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Number 61, June 2007, Level 1


Of all my experiences as a graduate student at Colorado State University in the early 1970s, the following is most certainly a pearl.

The class CE602 Transport Phenomena was required for all majors in the graduate program in hydraulics. One day, the professor came to class and, after the customary salutation, solemnly declared: "I have decided to do something different this time. The midterm will be take-home..." and he paused, to continue with a grin: "three-hour, closed book."

We looked at each other in amazement, while struggling to regain our composture. Specific instructions followed almost immediately: "You will pick up the exam tomorrow at 5 pm in my office, and return the completed exam by 8 am the following morning."

I can't vouch for the rest of my classmates, some ten in all. All I can say is that I knew that something was up, but I could not figure out what it was. As instructed, I picked up the exam, went home, had dinner, and started to work on it at about 8 pm. There were six problems, the likes of which I had never seen before. I knew almost immediately that this was not a three-hour exam, certainly not for me. At around 2:00 am, I finally completed the work, after having consulted at least two books. At 8:00 am, I returned the exam, half ashamed, but undaunted.

The next time the class met, the professor inquired: "How did it go?" My recollection of the events of that day is that everybody kept quiet, except for my colleague Fred Theurer, who said, pointedly: "Professor, I must tell you that it was impossible for me to do the exam in the allotted time, and without consulting any books. It took me nearly six hours, and I used several books."

I am certain that Fred got an A in the exam, while the rest of the group, including myself, had to settle for an also-ran B. We will never know if his honesty paid him handsomely that day, but I would not hesitate to place my bet on it.

Number 62, July 2007, Level 1


Computer programming remains a challenge for many people. In the past several years, this has led to the popularity of software applications with graphical user interfaces (GUI), which circumvent the need to program. Yet programming remains an indispensable tool in research and other specialized applications.

In many instances, debugging a computer program requires uncommon analytical ability and a dose of patience. However, a debugging trick that never fails is to print intermediate steps until the source of the trouble is identified.

In the early 1980's, a student came to me with a partially completed programming assignment, and said, "Prof. Ponce, I have been looking at this program for more than two hours and cannot find the bug. Can you help me?"

I promptly replied, "You can't just look at the code. You need to do something about it." And then, I proceeded to show the student a trick that I had learned very early during my graduate school days at Colorado State University.

"Place the message 'So far so good!' as a marker in several critical parts of your code, and pretty soon you will find where the problem is".

The student followed my advice and in very short order the assignment was completed.

Number 63, August 2007, Level 0


In one of my trips to Oaxaca, Mexico, in the early 2000's, an acquaintance told me the following story.

A group of people from a remote hamlet were planning to build a road. A delegation converged on the mayor of town to solicit his help. The mayor offered them a bulldozer and a few picks and shovels. He also mentioned that he would send an engineer. At that point, the head of the delegation said: "An engineer? What for? We haven't used one before."

The mayor explained that the engineer would help them to find where to put the road. The head of the delegation answered promptly: "In the past, when we needed to build a road, we just let a burro loose, and he would show us the best possible route."

Thus, the moral of the story: A burro's natural instinct can work engineering wonders.

Number 64, September 2007, Level 2


In July 2005, I attended the 20th anniversary celebration of the Feather River Coordinated Resource Management Group (FRCRMG), in Quincy, Plumas County, California. The three-day event included a tour of Red Clover Creek, which for many years has been at the center of this agency's efforts to manage river ecosystems in the California Sierras.

The story of Red Clover Creek teaches us some important lessons. Prior to the middle 1950s, Red Clover Creek was a relatively shallow stream with permanent baseflow supporting an excellent fishery. However, in the late 1940s and early 1950s, federal programs were introduced to eliminate willows [phreatophytes] using aerial herbicide spraying. At about the same time, over three hundred beaver were removed from the system. These actions, together with the longstanding effects of heavy grazing and a system of abandoned logging railroad grades in the valley, brought Red Clover Creek to the brink of disaster. The 1955 flood was the catalyst for the massive gully formation through the valley, which continued through most of the 1980s. Once the gully formed, the regional water table dropped, baseflow was all but lost, and erosion and sediment transport followed. Of all the reasons for the formation of the FRCRMG in 1985, none was more important than the loss of Red Clover Creek.

Happily, after many years of enlightened management, Red Clover Creek is now returning to its former state: stable, self-sustaining, and with permanent baseflow.1 The restoration work began in 1985 with the installation of four loose-rock checkdams. Ten years later, the FRCRMG developed a new technology to use in place of checkdams. Called "pond and plug," it seeks to eliminate the gully through onsite excavation and fill, forcing the water level in the valley to rise to meet the historic remnant channels and floodplain. In 2006 this technique was used on additional portions of Red Clover Creek below the original check-dam project. After treatment of 4.5 miles of stream channel, the project is now in its first season of recovery, as shown in the [before and after] photos below.2

  1 Ponce, V. M., and D. S. Lindquist. 1990. Management of baseflow augmentation: A review. Water Resources Bulletin, Vol. 26, No. 2, April.
  2 Photos courtesy of Jim Wilcox, Plumas County, California.

Number 65, October 2007, Level 0


Reading about the Spanish Conquest of Mesoamerica in the early XVI Century is a fascinating experience. One of the most remarkable stories is that of Fray Bartolomé de Las Casas, who almost singlehandedly engineered the institutional defense of the Indians as human beings and subjects of the Spanish Crown. De Las Casas was witty and extremely eloquent. He argued convincingly for many years in favor of better treatment for the Indians.

In one such meeting, in October of 1519, where King Charles I of Spain (Charles V of the Holy Roman Empire) was to hear the arguments on what to do with the Indians, Bishop Juan de Quevedo, who had just returned from five years in the Darién [in what is now Panama], quoted the Philosopher Aristotle as saying that "the Indians are slaves by nature." Never short of a response, de Las Casas countered that since Aristotle was a nonbeliever, he was presumably burning in Hell, so his argument held no ground.1

Such were the events that shaped the history of Latin America.

 1 Thomas, Hugh. 2005. Rivers of Gold: The Rise of the Spanish Empire, from Columbus to Magellan. Random House, New York.

Number 66, November 2007, Level 1


In 2002, I published a paper on the subject of drought characterization in the Ojos Negros valley, in Baja California. Mr. A. V. Shetty, one of my coauthors, had performed a detailed statistical analysis on the data for ten (10) climatological stations in the vicinity of the valley, located 25 miles east of Ensenada. The results showed that the average frequency of droughts in the region was 3.96, i.e., that droughts recurred in the valley approximately every four years.

Afterwards, we followed up with a visit to the valley, where we met the owner of the Ojos Negros Ranch. I struck a conversation with him and asked him what was the frequency of droughts in the valley. Without winking an eye, he said: "Every four years."

Number 67, December 2007, Level 0


Many urban people believe that the world ends at the outskirts of town. Yet, in my own experience, this is not so. Many years ago, I traveled to Lima, Peru, where I grew up in the 1950s and '60s. While there, I visited my father, who is from Huarochiri, one of ten provinces in the department of Lima. [The latter is one of twenty-four departments in Peru]. As was my father's custom, he invited me for an outing. After a little more than three hours, we reached the town of Antioquia, about 80 km east of Lima. The place, however, is largely unknown, because a lack of a paved road discourages most people from reaching it.

That evening I met some friends at a party. One of them asked me: How are you doing?" I said: Fine, I just came back from Antioquia." To which he solemnly responded: "There is no Antioquia here!"

Number 68, January 2008, Level 0


In 1993, I visited for the first time the Colca Canyon, tucked away in the Andes Mountains, a few hours drive from Arequipa, Peru. I was accompanied by a local colleague and a driver. To add a measure of interest to the trip, we decided not to backtrack from "El Mirador del Condor" (The Viewpoint of the Condor) to Arequipa, but rather to keep driving forward to meet the Panamerican Highway, essentially, making what amounted to an 18-hour circuit over little-traveled gravel roads.

Along the way, we were regaled with magnificient scenery and the familiar rural landscapes of the Peruvian Andes. Many people assume business as usual as they venture into these areas, without realizing that there are deep cultural differences. Upon reaching the town of Huambo, I had an urge to go to the bathroom, so I instructed our driver to stop at a suitable place. He stopped at a corner store, I jumped out of the car, entered the store, and said to the salesperson, almost pleading: "May I use your bathroom?"

She looked at me, half surprised, half nonchalant, and said: "We do not have that here." When I politely insisted on an explanation, she motioned to the outside, and said in a slow tone, so that she was sure that I got the message: "When people want to go, they manage somehow."

It was a lesson in rural Peru that I would never forget.

Number 69, February 2008, Level 1


In 1993, I spent three weeks in Bihar, India, on a consulting assignment with the National Institute of Hydrology. I was stationed in Patna, with an occasional trip to the countryside. The local weather is humid subtropical, with mean annual precipitation of 1,200 mm, and significant amounts of precipitation occurring in all seasons.

At night, I would huddle under the mosquito netting and feel confident that I was protected against the many bugs, some of which appeared to be very mean. However, once I turned the lights off, after a few moments, a shrieking and persistent sound would start somewhere in the room, as if many insects were busy eating away at something. When I would turn the lights on to inspect the surroundings, the mysterious sound would stop. This went on a number of times, until I would invariably tire out and fall sleep.

I never figured out exactly who or what was responsible for the sound, but I am certain that I was not alone during those nights in Bihar.

Number 70, March 2008, Level 1


In the Fall of 1993, I took a sabbatical leave at the famed Departamento Nacional de Obras Contra Secas (DNOCS) [National Department of Works Against Droughts], in Fortaleza, Brazil. This work led to several papers on drought hydrology, among them, Characterization of drought across climatic spectrum and Management of droughts and floods in the semiarid Brazilian Northeast - The case for conservation.

While in Fortaleza one evening, I went out to dinner with a former classmate from Colorado State University who happened to be in town for business. He had a very good reputation in stochastic hydrology going back to his years as a Ph.D. student.

Curious to find out what he was up to, I said: "José, what are you doing these days?"

He answered: "Urban hydrology." I said: "That is something new to you, isn't it?

He replied: "It is simple. All you do is build a channel in the middle of the street, and drain the water as fast as you can."

I said: "That's the way it used to be. Nowadays it is a lot more complex than that. Urban hydrology is not just drainage; it is also retention."

Number 71, April 2008, Level 0


In the Fall of 1997, I visited Disneyland, accompanied by two scientists from the National Institute of Hydrology in Roorkee, India. The scientists were spending a semester at SDSU on study leave, and I was showing them the Southern California attractions.

After enjoying several rides, we decided to get something to eat before continuing our visit. We found a burger place nearby, and proceeded to order some food. I ordered a hamburger; my companions, after much hesitation and consultation among themselves, ordered cheeseburgers.

When the food arrived, my companions were surprised to learn that a cheeseburger wasn't just cheese and bread, it had meat! They were vegetarians. We had to quickly chart an alternate plan so that our visitors would not go hungry that day.

Number 72, May 2008, Level 0


In the Spring of 1989, I visited Alkali Creek, in western Colorado, accompanied by a colleague, a biologist who worked for a federal agency. My objective was to observe the watershed restoration project that had been accomplished in the 1960s by the Forest Service. Eventually, I published a paper entitled: "Management of baseflow augmentation: A review," in which I documented this and other similar projects of watershed restoration.

After we had observed several of the more than one hundred check dams that were still standing, and having suffered the inclement weather for a couple of days, my colleague said to me, pointedly: "Victor, as I can see, the only difference between you and me is that you make three-thousand dollars more."

Number 73, June 2008, Level 2


Sediment problems in hydraulic engineering are difficult to solve. A case in point: In 1992, two sediment retention basins were built in the Aguaje de la Tuna watershed, in Tijuana, Baja California, Mexico. The intent was to catch the sediments in the event of a flood, while letting the water pass through. The objective was to reduce sediment deposition in the mouth of the watershed, based on the belief that sediment was more damaging than flood waters.

On January 8, 1993, a severe and unusual flood tested the sediment retention basins, which proceeded to fill up with sediment in short order. Apparently, the problem had been solved; however, experience indicates otherwise. To understand what may have happened, we examine Lane's relationship, which states that sediment discharge is proportional to water discharge.1 According to Lane, if sediment load is extracted from the flow, by any means, and water discharge is not reduced accordingly, the water flow becomes "hungry" and proceeds to entrain new sediment as it moves downstream. This explains the well known phenomenon of aggradation upstream of a dam and degradation downstream of it.

In the event of January 1993, approximately 400,000 cubic meters of sediment were deposited near the mouth of the Aguaje de la Tuna, despite the fact that the sediment retention basins had retained all the sediment they could (20,000 cubic meters).2 Two scenarios are possible:

  1. About 420,000 cubic meters of sediment (measured as sediment deposits) came down the watershed that night, 20,000 were retained by the basins, and the difference (400,000) was transported to the mouth; or

  2. About 400,000 cubic meters came down, 20,000 were retained by the basins, an additional 20,000 were later entrained by the "hungry water," and the sum (400,000) was transported to the mouth.

According to Lane's relationship, the second scenario appears more plausible. In the Aguaje de la Tuna, the hungry water [flowing from the sediment retention basin] scoured a depth of about 3 m in the streambed, down to bedrock [see photo]. Thus, the utility of building sediment retention basins, without providing for concurrent water storage, is cast into question.

1 Lane, E. W. 1954.   The importance of fluvial morphology in hydraulic engineering. Proceedings, ASCE, Vol. 81, Paper No. 745.
2 The data was provided by Henry Alberto Castro García.

Number 74, July 2008, Level 1


In the fall of 1993, I spent a sabbatical leave in Ceara, in the Brazilian Northeast, researching the subject of droughts.1, 2 At that time, the region was suffering from a crippling three-year drought. Emergency plans were under way to transfer water from the Orós reservoir in the backlands, through the Jaguaribe river to the coast, and through a specially made canal, into the [almost empty at the time] Pacajus reservoir, located within reach of the city of Fortaleza. The latter is home to a major population center in the region, with close to two million people.

The "Canal do Trabalhador" ("The Worker's Channel") was being built expressely for the water transfer.3 At the time, the canal project was regarded as a last ditch effort to mitigate the ravages of the drought. The alignment followed roughly along the coast of the state of Ceara, a distance of about 100 km. The construction of the canal was particularly difficult due to the unstable soils and the very mild slope of the canal (about 5 cm per km), which increases the risk of sedimentation.

Completed in a record period of six months, the canal started delivering the much needed water near the end of 1993. However, less than two months later, a series of heavy storms filled the Pacajus reservoir, bringing to an end the long drought and rendering the Worker's Channel essentially unnecessary.

Currently, the canal is not being used for its original purpose, but rather to supply irrigation projects along its alignment. Thus, the lesson to be learned is: "Weather prediction is difficult and failure prone."

1 Ponce, V. M. 1995. Management of droughts and floods in the semiarid Brazilian Northeast: The case for conservation. Journal of Soil and Water Conservation, September-October, Vol. 50, No. 5, 422-431.
2 Ponce, V. M. 2000. Characterization of droughts across climatic spectrum. Journal of Hydrologic Engineering, Vol. 5, No. 2, April, 222-224.
3 Ponce, V. M. 2004. "The Worker's Channel." Legacy tale, May.

Number 75, August 2008, Level 1


In March of 1974, Professor Koloseus1 arrived in class at the end of the [winter] quarter at Colorado State University, and announced that the final exam [in Open-channel Hydraulics] "... was going to be quite different this time." We, the students, who numbered around fifteen, were supposed to prepare our own questions and answer them as best we could. He would judge meaning, content, and accuracy, and assign a grade accordingly.

My recollection of the events has faded a bit over the years, but I remember clearly that we all complied. We submitted the self-prepared exam, and waited for a grade... and waited, and waited.... About a week later, Prof. Koloseus showed up, visibly exhausted, acknowledging that it had taken him quite some time to grade the exams. After thanking everybody for their efforts, he went on to say that the experience had been so demanding [of his time and energy], that he vowed never to do it again.

1 Dr. Herman J. Koloseus, known to all as "Ike," passed away on November 21, 2004.

Number 76, September 2008, Level 2


Not many people are aware that the renowned physicist Albert Einstein wrote an early piece on the cause of meandering.1 Likewise, not many people know that his son, the famed UC Berkeley Professor Hans A. Einstein, did not begin his career in hydraulics, but rather, turned to it after several years as a structural engineer. We can surmise that the elder Einstein had a keen interest in meandering and encouraged his son to pursue a career in river hydraulics. History tells us that toward the middle of the 20th century, Prof. Einstein made his mark as one of the greatest contributors to the nascent field of sedimentation engineering. His 1950 sediment transport model is the forerunner to the Modified Einstein (1955), Colby (1957) and Colby (1964) methods.2

Einstein's discussion on the cause of meanders is casual, but characteristically insightful. His attribution of secondary currents to the Coriolis force [produced by the Earth's rotation] may have been among the first. His explanation of how meanders form due to a balance between inertial and frictional forces in a direction perpendicular to the motion is masterful. To this date, we are still not 100% sure of the process, but one thing is certain: Einstein's thoughts have helped us come closer to unraveling the mysteries of river meandering.

1 Einstein, A., 1926. The cause of the formation of meanders in the courses of rivers and of the so-called Baer's Law. Read before the Prussian Academy, January 7, 1926. Published in Die Naturwissenschaften, Vol. 14. [English translation in "Ideas and Opinions," by Albert Einstein, Modern Library, 1994].
2 Einstein, H. A., 1950. "The bed-load function for sediment transportation in open channel flows." USDA Soil Conservation Service, Technical Bulletin No. 1026, Washington, D.C., September.

Number 77, October 2008, Level 2


There are three types of errors in mathematical modeling:

  1. errors due to inadequate physical and/or numerical formulation,

  2. errors due to inaccuracies in parameter estimation, and

  3. errors due to questionable quality of field data.

The first two types are widely recognized, while the third type is often overlooked. Data of questionable quality may be due to inappropiate procedures, recording errors, equipment defects, and/or nonstationary of the data. Thus, mathematical models must not necessarily seek, in all cases, to match the field data.

In 1995, I completed a study entitled "Hydrologic and environmental impact of the Parana-Paraguay waterway on the Pantanal of Mato Grosso, Brazil." Earlier, I had traveled to Rio de Janeiro, Brazil, and met with my friend Newton Carvalho, who had spent several years doing field measurements in the Upper Paraguay river. Together we visited the appropriate agency in search of the field data to use in the study.

There was plenty of gage data, which we collected dutifully. In addition, we found a limited amount of hitherto unpublished sediment data, consisting of monthly sediment concentration at two gaging stations, Cáceres and Porto Esperança, for a five-year period (1977-82). Newton himself had participated in the sediment measurements. I thought it important to publish the sediment data, not only to complement the hydrologic impact study, but also for purely historical reasons.

The study report was published in August 1995.1 Several months later, I got a call from Steve Hamilton, from Michigan State University. He mentioned to me that in his experience, there was something wrong with the published sediment measurements. Some of the concentration values appeared to be too high. A bit puzzled, I called Newton, looking for clarification.

I asked him: "Newton, can you think of anything wrong with the 1977-82 sediment data for the Upper Paraguay?" He paused for a moment and said: "As a matter of fact, now that you mention it, we had some sample leakage during transport, which may have caused some of the concentration values to be too high."

Thus, the moral of the story: "Publication of data does not imply that is it correct."

1 Ponce, V. M., 1995.   Hydrologic and environmental impact of the Paraná-Paraguay waterway on the Pantanal of Mato Grosso, Brazil. San Diego State University, August.

Number 78, November 2008, Level 1


In 1989, I purchased a popular hydraulic package from a software reseller in San Diego. The package came with a supplement, which consisted of ten programs to solve various hydraulic problems. I took the software to Santa Cruz de la Sierra, in Bolivia, and installed it in an IBM PC 286, which was used in those days. At the time, I was working on a sediment routing model for the Pirai river basin.

Great was my surprise to find one of the supplement programs all too familiar. It was a program to calculate the Modified Einstein Procedure (now available online). The form of its output left me no doubt that it was my own software, which I had developed at Colorado State University in the middle 1970s.

Number 79, December 2008, Level 1


During my time at Colorado State University in the late 1970s, I had the pleasure of casual interactions with Prof. Vujica Yevjevich,1 a man of many talents. At that time, he was in charge of the Civil Engineering Department's graduate Hydrology Program, while Prof. Daryl Simons was head of the Hydraulics Program. Many students who graduated in these programs now lead the development of hydrology and hydraulics around the world.

Prof. Yevjevich had a good sense of humor. Once he told a group of students that, judging by his own experience, if you were a hydraulics person, your progeny was going to be male; conversely, if you were a hydrology person, it was going to be female. For proof, he simply stated that he had three girls, while Simons was the father of three boys. Following this reasoning, if you work in both fields, as many civil engineers do, your progeny will be mixed. It did not take me too long to figure out that this was my case: I have a son and a daughter.

The Yevjevich progeny rule may not always apply; the exceptions confirm the rule. But one thing is for sure: it is a good tale. I wonder if it has something to do with hunting and gathering, the proverbial genetic traits of male and female. Hydraulics may be more in tune with hunting, while hydrology resembles gathering.

Number 80, January 2009, Level 2


The natural function of rivers is to carry the sediments and dissolved solids to the ocean. Humans interfere with this function as they utilize the water resources of the Earth, often without realizing that the water is already committed by Nature as a carrier of sediments to their ultimate destination.

To help us understand this process, we examine Lane's principle of fluvial hydraulics: 1

Qsd ∝ QwS

in which Qs = sediment discharge, d = particle diameter [sediment size], Qw = water discharge, and S = slope of the stream.

Although qualitative, this relation is extremely useful in sedimentation engineering because it links together four of its most important variables. Since, by definition, sediment concentration is:

Cs = Qs/Qw

Lane's relation could be interpreted as Cs being directly related to S and inversely related to d:

Cs = f(Sa/db)

where, in general, a and b remain to be determined (Ponce, 2008). According to Lane, an increase/decrease in any of these variables will trigger a corresponding change [increase or decrease] in one [or more] of the others, until [a new] equilibrium is established.

Lane's principle is applicable wherever any of the four aforementioned variables is subject to change. For instance, if we take water out of a river [through a diversion], a new equilibrium will establish itself in the downstream river reach and the diversion canal. Likewise, if we take only the sediment out [with a sediment retention basin], the "hungry water" flowing downstream of the retention will seek a new equilibrium, usually through additional erosion, either downcutting or bank caving, depending on local conditions. Thus, geomorphological adjustments are the net result of changes in water and/or sediment discharge.

1 Lane, E. W., 1955. The importance of fluvial morphology in hydraulic engineering. Proceedings, American Society of Civil Engineers, Vol. 81, Paper 745, July.

Number 81, February 2009, Level 2


In the late 1970s, I attended an ASCE Hydraulics Division Specialty Conference in College Park, Maryland. One of the papers presented there dealt with the numerical modeling of unsteady flow, a hot topic in those days. During the presentation, the speaker stated that flood wave attenuation was due to channel friction. I waited until the end and approached the speaker on a one-to-one basis. I said, "I do not think that channel friction, per se, is the cause of wave attenuation. If this is the case, how is it that kinematic waves, which are governed by friction, do not attenuate?"

The speaker sensed I had spoken correctly, and said: "You are right. We need to take another look at this." A few years later, seeking to clarify the issue, I wrote a technical note on the subject.1 We now know with certainty that wave attenuation is caused by the interaction of channel friction with the pressure gradient (the diffusion wave) or channel friction with inertia (the dynamic wave), but not by channel friction interacting with gravity (the kinematic wave).

1 Ponce, V. M. 1982. Nature of wave attenuation in open channel flow. ASCE Journal of the Hydraulics Division, Vol. 108, HY2, February, 257-262.

Number 82, March 2009, Level 1


The choice between vector and raster formats permeates all walks of computer-based contemporary life. The question is: Which one is better suited for a specific application?

Vector imaging is line-oriented, scalable, and uses scant computational resources. Raster imaging is pixel-oriented, nonscalable, and uses a comparatively greater amount of resources.

Vector imaging requires a considerable amount of work to achieve near photo quality. Raster imaging has a high photo quality from the start.

Vector is hard, raster is easy; vector is light, raster is heavy; vector is specific, raster is general; vector goes to the point, raster beats around the bush.

In certain cases, vector will be the better choice; in other cases, raster will be superior. A compromise may be the best strategy: Use vector when speed and effectiveness are paramount; use raster when graphical beauty outweighs every other consideration.

Number 83, April 2009, Level 2


Navigation on the Upper Paraguay river, between Cáceres, in Mato Grosso, and Porto Murtinho, in Mato Grosso do Sul, Brazil, has been a concern of many (see map below).1 In the late 1960s, the United Nations Development Programme (UNDP) funded a five-year study to collect hydrologic data on the Upper Paraguay, with the intent to use this data in future navigation development projects.2 The project was initiated in 1968, ending in 1973, with an expenditure of about U.S. $ 5 million.

Yet the Upper Paraguay was not to be tamed. The river remained in drought from 1962 to 1973, the longest on record (see figure below). The untimely drought on the Upper Paraguay meant that the five-year study was only able to collect data during low flows. Thus, the moral of the story: "When dealing with the weather, be prepared to lose."

1 Ponce, V. M. 1995. Hydrologic and environmental impact of the Paraná-Paraguay waterway on the Pantanal of Mato Grosso, Brazil: A reference study. San Diego State University, San Diego, California, August.
2 Departamento Nacional de Obras do Saneamento (DNOS), Ministerio do Interior, Brazil. 1974. Estudos Hidrologicos da Bacia do Alto Paraguai (Hydrological Studies of the Upper Paraguay River Basin), Rio de Janeiro, in four volumes.

Number 84, May 2009, Level 0


My wife Jane and I had invited our friend Alberto Castro to dinner at an Italian restaurant in San Diego. We have enjoyed Alberto's friendship for many years. Alberto is Mexican; he was born in the state of Tabasco and now lives in Tijuana.

The word "Tabasco" must have come up during the conversation, because we were surprised and amused when the waiter suddenly approached our table and said:

"Here is the Tabasco sauce that you ordered."

Number 85, June 2009, Level 1


In 1977, while I was on the faculty at Colorado State University, I had the pleasure of meeting and working with Dr. Horst Indlekofer, who was at CSU on sabbatical from the Technical University of Aachen, Germany. Horst and I wrote two papers on the convergence of numerical models of water and sediment routing.1,2 The numerical properties of sand-wave models was a particular focus of our research.

One day, Horst invited me to dinner at his home. While I was there, I noticed that he had several excellent paintings on the walls of his apartment. I learned then that he liked to paint as a way of relaxing after a tiring day at work. One painting particularly interested me, because it depicted in full color the instability of the sand waves that we were modeling at school.

A couple of weeks later, I invited Horst to dinner at my home. Horst arrived with his wife, and to my surprise, presented me with his painting on the instability of the sand waves. He said that since I liked it, I should have it.

Of all my experiences at CSU, this is certainly one of the most memorable. To this day, Horst's painting hangs on the wall of my house and brings back fond memories of bygone years.

1 Ponce, V. M., H. Indlekofer, and D. B. Simons. 1978. Convergence of four-point implicit water wave models. Journal of the Hydraulics Division, ASCE, 104(HY7), 947-958.
2 Ponce, V. M., H. Indlekofer, and D. B. Simons. 1979. The convergence of implicit bed transient models. Journal of the Hydraulics Division, ASCE, 105(HY4), 351-363.

Number 86, July 2009 Level 1


In the Fall of 1993, I was invited to give a lecture at the São Carlos School of Engineering, of the University of São Paulo, in São Carlos, Brazil. I spoke about the effect of cross-sectional shape on channel hydraulics, a topic which I had been researching at the time with Pedro J. Porras, one of our graduate students. Some time later, we published a paper in the ASCE Journal of Hydraulic Engineering.1

As he introduced me to his students, my host, Dr. Fazal H. Chaudhry, mentioned that in his opinion, we were one of the very few to research the subject of the cross-sectional effects on the flow hydraulics. He was correct, and I was very pleased with the uncommon recognition.

1 Ponce, V. M., and P. J. Porras. 1995. Effect of cross-sectional shape on free-surface instability. ASCE Journal of Hydraulic Engineering, Vol. 121, No. 4, April, 376-380.

Number 87 August 2009, Level 0


Many people shun failure without realizing that it is the path to success. In the early eighties, my friend Rick Fragaszy and I had season tickets to the SDSU Aztec basketball games. As with all spectator sports, Aztecs in particular, we had to sit through many mediocre games, but every ten games or so, an excellent game made it all worth it. It did not escape my attention at that time that if we had not had season tickets, we probably would have missed the good games altogether. Thus, the moral of the story: You have to experience a lot of failures before you can enjoy one success. Failure defines success; this is the true meaning of success.

Number 88, September 2009, Level 0


In the late 1990s, I invited a former graduate student, who was very successful in his practice, to give a guest lecture in one of my classes. After the lecture was over, one of the students in the audience asked him what he thought about our graduate program. He said, in a voice loud enough so that I could not help but overhear it:

"It is great. I recommend it highly. There are three professors: Chang, Ponce, and Stratton. Prof. Chang wrote everything on the board; you didn't want to miss anything, because it was going to be on the exam. Prof. Ponce was teaching us for the future, so you didn't have to write anything down. Prof. Stratton threatened to flunk us all on the first day of classes, so we were forced to study very hard. All three professors were quite different and, as a matter of fact, complemented each other very well."

Number 89, October 2009, Level 2


Rivers transport two types of suspended sediment: (1) bed-material load, and (2) wash load. Bed-material load is the fraction of sediment load whose particle sizes are significantly represented in the channel bed. Wash load is the fraction of sediment load whose particle sizes are not significantly represented in the channel bed. The bed-material transport rate depends on the hydraulics of the flow, while the wash load concentration is independent, for the most part, of the hydraulics of the flow.

Under steady conditions, there is a sediment rating curve, i.e., a unique relation between water discharge and corresponding sediment (bed material only) discharge. A calculation of sediment transport rate calculates a point (or points) of the rating curve. This sediment discharge is often referred to as the "sediment transport capacity," to denote that it is the amount of sediment that the river will always carry under steady equilibrium conditions.

Under unsteady conditions, several scenarios are possible, and the resulting effects are noted:

  1. An increase in the amount of sediment discharge at the upstream boundary, without a corresponding increase in water discharge, would lead to aggradation.
  2. A decrease in the amount of sediment discharge, without a corresponding decrease in water discharge, would lead to degradation.
  3. An increase in the amount of water discharge, without a corresponding increase in sediment discharge, would lead to degradation.
  4. A decrease in the amount of water discharge, without a corresponding decrease in sediment discharge, would lead to aggradation.

The second case, in particular, merits careful consideration due to the significant practical implications. This situation usually happens downstream of a dam impoundment. The dam ponds the water and retains most of the sediment. The water subsequently released is typically almost devoid of sediment; therefore, it is "hungry water." This water will have the tendency to pick up sediment as it moves downstream.1

The "hungry water" condition is exacerbated in the case of a sediment-retention basin. Holding on to the sediment behind the dam and releasing the water immediately, without the sediment, will produce channel and bank erosion downstream. Depending on the rate of water release, the amount of erosion will be commensurate with the quantity of sediment retained at the basin. Thus, a sediment-retention basin is generally not an effective strategy for sediment control in natural streams.

1 Lane, E. W. (1955). The importance of fluvial morphology in hydraulic engineering. Proceedings, ASCE, Vol. 81, Paper 745, July.

Number 90, November 2009, Level 2


The U.S. Army Corps of Engineers HEC-RAS model (Version 4.0) can perform three functions: (1) steady flow, (2) unsteady flow, and (3) movable boundary flow. The steady flow component uses the standard step method for the solution of steady gradually varied flow.1 The unsteady flow component uses a numerical solution of the equations governing gradually varied unsteady flow in open channels. The movable boundary component uses the sediment continuity and one of several sediment transport equations to calculate river bed aggradation/degradation.

• When should unsteady flow be used?

This question is of considerable practical interest, since unsteady flow is significantly more complex and requires more data than steady flow. However, the answer is not straightforward, requiring some elaboration.

• Steady vs unsteady flow

Under steady flow, the user inputs as boundary conditions a discharge upstream and a stage downstream. The model calculates stages throughout the interior points, keeping the discharge constant. Under unsteady flow, the user inputs a discharge hydrograph at the upstream boundary and a discharge-stage rating at the downstream boundary. The model calculates discharges and stages throughout the interior points.

Under steady flow the discharge-stage ratings are unique, i.e., kinematic. On the other hand, under unsteady flow the model itself calculates (dynamic) looped discharge-stage ratings according to the variabilities of the flow. Therefore, the specification of a unique discharge-stage rating at the downstream boundary contradicts the solution at that boundary.2 The model cannot be kinematic at the downstream boundary and dynamic everywhere else!

A way out of this difficulty is: (1) to move the downstream boundary further downstream, (2) to specify the unique discharge-stage rating at the artificial downstream boundary, and (3) to let the model itself calculate the looped ratings at the interior points, including the point where the real downstream boundary is located.3 Despite its apparent artificiality, this procedure works well and circumvents the need to know the discharge-stage rating (at the downstream boundary) before it is calculated.

• Kinematic vs dynamic waves

The decision to use unsteady flow will depend on whether the wave to be modeled is kinematic or dynamic. If the wave is kinematic, (1) the discharge will not vary in space; (2) the discharge-stage ratings will be unique; and (3) the downstream boundary can be specified as unique. In this case, the solutions of steady and unsteady flow are essentially the same; therefore, the unsteady flow calculation is not needed.

On the other hand, if the wave is dynamic, (1) the discharge will vary in space, attenuating as it moves downstream; (2) the calculated discharge-stage ratings will not be unique; and (3) for better accuracy, the downstream boundary should be artificially moved downstream to allow for an unsteady looped rating to develop at the real downstream boundary. In this case, the unsteady flow calculation is justified, assuming of course, that the wave is truly dynamic.

• Use of unsteady flow in channel design

This situation begs the question of whether a certain flood wave can be construed as either kinematic or dynamic. Or, better yet, whether a dynamic wave should be used at all to determine stages in the design of channel improvement projects. On typical projects, of limited channel lengths, a kinematic wave, which keeps its discharge constant, is a better assumption than a dynamic wave, which attenuates its discharge. Indeed, the kinematic wave assumption assures that the channel will contain all waves, kinematic or dynamic. Viewed in this light, the use of a dynamic wave for the calculation of stages in the design of channel improvements projects does not appear to be warranted.

1 Chow, V. T. (1959). Open-channel hydraulics. McGraw-Hill.
2 Abbott, M. (1976). Computational hydraulics: A short pathology. Journal of Hydraulic Research, Vol. 14, No. 4.
3 Ponce, V. M. and A. Lugo. (2001).
Modeling looped ratings in Muskingum-Cunge routing. ASCE Journal of Hydrologic Engineering, Vol. 6, No. 2, March/April, 119-124.

Number 91, December 2009, Level 1


In 1996, I visited the U.S. Army Corps of Engineers' Hydrologic Engineering Center, in Davis, California. There I met Arlen Feldman, who was at the time head of research at the famed center. I asked Arlen what was the status of the HEC-1 model, since I had heard rumors that it was being replaced with a graphical-user-interface (GUI) version. Arlen responded that they had placed HEC-1 on the back burner, and that they were working steadily to release the GUI version as soon as possible, to be renamed HEC-HMS, for "Hydrologic Modeling System." (Version 1.0 of HEC-HMS was released in 1998). I complimented Arlen on their efforts and was about to leave when he said: "You know, in order to acquire the GUI capability, we almost had to sell half of the shop."

Many other established hydrologic models have not made the transition to the GUI version. I wonder if it had something to do with what Arlen was referring to.

Number 92, January 2010, Level 0


In the summer of 1986, I spent two months in Brasilia, Brazil, on a consulting assignment with the Organization of American States (OAS) at PLANVASF (Development Plan for the São Francisco Valley). The work entailed developing and running a computer model of reservoir routing, a job which had me working around the clock with the computers of the day (a vintage mainframe Burroughs, which took all of six hours to run my job).

The last day of my stay, I decided I had worked long and hard, and looking for some adventure, I rented a car and headed for the new mall at the outskirts of town, intending to buy a present for my wife.

After spending a couple of hours at the mall, it was time to return to the hotel, but I could not remember which of the doors I had come in. They all looked alike! My concern turned into despair when I realized that I did not even remember the color or make of the rental car. There I was, in a singular predicament: The mall was an island surrounded by a sea of parking lot, and I didn't know where the car was. I couldn't even describe it, other than to say that it was a compact, a popular size in Brazil.

I spent at least an hour retracing my memory, and trying the key on several cars, hoping that nobody would notice; a most enduring experience that I swore never to be caught in again!

Number 93, February 2010, Level 1


In the early 1970s, I was employed as a civil engineer with a leading geotechnical consulting firm in Lima, Peru. Over a period of several years, I was in charge of many soil investigation studies. One such study took me to the site of the Sheraton Lima Hotel, a 20-story high-rise which was being planned at that time near the center of the city.

The geology of the region is well known, consisting of well compacted alluvial material, mostly sand, gravel, and boulders, an ideal material for foundations. However, the owner's engineer was not sure. To reduce the risk, he requested three exploratory drillings, each to a depth of 30 m, to make sure that the soil was competent to carry the design loads.

We argued that open pits would be cheaper and safer to properly ascertain the characteristics of the soil profile, and, on this basis, were awarded the contract to perform the study. We hired a team of tough, seasoned Peruvian miners from Huancavelica, led by a man named Zenón. Our team completed the three soil pits, each 1.5 m in diameter and 30 m in depth, in about three weeks. We confirmed the existence of well compacted granular material throughout the soil profile at all three sites.

Once the work was completed, the owner's engineer could hardly believe it! He was particularly impressed that we had accomplished the work without any bracing or fancy equipment, using just a pick and shovel and an old-fashioned tripod, pulley, and bucket assembly. He ordered the holes filled with concrete and the contract paid in full. Thus, the moral of the story: You don't have to be fancy to be effective.

Number 94, March 2010, Level 1


Not too many people know that Niccolò Machiavelli and Leonardo Da Vinci, the famed Florentines, collaborated on a singular civil/military engineering enterprise to deprive the city of Pisa of water, with the hope of subduing it. By the Spring of 1504, Pisa had been independent of Florentine rule for nearly a decade. At that time, Leonardo convinced the rulers of Florence, located upstream of Pisa, to construct a canal to divert the waters of the River Arno, thus depriving Pisans from the water that they had become accustomed to.

The scheme was difficult at best, but Leonardo had a reputation to uphold and was convinced that it could be done. Machiavelli, who at the time was Vice-Chancellor of the Florentine Republic, was put in charge of supervising the operation. The diversion of the Arno was promoted not only as a way to subdue the Pisans, but also to provide flood control to the city of Florence.1

While the canal was technically Leonardo's brainchild, the actual task of construction, which started on August 20, 1504, was entrusted to a relatively obscure engineer named Colombino. The builder made some changes to Leonardo's design, primarily to appease Machiavelli's urging for haste. When things did not work according to plans, Machiavelli began to doubt the canal design. To make matters worse, by the first week of October, a violent storm struck, which caused the walls of the canal to collapse. Thereafter, the project was speedily abandoned and the Pisans came out to fill the ditch.

Thus ended Machiavelli and Leonardo's brief and ill-fated incursion into hydraulic engineering.

1 King, R. 2007. Machiavelli, Philosoper of Power. Harper-Collins.

Number 95, April 2010, Level 0


In the early 1970s, I was employed as a civil engineer with a consulting firm in Lima, Peru. My job would usually take me on field assignments throughout the country, typically for a few days at a time.

Once assignment took me to Pucallpa, a relatively large city in the heart of the Amazon rainforest. I had planned to look for a suitable hotel, but a relative convinced me to stay at his house instead. The house, like many others in Pucallpa, was built on stilts, literally on top of the rainforest, presumably for flood protection.

The first night after work, I settled down for a well deserved rest. Suddenly, I noticed that I was not alone in the room. There was a big cockroach at a corner, apparently staring at me, so I decided to kill the intruder. And so I did.

As I turned off the lights, the dim clarity of the new moon came in through the open window. A few minutes later, I again had the strange feeling of not being alone, so I turned on the lights, this time only to see many of the despicable bugs, certainly too many to kill. Belatedly, I realized it was their house and that I was just a guest that night, so I decided to make peace with them. I turned off the lights and went back to sleep.

Number 96, May 2010, Level 2


In the mid-1970s, I was pursuing a Ph.D. at Colorado State University, and I was fortunate to be at the right time at the right place. There, I had the honor and pleasure of close association with a select crop of students from all over the world. One of these students was Fred Theurer, who, in 1975, completed a Ph.D. under the supervision of Dr. Everett Richardson, "Rich" to his many students.

After graduation, Fred returned to his employment with the Natural Resources Conservation Service, the former Soil Conservation Service (SCS), in Washington, D.C. He told his bosses that the convex method was no good, and that it had to be replaced by a better routing tool, still to be developed. Indeed, the convex method, developed by SCS in the mid-1950s, was a linear kinematic wave model featuring built-in, uncontrolled numerical diffusion. In practice, this meant that it lacked consistency, i.e., that a routed hydrograph could not be reproduced by substepping the reach length. In other words, the convex method was grid-dependent; two choices for grid size (time step and space step) would invariably give two different answers.

Seeking a proper replacement, in the late 1970s, SCS developed the Att-Kin model, which stands for "Attenuation-Kinematic." The Att-Kin method divided the routing into two sequential steps: the first designed to provide reservoir attenuation, and the second to provide pure kinematic translation. While the model fared well in tests designed to prove consistency, it was not without its pitfalls. The matter was clarified in the 1990s, when the Muskingum-Cunge method was further developed and tested.1 It is now generally agreed that the Muskingum-Cunge method is the only hydrologic channel routing method that is stable, convergent, and consistent (i.e., grid independent), when used within its recommended parameter ranges. This is because the Muskingum-Cunge method simulates not the kinematic wave model, but the diffusion wave model.2

1 Ponce, V. M., A. K. Lohani, and C. Scheyhing. 1996. Analytical verification of Muskingum-Cunge routing. Journal of Hydrology, 174(1996), 235-241.
2 Ponce, V. M., and D. B. Simons. 1977. Shallow wave propagation in open channel flow. Journal of the Hydraulics Division, ASCE, 103(HY12), 1461-1476.

Number 97, June 2010, Level 2


I met Prof. Arie Ben-Zvi, of Ben-Gurion University of the Negev, in New Delhi, India, in December of 1993, while attending the International Conference on Hydrology and Water Resources. This conference was convened to honor Dr. Satish Chandra, at the time Director of the [Indian] National Institute of Hydrology, on occasion of his retirement. I recognized Ben-Zvi by his nametag, and being somewhat familiar with his early work, I engaged him in conversation.

Ben-Zvi had a pleasant demeanor. He confirmed that in the early 1970s, he had completed a Ph.D. at the University of Illinois under the supervision of Prof. Ven T. Chow.1 His thesis dealt with the application of the dynamic wave to overland flow in a two-dimensional context. He confided to me that he had not used the model since the time of his graduation.

In hindsight, we now know that the dynamic wave does not apply to overland flow, because the prevailing slope is usually large enough to make the flow either kinematic or diffusive. For the dynamic wave to be applicable, the prevailing slope would have to be very small, say, on the order of 0.0001, which is typically not the case.

Many similar experiences confirm this conclusion. For instance, Woolhiser mentions that in the 1960s, he and Liggett set out to prove the applicability of the dynamic wave to overland flow, and, after much study, ended up changing their minds.2,3 Instead, they focused on the applicability of the kinematic wave, which led to the development of the kinematic flow number.

1 Chow, V. T., and A. Ben-Zvi, 1973. The Illinois Hydrodynamic Watershed Model III (IHW Model II). University of Illinois at Urbana-Champaign, Civil Engineering Studies, Hydraulic Engineering Series No. 26, 47 p.
2 Woolhiser, D., 1996. Search for physically based runoff model - A hydrologic El Dorado? Journal of Hydraulic Engineering, Vol. 122, No. 3, March 1996, 122-129.
2 Ponce, V. M. The competition between kinematic and dynamic waves. Legacy tale. http://ponce.sdsu.edu/legacy_tales_competition.html

Number 98, July 2010, Level 0


During my visits to India in the early 1990s, I had the pleasure of being invited to dinner on more than one occasion. Invariably, the experience was delightful, although the social customs were quite different.

Dinner was usually served much later than the time of the invitation. When appropriate, a strategically located curtain opened up to a view of a dining table filled with a great variety of dishes.

Later, I learned that it is a local custom to start preparing dinner only when the guests arrive, in order to assure freshness. All the while, the extra time before dinner encourages conversation. The great number of dishes showcases the diversity of Indian cuisine, while guaranteeing that the guests will not go hungry.

Number 99, August 2010, Level 0


In January 2010, we produced a webvideo featuring Japani, an ancient Peruvian community whose remains date back to the XVIth century. Japani is tucked away high in the mountains of the Santa Eulalia valley, near the present-day town of Carampoma, about 100 km northeast of Lima.1

On the return leg of the trip, we stopped at a local kiosk for well deserved refreshments. The vendor, a hardened old lady who appeared to be in her 80s, inquired where we were coming from.

I said: "We just came from Japani."

She promptly proclaimed: "There is no Japani here." She went on to say that she had lived in the valley all her life, and that she was pretty sure there was no place called Japani.

1 Ingeniería Hidráulica en Japaní  (Hydraulic Engineering in Japani), Visualab Productions, 2010.

Number 100, September 2010, Level 1


In the Winter of 1976, I spent three months in Pakistan performing the field work which was part of my doctoral dissertation. At that time, I was employed with the Alluvial Channel Observation Project (ACOP) and led a hydrographic surveying team. We were researching the meandering thalwegs that were developing on the Link Canals of the Indus Basin Irrigation System.1 Our assignment at the time was the Q-B Link (Qadirabad-Balloki), near Chuharkana, Punjab.

One day our field crew decided to start early, and had to miss breakfast at the Guest House. We had planned to pick up something to eat along the way.

We stopped at a very small and unassuming eatery, and I ordered two fried eggs and a glass of milk. To my pleasant surprise, the eggs tasted among the best ever.

I was curious to find out where they got their eggs, so I inquired with the attendant. He went in the backroom, and seconds later produced the hen that had laid the eggs. Those were fresh eggs, no doubt.

1 Ponce, V. M., and K. Mahmood. 1976. Meandering thalwegs in straight alluvial channels. Rivers 76, Third Annual Symposium of the Waterways, Harbors and Coastal Engineering Division, ASCE, Ft. Collins, Colo., 1418-1441.

Number 101, October 2010, Level 0


Over the years, I have had the pleasure of a close association with several scientists from the National Institute of Hydrology, in India. One of the things that caught my attention early on was the peculiar way in which the people from India move their head from side to side to express agreement [Moving the head from side to side means "no" in most Western countries]. One day, after I had repeated something three times and had gotten three side-to-side head motions, I finally realized that that was their way of saying "yes." It was a lesson in culture that I would not forget.

Number 102, November 2010, Level 2


I have taught open-channel hydraulics at San Diego State University for nearly three decades. I use Ven T. Chow's well-respected textbook, complemented with my own material on unsteady flow.

One formula that particularly intrigued me was Eq. 15-1 in Chow's book. This equation states that the efficiency of the hydraulic jump, i.e., the ratio of the specific energy after the jump to that before the jump, is equal to:

E2/E1 = [(8F12 + 1)3/2 - 4 F12 + 1] / [8F12(2 + F12)]

The proof of this formula is particularly challenging. In the early 1980s, having failed to solve the problem, I decided to pose the problem to the class, in the hope that someone would find the solution. Eventually one of our students accomplished the seemingly daunting task. Indeed, it was an intricate job of algebra, sure to test the skills and patience of most people.

Chow, V. T. 1959. "Open-channel hydraulics," McGraw-Hill, New York.

Number 103, December 2010, Level 0


In January of 1997, I joined a group of vulcanologists on a technical tour of the Pico de Orizaba, in the state of Veracruz, Mexico. The group was traveling in three vans around the volcano, studying the sedimentation produced by the eruptions over a period of 10,000 years.

One evening, as we approached Cordoba, the first van was stopped by two highway patrol officers for what appeared to be a routine check. Since we were traveling in a caravan, we all stopped and waited. After about 15 minutes, it was obvious to us that something had gone wrong.

A Mexican colleague and I came down from the third van and inquired about the delay, but we could get no resolution of the problem from either our tour leader or the police officers. Apparently, we had not done anything wrong; it was just that the cops wanted something, and our tour leader was uncompromising.

After a reasonable time had passed, my colleague said to me: "I will fix this right now..." He pulled 50 pesos and handed it over discreetly to one of the cops, who immediately pronounced to his companion: "These gentlemen are behaving rather nicely... let them go."

Relieved, we continued our trip. As we headed back to the vans, one of the cops approached me and said: "Here is a number... if you are stopped later, give them this number and they will let you go."

We had been given the Mexican vaccine.

Number 104, January 2010, Level 1


In November of 1998, I gave a keynote lecture at the XVIII Panamerican Conference on Engineering Education, in Lima, Peru. The topic of my presentation was: "The new engineer faced with the challenge of globalization and sustainable development." I showcased the emerging concept of sustainable development using my work on the Hydrologic and environmental impact of the Parana-Paraguay waterway on the Pantanal of Mato Grosso, Brazil.

At the conclusion of the lecture, a conference attendee asked if I had considered the ISO 14001 standard in our study. My answer was quick and left no room for misunderstanding: "The Pantanal of Mato Grosso is a unique ecosystem; therefore, it cannot be subjected to a standard."

Number 105, February 2010, Level 1


The indigenous Uros people have been building floating islands [islets] made out of totora reed on the shores of Lake Titicaca, near Puno, Peru, for more than 1000 years. They are self-sufficient, surviving by fishing and, more recently, from the sale of handicrafts to tourists. In the past few years, however, marked climatic changes are threatening to upset the delicate balance of nature in the region.

On a recent visit to Puno, an acquaintance of mine, the Uro teacher Jaime Coila Lujano, told me that local birds used to know where to locate their nests on the floating islets. During wet weather, when the lake was high, they would place their nests high on the reeds; conversely, when the lake was low, they would place their nests at much lower elevations.

Jaime mentioned that in the past few years the climate has been largely unpredictable, with the lake level fluctuating more than usual, often out of sinc with the season. He observed that the birds appear to be at a loss as to where to place their nests. Thus, we see that climate change is all encompassing and has a global reach.

Number 106, March 2011, Level 0


In October of 2001, I released a report on the flood hydrology of Cottonwood Creek - Arroyo Alamar, in San Diego County, California, and Tijuana, Baja California, Mexico. To accomplish the field work, I spent a lot of time inspecting the watershed on both sides of the border, in Eastern San Diego County, and in Baja California, specifically in Tijuana and Tecate.

One day my student assistant and I decided to take a break and enjoy a well deserved taco. We headed for Taqueria La Única, in one of the suburbs of Tijuana, but could not find a parking spot next to the taco shop. After some looking around, I was able to park in an empty spot next to a nearby ice cream stand.

After finishing our tacos, we headed back for the car. To my surprise, the young man at the stand signaled to me with his hand. I thought he was going to tell me not to park there again, or, at the very minimum, to extol a charge for the short time that I parked on his premises. Instead, to my surprise, he said: "Sir, you can park here any time you wish!" I confirmed one more time Tijuana's famed hospitality.

Number 107, April 2011, Level 0


The Rev. Richard Clifford, an American Catholic priest, spent the first twenty years of his ministry as a missionary in Lima, Peru, starting c. 1960. In January 2003 my wife and I visited him at San Sebastian parish in Mérida, Yucatán. During dinner at a local restaurant, Father Clifford remembered his life in Lima.

He loved Peru and was very fond of Peruvians. To make a point, he told me a story where he was called upon to administer the last rites to a moribund woman, who happened to live in one of the developing pueblos jovenes, or "young towns" which, at that time, surrounded the capital city.

It was a cold winter night. As he kneeled down next to the bed-ridden lady, he could not help but sneeze, given the circumstances. To his surprise and amazement, the lady sat straight up and said, softly but clearly, enough to be heard: "God bless you, Father."

Number 108, May 2011, Level 0


In the course of my career, I have often been asked the question: "How do you do it?"

In my opinion, success requires four ingredients: (1) knowledge, (2) determination, (3) commitment, and (4) luck.

Knowledge is developed every single day, and applied both for your employer, and for you, for the future of both.

Determination is absolutely essential in this imperfect world of ours, where time is of the essence and Murphy is just around the corner.

Commitment is akin to passion: Passion to consider the job you and you the job, so that you will rise to the A team and stay there.

Luck is always necessary, because an individual is only a grain of sand in the grand scheme of things. There is a Greater Being up there looking at you, and it is better if it is 'after you'.

Number 109, June 2011, Level 1


In the early 1990s, a Navy officer went through our graduate program in civil engineering. One day, I met him outside of the Engineering Building, and he greeted me warmly and asked: "Prof. Ponce, good to see you. What are you doing these days?"

I mentioned to him that I had recently published a paper on the subject of free-surface instability.1

Being a practical man, he said: "That's new stuff, isn't it?"

I said, proudly: "Sure, otherwise it would not have been published."

He added: "Well, if it is new, it has not been tested; and if it has not been tested, it cannot be used."

I sensed he had a point, but I had no ready answer for him.

1 Ponce, V. M., and P. J. Porras. 1995. Effect of cross-sectional shape on free-surface instability. ASCE Journal of Hydraulic Engineering, Vol. 121, No. 4, April.

Number 110, July 2011, Level 0


In the summer of 1995, my daughter Tina and I visited the northern rim of the Colca Canyon, in Peru, at 3200-m depth easily one of the deepest in the world. Our party consisted of a colleague, a guide, a driver, and us. We rented a van and headed for the canyon, deep in the Andes, several hours by road from Arequipa.

On the trip back, a school teacher hitched a ride with us. As we approached the next town, she stepped out of the van and told us she would return momentarily. After waiting for the teacher for a reasonable time, we decided to continue our trip without her.

A few hours later, as we reached the town of Aplao, we were detained by the police for questioning. The teacher had called to complain that we had "stolen" her bag. We explained to the chief of police that she had hitched a ride with us, had stepped out momentarily in the next town, and had not returned in a timely fashion, giving us no choice but to leave her behind. We knew nothing about a bag. The police were convinced, and we were allowed to resume our trip.

Upon reaching Arequipa, as we cleared the van, to our great surprise we found the teacher's bag tucked away under one of the seats.

Number 111, August 2011, Level 1


My association with the Universidad Autónoma de Baja California goes back to 1992, when I agreed to serve on Walter Zúñiga's graduate commitee. During those years, I had many chances to interact on a one-to-one basis with several UABC faculty members.

On one visit, a colleague confided to me that his department had just purchased a GIS software system.

This sparked my curiosity, and I said: "That's great... how much did it cost?"

He answered: "$28,000."

Somewhat suprised, and acknowledging my ignorance, I said: "What does it do?"

With an air of confidence, my interlocutor proclaimed: "Everything, it does everything!" Not knowing how to respond to such a claim, I kept silent.

Several months later, I encountered the same colleague, and remembering our pointed exchange, I asked: "How did you do with your GIS model? Did it indeed do everything?

Obviously unable to hide his embarrassment, he said: "No, it was a disappointment; it hardly did anything!"

Number 112, September 2011, Level 0


In the spring of 2003, during a visit to Tlaxiaco, in Oaxaca, Mexico, I was approached by a gentleman from the nearby hamlet of Los Angeles. He invited me to come to his town and give a talk of dry ecological latrines.

I accepted, promised to do it on my next visit, and proceeded to take his name and address.

He said: "Eugenio Dominguez Cruz, known address, San Miguel del Progreso."

I insisted: "What is your address?"

To which he responded: "known address."

I then realized that in a small town a formal address is usually not necessary.

Number 113, October 2011, Level 0


I have two Peruvian friends, one living in Lima and another in Washington, D.C. For many years, my friend in Lima dreamed of moving to Washington D.C. One day he was suprised to find out that our friend in D.C. had a similar longing, only that he wanted to move back to Lima. It did not take me too long to figure out that my friend in Washington had ample security, but it was at the expense of adventure. Conversely, my friend in Lima had tons of adventure, but security, economic or otherwise, was in short supply. I observed that extremes of security with no adventure or, conversely, adventure without security, usually result in unhappiness.

Number 114, November 2011, Level 0


In July 2002, my wife Jane and I visited Palenque, in Chiapas, Mexico. After spending a few hours at the site, we took a taxi back to the bus station. I inquired with the driver, whose nickname was "El Torito," about his fare and the time to drive us to Agua Azul Falls, which I knew was reasonably close to Palenque. He said it would be 500 pesos round trip and it would take less than two hours to get there.

To be difficult, I said: "We will go only if you promise to take us to the place where Ana Perez 1, the well known Mexican actress, almost fell to her death, only to be saved by (the also well known Mexican actor) Juan Lopez 1 in the nick of time."

El Torito said: "I will take you to the very place where Ms. Perez fell and was saved by Un servidor (the Mexican way of referring to himself)." Puzzled, I asked him to explain.

He said that he moonlighted as taxi driver, but that his real job was as location specialist for TV Azteca. He said that he was with the ill-fated party at the time of the accident. That indeed, while filming on location at the top of the falls, Ana slipped and almost fell to her death. He said that she clung to a safety rope as he pulled her up, only to be aided, moments later, by Juan, who was standing a short distance from them.

1 Actual names have been altered to protect confidentiality.

Number 115, December 2011, Level 9


In February of 2010, I traveled to Spain to participate in a dissertation exam at the University of Alcalá. While there, one of the faculty colleagues invited me to a weekend trekking of the Sierra Subbética, a mountain range in South Andalucía. The participants were a group of about forty people from Madrid, including some middle aged women, most of them well seasoned in the sport. The trip was supposed to take three hours and cover about 16 km of mountainous terrain.

Well into the trekking experience, our leader realized that he did not know the terrain well enough. So he decided to scout ahead of the pack, leaving his second-in-command in charge. After waiting for about an hour, the group realized that something had gone wrong. To make matters worse, it was the middle of the winter, it was raining heavily, and the clayey soil was soggy, so some of us were suffering.

Some in the group wanted to advance; others feared getting lost, so advised staying put. No decision had been made, and time was running out. Soon darkness would fall and it would be next to impossible for us to find our way out of that mountain.

Given the circumstances, despair was beginning to set in, when all of a sudden, we had a stroke of luck! Another party, headed by an experienced guide, was trekking on the same route, so we joined them. About a mile later, we found our leader, who was waiting for us at a point, wondering where we were. Our party arrived at Zuheros, Andalucía, three hours later than originally planned.

So, the moral of the story is: Either know the route well, or trek during the summer.

Number 116, January 2012, Level 1


Structures are commonly designed to withstand an earthquake of certain magnitude, say, the 50-yr earthquake, i.e., that of magnitude recurring once every 50 years. In 1967, I attended a one-week short course taught by the Late Prof. Alfonso Rico Rodriguez, a professional of great stature and experience. Professor Rico had headed a large government agency responsible for a large number of highway bridges in Mexico.

Professor Rico told his listeners that his agency had experienced a 100-yr earthquake during his tenure, and three bridges, out of more than 1000 total, had sustained structural damage. After the earthquake, he gathered his staff for a fact-finding meeting. The staff was prepared to answer questions about the failed bridges. Instead, Prof. Rico reminded his staff that since the earthquake was a 100-yr earthquake, and the design was for a 50-yr earthquake, theoretically, ALL the bridges should have failed. Thus, he wanted to find out why only three bridges had failed.

Number 117, February 2012, Level 0


The internet has brought much change into our lives, but this is not the first time we have had to change. In the late 1990s, I sent several emails, over a period of months, to a friend of mine who taught at a foreign university. Not having had a response, I wondered what was happening. The next time I met my friend personally, I inquired softly with him why he had not responded.

He apologized profusely, and said: "I am sorry... I am learning to type."

Number 118, March 2012, Level 0


An English-speaking tourist, sightseeing in La Paz, Bolivia, suddenly felt an urge to fulfill a most basic of necessities. The situation was extremely urgent, and the man was unfamiliar with the surroundings.

The imminence of disaster turned into desperation, and he could only think of shouting: "Bano! Bano! Bano!" to surprised passers by. Repeated calls of "Bano! Bano! Bano!" did not get the expected result, leaving our hero no choice but to go to the bathroom in the middle of the street.

Number 119, April 2012, Level 2


In September of 1976, I began work on a two-dimensional model of water and sediment routing, under the direction of Dr. Daryl B. Simons, who at that time was the associate dean for research, College of Engineering, Colorado State University, Fort Collins, Colorado. After a few months of painstaking model development, Dr. Simons had a chance to review our progress. The task at hand was to model the flow from a river, in and out of a side embayment. Our results showed that the flow appeared to convect properly, as shown in Fig. 1 (a); however, Dr. Simons was not convinced. He mentioned that in his experience, the circulating flow pattern was not supposed to be clockwise, but rather counterclockwise. We went back to the drawing board, eventually obtaining funds from the National Science Foundation to study two-dimensional flow circulation.

Our subsequent research provided an answer to the puzzle.1 Whether the flow through an embayment was clockwise, as our model originally indicated (Fig. 1 a), or counterclockwise, as Simons had experienced (Fig. 1 b), depended on the problem scale. Under large scale, friction dominated, ciculation was hampered, and the resulting flow was clockwise; conversely, under small scale, inertia played a dominant role, circulation was promoted, and the resulting flow was counterclockwise. Thus, in principle, both Dr. Simons and the model were correct.

1 Ponce, V. M., and S. B. Yabusaki. 1981. Modeling circulation in depth-averaged flow. ASCE Journal of the Hydraulics Division, Vol. 107, HY11, November, 1501-1518.

Number 120, May 2012, Level 2


In 1975, while working on my doctoral dissertation, I came across the method of linear stability, by which a differential equation could be converted to an algebraic equation and solved for a specific case. Sensing that this powerful tool had not been applied to the equations of one-dimensional, gradually varied unsteady flow (the so-called Saint Venant equations), I asked my graduate adviser for permission to spend time researching this subject, given that it was not directly related to my dissertation. He inquired whether there was a relation to sediment, since our research project dealt with alluvial river mechanics. I answered that, strictly speaking, this subject was unsteady flow, not alluvial river mechanics. On his advice, I left the subject on the back burner and hurried on to finish my dissertation, which I completed in July of 1976.

Immediately thereafter, I was offered a job as assistant professor of civil engineering at my alma mater, Colorado State University. I sensed an opportunity to discover something of tremendous importance, so I spent the next three months, three hours every evening, applying the method of linear stability to the Saint Venant equations. The effort required a high level of mathematical sophistication. The results were published in the December 1977 issue of the ASCE Journal of the Hydraulics Division.1 Two years later, in 1979, my coauthor, Dr. Daryl B. Simons and I were awarded the prestigious ASCE Karl E. Hilgard Hydraulics Prize, given to the author(s) of the best paper published in the Journal of Hydraulic Engineering in the year prior to the competition.

Our findings are summarized in the now famous series of S curves that portray the variation of the dimensionless relative wave celerity as a function of dimensionless wavenumber, for a suitable Froude number set. The S curves depict the progression, from left to right (see graph below), from kinematic (Seddon) to diffusive to dynamic and to inertia-pressure (Lagrangian) waves, throughout the "dimensionless scale" spectrum.

1 Ponce, V. M., and D. B. Simons. 1977. Shallow wave propagation in open channel flow. ASCE Journal of the Hydraulics Division, Vol. 103, HY12, December, 1461-1476.