3.51 - 1.82) cm/km × 28 km = 47 cm

Likewise, the average channel slope from Ladario to Porto Esperança is 2.70 cm/km. Therefore, a measure of the hump at Porto da Manga is:

(2.70 - 2.06) cm/km × 69 km = 44 cm

The extent to which these humps can cause backwater in these channels of extremely mild slope is evaluated in Section 4.1.1.

A similar calculation at Porto Murtinho is not possible because of lack of data at the river's mouth. However, the downstream river (i.e., the Middle Paraguay) has an average slope of 6 m/km throughout its 797-km length (Anderson et al., 1993). This much larger downstream slope points to the presence of a substantial geologic control upstream, at Fecho dos Morros, near the mouth of the Upper Paraguay river (Fig. 3). Significantly, this is precisely the location of the syenite sill mentioned by DNOS (1974).

Fig. A14  Eastern margin of the Upper Paraguay river near Porto Murtinho, Mato Grosso do Sul.


3.3.2  Flood Hydrology

The flood regime of the Upper Paraguay river is a result of complex climatic interactions at the various atmospheric spatial scales. The climate is determined primarily by the basin's geographic location (latitude and continental location) and secondarily by its topographic relief and surface features. Mean annual rainfall varies from as high as 1,800 mm at Chapada dos Parecis, the northernmost part of the basin, to as low as 800 mm in the alluvial fan of the Taquari river, near the basin's center (Projeto RADAMBRASIL, 1984). Within these limits, mean annual rainfall increases toward the mountains and high plains (planaltos) in the basin perimeter, and decreases toward the alluvial plains at the basin center.

Rainfall is concentrated in the summer months. The wettest three-month period is December-February; the driest is June-August. The temporal distribution of rainfall has a tendency to vary spatially in a general north-south direction. The percentage of annual rainfall in the wettest three-month period is greatest in the north (48% at Cáceres), gradually decreasing toward the south (to 36% at Porto Murtinho). Thus, the northern portion of the basin is prone to flooding from tributary streams. On the other hand, the percentage of annual rainfall in the driest three-month period is smaller in the north (3% at Cáceres), gradually increasing toward the south (8% at Corumbá, and 12% at Porto Murtinho) (EDIBAP, 1979). This indicates the possibility of local droughts recurring on an annual basis.

In any stream, the number of flood peaks per year is a good indication of the extent to which surface runoff is being diffused (i.e., attenuated) by the prevailing geomorphic conditions. If the number of flood peaks per year is high, say more than 10, there is little runoff diffusion. Conversely, if there is only one flood peak, runoff diffusion is at its maximum. The Upper Paraguay tributaries have a number of flood peaks, following intense storms that cover all or portions of their respective drainage basins. For instance, the Cuiabá river at Cuiabá has 15 flood peaks per year on the average; the Taquari river at Coxim has 18 flood peaks; the Miranda river at Miranda has 12 flood peaks (DNOS, 1974). A sequence of several flood peaks depicts the local nature of the floods as well as the absence of significant attenuation (the channel gradient varies from 7 to 50 cm/km, Table 3).

Unlike its tributaries, the Upper Paraguay river behaves quite differently with respect to the number of flood peaks. This reflects both its milder gradient (0.7 to 6.5 cm/km) and the presence of the Pantanal, which stores and further attenuates the flood peak. The overall effect of this hydrologic process is a reduction in the number of flood peaks. At Cáceres, close to the entrance to the Pantanal, there is an average of five flood peaks per year. However, the number of flood peaks decreases markedly downstream, to one at Amolar, one at Ladario, and one to two from Porto da Manga to Forte Coimbra. Downstream of Forte Coimbra, the number of peaks in creases somewhat due to local contributions. However, the locally generated peaks tend to be much smaller than the peak propagated from upstream (Hydrotechnic Corporation, 1979).

The floods in the Upper Paraguay river have been classified as follows (DNOS, 1974; Carvalho, 1986):

  • Common floods, which are exceeded 75% of the time (< 2-yr return period),

  • Mean floods, which are exceeded 50% of the time (2-yr return period),

  • Extraordinary floods, which are exceeded 25% of the time (4-yr return period), and

  • Exceptional floods, which are exceeded 10% of the time (10-yr return period).


The hydrographic records at Ladario (1900-95) show the strong attenuating capacity of the Pantanal upstream of this point. Throughout the 96-yr period of record, the flood wave at Ladario has always had a 12-month duration, i.e., one rise and one recession per year (Tables 13 and 14). The rise begins usually in December and finishes in June; the recession begins in June and finishes in December. The occurrence of the flood peak at Ladario varies with the flood level; it is accelerated (to May or April) during extraordinary and exceptional floods, slowed down (to June or July) during a typical flood year (common or mean flood), and again accelerated (to April, and in rare cases, late March) during multiannual droughts. The latter behavior is due to the drought flow being mostly contained within the river banks (Section 4.1.1).

Table 13.   Maximum seasonal water surface elevation at Ladario, 1900-95.1
Year Month Date Gage level
(cm)
Water surface
elevation
(m)
1900 06 25 432 86.47
01 06 10 439 86.54
02 06 04 500 87.15
03 05 16 271 84.86
04 06 03 500 87.15
05 05 11 662 88.77
06 05 06 561 87.76
07 07 13 369 85.84
08 07 23 369 85.84
09 05 27 277 84.92
10 03 23 200 84.15
11 06 21 217 84.32
12 06 17 510 87.25
13 04 08 639 88.54
14 07 10 357 85.72
15 04 12 151 83.66
16 07 25 326 85.41
17 06 14 513 87.28
18 07 22 345 85.60
19 07 08 300 85.15
20 05 12 637 88.52
21 04 07 607 88.22
22 06 13 426 86.41
23 06 14 550 87.65
24 07 04 341 85.56
25 07 20 230 84.45
26 06 18 547 87.62
27 07 02 407 86.22
28 07 08 287 85.02
29 06 04 531 87.19
30 06 06 520 87.35
31 06 03 550 87.65
32 05 21 598 88.13
33 05 16 511 87.26
1934 07 01 399 86.14
35 06 11 574 87.87
36 06 14 226 82.41
37 07 11 243 84.58
38 06 08 160 83.75
39 06 16 201 84.16
40 06 12 503 87.18
41 05 28 196 85.11
42 06 28 525 87.40
43 06 23 503 87.18
44 06 10 201 84.16
45 06 19 524 87.41
46 07 15 415 86.30
47 07 08 457 86.72
48 06 26 192 85.07
49 05 03 532 87.47
50 06 08 507 87.22
51 06 26 415 86.30
52 07 02 465 86.80
53 06 30 286 85.01
54 07 12 442 86.57
55 06 30 264 84.81
56 08 02 430 86.45
57 07 11 416 86.31
58 06 24 501 87.16
59 05 07 591 88.06
60 05 25 492 87.07
61 06 21 434 86.51
62 06 10 225 84.40
63 06 19 447 86.62
64 04 01 133 85.48
65 07 07 274 84.89
66 05 22 248 84.63
67 04 24 163 85.78
1968 06 06 205 84.20
69 05 31 180 83.95
70 06 16 213 84.28
71 05 28 265 84.80
72 05 25 187 84.02
73 06 18 209 84.24
74 05 25 543 87.58
75 07 16 433 86.48
76 06 22 485 87.00
77 04 20 552 87.67
78 05 02 536 87.51
79 03 24 628 88.41
80 04 18 617 88.32
81 05 19 546 87.61
82 04 21 652 88.67
83 05 10 536 87.51
84 05 23 507 87.22
85 04 15 607 88.22
86 06 27 433 86.48
87 06 07 499 87.14
88 04 17 664 88.81
89 05 13 612 88.27
90 06 26 450 86.65
91 05 27 549 87.64
92 06 17 538 87.53
93 05 18 516 87.31
94 07 12 394 88.09
95 04 14 656 88.71
1Source:  DNAEE (Departamento Nacional de Águas e Energia Elétrica), Brasília, and CPRM (Companhia de Pesquisa de Recursos Minerais), Rio de Janeiro.

Table 14.   Minimum seasonal water surface elevation at Ladario, 1900-95.1
Year Month Date Gage level
(cm)
Water surface
elevation
(m)
1900 12 01 172 83.87
01 11 04 112 83.27
02 12 25 135 83.50
03 10 03 031 82.46
04 11 07 200 84.15
05 12 28 190 84.05
06 11 22 085 83.00
07 11 25 145 83.60
08 10 29 202 84.17
09 10 07 021 82.36
10 10 17 -046 81.69
11 11 02 028 82.43
12 11 12 153 83.68
13 12 22 100 83.15
14 12 16 074 82.89
15 10 06 -031 81.84
16 11 14 026 82.41
18 01 02 078 82.93
18-2 11 18 102 83.17
19 11 14 127 83.42
20 12 21 294 85.09
22 01 07 142 83.57
22-2 11 23 102 83.17
24 02 18 197 84.12
24-2 11 18 034 82.49
25 10 08 110 83.25
26 12 22 148 83.63
27 11 29 050 82.65
28 11 13 090 83.05
29 12 06 138 83.53
30 11 06 155 83.70
32 01 14 217 85.32
32-2 11 30 202 85.17
33 12 07 118 83.33
1934 11 26 135 83.50
36 02 22 172 83.87
36-2 10 27 -013 82.02
37 11 22 037 82.52
38 09 19 -027 81.88
39 10 23 -021 81.94
40 12 09 113 83.28
41 10 16 000 82.15
43 01 02 095 83.10
44 02 12 137 83.52
44-2 10 05 -039 81.76
45 12 11 104 83.19
46 12 06 088 83.03
47 12 24 086 83.01
48 10 01 -018 81.97
49 10 31 059 82.74
50 11 21 102 83.17
51 12 06 087 83.02
52 12 15 096 83.11
53 11 17 057 82.72
54 12 16 082 82.97
55 11 30 007 82.22
56 12 12 156 83.71
57 11 05 174 83.89
58 12 18 236 84.51
59 12 30 153 83.68
60 12 12 150 83.65
61 12 24 085 83.00
62 11 30 010 82.25
64 01 12 030 82.45
64-2 09 15 -061 81.54
65 11 22 059 82.74
66 10 15 -004 82.11
67 10 12 -053 81.62
1968 10 18 -021 81.94
69 09 28 -053 81.62
70 12 28 -019 81.96
71 09 20 -057 81.58
72 10 09 000 82.15
73 10 19 -002 82.15
74 12 02 128 83.43
75 11 23 136 83.51
76 12 15 217 84.32
77 12 18 218 84.33
78 12 05 195 84.10
79 12 17 177 83.92
80 12 19 220 85.35
81 12 06 171 83.86
82 12 20 245 84.60
83 12 29 234 84.51
84 12 01 247 84.62
86 01 03 150 83.65
86-2 12 13 124 83.39
87 11 24 129 83.44
88 12 07 136 83.51
89 12 06 205 84.20
90 12 20 190 84.05
92 01 10 228 84.43
93 01 11 321 85.36
93-2 12 15 130 83.45
94 11 23 134 83.51
1Source:  DNAEE (Departamento Nacional de Águas e Energia Elétrica), Brasília, and CPRM (Companhia de Pesquisa de Recursos Minerais), Rio de Janeiro.

Prediction of flood flows along the Upper Paraguay river using mathematical modeling has been attempted by DNOS (1974) and EDIBAP (1979). Under a limited budget, the DNOS model continues to be operated to this date by the Companhia de Pesquisas de Recursos Minerais (CPRM), in Rio de Janeiro. It is a difficult undertaking because of the temporal and spatial variability and complexity of the hydrologic processes, which includes high channel sinuosity, branching, overflows, endorheic surface drainage, and the presence of aquatic macrophytes in the surface waters. This is compounded by the complex nature of the interaction between surface and subsurface water, since the Pantanal has a net gain of water in a wet year, and a net loss in a dry year (EDIBAP, 1979; Adámoli, 1986).

The speed of propagation of the annual flood wave can be readily extracted from the discharge measurements. Thus, it has been established that a typical flood wave takes about 130-150 days to travel from Cáceres to Porto Murtinho. This represents an average speed of propagation of only 0.09-0.11 m/s. This extremely low value is due to the substantial contribution of channel overflows to the overall flood wave propagation (Fig. A15).

Fig. A15  Flooding of the Isla Margarita, on the Upper Paraguay river, Paraguay.

Table 15 shows low flow, mean annual, and peak flood discharges along the Upper Paraguay river. Also shown are the ratio of peak flood to low flow discharge, and peak flood to mean annual discharge. The low values of these ratios (compared to other rivers in similar climatic settings) show that the Upper Paraguay river is very effective in decreasing the flood peaks and, correspondingly, increasing the low flows. This is due to the presence of the Pantanal. Thus, the Pantanal is the geomorphic feature that provides the mechanism for the spreading (i.e., attenuation, diffusion) of flood flows and, consequently, the increased permanence of low flows.

Table 15.   Comparison of low flow, mean annual, and peak flood discharges along
Upper Paraguay river.1

Station Low flow discharge1 Q1
(m3/s)
Mean annual discharge2 Qa
(m3/s)
Peak flood discharge1 Qp
(m3/s)
Ratio
Qp / Q1
Ratio
Qp / Qa
Cáceres 140 382 1,281 9.15 3.35
Descalvados 270 437 781 2.89 1.79
Porto Conceição 175 341 536 3.06 1.57
Bela Vista do Norte 27 144 215 7.96 1.49
Amolar 432 943 1,747 4.04 1.85
Porto São Francisco 492 1,046 2,801 5.69 2.68
Ladario 441 1,261 1,942 4.40 1.54
Porto da Manga 594 1,340 2,331 3.92 1.74
Porto Esperança 589 1,412 4,098 6.96 2.90
Forte Coimbra 635 1,467 3,510 5.53 2.39
Barranco Branco 573 1,505 3,455 6.03 2.29
Fecho dos Morros 586 1,549 3,748 6.40 2.42
Porto Murtinho 549 1,555 3,721 6.78 2.39
1Source:  DNOS (1974), DNAEE, and Hidrologia S. A. 2Source:  EDIBAP (1979).


3.3.3  Low Flows and Droughts

Table 14 shows the minimum seasonal water surface elevation at Ladario, from 1900 to 1994. The following conclusions can be drawn from these records:

  • The minimum seasonal flow occurs usually late during the calendar year, in the month of November or December, although occasionally it may be advanced to October, or delayed to January or February.

  • The minimum seasonal flow has been recorded at or below zero gage in the following years or drought periods:

    • In 1910 and 1915.

    • Five times during the nine-year drought period 1936-44.

    • In 1948.

    • Nine times during the ten-year drought period 1964-73.

As shown by the Ladario gage records, the Upper Paraguay river has a tendency toward multiannual droughts with a recurrence period of 28-30 years. The lack of more extensive data precludes a more thorough analysis. Nevertheless, the tendency is borne out by the data and should be acknowledged.

According to the EDIBAP study, the Ladario records, from 1900 through 1977, show a tendency for a decrease in both maximum and minimum seasonal flows (EDIBAP, 1979). In light of the wet period being experienced since 1974, this conclusion is in need of revision.


3.3.4  Basin Yield

The complexity of the hydrologic setting in the Upper Paraguay river precludes a detailed analysis of basin yield vs annual precipitation. However, an approximate analysis based on mean annual precipitation is possible. During a wet year, the annual precipitation P is split in three ways:

  1. Runoff R,

  2. Vaporization V, which consists of evapotranspiration from vegetation, evaporation from water bodies, and evaporation from bare ground; and

  3. Change in basin storage ΔS, which consists of surface, subsurface, and groundwater storage.


Deep percolation is usually small or intractable, and can be neglected on practical grounds (L'vovich, 1979). Conversely, during a dry year, annual precipitation plus (a fraction of) basin storage gointo runoff and vaporization.

A simple water balance equation can be formulated as follows:

P = R + V ± ΔS (3.1)

where ΔS is positive during a wet year and negative during a dry year (Adámoli, 1986a). In an average year, where change in basin storage is reduced to a minimum, the above equation reduces to:

P = R + V (3.2)

from which average basin yield can be calculated.

The spatially averaged mean annual rainfall in the Upper Paraguay basin is 1,380 mm according to EDIBAP (1979), or 1,180 mm according to RADAMBRASIL (1984). This estimate is based on isohyetal maps prepared for the Brazilian portion of the basin (71%). Comparable maps for the remainder of the basin, the portion which is in Eastern Bolivia and Northwestern Paraguay, are not readily available.

The mean annual discharge at the basin mouth (see Table 12) is 1,565 m3/s. According to DNOS (1974), the mean of six years of annual discharge measurements (1965-71) at Porto Murtinho is 1,212 m3/s. However, this value appears too low, since this was a particularly dry period (see Section 3.3.3). A longer and wetter period (1969-78) of measurement at Porto Murtinho (33 discharge measurements) gives 2,188 m3/s (Hidrologia S. A., unpublished data).

The basin drainage area at its mouth is 496,000 km2 (Section 2.2). Given this information, the mean annual runoff coefficient Kr, i.e., the ratio of runoff to rainfall, can be calculated as follows:

            (1,565 m3/s) (86,400 s/d) (365 d/y) (1,000 mm/m)            
Kr  =  ___________________________________________________  =  0.072
               (1,380 mm/y) (496,000 km2) (1,000 m/km)2      
(3.3)

A similar calculation, assuming an intermediate value of mean annual discharge Qa = 1,700 m3/s, with P = 1,180 mm/y leads to:

            (1,700 m3/s) (86,400 s/d) (365 d/y) (1,000 mm/m)            
Kr  =  ___________________________________________________  =  0.091
                (1,180 mm/y) (496,000 km2) (1,000 m/km)2      
(3.4)

Thus, the mean annual runoff coefficient for the Upper Paraguay basin can be taken as Kr = 0.08. That is, on an average year, runoff at the basin outlet amounts to 8% of rainfall, with the balance returned to the atmosphere as evaporation and evapotranspiration (i.e., the vaporization coefficient is Kv = 0.92). A similar analysis for the 11-year period 1965-76 showed a runoff coefficient varying in the range 7-14%, with a mean of 10% (EDIBAP, 1979).

The above calculation confirms that the Pantanal functions not only as an attenuating mechanism for flood flows (and consequent increases in low flows), but also as an abstracting mechanism for all flows, i.e., as an effective means of storing the would-be runoff and converting it instead into evaporation/evapotranspiration. Throughout millennia, this process has been responsible for sustaining the extraordinary biotic potential of the Pantanal (Tricart, 1982).

By way of comparison, the mean annual runoff at Cáceres, at the northern entrance to the Pantanal, is 382 m3/s, and the contributing drainage area is 33,860 km2 (Table 12). The mean annual precipitation of the subbasin varies from 2,000 mm at the headwaters to 1,300 mm at Cáceres (EDIBAP, 1979). This amounts to a runoff coefficient Kr = 0.22, which is 2.75 times that of the Upper Paraguay river at its mouth. Likewise, the mean annual runoff coefficient of the Paraná river at Corrientes (Argentina) has been calculated at Kr = 0.16 for the decade 1962-71, Kr = 0.19 for 1972-81, and Kr = 0.22 for 1982-91 (Ponce, 1994). These values are from 2 to 2.75 times that of the Upper Paraguay river at its mouth.

These calculations confirm that the markedly strong attenuating and abstracting property of the Upper Paraguay is due to the presence of the Pantanal, while the mean annual runoff coefficients of the Upper Paraguay river at Cáceres (immediately upstream of the Pantanal) and the Paraná river at Corrientes (964 km downstream of the Pantanal) depict more typical subhumid/humid basins.

The annual potential evapotranspiration in the Pantanal varies spatially from less than 1,100 mm to more than 1,400 mm, according to the Thornthwaite method (Alfonsi and Camargo, 1986). Measured pan evaporation data at Fazenda São João and Fazenda Rio Negro for 1971-72 shows 1,650 mm (Tarifa, 1986).

The actual evapotranspiration in an average year is estimated to be:

Ea = 0.92 × 1,180 mm = 1,086 mm (3.5)

or,

Ea = 0.92 × 1,380 mm = 1,270 mm (3.6)

depending on which value of mean annual precipitation is used in the calculation (Projeto RADAMBRASIL, 1984; or EDIBAP, 1979). Thus, on an annual basis, actual evapotranspiration in the Upper Paraguay basin is very close to potential evapotranspiration.

The calculation of runoff coefficient is based on surface runoff at the basin outlet, and does not include subsurface runoff at the basin outlet, which may be real but difficult to evaluate directly. The existence of a certain amount of subsurface runoff is postulated on the basis that the mean annual discharge at Asunción, on the Middle Paraguay, 542 km downstream of the Apa river confluence, is 2,700 m3/s (INTERNAVE, 1990). The increase of more than 1,000 m3/s is difficult to explain, particularly since there are no major intervening drainages. OEA (1975) has calculated that the combined contribution of the Apa, Aquidabán, and Ypané rivers, which are gaged, is about 180 m3/s. The contribution of the Aguaray-Guazú and other ungaged tributaries is estimated to be about 100 m3/s, based on areal comparisons. The subsurface runoff, if it does exist in substantial amounts, would have the effect of reducing the vaporization coefficient Kv to a somewhat lower value, say, around 0.88-0.90, which is still high in comparison to other basins in similar climatic settings.


3.3.5  Sedimentology

Measurements of suspended sediments, which include fine gravel, sand, silt, and clay particles along the Upper Paraguay river have been scanty. The longest existing records are those of Cáceres and Porto Esperança (Fig. 3).

The Cáceres data, shown in Table 16, consists of 55 once-monthly depth-integrated measurements of sediment discharge taken between March 1977 and February 1982. The Porto Esperança data, shown in Table17, consists of 52 once-monthly depth-integrated measurements taken between April 1977 and November 1981.

These measurements and related calculations were carried out by Hidrologia S.A. for the now defunct Departamento Nacional de Obras de Saneamento (DNOS). The methodologies utilized were the Modified Einstein and the Frijling-Kalinske methods.

Table 16.   Sediment discharge measurements, Upper Paraguay river
at Cáceres. 1

Date Water discharge
(m3/s)
Sediment discharge
(tons/day)
Sediment concentration
(mg/liter)
25MAR77 709 12,207 199
27MAY77 585 13,272 262
30JUN77 421 7,051 194
19JUL77 306 7,377 279
28AUG77 246 5,362 252
17SEPT77 232 6,531 326
25OCT77 271 7,359 314
20NOV77 349 15,300 507
31JAN78 930 13,452 167
16FEB78 618 8,061 151
06MAR78 963 14,973 180
22MAR78 911 9,651 123
08MAY78 624 20,256 376
13MAY78 666 22,655 394
10JUN78 557 13,804 287
10JUL78 395 6,190 181
03AUG78 305 6,310 239
09SEPT78 260 1,864 83
09OCT78 253 1,443 66
03NOV78 388 10,946 326
05DEC78 480 5,690 137
03JAN79 977 4,540 54
11FEB79 1,236 5,875 55
26MAR79 1,188 7,183 70
10APR79 1,094 5,172 55
19MAY79 695 3,605 60
08JUN79 544 2,998 64
04JUL79 434 1,577 42
09AUG79 334 1,895 66
04SEPT79 315 1,265 46
02OCT79 372 2,156 67
05NOV79 374 2,472 76
05DEC79 315 2,040 75
03JAN80 701 2,760 45
01FEB80 990 3,917 46
09MAR80 1,565 3,993 29
01APR80 991 12,674 150
07MAY80 760 18,730 285
01JUN80 724 13,540 216
02JUL80 422 2,147 59
01AUG80 329 1,567 55
05SEPT80 299 2,018 78
01OCT80 322 1,298 47
03NOV80 345 1,242 42
15DEC80 581 4,080 81
19JAN81 1,013 39,662 453
01FEB81 1,379 4,690 39
05MAR81 1,021 7,535 85
01APR81 997 4,333 50
12MAY81 606 1,460 28
26JUN81 408 1,783 51
10AUG81 287 1,202 48
05OCT81 302 1,239 47
14DEC81 521 2,440 54
02FEB82 895 24,051 311
1Source:  DNOS, DNAEE, and Hidrología S. A. (unpublished data).

Table 17.   Sediment discharge measurements, Upper Paraguay river
at Porto Esperança.1

Date Water discharge
(m3/s)
Sediment discharge
(tons/day)
Sediment concentration (mg/liter)
03APR77 3,520 160,020 526
28MAY77 4,152 172,469 481
04JUN77 4,223 103,238 283
18AUG77 2,730 77,263 327
16SEPT77 2,383 72,821 353
07OCT77 1,979 63,809 373
17NOV77 1,642 127,336 897
06DEC77 1,426 59,946 486
13JAN78 1,816 94,025 599
02FEB78 3,207 102,809 371
27MAR78 2,802 93,364 385
05MAY78 3,382 66,867 229
12MAY78 3,853 125,559 377
23JUN78 3,142 68,467 252
09JUL78 2,776 63,622 265
09OCT78 1,578 22,406 164
22DEC78 1,505 7,709 59
23JAN79 2,388 11,248 54
20FEB79 2,950 11,063 43
17MAR79 5,881 30,768 60
11APR79 5,312 17,046 37
09MAY79 4,469 18,888 49
19JUN79 3,718 12,359 38
20JUL79 3,146 19,445 72
30AUG79 2,568 8,552 39
26SEPT79 2,174 20,033 107
25OCT79 1,833 16,889 107
15NOV79 1,561 8,287 61
28DEC79 1,701 8,540 58
11JAN80 1,770 8,000 52
23FEB80 2,160 12,060 65
31MAR80 3,813 34,480 105
03APR80 5,623 46,804 96
16MAY80 5,078 20,379 46
26JUN80 3,754 17,357 53
10JUL80 3,536 9,116 30
06AUG80 2,866 9,780 39
06SEPT80 2,250 10,086 52
04OCT80 2,062 10,381 58
18NOV80 1,853 13,050 81
16DEC80 1,378 11,073 93
23JAN81 2,416 77,990 373
01FEB81 2,827 11,190 46
26MAR81 3,315 26,705 93
01APR81 3,573 17,005 55
22MAY81 4,220 18,491 51
11JUL81 3,803 5,998 18
24JUL81 3,332 3,483 12
17SEPT81 2,327 36,030 179
30SEPT81 2,060 31,968 179
16NOV81 1,565 14,226 105
27NOV81 1,460 13,523 107
1Source:  DNOS, DNAEE, and Hidrologia S. A. (unpublished data).

The values shown in Tables 16 and 17 are total sediment discharge, consisting of:

  • Bed load, i.e., coarse particles (primarily gravel and sand) transported by rolling and sliding along the bed,

  • Suspended bed material load, i.e., coarse particles transported in suspension, and

  • Wash load, i.e., suspended fine particles, the concentration of which depends on source availability and not on the flow hydraulics.

These measurements enable the following observations regarding total sediment transport in the Upper Paraguay river:

  1. The measured sediment concentration at Cáceres varies between 28 mg/liter and 507 mg/liter, with mean 147 mg/liter and standard deviation 122 mg/liter (Table 18).

  2. The measured sediment concentration at Porto Esperança varies between 12 mg/liter and 897 mg/liter, with mean 176 mg/liter and standard deviation 183 mg/liter (Table 18).

  3. The correlation between sediment discharge and water discharge at both gaging stations is somewhat poor. This is partly due to the presence of the wash load, whose concentration does not depend on the water discharge. Generally, the wash load concentration is a function of the degree of natural or human-produced watershed disturbance upstream of the gaging station.

Table 18.   Summary of sediment discharge measurements
in Upper Paraguay river and tributaries.1

River/tributary Gaging station No. of data points Maximum concentration (ppm)2 Mean concentration (ppm)2 Minimum concentration (ppm)2 Standard deviation (ppm)2
Paraguay Cáceres 55 507 147 28 122
Cuiabá Cuiabá 51 985 235 23 211
Piquiri Estrada BR-163 60 1,224 362 60 239
Taquari Coxim 60 2,504 845 198 557
Aquidauana Aquidauana 63 1,792 620 97 411
Miranda Estrada MT-738 60 2,650 626 112 551
Paraguay Porto Esperança 52 897 176 12 183
1Source:  Source: DNOS, DNAEE, and Hidrologia S. A., unpublished data.
2 At concentrations less than 5,000 ppm, 1 mg/liter is approximately equal to 1 ppm, i.e., 1 mg/liter is less than 1.01 ppm.

Table 18 includes a summary of (depth-integrated) sediment discharge measurements at gaging stations along the main tributaries of the Upper Paraguay river: Cuiabá, Piquiri, Taquari, Aquidauana, and Miranda. Figure 3 shows the location of the gaging stations. Based on this limited but significant data, a preliminary sediment budget analysis is performed in Section 4.2.

[Note the Errata in this online edition].


3.4  Ecological Setting

The ecological setting of the Upper Paraguay river basin and the Pantanal of Mato Grosso is unique in the American continent. The basin is strategically located contiguous to four major South American biomes, which surround it, exerting their influence on it (EDIBAP, 1979; Adámoli, 1986b):

  1. The tropical Amazon rainforest to the north and northwest

  2. The subhumid savanna woodlands (cerrados) of Central Brazil to the northeast, east, and southeast

  3. The humid Atlantic forest (Floresta Atlántica) to the south

  4. The semiarid scrub forest (Chaco) of Eastern Bolivia and Northwestern Paraguay to the west and southwest.


The unusual combination of geology, geomorphology, and hydrology (see Sections 3.1 to 3.3) has contributed to the richness and variety of the vegetation and associated microclimates of the Pantanal. In turn, this helps sustain a diverse group of ecosystems, where a complex assortment of permanent swamps, seasonal swamps, and terra firma is seasonally replenished with ample moisture, sediment, and nutrients. The entire process hinges on the high rate of vaporization (estimated at up to 92% on an average year) which characterizes the hydrologic budget of the Upper Paraguay river basin.


3.4.1  Flora

In the existing literature, the Pantanal vegetation is often marked as a single unit and referred to as the "Pantanal" complex. Actually, the latter is a mosaic of many different communities, with frequent abrupt changes, often correlated with topography, and many ecotones. The Pantanal has no endemic flora of its own; rather, it is made up of elements from mata (deciduous and semideciduous forests transitional to the tropical Amazon rainforest and the humid Atlantic forest), campo (open grassland), cerrado (savanna woodland), and caatinga (desert scrub forest).

There are three main vegetation zones in the Pantanal (Veloso, 1947):

  1. The aquatic and hydrophylous zone,

  2. The hygrophylous zone, and

  3. The mesophylous zone.


The hydrophylous zone is permanently flooded. It is characterized by three vegetation types:

  • Aquatics in flowing water (Eichhornia crassipes, Pistia, Elodea);

  • Floating aquatics in stagnant water (Eichhornia azurea, Marsilea, Reussia subovata); and

  • Aquatics largely rooted in shallow water (Echinodorus spp., Hydrocleis spp., Limnocharis spp., Victoria amazonica, Ludwigia natans) (Silva and Esteves, 1993).

The hygrophylous zone is divided into: (a) permanently flooded, and (b) seasonally flooded swamps, with the latter usually dominated by one species. Plant communities of the seasonal swamps include the Thalietum (dominated by Thalia geniculata), the Cyperacietum (dominated by Cyperus giganteus), and the Ipomoećtum (dominated by Ipomoea fistulosa).

The mesophylous zone coincides with noninundated alluvial soils. Many floristic associations occur in this soil type, as well as many transitional areas (ecotones). Veloso (1947) classified associations in order of successional development, and concluded that the region is in an active state of change toward a more mesic forest.

The most striking aspect of the Pantanal is its curious combination of mesic and xeric vegetation growing side by side, a result of its unique combination of climate and geomorphology (Tricart, 1982). Toward the center of the Pantanal, close to Corumbá, the climate is markedly seasonal, with a clearly defined drought period. Given the extremely flat topography, a small difference in elevation (one or two meters, or less) is all that is needed to make a great difference in seasonal soil moisture, particularly when the underlying strata is coarse alluvium.

Hoehne (1936) has referred to the Pantanal as a mixture of Amazonas (hylean) and Ceará (caatinga), and provided examples of the two types of flora by contrasting the gigantic candelabra cactus (Cereus peruvianus), and other cacti such as Opuntia stenarthra, with the aquatic Alismataceae and Victoria.

Prance and Schaller (1982) and Schaller (1983), among others, have noted the strong cerrado element in the Pantanal (Fig. A16). These cerrados are dominated by species such as Bowdichia virgiloides, Caryocar brasiliense, Curatella americana, Qualea parviflora, and Tabebuia caraiba, which are typical of the savanna woodlands (Planaltos) of Central Brazil. Cerrado occurs mainly in the nonflooded upland, but also towards the eastern edge of the Pantanal, where the land is inundated for only short periods at the height of the flood season. Such wet cerrado tends to consists of numerous islands of cerradão (dense cerrado forest) on slightly elevated areas that are not flooded.

Fig. A16  Paratudal (Tabebuia aurea), near Corumbá, Mato Grosso do Sul.

Cerrado species which are most resistant to waterlogging (e.g., Byrsonima crassifolia and Curatella americana) are common near the boundary cerrado/campo, and on raised islands of ground in wet campos (Furley and Ratter, 1988) (Fig. A17). The distribution of these islands produces the campos de murundus, consisting of an expanse of wet campos dotted with a regular pattern of raised earthmounds bearing cerrado trees, shrubs, and often termitaria. The larger earthmounds, or capões, are circular or elliptical in shape, of lengths up to 300 m, and sparsely distributed across the seasonally flooded campos (Ponce and Cunha, 1993).

Fig. A17  Large vegetated earthmound in the Pantanal of Mato Grosso.

The sharpness of the campo/cerrado boundary has been documented by Eiten (1975). Within 1 m, or even 0.5 m, the change from the shrubs and low trees of the cerrado to the grassy layer without woody plants of the campo is complete. The reason for this abrupt change appears to be that the cerrado plants cannot establish themselves from seed in continually wet soil. In general, the campo occupies a site with a lower and more fluctuating water table, whereas the cerrado occupies the higher ground, where the soil seldom if ever remains saturated. In almost all cases, the cerrado stops suddenly at the edge of the campo, apparently due to the competition between the two vegetation types as whole plant communities. Cerrado species tolerant of waterlogging are able to grow in open campos in places where the soil level is only a few centimeters higher than elsewhere. The observation that larger islands on Pantanal landscape are thickly clothed with cerrado vegetation confirms that groundwater level exerts a precise control on the cerrado/campo boundary.

In the Pantanal, the main trend of vegetational variation is highly correlated with soil moisture and topography. The patent lack of trees in the wet campos is striking, particularly since a wide range of woody species successfully colonizes both the interfluves, which are drier than the campos, and the stream sides (riparian areas, or gallery forests) which are wetter. The absence of tall, woody species from areas which are intermediate in their physical characteristics is attributed to the fluctuating nature of the water table and associated soil moisture. Thus, trees are able to tolerate both permanently wet (gallery forest) and moist-to-dry (cerrado) environmental conditions, but not an extreme alternation of saturation and desiccation (Cole, 1960). Areas subject to the latter are successfully colonized by the grassy elements (campos).

In summary, the Pantanal is extremely rich in floristic diversity and physiognomic composition (Fig. A18). Its floristic diversity is due to its location, in the middle of four great South American biomes: the tropical Amazon rainforest, the subhumid savannas of Central Brazil, the humid Atlantic forest, and the semiarid scrub forest of the Chaco. Its diverse physiognomic composition is due largely to its variety of geomorphic/topographic features, which include baías, barreiros, cordilheiras, vazantes, corixos, capões, murundus, and aterros de bugre (Cunha, 1990; Ponce and Cunha, 1993). The annual flood pulse replenishes the Pantanal ecosystems with ample water, sediment, and nutrients, assuring their continuance and survival (Junk et al., 1989).

Fig. A18  Seasonally flooded savanna woodland near Miranda, Mato Grosso do Sul.


3.4.2  Fauna

The ecological diversity of the Pantanal ecosystems has conditioned their suitability as habitat for a variety of animal species, among which are numerous species of mammals, reptiles, fish, birds, butterflies, and other invertebrates (Brown, 1986). It also serves as the resting place for many species of migratory birds from the Northern Hemisphere and other regions of South America (Antas, P. T. Z., 1983; Brown, 1986; Cintra and Yamashita, 1990).

Fig. A19  Wildlife in the Pantanal of Mato Grosso.

Terrestrial and amphibious species inhabiting the Pantanal include (EDIBAP, 1979; Bucher et al., 1993):

  • caiman (jacaré, Caiman crocodilus yacare)

  • armadillo (tatú bola, Tolypeutes tricinetus)

  • bush dog (cachorro do mato vinagre, Speothos venaticus)

  • capybara (capivara, Hydrochoerus hydrochaeris) (Fig. A20)

  • crab-eating fox (cachorro do mato, Dusicyon thous)

  • giant anteater (tamandúa bandeira, Myrmecophaga trydactyla)

  • giant armadillo (tatú canastra, Priodontes giganteus)

  • giant otter (ariranha, Pteronura brasiliensis)

  • jaguar (onça pintada, Pantera onça)

  • maned wolf (lobo guará, Chrysocyon brachyurus)

  • marsh deer (cervo do pantanal, Blastocerus dichotomus)

  • neotropical river otter (lontra, Lutra longicaudis)

  • ocelot (jaguaritica, Felis pardalis)

  • pampas deer (veado campeiro, Ozotocerus bezoarticus)

  • rhea (ema, Rhea americana)

  • tapir (anta, Tapirus terrestris)

  • peccary (porco monteiro, Tayassu pecari).

These species selectively inhabit the campos, capões, cordilheiras, gallery forests, and water bodies (baías, vazantes, corixos) of the Pantanal. In particular, the higher ground (capões, cordilheiras) is used by terrestrial species as temporary shelter during the seasonal flooding. The impressive biodiversity of the Pantanal is due in large measure to its unusual geological, geomorphological, and hydrological setting.

Fig. A20  Capybara (Hydrochoerus hydrochaeris) along the banks of the São Lourenço river, Mato Grosso.

Wildlife management in the Pantanal has been discussed by Dourojeanni (1980), Paiva (1984), and Alho (1986), among others. Wildlife conservation in the Pantanal, particularly with regard to the jaguar (Pantera onça), has been discussed by Quigley and Crawshaw (1992).

Fig. A21   The jabiru stork, or tuiuiu (Jabiru mycteria), symbol of the Pantanal of Mato Grosso.


4.  HYDROLOGIC AND ENVIRONMENTAL IMPACT OF THE HIDROVIA PROJECT
[Summary]   [References]      [Top]   [Executive Summary]   [Introduction]   [Geographical Background]   [Upper Paraguay River]  

This section evaluates the hydrologic impact of the Hidrovia project on the Pantanal of Mato Grosso, that is, the changes in water and sediment runoff to be expected as a result of project implementation. An analysis of possible downstream impacts and other related environmental impacts is included.

The evaluation is divided into four parts:

  1. Runoff impacts

  2. Sediment impacts

  3. Impact on the flood regime of the Paraná river

  4. Other related environmental impacts.

This section analyzes, interprets, and expands on the previous sections.


4.1  Runoff Impacts

The runoff impacts of the Hidrovia project on the Upper Paraguay river and the Pantanal of Mato Grosso can be considered under four categories:

  1. Changes in flood regime

  2. Changes in baseflow
  3. Changes in water yield

  4. Changes in drought regime.

Normally, the effects of natural or human-induced changes in runoff patterns are subject to evaluation using mathematical (i.e., computer) modeling. While computer modeling is routine practice in small and midsize basins, it is a complex undertaking--and often a logistical nightmare--in very large basins, particularly those located in remote and inaccessible regions. The Upper Paraguay river basin, with its 496,000 km2 (of which 145,000 km2 located in Bolivian and Paraguayan territory are largely without data), does not lend itself readily to mathematical modeling. This is due to its unusual spatial complexity, which includes high channel sinuosity, numerous bifurcations, seasonal over flows, and endorheic and often confusing drainages. In addition, there is a seasonal abundance of aquatic macrophytes in the surface waters, and an active--and for all practical purposes, intractable--interaction between surface water and groundwater.

The modeling carried out in the early 1970's by DNOS, with the technical assistance of UNDP/UNESCO, proved to be a challenge (DNOS, 1974). The SSARR model (Streamflow Synthesis And Reservoir Regulation), developed by the North Pacific Division of the U.S. Army Corps of Engineers was used to model the response of the Upper Paraguay river basin to distributed precipitation inputs (U.S. Army Engineer North Pacific Division, 1975). The objective was to develop a flood forecasting capability so that sufficient warning could be given in the event of an extraordinary or exceptional flood.

With a limited budget, the model continues to be operated to this date (1995) by the Companhia de Pesquisa de Recursos Minerais, in Rio de Janeiro. In light of the unusual complexity of the Upper Paraguay river system and adjoining Pantanal, the predictive capability of the model often falls short of expectations. The difficulty appears to be the inability of the model to adjust its parameters in real time to account for the variability of the flow (inbank, overbank, and high overbank). SSARR is a conceptual runoff model based on the cascade of linear reservoirs, while the Upper Paraguay river and adjoining Pantanal have marked two- and three-dimensional flow patterns, in addition to strong nonlinear interactions between inbank and overbank flows (Fig. A22) (Ponce, 1989). These nonlinear interactions results in the flood peak typically being accelerated during exceptional and extraordinary floods, slowed down during common and mean floods, and again accelerated during drought years (Section 4.1.1) (PORTOBRAS, 1983).

Fig. A22  Nonlinear interactions between inbank and overbank flows.

To compound its spatial diversity, the Upper Paraguay river is constantly changing its bed to adjust to changes in water and sediment discharge. Furthermore, the river is subject to geologic controls (rock outcrops and abutting rocky hills) that condition the development of its gradient in the geologic time scale. No currently available mathematical model is effectively able to account for all these features and their variabilities. This study will use analysis based on established principles of hydrology and river hydraulics to evaluate the hydrologic impact of the Hidrovia on the Pantanal of Mato Grosso.


4.1.1  Changes in Flood Regime

The question is whether the proposed navigation improvements on the Upper Paraguay river will change the river's flood regime and affect the Pantanal of Mato Grosso. The proposed navigational improvements include: (a) channel straightening by realignment and cutoffs, (b) dredging, blasting of rocky sills and other rock out crops, and (c) the possibility of hydraulic control structures (IDB, 1995). These interventions are likely to have a substantial impact on the flood regime, the degree of which will vary depending on the type and extent of intervention, and its location along the river.

In order to evaluate the impact, the needs of the Hidrovia are contrasted here with the nature of the river. The Hidrovia needs a channel sufficiently straight, wide, and deep:

  • Sufficiently straight, to shorten the distance of travel (that could, in turn, reduce transportation costs), and to minimize the need for cumbersome and time-consuming maneuvers around sharp bends (such as breaking the tow apart), and

  • Sufficiently wide and deep, to allow ample lateral space and draft for the safe passage of sea-going vessels throughout the year.

While the dimensions of the proposed navigation channel have yet to be determined, a 50-m wide, 3-m deep channel has been initially considered (CEBRAC/ICV/WWF, 1994). Whether the 3-m depth requirement will be demanded all the way to Cáceres, the furthest upstream point of the Hidrovia, is still under study.

In contrast with the first requirement of the Hidrovia, the river traces a sinuous or meandering path. (Sinuosity is defined as the ratio of river length to valley length). The sinuosity of the Upper Paraguay river varies widely, from 2.93 from 40 km downstream of Porto Conceição to Refúgio das Três Bocas, to 1.17 from Corumbá to the confluence with the Taquari Velho (Table 1). Within individual reaches, the highest sinuosity is in the vicinity of Porto Conceição, where the ends of a 50-km reach are separated by a straight distance of only 13 km, i.e., a sinuosity of 3.85 (INTERNAVE, 1990). Particularly upstream of Corumbá, where the river is more sinuous, channel straightening is likely to bring about substantial changes in the flood regime.

The effect of channel straightening on flood runoff is evaluated by examining the flood peak at Ladario, close to the center of the Pantanal (Fig. 3). Figure 8 shows a plot of peak flood stage vs date of occurrence at Ladario. [Note of the online edition: This figure has been referred to as the "boomerang-shaped cloud" by later studies of Hidrovia hydrologic and environmental impact].

The median peak flood stage for the entire period of record (1900-1995) is 4.45 m. Examination of Fig. 8 leads to the following conclusions:

  • Common (less than 2-yr) and mean (2-yr) flood peaks (stage lower than 4.45 m) are slowed down to late June or July, and in rare cases, to early August.

  • Extraordinary (4-yr) and exceptional (10-yr) flood peaks (stage equal to or higher than 4.45 m) are accelerated to early June, May, or April, and in rare cases, to late March.

  • During drought years, the flood peak is also accelerated (to April or even late March), since the flood is mostly contained inbank and is able to travel faster.


Fig. 8  Upper Paraguay river at Ladario:  Peak flood stage and date of occurrence.

As shown in Table 13 and Fig. 8, in the past 22 years (1974-95) the median peak flood stage for the entire period of record has been exceeded 19 times, i.e., 86% of the time! The implication of this fact is that some extraordinary floods may be downgraded to mean floods, possibly due to changes in hydrologic response which may already be occurring in the basin (Section 4.1.4). Thus, it is concluded that during high mean floods (2-yr), extraordinary (4-yr) and exceptional (10-yr) floods, channel straightening will accelerate the concentration of flood runoff and increase the flood wave peak.

The sinuosity reflects the river's tendency to meander, a natural process which is conditioned by its water and sediment discharge, channel slope, and boundary friction (bed and bank friction). A decrease in sinuosity as a result of channel straightening increases channel slope, leads to changes in water and sediment discharge, and triggers morphological channel adjustments in search of a new equilibrium. Due to spatial heterogeneity, in many instances these adjustments are difficult to evaluate a priori. However, it is known that sinuosity is directly related to channel stability; therefore, a reduction in sinuosity is likely to decrease channel stability (Blench, 1986).

In contrast with the second requirement of the Hidrovia, the river provides its own width and depth, a function of its water and sediment discharge, channel slope, boundary friction, and degree of geologic control. Table 1 shows that the inbank top width of the Upper Paraguay river varies from 120 m from Boca do Bracinho to Barra do Bracinho, to 600 m from Barra do Nabileque to the Apa river confluence. Table 19, Column 3, shows measured minimum average flow depths, which vary from 1.25 m at Cáceres to 8.83 m at Porto Murtinho. (The average flow depth of a river cross section is defined as the flow area divided by the top width, Chow, 1959). These are measured minimum average flow depths (taken across the river's width), and not seasonal minimum flow depths in the deepest section of the channel, as would be required for navigation.

Table 19.   Measured average flow depths along Upper Paraguay river.1,2
Station No. of data points Minimum Mean3 Maximum Range
Cáceres 95 1.25 3.12 4.78 3.53
Descalvados 22 1.84 2.93 3.72 1.88
Porto Conceição 29 3.83 5.09 6.60 2.77
Bela Vista do Norte 39 2.69 4.00 6.52 3.83
Refúgio das Três Bocas
a. Upstream 17 2.08 3.40 5.13 3.06
b. Downstream 17 3.71 4.55 5.45 1.74
Amolar 28 2.34 5.43 7.82 5.48
Porto São Francisco 53 4.77 7.16 9.32 4.55
Ladario 100 3.29 5.24 8.57 5.28
Porto da Manga 46 4.19 7.32 9.79 5.59
Porto Esperança 82 5.94 8.39 12.02 6.08
Forte Coimbra 32 5.49 11.74 17.44 11.95
Barranco Branco 28 5.50 8.54 12.87 7.37
Fecho dos Morros 74 4.60 7.15 11.67 7.08
Porto Murtinho 33 8.83 12.28 15.74 6.91
1Source:  DNOS (1974), DNAEE, and Hidrologia S. A. (unpublished data).
2 Average depths, in meters, were obtained by dividing measured flow area by measured top width.
3 Value shown is the mean of all measurements.

On the basis of Table 19, it is concluded that the Upper Paraguay river upstream of Porto São Francisco is incapable, without extensive artificial channel deepening, of accommodating ocean-going vessels (with a 3-m draft requirement) throughout the year.

Table 19 shows that downstream of Porto São Francisco, the river is sufficiently deep even during low-flow periods. Since Porto São Francisco is very small, and located only 146 km upstream of the major commercial port of Corumbá/Ladario, the latter is usually considered as the destination point of upstream-bound traffic. Current barge traffic from Corumbá downstream, towards Asunción and Buenos Aires is at least two orders of magnitude greater than the traffic from Corumbá upstream, towards Cáceres. According to A Gazeta of Cuiabá, of February 21, 1995, only two boats with 5,000 tons of soy left the port of Cáceres toward Corumbá in 1994 (International Rivers Network, 1995). Thus, the Hidrovia appears to be feasible up to Corumbá without major modifications to the natural channel. However, the extension of a 3-m navigation channel all the way to Cáceres will require major interventions in the natural channel.

Aside from the measured minimum average flow depths shown in Table 19, seasonal minimum flow depths in the navigation channel can be less than 3 m on several locations along the Upper Paraguay river, from Porto Murtinho to Cáceres. These locations are referred to as passos in Portuguese (a shallow or pass in English), and identified as such in navigation charts (Marinha do Brasil, 1974). Table 20 lists the 54 passes identified along the Upper Paraguay river. It is seen that 40% of these passes (22 out of 54) are concentrated in the most upstream reach, Descalvados-Cáceres, where navigation is difficult at best. The INTERNAVE (1990) report has noted that the minimum flow depth in the passes located between Descalvados and Cáceres ranges from 0.2 m to 1.5 m in dry years. Moreover, the Japuira pass, in the Porto Conceição-Descalvados reach, appears to be extremely shallow, with minimum flow depth of only 0.1 m during dry years.

Table 20.   List of passes (shallows) along
Upper Paraguay river.1

Reach/Name Km. Start Km. End
Porto Murtinho-Fecho dos Morros 2,235 2,271
Passo Tarumã 2,251 2,252
Fecho dos Morros-Barranco Branco 2,271 2,322
Passo Cambá Nupá2 2,281  
Passo José Kirá2 2,295  
Barranco Branco-Forte Coimbra 2,322 2,561
Passo Curuçu Cancha2 2,350  
Passo do Cururu 2,470 2,471
Passo Mbiguá2 2,531  
Passo Rebojo Grande 2,538 2,540
Passo Coimbra 2,553 2,554
Forte Coimbra-Porto Esperança 2,561 2,628
Passo Piuvas Inferior 2,573 2,574
Passo Piuvas Superior 2,577 2,578
Passo Gaivota2 2,603 2,605
Passo do Conselho 2,607 2,609
Porto Esperança-Porto da Manga 2,628 2,686
Passo Jacaré2 2,630 2,633
Passo da Figueirinha 2,633 2,635
Passo Caraguatá2 2,660  
Porto da Manga-Ladario 2,686 2,755
Passo Miguel Henrique 2,712 2,715
Passo do Formigueiro 2,722 2,724
Passo de Santana (Jatobá)2 2,729 2,730
Ladario-Porto São Francisco 2,755 2,908
Passo da Faia 2,803 2,804
Passo Domingos Ramos Inferior2 2,831  
Passo Domingos Ramos Superior 2,834  
Passo Tucano2 2,863  
Passo São Francisco 2,906 2,907
Porto São Francisco-Amolar 2,908 2,966
Passo Coqueiro2 2,920  
Passo Rufino 2,937 2,938
Passo Piuva Inferior 2,952 2,953
Passo Piuva Suferior 2,954 2,956
Passo Amolar 2,961 2,963
Amolar-Porto Conceição 2,966 3,182
Passo Capitão Fernandes2 3,147 3,148
Porto Conceição-Descalvados 3,182 3,303
Passo Quebra Mastro2 3,266 3,267
Passo Japuira 3,267 3,268
Passo Descalvados 3,301 3,302
Descalvados-Cáceres 3,303 3,442
Passo Paratudal 3,310  
Passo Descalvadinho2 3,311  
Passo Papagaio2 3,317  
Passo Presidente 3,320  
Passo Morro Pelado 3,322 3,324
Passo Baia das Eguas 3,332 3,333
Passo Corichão 3,335 3,336
Passo Baiazinha 3,340 3,343
Passo do Beiçudo 3,345 3,346
Passo Barranco Vermelho 3,349  
Passo do Soldado 3,350 3,352
Passo Tucum 3,356 3,357
Passo do Pote 3,359 3,360
Passo Cambará 3,360 3,362
Passo Jauru 3,363 3,366
Passo Acuri 3,366 3,368
Passo Simão Nunes Inferior 3,372 3,373
Passo Simão Nunes Superior 3,375 3,377
Passo do Alegre2 3,393  
Passo Passagem Velha 3,403 3,406
Passo Retiro Velho 3,411 3,412
Passo da Ponte 3,440 3,441
1Source:  INTERNAVE (1990). 2Source:  Marinha do Brasil (1974, and revisions).

The bottom (bed) of the Upper Paraguay river is predominantly sandy, but with significant rock outcrops throughout its length (See Table 8). Observations of stage-discharge relations have confirmed the so-called autodredging phenomenon, by which the river seeks to maintain a minimum depth during seasonal low flows (PORTOBRAS, 1983; INTERNAVE, 1990). This autodredging mechanism functions only as long as the river is able to move its bed freely. Apparently, by adjusting the shape and configuration of its bedforms, the river is able during low flows to reduce its discharge while maintaining an approximately constant stage (and a minimum flow depth). In the Upper Paraguay river, this minimum depth is 1.2 m, except where rock outcrops do not permit autodredging to take place (PORTOBRAS, 1983). Thus, if it were not for the rocky sills, the river would produce a minimum depth of 1.2 m through out its length. To the extent that this minimum depth is violated in many places along the river, it is concluded that the slope of the Upper Paraguay river is geologically controlled.

The Hidrovia project includes channel straightening, dredging, and blasting of rocky sills (IDB, 1995). Each of these interventions is discussed here separately.

Channel Straightening

Channel straightening shorthens the path of runoff, decreases the time of concentration, accelerates runoff concentration, and leads to increases in flood peaks. This type of intervention in the natural channel is being considered upstream of Amolar, where the river is more sinuous. For instance, the Internave report has proposed shortening by 62 km the distance between Cáceres (km 3,442) and Ponta do Morro (km 3,030) (INTERNAVE, 1990). Without the necessary details, it is difficult to evaluate the hydraulic effect of this significant intervention in the river. Nevertheless, some approximations are possible at this time. From Table 12, the average channel slope from Cáceres to Bela Vista do Norte (km 3047), 17 km upstream of Ponta do Morro (Fig. 7), is:

(110.09 m - 89.80 m) (100 cm/m) /(3442 km - 3047 km) = 5.14 cm/km

which would increase to

(110.09 m - 89.80 m) (100 cm/m) /(3442 km - 3047 km - 62 km) = 6.09 cm/km

with the implementation of the proposed channel straightening.

Based on the Manning equation (Chow, 1959), and assuming for simplicity average flow conditions and a rigid boundary, this increase in channel slope represents an increase of 5% in mean velocity and a decrease of 5% in flow depth.

The effect of channel slope changes is also subject to evaluation using the well known Lane relationship, which states that the product of water discharge and channel slope is proportional to the product of sediment discharge and particle size, as follows (Lane, 1955):

Qw S Qs d (4.1)

in which Qw = (water) discharge, S = channel slope, Qs = sediment discharge (taken as the sum of bed load plus suspended bed material load, excluding wash load), and d = particle size diameter. Since sediment concentration is

Cs = Qs / Qw (4.2)

it follows that for a given particle size (constant d)

CsS (4.3)

i.e., an increase in channel slope will cause a proportional increase in sediment concentration. In this case,

Cs-final / Cs-initial = 6.09 / 5.14 = 1.18 (4.4)

Thus, the proposed channel realignment is likely to cause an increase of close to 20% in the concentration and transport of bed material sediment.

Dredging

Dredging increases the cross-sectional area of the channel, albeit temporarily. This increases channel conveyance and the channel's ability to transport runoff (Chow, 1959). The hydraulic effects of dredging are difficult to evaluate directly, since the river reacts to dredging by adjusting its bed material load (suspended load and bed load) to eventually reach a new equilibrium. According to Jansen et al. (1982), in the long term, there will be upstream degradation, i.e., a lowering of the channel bed which will lower the groundwater level in the vicinity, resulting in a decrease in baseflow.

Blasting of Rocky Sills

Blasting rocky sills as a means of deepening the navigation channel will have an irreversible impact on the hydrology of the Upper Paraguay river. This is the the most significant planned intervention; if pursued, it is likely to change the Pantanal forever. Analysis of navigation charts show that, in general, the river has been able, through geologic time, to carve a sufficiently deep channel through most of the rock outcrops. For instance, in the vicinity of Amolar, at km 2,958, where the river has partly eroded into the Serra do Amolar, the flow depth can reach values greater than 14 m, cutting mostly through rock. Likewise, a short distance downstream, at Morro Dourados (km 2,956), the flow depth on the right bank, abutting with the adjacent hill, is greater than 22 m! (Marinha do Brasil, 1974).

Yet, in other places, where rocky sills protrude into the channel, the depth is shallower because the river has not yet carved an opening through these rocks. The Pantanal exists because of these rock outcrops, which influence the regional flow patterns in at least three places: Amolar, Porto da Manga, and Fecho dos Morros (Section 3.3.1). In particular, the hump at Amolar, together with a possible geologic control in the vicinity of the exit of Lagoa Gaíba, are instrumental in the creation of the Pantanal of Paiaguás, an important region of biological species diversity (Fig. 4).

The extent to which bed profile convexities (humps) can cause backwater in the Upper Paraguay river can be estimated using principles of open-channel hydraulics (Chow, 1959). Table 21 summarizes water surface profile computations for Amolar and Porto da Manga, where significant humps have been identified (Section 3.3.1). A hypothetical prismatic channel is assumed for simplicity. The hump at Amolar (47 cm) is shown to increase the flow depth up to a distance of 339 km (99% of downstream depth increase), which could affect the stage as far upstream as Descalvados. Likewise, the hump at Porto da Manga (44 cm) increases the flow depth up to a distance of 417 km, which could affect the stage as far upstream as Bela Vista do Norte. These calculations confirm that relatively minor changes in grade, which would necessarily take place as a result of blasting rocky sills, can affect the upstream hydraulics to greater lengths than may have been anticipated.

Table 21.   Estimation of length of hypothetical M1 water surface profile (backwater)
upstream of Amolar and Porto da Manga.1

Station
Property Units Amolar Porto de Manga
Mean annual discharge m3/s 943 1,340
Bottom width, estimated 2 m 300 300
Side slope, estimated m 1:1 1:1
Channel slope 3 cm/km 1.82 2.06
Channel slope m/m 0.0000182 0.0000206
Manning friction coefficient n 4 - 0.015 0.02
Normal depth (yn) m 4.296 6.113
Downstream depth increase (Dy) 5 m 0.470 0.440
Downstream depth (yn + Dy) m 4.766 6.553
Amolar
Distance to Porto Conceição 6 km 216 -
Length of M1 profile (95% of Dy) km 225 -
Distance to Descalvados 6 km 337 -
Length of M1 profile (99% of Dy) km 339 -
Distance to Cáceres 6 km 476 -
Porto da Manga
Distance to Amolar 6 km - 280
Length of M1 profile (95% of Dy) km - 280
Distance to Bela Vista do Norte 6 km - 361
Length of M1 profile (99% of Dy) km - 417
Distance to Porto Conceição 6 km - 496
1 Based on direct step method, assuming a prismatic channel and a 0.001 m depth interval (Chow, 1959).
2 From Table 1. 3 From Table 12.
4 Average measured value, based on streamflow data from DNOS (1974), DNAEE, and Hidrologia S. A.
5 Taken from Section 3.3.1. 6 Distance measured along the river.

The great extent of the backwater profile is the reason why proposals for artificial control structures (e.g., dams, levees, and polders) in the Upper Paraguay river and Pantanal are usually controversial. Their permanent flooding of extensive adjoining areas which were either previously dry or only seasonally flooded can hardly be justified (Silva, 1990). For the same reason, proposals for the artificial removal of rocky sills, which act as natural dams, are also controversial. If implemented, they will dry out extensive areas which were normally subject to seasonal flooding. The point to emphasize with regard to the Pantanal is that any change will have wide-ranging spatial impacts.

Besides being irreversible, the blasting of rock outcrops may prove to be unsustainable in the long run. The elimination of a rocky sill will cause upstream channel degradation until a new equilibrium bed, lower than the initial level, is attained (Jansen et al., 1982). This will lower the groundwater level and reduce the baseflow. More importantly, however, the removal of one rocky sill may lead to the appearance of another rocky sill which was previously submerged (Jansen et al., 1982) (Fig. A23). This is a definite possibility in the Upper Paraguay river, which has a rock outcrop every 40 km on the average (Table 8), and where the prevailing channel slopes are so mild (1-2 cm/km) that the backwater effect of a 0.5-m flow obstruction may be felt for about 400 km upstream (Table 21).

Fig. A23  Farolete Balduíno, on the Upper Paraguay river, near Corumba, Mato Grosso do Sul.

In summary, the following is concluded:

  • Channel straightening will shorthen the path of surface runoff, accelerate the concentration of flood runoff, and increase flood peaks during high mean (2-yr), extraordinary (4-yr) and exceptional (10-yr) floods.

  • Channel deepening by dredging of sandy bed material may provide some relief for navigation, but this will be temporary and often short-lived, as the river tends to move its bed constantly in a more or less unpredictable fashion.

  • Blasting rocky sills will produce permanent and irreversible changes in the hydraulics and hydrology of the river, increasing the velocities, accelerating the concentration of flood runoff, and increasing flood peaks.


If implemented, these actions will have more serious impacts upstream of Corumbá/Ladario, particularly upstream of Porto São Francisco, where minimum flow depths are well below the proposed 3-m channel depth required for the navigation of ocean-going vessels.


4.1.2  Changes in Baseflow

A well known principle of hydrology is that changes in flood regime produce changes in baseflow. This principle is predicated on the observation that the higher the flood peak, the lower the baseflow; conversely, the lower the flood peak, the higher the base flow. The rationale for this inverse relation is that a drop of rainfall that does not make it into the basin surface runoff is retained as basin wetting (Ponce and Shetty, 1995a), to follow one of two possible paths:

  • Return to the atmosphere as evaporation or evapotranspiration, or

  • Percolate through the soil profile and eventually exfiltrate to the drainage network in the form of interflow or groundwater flow. The fraction of runoff which follows the path of groundwater flow is referred to as baseflow.

Thus, on the average, a drop of basin wetting has about a 50% chance of becoming baseflow. While the baseflow-wetting relations for the Upper Paraguay river remain to be established, a subhumid basin such as the Upper Paraguay does have a substantial baseflow component. It is noted that the minimum measured discharge at Porto Murtinho is 549 m3/s (Table 13). The well-known sponge effect of the Pantanal on the Upper Paraguay river (Bucher et al., 1993) is partly accounted for by the conversion of the faster surface runoff into slower subsurface runoff.

It follows that accelerating the concentration of flood runoff and increasing the flood peaks will produce a decrease in baseflow, which will lead to decreases in minimum flow depths, particularly in those locations where the self-dredging action is minimal or nonexistent. In the absence of more detailed studies, it is difficult to ascertain the extent of this decrease, but the tendency is there and must be acknowledged.

Changes in baseflow regime (either losses or gains), although in smaller catchments, have been documented in the United States and other countries (for a recent review, see Ponce and Lindquist, 1990). Generally, a decrease in environmental moisture (i.e., less precipitation, less vaporization, and less total runoff) leads to baseflow losses, while an increase in environmental moisture (more precipitation, more vaporization, and more to tal runoff) leads to baseflow gains. The amount of baseflow is shown to be highly correlated with climatic regime. Loss of baseflow invariably leads to climatic changes in the direction of greater aridity.

The issue of potential changes in baseflow is extremely relevant as far as the feasibility (and sustainability) of the Hidrovia project is concerned, since extensive channel modifications will lead to increases in high flows (flood peaks), which in turn will lead to decreases in low flows (which are mostly baseflow). Thus, it is expected that channel modifications (straightening, dredging, and blasting of rocky sills) will destabilize the river's baseflow regime. In turn, this will demand additional future action to continue to maintain the required minimum draft, i.e., it will set in place a vicious circle of channel interventions. This is an extremely serious issue, since it can potentially jeopardize the existence of the Pantanal.


4.1.3  Changes in Water Yield

The Upper Paraguay river has a mean flow of 1,565 m3/s. This value was estimated at the Apa river confluence, based on existing measurements at Porto Murtinho and Fecho dos Morros (Table 12). Based on estimates of spatially averaged mean annual precipitation, a runoff coefficient of Kr = 0.08 (the ratio of runoff to rainfall) has been calculated (Section 3.3.4). How will this runoff coefficient be affected by the execution of the Hidrovia project? In the absence of detailed hydrologic analyses, experience with neighboring basins can provide useful guidelines as to the possible impacts.

The relationship between the runoff coefficient Kr and the annual precipitation P is a characteristic of each basin, with dKr /dP being always positive, i.e., the runoff coefficient increases with annual precipitation (Ponce and Shetty, 1995b). This function is part of the basin's hydrologic signature, a characterization of its annual water yield or basin response to the given precipitation input. Changes in flood regime and baseflow (in creases in flood peaks and consequent decreases in baseflow) may produce changes in mean flow regime, and eventually lead to climatic changes, i.e., changes in

  • Annual precipitation amounts, patterns, and spatial and temporal distribution,

  • Evaporation/evapotranspiration amounts,

  • Floristic species composition, a function of moisture content in soil and atmosphere, and

  • Runoff nature (i.e., surface vs subsurface) and amounts.

For instance, the Paraná river at Corrientes, Argentina (Middle Paraná) (Fig. 1) has seen its runoff coefficient increase from Kr = 0.16 in the decade of 1962-71 to Kr = 0.22 in 1982-91, an increase of more than 35% in about 20 years (Ponce, 1994). Part of this increase may be accounted for by increases in annual precipitation (Anderson et al., 1993), while another part may be attributed to land use changes (Ponce, 1994).

Changes in land use which have the effect of increasing surface runoff have been occurring in the Upper Paraná basin since the late 1960's, when the land was converted from coffee plantations to the production of soy beans and sugar cane. In Eastern Paraguay alone, upstream of Confluencia, forest cover has decreased from 55% in 1945 to about 15% today (Anderson et al, 1993). Confirming this trend, similar increases in mean annual runoff (34% in the 20-yr period 1971-90, using the data for the 40-yr period 1931-70 as the baseline) have been recently documented at Itaipú Dam, on the Upper Paraná (N. Carvalho, personal communication, 1995). Thus, it is concluded that basin/river interventions that have the effect of increasing and/or accelerating surface runoff produce significant changes in the long-term hydrologic response of a basin. Such changes may eventually produce climatic changes in the direction of greater aridity (See Section 4.4.1).

On the basis of the recent Paraná experience, it is expected that the Hidrovia project will, in the short term, increase the mean annual runoff coefficient above 0.08, thereby reducing the vaporization coefficient below 0.92. The reduction in evapotranspiration amounts will have a negative impact on the vegetative biota. It will lead to decreases in actual evapotranspiration, and, through species displacement, to increases in potential evapotranspiration, followed by decreases in annual precipitation and environmental moisture (the moisture present in soil and air). The extent and timeframe of these potential climatic changes remains to be ascertained.

The response of a river system is the result of complex interactions between the hydrology of the upland subbasins (the supply of runoff, both water and sediment, to the drainage system) and the hydraulics of the drainage system (the channel characteristics, i.e., width, depth, slope, and boundary roughness, both form and grain roughness). In the Upper Paraguay, channel slope is controlled by the local geology, while channel widths and depths have adjusted through millennia to the prevailing water and sediment discharge, channel slope and boundary roughness.

To give an example, the reach from Boca do Bracinho to 40 km downstream of Porto Conceição, a distance of 146 km along the river, is only 120-150 m wide (Table 1). This unusually narrow reach is due to the intervening overbank flows (both water and sediment). The overbank flows reduce the mean annual discharge, from 437 m3/s up stream, at Descalvados, to 341 m3/s at Porto Conceição, and to 144 m3/s further downstream, at Bela Vista do Norte (Table 12). Frequently, this reach (from Boca de Bracinho to 40 km downstream of Porto Conceição) is temporarily obstructed by floating islands of biomass which originate in the numerous neighboring baías (Fig. A24). The seasonality of these obstructions, which are regionally referred to as batume or bacero, have been studied by Silva and Esteves (1993).

Fig. A24  Floating vegetation (camalotes) on the Upper Paraguay river.

Changing the river channel dimensions (width and/or depth) through dredging will trigger changes in water and sediment discharge and an eventual adjustment to the new conditions. Pending detailed studies, a reference assessment of the hydrologic impact can be accomplished by assuming a rectangular 300-m wide, 1.5-m depth natural channel, applicable upstream of Amolar, with flow area

Ainitial = (300 m) (1.5 m) = 450 m2 (4.5)

A 50-m wide 3-m deep navigation channel will increase the flow area to

Afinal = 450 m + (50 m) (1.5 m) = 525 m2 (4.6)

Asumming for simplicity constant channel slope and boundary roughness, the flow area ratio

Afinal / Ainitial = 525 / 450 = 1.17 (4.7)

leads, through the use of the Manning equation (Chow, 1959), to

Qfinal / Qinitial = (Afinal / Ainitial)5/3 = 1.3 (4.8)

i.e., to an increase of 30% in water discharge.

The assumed 1.5-m minimum channel depth tends to be low in most cases where the river is actively moving its bed (a sandy channel bottom), and high in places where there are significant rock outcrops encroaching into the channel. Detailed bathymetric data and analysis throughout the length of the Upper Paraguay river, particularly in the regions of more intensive channel intervention (the passes proposed to be dredged or blasted), will be required to further refine this assessment.


4.1.4  Changes in Drought Regime

The flood regime of the Upper Paraguay river and adjoining Pantanal is characterized by one annual flood pulse, the rise of the flood wave rise lasting up to six months. This is certainly the case at Amolar and Ladario, both of which are strategically located near the center of the Pantanal (Fig. 2). The annual flood wave varies in magnitude and time of peak occurrence (see Section 4.1.1).

The longest streamflow records for the Upper Paraguay river are at Ladario, where stage and discharge measurements have been made since the turn of the century. The Ladario records show the presence of several multiannual drought periods, i.e., periods of unusually low flows, each lasting several years. Examination of the record enables the identification of three such drought periods: 1909-16, 1936-44 and 1964-73 (Fig. 9). The sparseness of the data precludes a more precise definition of the recurrence interval; however, the data appears to suggest that the Upper Paraguay and Pantanal begin a multiannual drought roughly every 30 years on the average. Following this reasoning, the next drought period is now overdue in the Pantanal. The persistence to this date of the wet period which began in 1974 could be partly attributed to hydrologic changes which may already be taking place in the Upper Paraguay basin, due to changes in land use (Silva, 1990). In this regard, Silva et al. (1995) have recently documented an exponential rate of deforestation in the Pantanal. Additional study is urgently needed in this area.

Fig. 9  Upper Paraguay river at Ladario:  Recorded seasonal maximum and minimum stages..

How will the Pantanal's drought regime be affected if the floods in the Upper Paraguay are exacerbated by the projected Hidrovia? In the absence of additional data and more detailed analysis, this remains an open question. However, it is instructive to compare the Pantanal experience with that of other basins in Brazil, across the climatic spectrum. For instance, a semiarid region such as the Brazilian Northeast is subject to multiannual drought periods which recur once every eleven years on the average (Guerra, 1981; Ponce, 1995). Moreover, the intervening floods are often disastrous in terms of loss of life and property. On the other hand, a humid tropical region such as the Lower Amazon basin is annually visited by one flood pulse of predictable magnitude and regularity, while being hardly affected by river droughts (Richey et al., 1989). Thus, the sequence of floods and droughts is shown to be a characteristic of the climatic regime, wherein floods predominate over droughts in subhumid and humid regions, while the converse holds true for arid and semiarid regions.

It is hypothesized that increases in flood magnitude, to be expected as a result of the Hidrovia project, will change the multiannual drought regime in such a way that droughts will be more intense and recur more often. If this climatic change sets in, the Hidrovia project will prove to be unsustainable in the long run. The accumulation of structural interventions in the river (channel straightening, dredging, and blasting of rocky sills) will promote the intensification of floods and droughts, increase the difference between seasonal maximum and minimum stages (Fig. 10), and decrease usable flow depths during the increasingly pronounced low-flow season.

Fig. 10  Upper Paraguay river at Ladario:  Seasonal maximum stage difference vs peak flood stage.

In conclusion, the acceleration of runoff concentration caused by navigation improvements will intensify high mean, extraordinary and exceptional floods, potentially reduce the recurrence interval of drought periods, and may eventually lead to climatic changes in the direction of greater aridity (lesser precipitation, lesser evaporation/evapotranspiration, and lesser runoff amounts).


4.2  Sediment Impacts

The sediment impacts of the Hidrovia project on the Upper Paraguay river and the Pantanal of Mato Grosso can be considered to fall into two categories:

  1. Changes in sediment discharge due to changes in flood regime

  2. Changes in sediment discharge due to long-term climatic changes.

It is generally recognized that the Upper Paraguay river basin functions to date as an extensive surface of sediment accumulation. The sediment entering the basin by way of the tributaries (Cuiabá, Taquari, and Miranda, to name the most important) is distributed by channel overflows on the coalescing alluvial fans, and/or trapped in the numerous wetlands and endorheic drainages of the Pantanal.

The highly dissected plains (planaltos) of Mato Grosso and Mato Grosso do Sul have, through millennia, contributed a healthy supply of sediment to the neighboring lowlying Pantanal (Fig. A25). For instance, the Taquari river carries a sizable sediment load, which at times can be as high as 2,500 ppm at Coxim (Fig. 3). This high sediment load accounts for the great dimensions of its alluvial fan, which covers, starting at its apex near Porto Rolon, extensive areas of Pantanal. In fact, the Taquari river, which used to be navigable by small vessels from its mouth upstream all the way to Coxim, is no longer navigable, presumably due to anthropogenic pressures in the upper basin (changes in land use from forest to intensive agriculture), which have had the effect of accelerating upland erosion (Alho et al., 1988).

Fig. A25  Bank erosion on the Apa river.

Monthly depth-integrated sediment discharge measurements along the Upper Paraguay river and its major tributaries have been performed for DNOS by Hidrologia S.A. for a 5-year period spanning the late 70's and early 80's. A summary of these measurements is shown in Table 18. Significantly, the measured mean sediment concentration at Porto Esperança, downstream of the major Upper Paraguay tributaries, is only 176 ppm. This value should be compared with the measured mean sediment concentration entering the Pantanal through the tributaries: 235 ppm for the Cuiabá, 362 ppm for the Piquiri, 845 ppm for the Taquari, 620 ppm for the Aquidauana, and 626 ppm for the Miranda. Thus, it is seen that a large percentage of the tributary sediments remains in the Upper Paraguay basin. Based on these limited but significant data, it is concluded that the Pantanal is still a surface of sediment accumulation.

The poor correlation between sediment discharge and water discharge (refer to Tables 16 and 17) may not sufficient grounds to disqualify the sediment data. The data shown in these tables is total sediment load, which includes fine sediment load (wash load), a function of upstream supply (degree of upper basin natural or anthropogenic disturbances), and not of the flow hydraulics (depth and velocity). In the absence of channel overflows, once the wash load gets into the channel, its tendency is to remain there to be eventually exported from the terrestrial ecosystem(s). In addition, the monthly sediment data record has implicit within it the hysteresis in the sediment rating, i.e., the tendency of the flow to transport more bed material load during the rising stage than during the receding stage (Leopold et al., 1964). Thus, monthly sediment data is only an approximate indication of the sediment budget of a basin.


4.2.1  Changes in Sediment Discharge due to Changes in Flood Regime

In general, changes in flood regime produce changes in sediment discharge. This is a well known principle of hydrology, having been amply documented for many decades (U.S. Department of Agriculture, 1940). However, due to nonlinear interactions between stage and mean velocity, the nature of this relationship is not readily apparent in the Upper Paraguay river. During common and low mean floods, increases in stage may reduce mean velocity and delay the occurrence of the flood peak to late June, July, or early August, reducing sediment transport and export from the basin. On the other hand, during high mean, extraordinary and exceptional floods, increases in stage will increase mean velocity and accelerate the occurrence of the flood peak to early June, May, April, or late March, increasing sediment transport and export from the basin (Section 4.1.1).

Aside from the complexities of sediment transport in the Upper Paraguay river, increases in mean velocity invariably lead to increases in sediment transport capacity. The relationship between sediment (bed material) discharge (Qs) and mean velocity (v) is highly nonlinear, the exponent of mean velocity varying in the range 3-7 (Colby, 1964). Thus, a 5% increase in mean velocity (Section 4.1.1) amounts to a 15-40% increase in sediment discharge, as follows:

Qs-final / Qs-initial = (vfinal / vinitial)3 = (1.05)3 = 1.15 (4.9)

Qs-final / Qs-initial = (vfinal / vinitial)7 = (1.05)7 = 1.40 (4.10)

This indicates that increases in runoff and flow velocities will lead to proportionally larger increases in sediment loads and, consequently, in sediment export from the basin. To give an example, the increasing sediment loads reaching the Lower Paraná in the past two decades (H. Benito, personal communication, 1995) appear to be the result of increasing water yield in the Upper Paraná (Anderson et al., 1993; Ponce, 1994).


4.2.2  Changes in Sediment Yield due to Long-term Climatic Changes

In the long term, climatic changes in the direction of greater aridity (from dry subhumid to semiarid in the case of the Pantanal) will lead to increases in sediment yield, i.e., the sediment discharge at an evaluation point, integrated over the entire year. It is widely recognized that the sediment yield from a drainage basin peaks at an annual precipitation P of about 12 in. (304.8 mm) (Langbein and Schumm, 1958); or, alternatively, at an annual runoff Q of about 2 in. (50.8 mm) (Dendy and Bolton, 1976).

An arid climate (P between 50 and 250 mm) has lesser rainfall and runoff, and consequently, a lower capacity to entrain and transport sediment. A semiarid climate (P between 250 and 500 mm) encompasses the peak of sediment yield. Subhumid (P between 500 and 1,000 mm), humid (P between 1,000 and 2,000 mm), and extremely humid (P greater than 2,000 mm) climates have greater rainfall and runoff, but in these cases erosion is controlled by the increasingly abundant vegetation (Bull, 1991).

The Dendy and Bolton method is used in the United States to calculate sediment yield from ungaged catchments (Dendy and Bolton, 1976). The method specifies a runoff threshold Qt = 2 in., below which sediment yield is directly related to annual runoff Q (by a power function), and above which sediment yield is inversely related to Q (by an exponential decay function). Thus, sediment yield increases as annual runoff approaches the threshold value of 2 in. from either side, i.e., increasing to 2 in., or decreasing to 2 in.

The power function is:

S = 1280 Q 0.46 (1.43 - 0.26 log A) (4.11)

applicable for Q less than Qt.

The exponential decay function is:

S = 1965 e-0.055 Q (1.43 - 0.26 log A) (4.12)

applicable for Q greater than Qt. In these equations, S = sediment yield (ton/mi2/yr), Q = liquid runoff (in.), and A = drainage area (mi2).

These formulas were developed for small and midzise catchments in the United States, and their applicability to the Upper Paraguay basin remains to be established. Nevertheless, the pattern of sediment yield changes with climatic change is general and should be recognized across geographical boundaries.

In conclusion, long-term climatic changes in the direction of greater aridity will lead to increases in sediment yield in the Upper Paraguay basin. Normally, climatic changes are slow and not readily amenable to evaluation using conventional mathematical modeling. However, if a climatic change sets in, it will offset the flow depth gains implemented by the Hidrovia project. This is a significant impact, which could affect the sustainability of the project over the long term.


4.3  Impact on the Flood Regime of the Middle Paraná River

There is some concern that changes in the flood regime of the Upper Paraguay river may increase flood magnitudes downstream, in the Middle Paraná (Bucher et al., 1993). The Pantanal delays runoff peaks from the Upper Paraguay by three months or more, such that they are out-of-phase with runoff peaks from the Upper Paraná arriving at Corrientes (Fig. 1). Compounding this concern, flood peaks and annual runoff volume are already on the increase in the Upper Paraná. The marked increase (34% in the past 20 years) has been attributed to increases in precipitation and land-use changes in the Upper Paraná and Middle/Lower Paraguay rivers, and not necessarily to changes in the Upper Paraguay (Anderson et al., 1993; Ponce, 1994).

The Paraná-Paraguay river basin is part of the La Plata basin system, and its most important in terms of both discharge (75%) and catchment area (84%) (Section 2.1). The La Plata basin system is enclosed within two large climatic zones (OEA, 1969): (1) tropical zone (V), and (2) subtropical temperate/warm zone (IV), with the following subzones (Fig. 11):

  • V1: Wet tropical climate, with a rainy season lasting 9.5 to 12 months.

  • V2: Average tropical climate, with a summer rainy season lasting 7 to 9.5 months.

  • V3: Dry tropical climate, with a rainy season lasting 4.5 to 7 months.

  • IV3: Steppe climate, with dry winter season and short summer rainy season lasting 5 months.

  • IV4: Rainy climate, with dry winter season and long summer rainy season lasting 6 to 9 months.

  • IV6: Permanently humid climate, with no clearly defined dry or rainy season.

  • IV7: Permanently humid climate, with a clear summer rainy season.


Fig. 11  Climatic zones of the La Plata basin system (OEA, 1969).

Figure 11 shows the following: (1) most of the Upper Paraguay basin lies within the tropical subzone V2 (Brazil, in Mato Grosso and Mato Grosso do Sul); (2) most of the Middle and Lower Paraguay basins lie within the tropical subzones V1 (Paraguay, east of the Paraguay river) and V3 (Paraguay, Argentina, and Bolivia, west of the Paraguay river); and (3) most of the Upper Paraná (Brazil) basin lies within the tropical subzone V1.

Thus, the rainfall regimes of the Upper Paraguay, the Middle/Lower Paraguay, and the Upper Paraná rivers are quite different. Rainfall in the Upper Paraguay is concentrated in the summer months. According to the EDIBAP study, the wettest three-month period is December-February, representing 48% of total rainfall in the north of the basin (Cáceres), gradually decreasing to 36% in the south of the basin (Porto Murtinho) (Section 3.3.2) (EDIBAP, 1979). On the other hand, rainfall in the Middle/Lower Paraguay (Eastern Paraguay) and Upper Paraná basins is more evenly distributed throughout the year.

Table 22 and Fig. 12 show monthly distributions of measured annual flood peaks at key stations along the Paraguay and Paraná rivers. Three stations are listed in the Upper Paraná: (1) Cáceres, at the entrance to the Pantanal; (2) Ladario, next to Corumbá, downstream of the Pantanal of Paiaguás and the Pantanal of Cuiabá-Bento Gomes-Paraguaizinho (Fig. 4); and (3) Porto Murtinho, close to the mouth of the Upper Paraguay river. One station is listed in the Middle Paraguay (Asunción, Paraguay), another in the Upper Paraná (Posadas, Argentina), and another in the Middle Paraná (Corrientes, Argentina). The lack of data sets of comparable length (the record length varies from 20 years at Cáceres to 96 years at Ladario) imposes a limitation on the analysis, which is not readily resolved, since this is the only available data.

Table 22.   Monthly distribution of measured annual flood peaks at key stations
along Paraguay and Paraná rivers.1

River at
Station (location)
No. of
years
Monthly distribution (percentile)
Sept Oct Nov Dec Jan Feb Mar Apr May Jun Jul Aug
Upper Paraguay river at
Cáceres (Km 3442)2
20 0 0 0 0 5 40 504 5 0 0 0 0
Upper Paraguay river at
Ladario (Km 2755)2
96 0 0 0 0 0 0 2 11 24 41 21 1
Upper Paraguay river at
Porto Murtinho (Km 2235)2
46 2 4 0 2 2 0 4 7 22 20 20 17
Middle Paraguay river at
Asunción (Km 1630)2
87 2 5 3 6 13 7 2 5 17 29 10 1
Upper Paraná river at
Posadas (Km 378)3
92 2 5 6 9 18 19 18 6 5 10 2 0
Middle Paraná river at
Corrientes (Km 1208)2
92 1 3 1 12 8 23 25 9 3 11 4 0
1Source:  Anderson et. al. (1993) and DNAEE/CPRM (unpublished data). 2 Km of Hidrovia, starting at Buenos Aires.
3 Distance measured from Corrientes. 4 Bolded figures indicate the mode (the largest value) of the distribution.

Fig. 12  Monthly distribution of annual flood peaks at key stations
along Paraguay and Paraná rivers.

The distances along the Hidrovia are: Corrientes, km 1,208; Asunción, km 1,630; Porto Murtinho, km 2,235; Ladario, km 2,755; and Cáceres, km 3,442. Furthermore, Posadas (Fig. 1) is located 378 km upstream of Corrientes, on the Upper Paraná.

Table 22 shows that 50% of the annual flood peaks measured at Cáceres occurred in March (and 90% in the period February-March), while 41% of those in Ladario occurred in June (and 86% in the period May-July). This shows that it takes about 105 days on the average (end of February to middle of June) for the flood peak to travel from Cáceres to Ladario, a distance of 687 km, at a speed of (687 km X 1000 m/km X 100 cm/m)/ (105 days X 86400 sec/day) = 7.5 cm/sec.

The calculation of the flood wave speed from Ladario to Porto Murtinho is complicated by the effect of local contributions. For instance, the mode of the distribution at Porto Murtinho occurs in May, but the distribution is strongly represented throughout four months (May to August), while that of Ladario occurs predominantly in June. Furthermore, while 23% of the annual floods at Porto Murtinho peaked late in the season (August to October), only 1% of those at Ladario peaked late (August) (Table 13). Thus, the delay of the flood peak from Ladario to Porto Murtinho is not clearly discernible by the record, although there is enough reason to believe that it may be up to two months or more (Carvalho, 1986) (Fig. A26).

Fig. A26  Flooding on the Upper Paraguay river near Porto Murtinho, Mato Grosso do Sul.

Figure 12 shows that the annual flood peak at Asunción, on the Middle Paraguay, can occur at any time throughout the year, with no clearly defined dry period. On the other hand, a clear dry period was the case of Cáceres (May-December) and Ladario (September-February). The highest frequency of annual floods in Asunción is in June (29 percent), followed by May (17%), and January (13%). Since the Upper Paraguay river does not contribute to the January flood peaks at Asunción, the latter must originate in local contributions of the Middle Paraguay, including that of the Apa.

The measured stage hydrographs at Ladario and Asunción are quite different. Those at Ladario are unimodal, showing one annual flood peak (around midyear) and little variability in low flow (around the end of the year). Those at Asunción are multimodal, showing several hydrograph peaks and valleys throughout the year, an annual flood peak being possible at any time of the year (PORTOBRAS, 1983). Closer examination of the hydrographic records shows that at least some extraordinary and certainly all exceptional flood waves at Ladario are also felt as such at Asunción. For instance, the 1980 flood peaked at Ladario on April 18, at Porto Murtinho on July 1, and at Asunción on July 10 (PORTOBRAS, 1983).

Thus, it is expected that extraordinary and exceptional flood peaks at Porto Murtinho, on the Upper Paraguay, will be felt both at Asunción, on the Middle Paraguay (605 km downstream of Porto Murtinho), and at Corrientes, on the Middle Paraná (422 km downstream of Asunción).

Table 22 and Fig. 12 show that the annual flood peak at Posadas, on the Upper Paraná, can occur throughout the year, with no clearly defined dry period. However, unlike Asunción, which shows a mode of 29% in June, the mode at Posadas is in February, and only 19%. Thus, runoff from the Upper Paraná reaches Posadas typically in mid- to late summer (January-March). Runoff from the Upper Paraná and Paraguay rivers join together at Confluencia, and is measured at Corrientes (Argentina), 32 km downstream. At Corrientes, the highest frequency of annual floods is in March (25%), followed by February (23%), December (12%), and June (11 percent). Thus, a flood peak at Corrientes can originate in one of three sources:

  1. Runoff from local contributions, peaking in December.

  2. Runoff from the Upper Paraná, peaking in February or March.

  3. Runoff from the Paraguay basin, peaking in June or July.

The latter includes some extraordinary and all exceptional floods in the Upper Paraguay river basin, which are attenuated by the Pantanal into a unimodal flood wave.

The preceding analysis leads to the following conclusions:

  • The Pantanal delays by more than three months, usually until June or July, the flood peak of the Upper Paraguay at Porto Murtinho.

  • The flood peaks of the Upper Paraguay at Porto Murtinho and Middle Paraguay at Asunción appear to be unrelated (uncoupled) for common and mean floods, and related (coupled) for some extraordinary and all exceptional floods.

  • The flood peaks on the Upper Paraná at Posadas occur throughout the year, with a tendency toward January-March.

  • The flood peaks on the Middle Paraná at Corrientes occur throughout the year, with a tendency toward February-March.


The Hidrovia project will accelerate the concentration of flood runoff in the Upper Paraguay during high mean, extraordinary and exceptional floods. This will lead to higher and earlier flood peaks at Ladario, occurring typically in May or April, instead of June or July. The extent to which an increase of the flood peak at Ladario (and, consequently, at Porto Murtinho) will lead to an increase of the flood peak at Corrientes remains to be determined. Mathematical modeling (flood routing) will be required to ascertain the precise nature of this increase.

In the absence of detailed modeling, the present conclusions regarding downstream effects of the Hidrovia project should be regarded as preliminary:

  • Significant interventions in the Upper Paraguay river, with the potential to jeopardize the existence of the Pantanal, will increase and accelerate extraordinary and exceptional flood peaks at Ladario and Porto Murtinho, and contribute to a substantial increase in the summer flood peak at Corrientes (February or March).

  • Less significant or limited interventions in the Upper Paraguay river will increase and accelerate extraordinary and exceptional flood peaks at Ladario and Porto Murtinho, and contribute to an increase in the summer flood peak at Corrientes. The precise extent of this increase remains to be determined by further analysis.


4.4  Other Related Environmental Impacts

Other related environmental impacts of the Hidrovia project include the following:

  • Impact on the mean albedo of the Upper Paraguay basin

  • Impact on the nutrient balance

  • Impact on the biota.


Changes in the hydrologic regime (magnitude and frequency of floods and droughts, and changes in water yield) of the Upper Paraguay river will have an impact on the thermal balance of the lower atmosphere, through changes in the mean albedo. Changes in the sediment balance will impact the nutrient balance, which in turn, will affect the vegetative biota (species composition and diversity) and modify, through displacement, animal populations (birds, reptiles, and mammals) and habitats (Section 3.4.2). The impact of these changes is wide ranging and long term, deserving of a thorough study prior to project implementation.


4.4.1  Impact on the Mean Albedo of the Upper Paraguay Basin

Changes in the mean flow regime of the Upper Paraguay river will result, in the long term, in an increase in the mean albedo of the Upper Paraguay basin. (Albedo is the reflectivity coefficient of a surface, i.e., the ratio of the total reflected short wave radiation flux to the total downwelling solar flux, Fig. A27). The increase in albedo will cause changes in the thermal balance of the lower atmosphere, and will eventually lead to climatic changes in the direction of greater aridity (Charney, 1975). Thus, mean annual precipitation and mean annual runoff will be eventually reduced, resulting in the reduction of flow depths in the Upper Paraguay river, and the shrinking of the Pantanal. Currently, the mean annual precipitation in the Upper Paraguay basin Pa is about 1,280 mm, and the mean annual runoff coefficient is Kr = 0.08 (Section 3.3.4). Therefore, the mean annual runoff is:

Ra = Kr Pa = (0.08) (1,280 mm) = 102.4 mm (4.13)

Fig. A27  Variation of albedo with color and texture of the Earth's surface.

The scenario in which increases in albedo and associated climatic changes may take place is the following:

  1. Increases in mean annual runoff coefficient (i.e., water yield) will cause decreases in surface water storage (lakes and baías) and subsurface water storage (soil moisture), leading to decreases in vaporization coefficient (the ratio of evaporation to rainfall).

  2. Decreases in vaporization coefficient will reduce actual evapotranspiration, eventually leading to changes in vegetative species composition, i.e., to the progressive replace ment of hygrophytes by mesophytes in lower ground (adjoining riparian areas), and mesophytes by xerophytes in higher ground (the interfluves).

  3. Increases in xerophytes will decrease vegetative density and cover, increasing the size and frequency of patches of bare ground.

  4. Increasing size and frequency of patches of bare ground will increase the mean albedo, reflecting more radiant energy to the atmosphere and reducing the energy available for productive processes (photosynthesis and evapotranspiration).

The relation between surface albedo and climate is well known in the literature of climatology and meteorology. An extremely productive biome such as the tropical Amazon rainforest has albedos in the range 0.14-0.21 (Gutman, 1994), while a hyperarid desert such as the Sahara has an albedo of 0.5 (Courel et al., 1984). While the albedo of water surfaces is 0.03-0.10, that of sand dunes is 0.3-0.6 (Sumner, 1988).

Charney et al. (1975) reasoned that a decrease in plant cover is usually accompanied by an increase in albedo. This leads to a decrease in the absorbed radiation and an increase in the radiative cooling of the air. Thus, the air would sink to maintain thermal equilibrium, and cumulus convection and associated rainfall would be suppressed. The reduced rainfall would in turn have an adverse effect on plants and would tend to enhance the original decrease in plant cover (Charney et al., 1977).

For arid and semiarid regions, Sud and Molod (1988) have confirmed that the overall effect of high surface albedo is that of cooling inside the planetary boundary layer (PBL). This induces sinking aloft and moisture divergence near the surface, both of which suppress moisture convection and rainfall. Therefore, in a desert border region, such as in the limit between subhumid and semiarid, an increase in surface albedo would be expected to reduce the convective rainfall locally.

Garratt (1993) has recently summarized the response of global climate simulations to changes in albedo. Results of eleven studies showed that an increase in albedo causes:

  1. Decreased land evaporation,

  2. Decreased land precipitation, and

  3. Increased precipita tion over the seas (in the global change cases).

These and other similar studies have shown conclusively that increases in albedo cause climatic changes in the direction of greater aridity, resulting in decreased precipitation, decreased runoff, and increased sediment yield (the latter as in the Pantanal, where the climatic change would be from dry subhumid to semiarid).

Are changes in the runoff regime of the Upper Paraguay river, attributable to the Hidrovia project, likely to lead to substantial changes in mean albedo? The answer to this question is affirmative, although the timeframe for these changes is not readily discernible without further analysis. If the Hidrovia project increases in the short-term the runoff coefficient of the Upper Paraguay river, it will trigger a series of chain reactions to include:

  • Reduction in mean annual vaporization,

  • Reduction in baseflow,

  • Changes in biotic species composition, of both plants and animals,

  • Increase in mean albedo,

  • Increase in sediment yield,

  • Reduction in mean annual precipitation,

  • Reduction in mean annual runoff,

  • Increase in the magnitude and frequency of floods and droughts, and eventually

  • Climatic changes in the direction of greater aridity.


Climatic changes are natural processes normally measurable in a geologic timescale. The Upper Paraguay basin itself has been through several climatic changes, e.g., from semiarid in the Jurassic to humid in the Cretaceous (Section 3.2). The great depth of the Quaternary deposits (420 m at Fazenda São Bento, in the Taquari alluvial fan), can only be explained by an active geodynamical process associated with a semiarid climate prevailing in the geologic past. The point to be made is not climatic change, which is always present, but rather, the rate of climatic change. It is now widely believed that anthropogenic climatic change is possible, and that it can occur within decades, rather than millennia.


4.4.2  Impact on the Nutrient Balance

The close relationship between hydrologic and nutrient budgets has been known for some time. For instance, Likens and Bormann (1975) studied the Hubbard Brook Experimental Forest in New Hampshire. Deforestation increased surface runoff and resulted in large increases in streamwater concentration for all major ions (Ca++, K+, NO3-), excepting a few (NH4+ and SO42-). The annual overall loss of phosphorus was about an order of magnitude greater as a result of deforestation. Total export of dissolved substances, exclusive of dissolved organic matter, averaged 81 ton/ha-yr for the deforested catchment, compared to 13 ton/ha-yr for the undisturbed control catchment. The nitrate concentration in the runoff water almost continuously exceeded, and at times, almost doubled, the maximum concentration recommended for drinking water.

Likens and Bormann (1975) cautioned that unless such ecological interrelationships are better understood, human interventions in natural ecosystems can produce unexpected and potentially deleterious results. In a similar study, Elwood and Henderson (1975) emphasized the need for baseline studies of hydrologic and nutrient budgets prior to project implementation or land management decisions.

An example of the relation between hydrologic and nutrient cycles in the Pantanal is given by Silva (1990), who noted that the concentrations of calcium, potassium, and magnesium in the watercourses of the Pantanal of Barão de Melgaço, near Cuiabá (Fig. 2), are greater during flood (cheia) that during low flow (estiagem).

The Pantanal exists because its geologic/geomorphologic setting conditions it to retain water, soil moisture, sediment, and nutrients (Tricart, 1982; Junk, 1989). The extensive and long inundation patterns and the retained soil moisture lower the mean albedo, favoring locally generated rainfall (Stidd, 1975; Balek, 1983). Soil moisture typically lowers mean albedos by a factor of two (Dickinson, 1983). The sediment and associated nutrients imported from upland subbasins tend to remain in the Pantanal, assuring a constant source for replenishment (Carvalho, 1984; Silva, 1990). The retained water sustains the evapotranspiration needs of the vegetation, the sediments continue the valley buildup, and the nutrients are largely filtered out and taken up by the vegetation.

A characteristic feature of the Pantanal ecosystems is the annual flood pulse (Junk et al., 1989). Modifications in the annual flood pulse will lead to changes in the Pantanal, both biotic and abiotic (Sparks, 1995). Wildlife breeding cycles are closely linked to the annual flooding and receding cycle (Bayley, 1995; Campos, 1993). Increases in flood magnitude will result, in the short term, in an increase in sediment yield and a change in the basin's nutrient budget. Loss of nutrients to runoff will mean less biotic productivity and the eventual loss of the Pantanal ecosystems' character as savanna woodlands, where both wildlife and domesticated animal species can coexist.

The most important economic activity in the Pantanal is the raising of cattle. Antunes (1986) has estimated the number of cattle at 3.5 million. On the other hand, Alho et al. (1988) have stated that the seasonal grasslands have fed up to 8 million head of cattle. For centuries, low-density cattle raising has been the predominant land-use activity in the Pantanal. Prance and Schaller (1982) have stated that the natural vegetation of the Pantanal can be maintained together with the ranches, provided that the cattle population is kept within reasonable limits, and that areas are set aside for the conservation of flora and fauna.

The environmental impact of cattle ranching in the Pantanal appears to have been minimal (Alho et al., 1988). Overgrazing, an insidious problem which plagues semiarid and subhumid exorheic basins in other parts of the world, is not a serious problem in the Pantanal. The flood pulse serves the dual purpose of effectively controlling overgrazing, by temporarily impeding grazing in flooded areas, while replenishing the soil with fresh nutrients attached to the fine sediments (Silva, 1990). More importantly, the flood pulse is instrumental in maintaining the grasslands, since competing vegetation types, particularly the woody species, are not well adapted to the flood pulse (Cole, 1960).

Antunes (1986) has pointed out that during the drought of 1965-73, cattle ranching expanded in the Pantanal, as many areas that had previously been seasonally flooded remained nonflooded for more than one season. Beginning in 1974, the flood period returned with an unusual force. This led to the overgrazing of the remaining campos by the suddenly spatially constrained herds. To compound the problem, the campos were already threathened by the invasion of woody species which had taken advantage of the long drought to establish themselves on the dry campos. Similar examples of the invasion by woody species of areas of Pantanal that have been artificially protected from flooding by the use of polders have been reported (H. Benito, personal communication, 1995).

The inundation patterns of the Pantanal have been recently quantified by Hamilton et al (1995) using remote sensing. During exceptional flood years, up to 100,000 km2 (73 percent) of the Pantanal is simultaneously flooded for at least 30 days, controlling over grazing through inundation while replenishing the land with nutrients. On the other hand, during the dry season in drought years, less than 6,770 km2 (5%) of the Pantanal may be flooded, encouraging overgrazing and virtually eliminating nutrient replenishment by natural means.

In conclusion, the flood pulse is the mechanism that provides the nutrient replenishment, overgrazing control, and grassland maintenance on which the natural biotic productivity of the Pantanal hinges.


4.4.3  Impact on the Biota

Changes in the hydrologic regime of the Upper Paraguay river basin will have a definite impact on the biota. Currently, there is a delicate balance between the various types of vegetation, reflecting the predominance of an average tropical climate, with a clear summer rainy season lasting 7 to 9.5 months. Changes in hydrologic signature in the direction of greater aridity will increase the competitiveness of the semiarid scrub forest (caatinga) in higher ground, and lead to reductions in savanna woodland species (cerrados), which currently dominate in the Pantanal (Prance and Schaller, 1982).

The interaction between hydrology and geomorphology is the basis of the biotic makeup of the Pantanal, with the flood pulse being the cornerstone of ecosystem function (Junk et al., 1989). Unlike woody species, herbaceous species are well adapted to the flood pulse, since they are able to tolerate extreme alternations of saturation (flooding lasting from one to three months) and desiccation (dry season lasting 2.5 to 5 months) (Cole, 1960). Thus, changes in hydrologic regime resulting in decreased flood periods and increased drought periods will produce changes in vegetation species composition from herbaceous to woody (Veloso, 1972). This will change the character of the Pantanal ecosystems, from savanna woodlands (with sparsely distributed islands of cerradão) to more mesic forests, reflecting a predominance of the woody over the herbaceous vegetation. In turn, this will produce a change in animal species and populations, wherein those species better adapted to the cerrado will predominate over those adapted to the campos. The decreasing areal coverage of grasslands will have an impact on the cattle ranching industry, which will not be able to support as many animal units as it currently does. In addition, the human use of fire for the control of woody vegetation is likely to increase, negatively impacting air quality.

Thus, the spiral of environmental degradation begins with changes in the hydrology (changes in flood, baseflow, yield, and drought regimes), and eventually has impacts on the biota, both vegetative and animal, including the human species.


4.5  Summary

This section describes the possible hydrologic impacts of the Hidrovia project on the Pantanal of Mato Grosso. The evaluation considers impacts on the water, sediment, and nutrient balance as a direct and indirect consequence of proposed navigational improvements, to include channel straightening, dredging, and blasting of rock outcrops. The following is a summary of the main points established in this section:

  • The Upper Paraguay river upstream of Porto São Francisco (located 146 km upstream of Corumbá) is incapable, without extensive artificial channel deepening, of accommodating ocean-going vessels (with a 3-m draft requirement) throughout the year. The extension of the proposed 3-m navigation channel all the way to Cáceres will require major interventions in the natural channel.

  • Currently, a 1.2 m minimum depth is maintained by autodredging, except in the places where rock outcrops do not permit autodredging to take place. The Pantanal exists largely because of these rock outcrops, which act as natural dams, influencing the regional flow patterns in at least three places: Amolar, Porto da Manga, and Fecho dos Morros.

  • Blasting rocky sills as a means of deepening the navigational channel will have an irreversible impact on the hydrologic regime of the Upper Paraguay river, particularly upstream of Corumbá. In essence, the blasting amounts to natural dam removal, which will increase runoff and accelerate runoff concentration, intensifying floods.

  • Relatively minor changes in grade, which would necessarily take place as a result of blasting rocky sills, can affect the upstream hydraulics to greater lengths than may have been anticipated. For instance, the backwater effect produced by a 0.47-m hump in the bed profile at Amolar may be felt for a distance of 375 km upstream.

  • Unlike a typical alluvial river, the longitudinal profile of the Upper Paraguay river is convex when observed from above, revealing the presence of substantial geologic controls. A rock outcrop has been documented along the Upper Paraguay river every 40 km on the average (Fig. A28).

  • It is expected that the removal of rocky sills may lead to the appearance of other rocky sills, which were previously submerged. This will open up a spiral of environmental degradation, in the form of loss of water, sediment, and nutrients, and produce ecological changes which would be extremely difficult to control.

  • Channel modifications (straightening, dredging, and particularly blasting of rocky sills), will destabilize the river's baseflow regime, and will demand future action in the river to continue to maintain the required minimum draft for navigation, i.e., it will set in place a vicious circle of channel interventions.

  • The Hidrovia project will, in the short term, increase the mean annual runoff coefficient above its current value (0.08), reducing evapotranspiration amounts and negatively affecting the vegetative biota.

  • The acceleration of runoff concentration caused by navigational improvements will intensify high mean, extraordinary and exceptional floods, potentially reduce the recurrence interval of multiannual drought periods, and may lead in the long term to climatic changes in the direction of greater aridity.

  • Runoff losses will greatly increase sediment and nutrient losses, destabilizing the Pantanal ecosystems by modifying the nutrient budget, resulting in reduced biotic productivity.

  • Long-term changes in the hydrologic regime of the Upper Paraguay river in the direction of greater aridity (lesser precipitation, lesser evaporation/evapotranspiration, and lesser runoff amounts) will have a definite impact on the biota. The competitiveness of the semiarid scrub forest (caatinga) will increase, adversely affecting the delicate balance between the diverse plant communities that inhabit the Pantanal.

  • Modifications in the flood pulse, coupled with long-term climatic changes in the direction of greater aridity, will produce an ecological succession from herbaceous to woody species. The size and number of vegetated earth mounds (capões) will increase, with the grasslands (campos) expected to be the net losers. Both wildlife and domesticated animal species will be adversely affected.

Fig. A28  Typical rock outcrop along the Paraguay river.


5.  SUMMARY
[References]      [Top]   [Executive Summary]   [Introduction]   [Geographical Background]   [Upper Paraguay River]   [Environmental Impact]  

This last section summarizes the findings of this study. It is divided into three subsections:

  1. The Pantanal of Mato Grosso

  2. The Hidrovia Project

  3. The Hydrologic and Environmental Impacts.

Each subsection summarizes the main points established in this study. Additional details can be found in the respective sections of this report: the Pantanal of Mato Grosso, subsection 2.3 and Section 3; the Hidrovia Project, subsection 2.4; and Hydrologic and Environmental Impacts, Section 4. A subsection entitled "Concluding Remarks" ends this section of the report.


5.1  The Pantanal of Mato Grosso

The following points were established during the course of this study:

  • The Pantanal of Mato Grosso is a seasonally inundated depression wholly contained within the Upper Paraguay river basin, encompassing 136,700 km2 in Mato Grosso and Mato Grosso do Sul, Central Western Brazil. The Pantanal is an immense and biologically diverse wetland, geomorphologically and hydrologically positioned to attenuate and reduce the runoff from the Upper Paraguay basin.

  • The predominantly Upper Precambrian formations underlie extensive Quaternary deposits, with significant rock outcrops. Geomorphologic evidence reveals the presence of a substantial amount of tectonic activity in the form of subsidence and uplift.

  • The bed of the Upper Paraguay river is controlled by the prevailing geology. The longitudinal profile of the river is convex when observed from above, revealing the presence of substantial geologic controls. There are thirty-two (32) documented rock outcrops within 1,270 km of river, an average of one every 40 km.

  • The abnormally low runoff coefficient of the Upper Paraguay river at its mouth (a value of 0.08) is a direct result of its hydrologic interaction with the Pantanal. The latter functions as an immense surface/subsurface reservoir which stores water in both annual and multiannual timeframes.

  • The Upper Paraguay river is very effective in decreasing the flood peaks and correspondingly increasing the low flows. The presence of the Pantanal provides the mechanism for the diffusion of flood flows and the increased permanence of low flows.

  • The hydrographic records at Ladario show the extremely strong attenuating capacity of the Pantanal upstream of this point. Throughout the entire period of record (1900-95), the flood wave at Ladario has always been unimodal (only one rise and one recession per year).

  • The Pantanal functions not only as an attenuating mechanism for flood flows, but also as an abstracting mechanism for all flows, i.e., as an effective means of storing the would-be runoff and converting it instead to evaporation and evapotranspiration. Throughout millennia, this process has been responsible for sustaining the extraordinary biotic potential of the Pantanal.

  • The Pantanal is still a surface of sediment accumulation, with a net annual gain of sediment and nutrients.

  • The Pantanal is extremely rich in floristic diversity and physiognomic composition. Its floristic diversity is due to its privileged location, surrounded by four great South American biomes: the tropical Amazon rainforest, the subhumid savannas of Central Brazil, the Atlantic humid forest, and the semiarid scrub forest of the Chaco. Its diverse physiognomic composition is due to its variety of geomorphic/topographic features.

  • The Pantanal remains a unique repository for a variety of wildlife species, including numerous species of birds, fish, reptiles, and mammals. Many species selectively inhabit the campos, vegetated earthmounds (capões, cordilheiras), gallery forests, and water courses (baías, corixos, vazantes) of the Pantanal. Such impressive biodiversity is due in large measure to the unique geologic, geomorphologic, and hydrologic setting of the Pantanal.


5.2  The Hidrovia Project

The following points were established during the course of this study:

  • The Paraná-Paraguay river system has been used as a waterway for transportation for several centuries. The river system encompasses the Upper, Middle, and Lower Paraguay rivers, and the Middle and Lower Parana rivers. It drains portions of Brazil, Paraguay, Bolivia, and Argentina.

  • The Paraná-Paraguay Waterway Project, known locally as the Hidrovia Paraná-Paraguay, for short, Hidrovia, is currently being considered for funding by the Inter-American Development Bank.

  • The executive agency for the Hidrovia project is the Comité Intergubernamental de la Hidrovía (CIH), an intergovernmental agency set up by the governments of the five countries which have jurisdiction in the waterway: Argentina, Bolivia, Brazil, Paraguay, and Uruguay.

  • The Hidrovia project entails navigational improvements along the existing Paraná-Paraguay Waterway. The project considers extensive river engineering works, including channel straightening, dredging, blasting of rocky sills, and other structural interventions to render 3442 km of the river navigable for ocean-going vessels, from the downstream point at Nueva Palmira, Uruguay, to the upstream point at Cáceres, Mato Grosso, Brazil, near the headwaters of the Upper Paraguay river.

  • Since the port of Cáceres is located upstream of the Pantanal of Mato Grosso, it is expected that the Hidrovia project, if implemented as currently envisioned, will threaten the Pantanal's preeminent status as the largest remaining wetland in the American continent and the world.

  • In February 1995, the Inter-American Development Bank and the United Nations Development Programme commissioned engineering and environmental impact studies of the proposed project. These studies are ongoing, with results expected in late 1996.

  • To this date, the only comprehensive document on the Hidrovia project is the INTERNAVE report, completed in 1990 by the Brazilian company Internave. This report is essentially an economic feasibility study of the Hidrovia project.

  • The physical aspects of the proposed Hidrovia (channel straightening, dredging, and blasting of rocky sills) are the source of significant concern among diverse segments of the national and international communities, including indigenous peoples, environmental organizations, nongovernmental organizations (NGOs), professional associations, and universities in Brazil, the American continent, and the rest of the world. The concern is that the Hidrovia project may cause irreparable harm to the Pantanal wetlands, a significant focus of biodiversity in the American continent.


5.3  The Hydrologic and Environmental Impacts

The following points were established during the course of this study:

  • The proposed navigational improvements (channel straightening, dredging, and blasting of rocky sills) will have a substantial impact on the flood regime of the Upper Paraguay river. The degree of the impact will vary depending on the type and extent of intervention, and its location along the river.

  • During high mean (2-yr), extraordinary (4-yr), and exceptional (10-yr) floods, channel straightening will accelerate the concentration of flood runoff and increase the flood wave peak at Ladario.

  • The Upper Paraguay river upstream of Porto São Francisco (located 146 km upstream of Corumbá) is incapable, without extensive artificial channel deepening, of accommodating ocean-going vessels (with a 3-m draft requirement) throughout the year. The planned extension of a 3-m navigation channel all the way to Cáceres will require major interventions in the natural channel.

  • The Upper Paraguay river is subject to the "autodredging" phenomenon. By adjusting the shape and configuration of its bedforms, the river is able, during low flows to reduce its discharge while maintaining an approximately constant stage (and minimum flow depth). In the Upper Paraguay river, this minimum depth is 1.2 m, except where rock outcrops do not permit autodredging to take place. To the extent that this minimum depth is violated in many places, it is concluded that the slope of the Upper Paraguay river is geologically controlled.

  • Blasting rocky sills as a means of deepening the navigation channel will have an irreversible impact on the hydrology of the Upper Paraguay river. This is the most significant planned intervention. If pursued, it is likely to change the Pantanal forever.

  • Navigation charts shows that the river has been able to carve a sufficiently deep channel through most of the rock outcrops. Yet, in other places, where the depth is shallower because rocky sills protrude into the channel, the river has not yet carved an opening. The Pantanal exists because of these rocky sills, which influence the regional flow patterns in Amolar, Porto da Manga, and Fecho dos Morros.

  • Backwater calculations confirm that relatively minor changes in grade, which would necessarily take place as a result of blasting rocky sills, can affect the upstream hydraulics to greater lengths than may have been anticipated. The rocky sills act as natural dams; if they are removed, extensive areas of the Pantanal will no longer be subject to seasonal flooding.

  • Removal of one rocky sill may lead to the appearance of another rocky sill which was previously submerged. This is a distinct possibility in the Upper Paraguay river, where rock outcrops have been documented to occur every 40 km on the average, and where the prevailing channel slopes are so mild that the backwater effect of a 0.5-m obstruction or hump may be felt for about 400 km upstream.

  • It is expected that channel modifications will destabilize the river's baseflow regime and will demand additional future interventions in the river to continue to maintain the required minimum draft, i.e., it will set in place a vicious circle of channel interventions.

  • The acceleration of runoff concentration caused by navigational channel improvements will intensify high mean, extraordinary and exceptional floods, potentially reduce the recurrence interval of drought periods, and may eventually lead to regional climatic changes in the direction of greater aridity.

  • Extraordinary and exceptional flood peaks on the Upper Paraguay river will be felt earlier downstream, at Asunción, on the Middle Paraguay, and at Corrientes, on the Middle Paraná. The precise extent of this effect remains to be determined by further analysis.

  • Changes in the runoff regime of the Upper Paraguay river are likely to lead to substantial increases in mean albedo. In other parts of the world, the evidence (circumstantial and experimental) is mounting linking increases in mean albedo to climatic changes in the direction of greater aridity. The Pantanal is not immune to climatic changes, which have occurred in the geologic past; the point to be made is the rate of climatic change. It is now widely believed that anthropogenic climatic change is possible and that it can occur in decades, rather than millennia.

  • The Pantanal exists because its climatic/geologic/geomorphologic setting conditions it to retain water, sediment, and nutrients. Modifications in the annual flood pulse will lead to changes in the Pantanal, both biotic and abiotic. Increases in flood magnitude will result in increased sediment and nutrient losses.

  • The annual flooding of extensive areas of Pantanal serves the dual purpose of effectively controlling overgrazing and replenishing the soil with fresh nutrients. More importantly, the seasonal flood pulse is instrumental in maintaining the grasslands, since competing vegetation types, particularly the woody species, are not well adapted to the extreme alternations of saturation and desiccation.

  • Changes in hydrologic regime resulting in increased floods and droughts will impair nutrient replenishment and lead to reductions in biotic productivity. These changes will produce a succession from herbaceous to woody species, which will change the dominant character of the Pantanal from savanna woodlands to more mesic forests. The open grasslands will shrink, and this will have a negative impact on cattle ranching.


5.4  Concluding Remarks

The Hidrovia project is expected to have a significant hydrologic and environmental impact on the Upper Paraguay river and the adjoining Pantanal of Mato Grosso. The latter is a unique terrestrial region where an unusual combination of continental location, climate, geology, geomorphology, and surface and groundwater hydrology has contributed, through millennia, to the establishment of a delicate ecological balance. Throughout the past two centuries of human settlement, the environmental impact of cattle ranching, considered to be the most important economic activity in the Pantanal, appears to have been minimal.

In essence, the Hidrovia project seeks to convert a portion of the water resources, from the maintenance of an environment suited to low-density cattle ranching and diverse wildlife habitats, to the maintenance of an inland waterway for the transportation of goods, primarily for export. For this purpose, the project proposes to carve a channel, sufficiently straight and deep to be suited for ocean-going vessels, all the way to Cáceres, upstream of the Pantanal.

The Upper Paraguay river, from its mouth at the Apa river confluence to the city of Corumbá (a distance of 590 km upstream), is generally straight and deep enough for the passage of large vessels, excluding a few locations where some dredging may be required if the navigation project is implemented up to Corumbá. However, upstream of Corumbá, toward Cáceres (a distance of 680 km), the river is too shallow and in some places too sinuous to effectively function as a commercial year-round waterway. This is why current commercial river traffic between Corumbá and Cáceres is almost nonexistent. The artificial straightening and deepening of the Upper Paraguay river all the way to Cáceres will provide a navigation channel, but at the cost of substantial losses of water, sediment, and nutrients.

How these losses will compare with the project gains (expected reductions in transportation costs) is a question that deserves a clear and definitive answer prior to project implementation. This is particularly crucial in the case of the Pantanal, where irreversible interventions in the natural channel (the blasting of rocky sills) have the potential to destabilize the hydrologic regime. The Pantanal ecosystems are extremely complex, and their myriad of biotic/abiotic interrelations are only now being thoroughly examined (Prado et al., 1994; Heckman, 1994; and others). Unless all costs are effectively incorporated into the economic analysis, the prudent course of action is to preserve the Pantanal's preeminent status as the largest and most biologically diverse wetland of the Americas and the world.


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   [Top]   [Executive Summary]   [Introduction]   [Geographical Background]   [Upper Paraguay River]   [Environmental Impact]   [Summary]  

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Fig. B1  Front cover of the original report.

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