Level 0:  Least technical
Level 1:  More technical
Level 2:  Most technical

Number 1, June 2002, Level 1


During an inspection visit to the Chané river, in Eastern Bolivia, in January of 1990, a colleague who taught at a Colombian university engaged me in conversation: "Ponce... What are you doing these days?"

I answered that I had recently completed a paper on the Vedernikov number.

Acknowledging his ignorance of the subject, he said, "The... what number?"

I retorted that he should know, since I understood that he taught Open-channel Hydraulics. Noticing that he was still clueless, I added, "Don't you teach with Chow?" 1

To which he answered, "Yes, of course."

I then said, "Well, it is there... in Chow."

He said, "Where?"

To which I responded, "In Chapter 8."

He then said, "Which one is that?"

And I responded, "The one titled 'Theoretical Concepts...'"

Finding himself totally at a loss, he acknowledged with a grin, "Oh, yeah... that's the one we skip!"

 1 Chow, V. T. 1959. Open-channel hydraulics. McGraw-Hill, New York; the standard text on the subject.

Number 2, July 2002, Level 1


During my conversation with Vic Mockus, the developer or the SCS runoff curve number, in July of 1996, Vic told me that, in his opinion, there were three kinds of hydrologists. Noting that he had sparked my interest, he went on:

"The first kind of hydrologist is one who works on the computer, and is reluctant to go to the field."

He continued:

"The second kind of hydrologist is one who goes to the field to gather data."

And finally, he made his point with a grin:

"The third kind of hydrologist is one who goes to the field to gather data when it is raining."

He added that it was absolutely necessary to go to the field to check the equipment when it mattered most, that is, when it was raining. His group at SCS at that time (1940-60's) were hydrologists of the third kind.

Number 3, August 2002, Level 2


In 1988, I wrote a paper entitled "Ultimate sediment concentration," 1 which interpreted a statement in Chapter 4 of the ASCE Manual No. 54: "Sedimentation Engineering" regarding sediment-rating curves. The paper concluded that typical sediment-rating curves show a trend toward a constant concentration of suspended bed material load at sufficiently high discharges.

The following year, right at the end of the Spring semester, I visited Colorado State University in Fort Collins, my alma mater, where I met Prof. Johannes Gessler accidentally in the hallway of the College of Engineering.

Gessler said: "Ponce, can I buy you a cup of coffee?" I answered in the affirmative, and we had coffee at the Student Center Cafeteria, the site of many memorable experiences during my years at CSU in the late sixties and early seventies.

During the conversation, Johannes confided to me: "I want you to know that I was so impressed by that paper that you presented at Colorado Springs last year, that I decided to do something different this year in my graduate class in River Mechanics. I told the students that the final would consist of an analysis of your paper. There were twelve students in the class, and there was a three-way split. One third thought the paper was great, and that it had clearly thrown additional light on the subject. Another third said that the paper was faulty, and that the concepts expressed were outright wrong. The last third said they couldn't figure out for sure."

 1 Ponce, V. M., 1988. "Ultimate Sediment Concentration,"  Proceedings, ASCE National Conference on Hydraulic Engineering, Colorado Springs, Colo., Aug. 8-12, 311-315.

Number 4, September 2002, Level 1


In April of 1996, I was invited to participate at a Conference in Santa Catarina, Brazil, convened by Universidade Regional de Blumenau (URB) to examine the environmental impacts of the proposed levee scheme for flood control in the Itajai river at Blumenau.

The evening of the first day of the conference, I joined several attendees for dinner at a local restaurant. I struck up a conversation with a young man, who told me that he was finishing his Ph.D. at the University of Milan, and would soon rejoin the civil engineering faculty at URB.

I asked him about the topic of his dissertation, and he said that he was applying the diffusion wave in a DTM context to model distributed catchment runoff. Noticing that he had sparked my interest, he went on to say:

"I used the Muskingum-Cunge diffusion-wave model, with lateral inflow calculated with the routing coefficient C3 derived by this guy named Ponce." 1

My response nearly toppled him. I said: "I am that guy."

 1 Ponce, V. M., 1986. "Diffusion wave modeling of catchment dynamics,"  Journal of Hydraulic Engineering, ASCE, 112(8), 716-727.

Number 5, October 2002, Level 0


I met my friend Newton Carvalho in 1979, while on assignment for EDIBAP, to model the flood runoff of the Pantanal of Mato Grosso. Newton first described to me the "pororoca," the giant tidal wave of the Amazon and surroundings. 1

Ten years later, in 1989, I decided to go in search of the pororoca. Following Newton's advise, I flew to Macapa, at the mouth of the Amazon river, and looked for a guide who would take me to sight the "pororoca." There I met Sebastião Mota Dias, who arranged for a plane to fly out on January 22, at 6 am, toward the mouth of the Araguari river, where the elusive natural phenomenon was expected that morning.

The plane was a vintage single-plane Cessna, and the party consisted of Mota, an assistant, the pilot, and myself. We flew for two hours over the state of Amapa toward the northeast, and sighted the pororoca at 8 am, as expected, at the mouth of the Araguari. Delighted to have accomplished my objective, I recorded the experience on film.

On the way back, admiring the inmensity of the rain forest below us, I wondered just how long my luck would continue. I struck a conversation with the pilot, a time-tested, middle-aged man. I said: "Luis, how long have you been piloting in this region?

Luis answered: "A litle less than 30 years."

I said: "This plane is pretty old. Has it ever malfunctioned?"

Luis answered casually: "Yes, many times."

Noticing my mix of surprise and preoccupation, he reassured me: "Whenever this happens, I just look around for a place to land."

From that moment, I felt pretty confident that my luck was not going to run out that morning.

 1 Ponce, V. M., 1989. What a Bore!  South American Explorer, 21, 26-28.

Number 6, November 2002, Level 0


In August of 1984, I attended, with my friend Miguel Coutinho, who teaches civil engineering at IST/Technical University of Lisbon, the ASCE Hydraulics Division Specialty Conference at Coeur D'Alene, Idaho.1

We flew from San Diego to Seattle, rented a Lincoln Towne Car at the airport, and headed east to Idaho while managing to do some sightseeing along the way.

As the Conference came to an end, Miguel and I prepared to return to Seattle. I told Miguel I would go get the car and pick him up at the curb at the hotel entrance.

Miguel was waiting for me as I pulled up to the curb. At the same time he got into the passenger seat, another conference attendee also entered the car through the rear door. I thought Miguel had invited him, so I didn't say anything. Miguel thought I had invited him, so he didn't say anything either.

A couple of blocks down the road, noticing something strange, our absent-minded, would-be intruder said: "Driver, is this the limo?"

 1  Ponce, V. M.. 1984. Kinematic shock: Sensitivity analysis.  Proceedings, ASCE Hydraulics Division Specialty Conference, Couer D'Alene. Idaho, August 13-17, 880-884.

Number 7, December 2002, Level 0


In December of 1993, I took a one-month assignment to India on an invitation from the Indian National Institute of Hydrology (NIH). The main part of the assignment, funded by the United Nations Development Programme (UNDP), was a three-week visit to the NIH Ganga Plains Regional Centre in Patna, Bihar, in Eastern India. While at Patna, I traveled to Birpur, 400 km East, and then North by land about 200 km to Chatra, on the Nepalese border, to visit the Kosi project, accompanied by Messrs. Jha, Lohani and Thakur, staff scientists from the Regional Centre at Patna.

On the way back, our party took the first-class sleeper train from Birpur to Patna, and, after a good chat, settled down to a well deserved rest. Great was our suprise to notice that on one of the many scheduled stops, the train was suddenly invaded by hundreds of people, desirous to catch a ride to some destination further along the way. One of my companions speculated that these people were going to a political rally, and that there was no other way to travel but boarding (invading) the train in mass. There were people everywhere, packed like sardines, so it was impossible for us to get out of our first-class cabin, even to go to the bathroom. It did not escape my attention that had I wanted to do precisely that, I would have had to find alternate means to satisfy this most basic of needs.

Luckily for us, the train made an unscheduled stop in the next town, and the intruders were routed out by scores of policemen, who dutifully conducted them to jail, marching in three columns in an orderly fashion, restrained between the train on one side and a cord on the other. As the events unfolded, I stuck my head out of the train's window, and the scenery that cold morning reminded me of one of those Hollywood scenes which I dearly loved, complete with populace, train station, policemen, local color, and above all, that orderly chaos which well describes the typical Indian urban scene.

Number 8, January 2003, Level 1


During my college days at Colorado State University in the mid-seventies, the Hydraulics graduate students at the Engineering Research Center were well aware of what it took to conquer the hurdles. Prof. Daryl Simons had a reputation for toughness; however, he always asked the same question on the preliminary exam:

"If you drop a spherical particle in a flask full of water, what is the velocity distribution in the space between the particle and the inner wall of the flask?"

Everybody knew the answer, and Prof. Simons invariably started every prelim exam with the famous question.

One day, a student worked up some courage, and asked him: "Prof. Simons, you always ask the same question on the prelim. Everybody knows the answer. Why?"

Simons responded with a smile: "Its simple; whoever does not know the answer, I flunk him."

Number 9, February 2003, Level 1


In 1984, I wrote a paper, with Zbig Osmolski and Dave Smutzer, on the flood hydrology of the Santa Cruz river, in Southeastern Arizona. The paper was submitted to the ASCE Journal of Hydraulic Engineering, and it was published in September of 1985, with the title: Large Basin Deterministic Hydrology: A Case Study.

Prior to publication, the manuscript was returned to me after copy editing, with a change: When discussing the storm of September 1983 over southeastern Arizona, my reference to "Baja California" has been purposely edited to read:  Baja, California. Noticing the mistake, I corrected the copy back to the intended "Baja California."

To my surprise, when the galley proofs came back two months later, the comma had been again returned to the copy, which now read, in print:  Baja, California.

I called the ASCE editor in New York and explained to him that my intent was to refer to the state of Baja California, in Mexico, and not some city named Baja, in California. The editor readily apologized and proceeded to correct the galley, but I felt I needed to complete the reference to Baja California, Mexico," to avoid any further misunderstanding.

Number 10, March 2003, Level 2


In December of 1993, I was invited to lecture at the National Institute of Hydrology, in Roorke, India. My presentation was titled "Management of floods and droughts in semiarid regions." One of the topics covered was Budyko's hydroclimatological model of a coupled land surface-atmosphere system.

The main feature of Budyko's model is the separation of precipitation into its advective and evaporative components. A key step is the quantification of the water vapor advected into the control volume.

At the end of the lecture, one of the participants confided to me: "Prof. Ponce, I have been in the field of hydrology for about ten years, and have never heard anybody talk about advective precipitation."

In fact, advective is a term that belongs to fluid mechanics, and, in our context, to hydroclimatology. Yet in hydrology it is largely unknown. In its path, the hydrologic cycle crosses a gamut of fields of knowledge, including oceanography, meteorology, climatology, hydrology and hydraulics, each with its own vocabulary. Needless to say, this diversity of terminology contributes to make the holistic view of science all the more challenging.

Number 11, April 2003, Level 1


The community of Tlaxiaco, in Oaxaca, Mexico, is caught in a serious predicament which is typical of cities of its size in developing areas in Mexico and Latin America.

In the past three decades, sewage piping has been installed in urban areas, while sewage treatment was being dismissed as too expensive. Over the years, this has led to the pollution of nearby streams, which have gradually turned into open sewers. Significantly, the rural areas, which are extensive in Tlaxiaco, have managed to avoid drainage, relying instead on dry sanitary latrines and septic tanks.

The need to clean the streams has been now recognized; yet, there is increasing social pressure for the rural areas to be connected to the sewage system, increasing the load to be treated.

In November of 2000, I met with the mayor of Tlaxiaco and his council, and explained to them the problems they faced: The greater the number of people who flushed, the larger the required capacity of the treatment system. I advocated a mixed solution, a combination of drainage and retention, through the use of an oxidation pond and constructed wetland for the treatment of the wastewater from urban areas, and dry ecological latrines for the rural areas. Still, some argued that everybody should be allowed to drain, since it was the modern thing to do.

Near the end of the meeting, a senior councilman from one of the rural areas, who appeared to be new to the toilet-and-drainage system, said, in a pleading tone: "I do not understand it! They are going to use all our water! We are not going to have any left to drink!"

Number 12, May 2003, Level 1


In 1997, I wrote a paper which generalized the classical Horton-Izzard conceptual model of overland flow for rating exponents in the range of 1-3. The results were based on the integration of several complex mathematical functions. 1   Our first attempt was to use existing software, but we soon realized that something was wrong: The outflow hydrograph was not as expected... the water was actually flowing uphill!

I told my coauthor, graduate student Sumner Hasenin: "There is something wrong with this solution. Water does not flow uphill." I instructed her to start from basic principles, to integrate the functions by parts, and to develop the correct mathematical solution for this problem.

Two weeks later, Sumner came back with the answer to the puzzle. The software that we were using had an error: A minus sign had inadvertently been changed to a plus sign. Once we placed the minus sign were it belonged, the solution behaved as expected, correctly depicting the rising limb of typical overland flow hydrographs.

Thus, the moral of the story: If you are solving a physical problem, it behooves you to have some knowledge of the physics; otherwise you will be unable to assess the accuracy of the calculated results.

 1 Ponce, V. M., et al. 1997. "Generalized conceptual modeling of dimensionless overland flow hydrographs,"  Journal of Hydrology, 200(1997), 222-227.

Number 13, June 2003, Level 0


In the summer of 1995, I traveled to the northern rim of the Colca Canyon, in Arequipa, Peru, accompanied by my daughter Tina and Carlos Machicao, a colleague and friend who at the time, used to teach civil engineering at Arequipa's National University of San Agustin. Our party included a driver and a local guide.

We left Arequipa early on the morning of July 28, and after several hours of arduous travel across deep canyons and majestic mountaintops, managed to reach a town where we found many people gathered in the main plaza, celebrating the anniversary of Peruvian Independence.

Unaware of our exact whereabouts, I introduced myself to a distinguished lady in the crowd and intently asked her the name of the town. She said: "This is Machahuay."

I asked her: "Is this the town that the "Mambo de Machahuay" was named after?

She answered: "You are quite right."

We were pleasantly surprised and proceeded to engage the locals in spirited conversation. Later on, accompanied by the lady, our party climbed a nearby hill to get a better view of the breathtaking surroundings. Once there, led by its composer, we sang, at full volume, the "Mambo de Machahuay."

The experience was one that would be hard to forget.

Number 14, July 2003, Level 0


In the Spring of 2001, I traveled to Oaxaca, Mexico, as part of an SDSU faculty delegation to the UABJO (Universidad Autonoma Benito Juarez, Oaxaca). One afternoon, Pablo Lopez Hernandez, Dean of the School of Arquitecture at UABJO, invited me to visit the alternative sewage treatment plant at Etla, at the northern end of the city.

We arrived late that afternoon and found the plant closed. My companion noticed an opening through the back of the facility, and proceeded to gain entry. I followed dutifully, without realizing that a small garbage dump separated us from the treatment plant. We had to pass through it quickly, a distance of about 60 m, hoping for the best. Before reaching the end, I stepped on what must have been a wasp nest, because they came out of nowhere and proceeded to attack the intruder, that is, me!

The whole incident lasted about five seconds, and I defended myself the best I could, but one wasp managed to bite me on the back of the hand. Realizing I was in trouble, I sought help from Pablo, who said: "Don't worry, my wife is a doctor... we will call her, and she will prescribe something."

Within two minutes, he pulled out his cell phone, called his wife, got the prescription, and we were en route to the closest pharmacy, which we found in the next corner (In Mexico, there seems to be a pharmacy on every corner). Much sooner than I had expected, I was on my way to full recovery from the bite of the Etla Wasp.

Number 15, August 2003, Level 1


In 1978, I wrote a paper about the classification of open-channel flow regimes. In this paper, I identified three characteristic celerities and three characteristic diffusivities, from which only four independent dimensionless numbers could be defined. Three of them were well known: the Froude, Reynolds, and Vedernikov numbers. The fourth number was new, and not finding an appropriate reference in the literature, I called it the "Ponce-Simons" number, to include my professor and coauthor Daryl B. Simons.

The Ponce-Simons number characterized unsteady open-channel flow as kinematic (small value), dynamic (intermediate value) or inertial (large value). The idea was based on an earlier paper (1977) entitled "Shallow wave propagation in open-channel flow," which had been well received.

I submitted the manuscript to the ASCE Hydraulics Division Journal, but the paper was rejected. It was returned to me with the following comment from one of the referees: "To range one's name along such illustrious antecessors as Froude, Vedernikov, and Reynolds, is surely the ultimate in chutzpah."

Shortly thereafter, I published a reduced version of the paper 1 in the proceedings of the Fourth Canadian Hydrotechnical Conference. Yet, the experience had taught me a valuable lesson: You can't name something after yourself; recognition is to be bestowed only by others.

1 Ponce, V. M. 1979. "On the classification of open channel flow regimes," Proceedings, Fourth National Hydrotechnical Conference, Vancouver, Canada, May.

Number 16, September 2003, Level 0


The Colca Canyon, in Arequipa, Peru, is famous for its condor sightings. In 1995, during a visit to the canyon, Bernardino, our local guide, shared with me the following story.

An acquaintance of his, a time-tested Colca guide, had told a group of tourists that he could help them sight the elusive condor in a grand way. Hired to do the job, he proceeded to kill a burro and deposit its remains in a strategic location, where he knew the condor would take notice. He then asked the party to leave and to return five days later, explaining that the condor does not eat fresh dead meat.

On the morning of the fifth day, a couple of condors appeared on the horizon and proceeded to inspect the site without actually descending on the burro's carcass. The following day, an enormous condor, apparently the head of the group, descended on the carcass, duly accompanied by his understudy. They proceeded to feast only on the eyes and the anus, leaving immediately afterwards. Some time later, a group of more than twenty condors descended on the site, and rapidly took care of the rest of the carcass. The tourists were pleased, and Bernardino's friend showed once more that he was a master of the ways of the condor.

Number 17, October 2003, Level 1


In October 1998, I was invited to lecture at a three-day short course at Snowbird, Utah, on the FLO-2D model of Jim O'Brien. The course was sponsored by Colorado State University. The second day of the meeting, a participant who was a professor at a European university approached me during a coffee break and said:

"Prof. Ponce, I want you to know that I have been in the field of hydraulics for more than 15 years, and have never heard of the Vedernikov number 1 that you talk about so elocuently. I am going to go back and inquire with my professors how is it that we have missed such an important subject. Just the learning of this concept has justified my trip here this week. Thank you."

 1 Ponce, V. M., 1991. "New perspective on the Vedernikov number,"  Water Resources Research, 27(7),1777-1779.

Number 18, November 2003, Level 2


In the summer of 1989, I went to Santa Cruz, Bolivia, on a consulting assignment in relation to the flood control scheme for the Pirai river basin. My assignment was to do the sediment routing, i.e., to establish the rates of sand deposition on several critical reaches of the Pirai river.

At our first technical meeting, I proposed to use the Colby method for sediment transport in the sand-bed channels, and the Meyer-Peter Muller method for coarse-sand and gravel transport. My proposal met with the opposition of one of the supervisors, who argued that the Colby method's applicability to Bolivian rivers had not been demonstrated. I countered that I saw no other method better suited for sand-bed rivers, and that quartz sand was quartz sand everywhere. Since there is no sediment transport method specifically developed for Bolivian rivers, we used the Colby method, pending field verification.

The field data was collected in the winter of 1990. We plotted the sediment rating curve, a plot of sediment discharge vs water discharge, and proceeded to compare measured and calculated sediment transport. To everyone's amazement, the agreement was excellent, showing measured sediment discharge closely matching calculated sediment discharge throughout a wide range of water discharges. Thus, I proved my point: That quartz sand was the same, regardless of location, and the Colby method was applicable to the Pirai.

Closer examination of the data revealed, however, that individual measured data points could be in error by as much as 100%, a fact well known by experienced hydraulic engineers. It is almost impossible to get a perfect match when dealing with sediment transport rates, which typically vary several orders of magnitude from low flow to high flow.

Number 19, December 2003, Level 1


Rivers are much wider than they are deep, although this may not be apparent to a layman. For example, the Upper Paraguay river at Ladario is about 6 meters deep and 300 meters wide. The Amazon river measured at the Obidos narrows is about 60 meters deep and 1600 meters wide. Yet, people who have not seen the data have a tendency to believe that rivers are much deeper than they actually are.

During a field reconnaisance of the Upper Paraguay river near Ladario in January 1995, 1 I asked a local fisherman if he had been on the river for very long.

He quickly responded: "All my life."

I followed with a question: "How deep is the river at this point?"

He looked at the river, and pronounced: "At least 100 meters deep."

I learned then that local knowledge, no matter how close to the source, had its shortcomings.

 1  Ponce, V. M.. 1995. Hydrologic and environmental impact of the Parana-Paraguay waterway on the Pantanal of Mato Grosso, Brazil, A Reference study. San Diego State University, San Diego, California, August, 124 p.

Number 20, January 2004, Level 1


In 1979, I traveled to the Pantanal of Mato Grosso, in Brazil, for the first time, on a consulting assignment. The objective was to evaluate the retention of water by several dams which were being proposed in the upper basin.

An inspection trip to the Pantanal took our party to the town of Porto Murtinho on April 24, in time to witness its temporary relocation to higher ground, in preparation for the annual flood, which was expected to peak about three weeks later. Porto Murtinho is located close to the most downstream point of the Pantanal and the Upper Paraguay river. Therefore, it was not unusual for the annual flood to overflow its banks and send the flood waters moving slowly into the adjacent lowlands.

I returned to Porto Murtinho in the summer of 1992, and this time the situation was quite different. With European advice, a polder had been built in the interim, and the town was now encircled by a 3-m high levee. This effectively circumvented the annual flooding and gave the town a newfound assurance.

As I stood on top of the levee, I could not help but to think that the town's flood control success story rested on the loss of the view of the river. Thus, I confirmed once more that something good always has within it something bad.

Number 21, February 2004, Level 1


Unsteady flow in open channels is a fascinating subject, but one that, in my experience, has yet to reach most engineers in practice. In the Spring of 1987, I was invited to give a lecture at the U.S. Army Corps of Engineers' Hydrologic Engineering Center, in Davis, California. The meeting was attended by approximately forty army engineers from various parts of the United States.

The topic of my presentation was "Unsteady flow in open channels." I spoke about kinematic, diffusion and dynamic waves. I compared Manning's flow velocity with Seddon's kinematic wave celerity, and described the exponent of the rating, which characterizes Seddon's celerity, i.e., the velocity of flood waves. Indeed, as early as 1900, Seddon, working the Lower Mississippi river, had experimentally laid the foundations of flood routing, one of the subjects in unsteady flow in open channels.

At the end of the lecture, one of the more senior participants, obviously an experienced hydraulic engineer, asked a question: "How do you spell 'Seddon'? I have never heard about him before."

Number 22, March 2004, Level 2


Early in my career, in the Spring of 1979, I accepted a two-month assignment in Brazil doing hydrologic modeling for EDIBAP (Estudo do Desenvolvimento Integrado da Bacia do Alto Paraguay), in Brasilia. The task was to model the tributaries of the Upper Paraguay River, with and without proposed developments, to study the impact on the downstream flow. Our results fed the SSARR model of the Upper Paraguay, operated by the Brazilian government. My supervisor was Hugo Benito, a hydrologic engineer with extensive experience in the modeling of large river systems in South America.

Being just a few years out of school, I lacked experience with large rivers, particularly those that regularly overflow their banks. I had a certain mindset on how kinematic flood waves--and most flood waves are kinematic--will have a tendency to steepen as they propagate downstream. As I discussed our findings with Hugo, I spoke about the steepening and how I expected our calculations to show it. To my great surprise, he said: "Flood waves do not steepen. At least not in the Paraguay!"

I sensed he knew what he was talking about, and I was not in a position to argue. Later, after additional study, I learned that flood waves can either steepen or flatten, depending on the interaction of the flow with the cross-sectional geometry. When inbank, flood waves have a tendency to steepen; conversely, when out of bank, they will flatten. 1 Indeed, Hugo and I were both right, and the experience served to strengthen my knowledge of flood wave behavior.

1  Ponce, V. M. 1985. Kinematic shock: Sensitivity analysis.   Journal of Hydraulic Engineering, ASCE, Vol 111, No. 4, 600-611.

Number 23, April 2004, Level 2


In November of 1994, an international symposium was convened in Tucson, Arizona, to honor Dr. Ken G. Renard on the occasion of his retirement. Ken had directed the USDA ARS Lab in Tucson (now the Southwest Watershed Research Center) for more than three decades.

In one of the meetings at that symposium, Ken confided to his audience how the lab hab been originally established in the early 1950's with the purpose of evaluating how upstream conservation programs would affect downstream water yield. USDA had programs with local ranchers to improve conservation practices, but downstream users objected to the programs because prior appropriation water laws entitled them to water produced upstream. Thus, the lab's original mission was to quantify the cause/effect hydrologic phenomena in semiarid regions.

It soon became apparent that factors applicable in more humid areas were not applicable in drier climates. Much effort was spent on quantifying the various components of the hydrologic cycle, and the original mission was altered to include modeling, water quality, remote sensing, and rangeland health.

A clearer picture of the hydrologic cycle has emerged since the ARS Tucson experience. We now know that the behavior is not so much one of cause/effect (characterized by subtraction in one part of the system bringing an addition to another) but, rather, one largely controlled by cybernetic (biofeedback) processes. Anthropogenic reductions in evapotranspiration can trigger local climatic changes which have the net effect of reducing runoff. Likewise, increases in evapotranspiration will bring forth increases in runoff. 1

1 Ponce, V. M., and A. K. Lohani, and P. T. Huston. 1997. Surface albedo and water resources: Hydroclimatological impact of human activities.  ASCE Journal of Hydrologic Engineering, 2(4), October, 197-203.

Number 24, May 2004, Level 1


In the Fall of 1993, I took a sabbatical leave at the Universidade Federal do Ceará, in Fortaleza, Brazil, to study droughts at Brazil's Drought Polygon. At that time, the region was suffering from a crippling three-year drought. Emergency plans were in place to transfer water from the Oros reservoir, in the sertão (backlands), to the urban center at Fortaleza.

The "Canal do Trabalhador" or "The Worker's Channel" was being built expressely for the water transfer. It was widely regarded as a last ditch effort to mitigate the ravages of the drought. The canal's alignment followed roughly along the coast of the state of Ceara, a distance of about 100 km.

One day, I was invited by a local colleague to join the daily reconnaisance flight which was documenting the progress of the canal's tight construction schedule. The flight lasted for about two hours, and the plane flew very low, as was required to videotape the progress. My inexperience with low flights showed: I threw up several times, using a convenient bucket that was onboard ostensibly for that purpose.

After the plane landed, my colleague greeted me with a smile and, all-too-aware of what I had gone through, asked me, point blank: "How many times?"

I knew exactly what he was referring to, and answered, meekly: "Three."

He said: "Good... that's not too many... other people had more than that."

Number 25, June 2004, Level 0


In November of 1999, I went on a field trip to the Ojos Negros valley, in Baja California, Mexico, accompanied by my colleague Thalia Gaona, who teaches Economics at the Universidad Autonoma de Baja California. Our intended purpose was to do a photographic documentation as part of our SCERP research project on the sustainable management of water in the valley.

We decided to reach the top of Cerro Doña Eulalia, from which we were sure the view of the valley would be ummatched. As we got there, we admired the breathtaking view and prepared to shoot our film. Suddenly, we were disturbed by a group of buzzards, who hurriedly flew out of the crevices of a pile of rocks located at the top of the hill.

We took pains to make sure that the buzzards understood that we were not there to harm them. As we quieted down from the experience, I could not help but ponder that I had never ran across a buzzards' nest before. These elusive creatures are experts at making sure that they stay at arm's length from the rest of us, particularly if we give any indication of being alive.

Number 26, July 2004, Level 1


In the Summer of 1997, I attended the ASCE Hydraulic Engineering Conference in Anaheim, California. A social gathering of Colorado State University (CSU) alumni had been planned for one of the evenings of the conference. I arrived at the party early, and noticed my former professor Dr. Everett Richardson as he made his entry to the room. Upon realizing that I was there, Rich, as he was warmly addressed by his students, made a point of coming to meet me and, after the customary salutation, said:

"Ponce, I want you to know that I am teaching with your book, 1 and so is my son Jerry at the University of Missouri at Kansas City." He went on to say that Chapter 15, entitled "Sediment in the Hydrologic Cycle," had done a superb job of summarizing knowledge on the subject.

Needless to say, the best praise is that which comes from your teachers. Rich had been my advisor in the early 1970s when I was at CSU completing my doctoral studies.

 1 Ponce, V. M., 1989. "Engineering Hydrology, Principles and Practices,"  Prentice Hall, Englewood Cliffs, New Jersey.

Number 27, August 2004, Level 2


In the Fall of 1993, I took a sabbatical leave in Fortaleza, Brazil, to study droughts at the famed Departamento Nacional de Obras Contras Secas (DNOCS) (National Department of Works Against Droughts). During my stay in Brazil, I was associated with the Universidade Federal do Ceara (UFC).1

One day I was asked by a colleague to help review a doctoral thesis that was near completion. The student explained that he was coupling remote sensing techniques with a numerical model of flood propagation in a spatial grid context. After reviewing the manuscript, I asked the student what equation was he using for the routing. With a mix of surprise and confidence, he answered: "The Manning equation."

I countered that if he was routing floods, that the steady-flow Manning equation did not suffice; that he had to use an unsteady form of the open-channel flow equations, one that would take into account the well established--yet surprisingly little known-- Seddon's law. Moreover, I said that it was also necessary to account for the subsidence of the flood waves by means of Hayami's hydraulic diffusivity.

Thus, the moral of the story: You cannot do flood routing just using a steady-flow equation such as Manning's.

Number 28, September 2004, Level 0


In the Summer of 2002, I was invited by my friend and colleague Dr. Carlos Rodriguez to participate in a reconnaissance flight of the Rio Meta, in eastern Colombia, where his consulting firm was performing hydrologic and hydraulic studies.

The morning of the flight, our study team assembled at the airport in Villavicencio and proceeded to board the plane, a single-engine Cessna. About two hours into the flight, we had to abort the mission because suddenly the sky became overcast, making it virtually impossible for us to see the ground. The pilot proceeded to make a U-turn and we headed back, disappointed but promising to return at some other time.

As we got off the plane, we were detained by airport security for questioning. They told us that we had circled above a Colombian navy base on the river and demanded an explanation.

It took us a while to explain to them that our objective was civilian reconnaissance, that we were unaware of the base's existence, and that our pilot's U-turn, precisely in the airspace above the base, was merely an unfortunate coincidence.

Number 29, October 2004, Level 0


In the Fall of 1997, I went on a field trip to the Salton Sea, in Imperial County (California), accompanied by Messrs. Sudhir Kumar and Rajendra Pandey, staff scientists of the National Institute of Hydrology, Roorkee, India. At that time, Kumar and Pandey were on four-month assignments at San Diego State University, funded by the United Nations Development Programme.

The Salton Sea is an artificial lake located in the Salton depression, well below mean sea level. The lake has been sustained since the 1930's by agricultural drainage from the Imperial and Coachella valleys.

In the hope of learning more about the sea, we decided to inspect the entire shore and its environs. At the time, we were researching a paper about the restoration of the Salton Sea.1 Since the inland sea is fairly large (with a surface area of about 979 km2), we planned a two-day visit, which included camping at the Salton Sea State Recreation Area on its northeastern edge. As the night approached, we pitched our tent and settled down for a well deserved rest.

Little did we suspect that, in the middle of the night, we were going to be awakened by a loud noise that first appeared quite distant, but kept getting louder. We soon realized that it was the sound of a train. As it got closer, the trembling of the earth below us and the crescendo of the noise combined to produce in us an erie feeling. There we were, in the middle of the desert, with darkness and frigid weather all around us, hopelessly pinned down inside a tent. We figured that there was nothing we could do; just wait until the train passed. My sense told me that we were safe; nevertheless, the experience was quite frightening.

The next morning we confirmed our suspicion: we had pitched our tent too close to the tracks. Fortunately, we survived to tell the story.

Number 30, November 2004, Level 1


Many years ago, I was "accused" by the Late Loren McIntyre, the distinguished photographer and South American explorer, of throwing apples and oranges at him. The issue had to do with a statement he made in a specialty magazine that the Amazon river did not have 1/5 of the world's water; that this number was more likely to be 1/10000. Being knowledgeable on the subject, I was eager to set the record straight, and convinced the editor of the magazine to publish a correction, hoping to shed light on the issue.

And so I did. To compare the Amazon's annual supply of fresh water to the total amount of fresh water on Earth is one thing; I called this an "apple." On the other hand, to compare the Amazon's annual supply of fresh water to the annual supply of fresh water that returns to the sea from the land (the river runoff) is another thing; this I called an "orange."

McIntyre was referring to the apple, but when people talk about the Amazon's water, they are usually referring to the orange. In fact, my own calculations confirmed that the Amazon's runoff was about 1/6 of the world's total runoff. Needless to say, the confusion between volume and discharge remains common among laymen.

Number 31, December 2004, Level 2


Several years ago, I participated as a lecturer in a short course at a university in Europe. There were several speakers and about 40 participants. One of the speakers gave a lecture on mathematical modeling of unsteady flows and its application to flood routing. He mentioned that he had calculated the Courant number and was surprised to learn that it was rather high, around 10, although his results looked very reasonable and matched measured data (A Courant number equal to 1 generally means good convergence properties, while a Courant number equal to 10 does not).

I asked him what celerity had he used to define his Courant number. He was a bit surprised at my question, and said: "Of course, I used the Lagrange celerity."

I said: "You are dealing with flood flows, therefore, you should use the much smaller Seddon celerity. If you do this, you will find that your actual Courant number is probably much closer to 1."

In my experience, while many people recognize the Lagrange celerity, the same statement does not follow for the Seddon celerity, even though Seddon first advanced this concept in the year 1900. These two celerities are the only characteristic celerities in unsteady flow in open channels. While the Lagrange celerity describes "short" waves, the Seddon celerity describes "long" waves. Either may be used in the definition of the Courant number, depending on the application.

Number 32, January 2005, Level 0


Tlaxiaco is the capital of the High Mixtec region of Oaxaca, in southern Mexico. It is a city of about 20,000 people, nested high in the mountains.

During a recent visit, I learned from my friend José Perez that Lila Downs, the famous singer, was born and raised in Tlaxiaco, and had lived there most of her early years. Being a fan of Lila's, I decided to present one of my associates with one of her records, and said to my friend: "Please take me to buy a record of Lila Downs."

He said: "Of course." And we headed toward the center of town. Once there, José stopped the car at a corner, pointed at a store, and said: "There."

I jumped out of the car and went inside the store, and out again, and told José: "This is a hardware store!"

He smiled and said: "That is where you will find Lila's records." He jumped out of car, walked into the store, and showed me a collection of Lila's records on display on one side.

Puzzled, I said: Why is this store selling Lila's records?"

He answered in an explanatory tone: "This is Lila's family's store. They are her relatives. They sell her records here."

Number 33, February 2005, Level 1


I have been researching the kinematic wave since 1976. In 1991, I published "The kinematic wave controversy," 1 where I elaborate on some common misunderstandings about such an important concept.

In my experience, the words "kinematic wave" arouse in the average hydrologic practitioner thoughts ranging anywhere from technical sophistication (a wave which transports mass, and which can develop into a kinematic shock) to physical unrealism (is it there, or not?). This has continued to fuel the controversy, despite more than one-hundred years of practical experience and fifty years of theoretical research. In fact, the kinematic wave was identified and measured by Seddon in 1900, and christened by Lighthill and Whitham in 1955. Yet, even the well respected U.S. Army Corps of Engineers' HEC-1 model had confused the concept of kinematic wave.

In the summer of 1995, I attended the ASCE Hydraulic Engineering Conference, in San Antonio, Texas. One morning, I joined a group of attendees in the lobby of the hotel, and coming in at the middle of the conversation, heard one of them say: "We applied the kinematic wave and had good results with it."

Anxious to make a point, and pretending not to have a clue, I said: "What is it? Can you explain it to us?"

The man's face suddenly turned red, and he said, abruptly: "I've just remembered I have something else to do. See you later."

Number 34, March 2005, Level 1


In the summer of 2002, while researching the writing of Milestones of Hydrology. I noticed that Ven T. Chow had mentioned the Froude number in his popular textbook, 1 but had not elaborated on its origins. The Froude number, a fundamental principle of open-channel hydraulics, is defined as the ratio of the mean velocity (Manning or Chezy velocity) to the relative celerity of small surface perturbations (Lagrange celerity).

In an effort to tell the story accurately, I consulted several books and learned that Froude had not developed the Froude number. Furthermore, Froude's major work, published in 1871, had dealt not with open-channel hydraulics, but with ship stability and hydrodynamics.

Froude's contributions to society, however, were of such importance that he was highly regarded by his peers. To honor his memory, they attributed to him the concept which now bears his name. Thus, the moral of the story: A great man's glory is controlled less by his own actions than by those of his peers.

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

Number 35, April 2005, Level 0


Several years ago, my daughther Tina and I went on a well deserved vacation which took us to several sites in Southern Peru. One of our visits was to the Colca Canyon, at about 3000 m depth easily one of the deepest in the world. Having visited the canyon from the southern rim two years earlier, I proposed this time that we go by the lesser travelled northern rim, following the road to Machahuay, in Peru's Arequipa department.

Upon reaching Machahuay, our party, consisting of Tina and I, a colleague, a guide and a driver, rested while admiring the splendid mountainous scenery that surrounded us. I struck a conversation with Bernardino, our time-tested guide, and said: "It feels great to be in deepest Peru."

Pointing east of us, he said: "This is not deepest Peru... deepest Peru is out there, three hills east of here... where even I am not welcomed."

Number 36, May 2005, Level 0


In the winter of 2002, our Ojos Negros research group visited Arroyo El Barbon, in Baja California, Mexico. The task at hand was to locate and inspect several water wells in the vicinity. We hoped to use this information to learn more about the depth to the water table. Evolving sand-mining regulations were requiring an operator to maintain an undisturbed, unsaturated layer of 4-m minimum thickness for the protection of the aquifer.

As we approached one of the wells, we noticed something unusual. We soon realized that it was poorly maintained and that bees had established a hive on the well head.

A junior member of our team suggested that we get rid of the bees and proceed to inspect the well. My response was quick and left no room for misunderstanding. I said: "Let's get the heck out of here." It is an extremely risky proposition to disturb a beehive, no matter how important the task.

Number 37, June 2005, Level 1


In the Fall of 1987, I was invited to participate in the International Seminar on Physical and Mathematical Modeling of Hydraulic Structures, in Lahore, Pakistan. As part of the visit, the six-member U.S. delegation toured Tarbela Dam, on the Indus river, the largest earth-filled dam in the world.

One evening, after dinner at the guest house, one of the members of the team posed the following question to me: "Could you tell us what the difference is between deterministic and stochastic modeling?"

I said: "It is simple: If you have a signal, the process should be modeled deterministically; on the other hand, if all you have is noise, the process should be modeled stochastically."

In fact, it would be a mistake to handle a signal-driven process such as flood wave routing with a stochastic model. On the other hand, daily flows in upland watersheds usually lack enough diffusion to develop a signal; therefore, they are better handled with a stochastic approach. Both deterministic and stochastic models are useful tools in applied hydrology.

Number 38, July 2005, Level 0


In 1971, my wife Jane was hired to translate the text of a book entitled "Peru in living color", by John W. Majewksi, a Canadian photographer.

During the performance of the work, we had a chance to meet the author. Later, we admired the book, which contained more than 120 excellent photographs. Pleasantly surprised at the quality, I asked the author how he managed to take such good pictures. His answer was almost self-deprecating: "You should have seen the three-thousand pictures that I did not publish."

I then confirmed that a sure path to quality is through quantity. I have since followed this time-tested dictum in my photographic endeavors.

Number 39, August 2005, Level 1


In 1984, I visited Colorado State University, my alma mater, to attend a retirement dinner for one of my professors. The following day, I traveled to Denver to visit an acquaintance from my college days at CSU in the early 1970's.

In the evening, we went to a slide presentation in the local community center. A lady was showing the pictures she had taken in a recent trip to Peru. Among the photos were several slides of the terraces of Pisac, without a doubt some of the most impressive and best preserved agricultural terraces built by the Incas.

At the end of the presentation, in response to questions from the audience, she proclaimed: "Nobody knows how the Incas pumped the water from the streams to the terraces."

Obviously, she had missed the fact that the terraces held the runoff, eliminating the need for pumping.

Number 40, September 2005, Level 0


In January of 1992, I spent three weeks in Belgaum, India, in a UNDP-sponsored consulting assignment with the Hard Rock Regional Centre of the (Indian) National Institute of Hydrology. My job was to train the centre's scientists on catchment hydrology. My visit led to the publication, in 1995, of two papers on catchment water balance.1, 2

One evening after work, one of the scientists invited me to dinner at a local restaurant. As we walked to the restaurant, my companion remembered that he had to do his daily prayers, and asked me to join him at a local temple, promising that it would be quick. I thought it was going to be a different experience for me, so I agreed.

After witnessing an hour of chanting coupled with other religious rituals, the ceremony finally finished and we headed for the restaurant. Trying to be polite, I asked my companion how he remembered the chants for such a long time? He answered, calmly: "It is easy. Every three minutes we repeated the same chant."

1 Ponce, V. M. and A. V. Shetty. 1995. A conceptual model of catchment water balance.  1. Formulation and calibration. Journal of Hydrology, 173(27-40).
2 Ponce, V. M. and A. V. Shetty. 1995.
A conceptual model of catchment water balance.  2. Application to runoff and baseflow modeling. Journal of Hydrology, 173(41-50).

Number 41, October 2005, Level 1


In the spring of 1992, I lectured at the Instituto Superior Tecnico (ISP), in Lisbon, Portugal, invited by my friend and colleague Miguel Coutinho, who teaches hydraulics at that university. One afternoon, I had coffee with Emidio Santos, a former student of mine during my days at Colorado State University in the late seventies. Emidio teaches hydrology at the ISP.

At that time, my book (Engineering Hydrology, Principles and Practices) had been published for a few years. Curious about Emidio's opinion of it, and knowing that he would give me a straight and informed answer, I asked:

"Emidio, what do you think about my book?"

To which he responded, after some thought: "It is a fine book, but it is more hydraulics than hydrology."

Number 42, November 2005, Level 0


On vacation in the state of Veracruz, Mexico, in June 1996, my wife Jane and I weathered the leading edge of Hurricane Alma as it made its way from the Caribbean into the western coast of Mexico. We were driving through the mountains from Fortin to Jalapa, the capital of the state of Veracruz, in a rented VW, and reached Jalapa well into the evening, two hours behind schedule.

We had intended to meet an aquaintance, and, since we were already late, we looked around intently for directions. It was raining very heavily, and I was barely able to read the street signs. One of them read: Jalapeños Ilustres.

I said to my wife: "These people are unusual... they name their streets after a famous chili pepper." Suddenly I realized that the original Jalapeños were the people of Jalapa, and not the popular chili peppers.

Number 43, December 2005, Level 0


In the early seventies, I was employed as a civil engineer with a consulting firm in Lima, Peru. My job entailed frequent visits to the field, and I often found myself supervising technicians.

One day, an assistant asked me what was the meaning of "f/stop." Knowing little photography at the time, I hesitated to give an uninformed opinion, so I told him that I would give him an answer later.

That evening, I purposely visited a friend and borrowed a couple of photography books from him, which I proceeded to read avidly. I learned the meaning of the f/stop but, more importantly, the experience launched my initiation into photography. My interest continued long after I got back to my assistant with the correct answer.

Over the course of my career, photography has been for me both a pleasure and a passion. The quality of the pictures featured on my website would not have been possible had an assistant not challenged me early on the meaning of the f/stop.

Number 44, January 2006, Level 1


In the Spring of 1993, I visited the Ojos Negros valley, in Baja California, for the first time, accompanied by Walter Zuñiga, who at the time was a graduate student at UABC/Ensenada. The purpose was to examine the damage caused by the winter rains on the outlet of Laguna Hanson, high up in the Sierra Juarez. Soon thereafter, Miguel Vélez, the municipal delegate, invited us to a jaripeo, the local rodeo.

The attraction of the rodeo was "El Mofle," a huge horse that must have been at least 16 hands high. As the horse made his entry to the arena, it looked like we were in for some excitement. But, something went wrong at the last minute, and "El Mofle" came out running like a mad horse, directly toward us, who were seated on the second bench row on the opposite side of the arena. Before we realized it, he jumped into the stands and almost fell on the lady who was seated in front of us. The whole incident lasted only a few seconds, and the lady was miraculously spared from serious injury, but she bruised her left leg.

The lady was Doña Rosita Bustamante, mother-in-law of the municipal delegate and a long-time resident of the valley. I helped Rosita treat her leg with some first-aid lotion that I had handy, and pretty soon she was on her way to full recovery.

After the accident, she became a very good friend. My visits to the valley, which became more frequent as time went on, always included a stop at Doña Rosita's. Despite her age, her conversation was agile and spirited, and she appeared to have the benefit of knowledge that only time can bestow. It was she that first encouraged us to research the climatic changes of the valley, which we began in 1998, some time after her death.1

1The Ojos Negros Research Group, 2002. Sustainable management of water in the Ojos Negros valley, Baja California, Mexico. http://.../ojos_negros_report_final.html

Number 45, February 2006, Level 2


In the winter of 1982, my friend Newton Carvalho invited me to inspect the failure of the cofferdam for Norte Dam, which was under construction at that time on the Itajai river, in Santa Catarina, Brazil. The dam was being built by the Departamento Nacional de Obras Sanitarias (DNOS) [National Department of Sanitary Works].

The cofferdam had failed because an unusual storm event followed on the heels of a drought. Thus, the storm mobilized an extraordinary amount of debris, which clogged its two Morning Glory spillways (see photo below).

The same day of our visit, a meeting took place at the damsite between government officials and representatives from a local Indian reservation. I attended the meeting as an observer.

The dam's spillway had been sized using the 10,000-yr design flood, a return period roughly comparable to the Probable Maximum Flood in the U.S. The Indians protested that the design flood would place a portion of their lands under water. They wanted the project stopped or at least changed so that it would not compromise their lands. The government countered that the risk of flooding was real, but that it was extremely low; and that it was a small price to pay for the flood control benefits to accrue to the downstream valley.

The dam was built anyway, and the 10,000-year flood is still waiting to happen.

Number 46, March 2006, Level 2


In the middle of the 1980's, I attended an ASCE Hydraulics Division Specialty Conference and found myself listening to a presentation by a well known government engineer who, over the years, had led the development of the dynamic wave. The dynamic wave is the most complete model of unsteady flow in open channels, including all terms in the Saint Venant equations. The latter are also referred to as the equations of continuity and motion.

He described a case study using the dynamic wave. To reinforce his findings, he mentioned that he had calculated the Courant number and had found it to be within acceptable ranges for accuracy.

Knowing that the Courant number can be defined using either kinematic or dynamic wave celerities, and curious to find out which one he had used, I asked him: "Which celerity did you use to define your Courant number?"

He answered, pointedly: "The kinematic celerity."

Therein the dichotomy: The model was dynamic, but the wave behavior was better represented with the Courant number defined in terms of the kinematic celerity. While the model was capable of describing dynamic waves, the flood wave actually being modeled was either a kinematic or diffusion wave. In fact, it has been since confirmed beyond reasonable doubt that most flood waves are actually kinematic or diffusion, and not necessarily dynamic.

Number 47, April 2006, Level 0


In December 1993, I went to Patna, in Bihar, India, on a UNDP consulting assignment at the Water and Land Management Institute (WALMI). After the first day of work, I retired to my assigned quarters at the guest house. Noticing that there was no toilet paper in the bathroom, I requested to the housekeeper that the problem be taken care of as expeditiously as possible.

Two days later my request had not been granted, so I spoke again, this time rather sternly, to the housekeeper. He apologized and said that they had been looking for toilet paper all over town, but could not find it. I thought this was strange, and insisted that they accomodate my request, and they finally complied.

Many years later, while researching the subject of alternative sanitation, I learned that people in this world are classified into wipers and washers. While most people in the West are wipers, most in the East are washers. Only then did my experience in Patna made any sense: I may have been a lone wiper among a sea of washers.

Number 48, May 2006, Level 1


In April of 1996, I went to Blumenau, in the state of Santa Catarina, Brazil. I had been invited by a colleague at the Universidade Regional de Blumenau to participate in a symposium convened to analyze the impact of a proposed flood control scheme on the Itajai river. The concern was that the proposed solution, a conventional hold-by-levee system, would have serious ecological, aesthetic, and other impacts.

The participants came from governments, universities, and the professions, and belonged to a host of natural and social science disciplines, including physics, chemistry, biology, history, anthropology, and education.

The first day of the conference, hoping to break the ice, one of the participants approached me and said: "May I ask what is your field?"

I said: "Civil engineering." She answered, smiling: "Oh, then, you don't know anything."

Number 49, June 2006, Level 2


In December 1993, on my second trip to India to work at the National Institute of Hydrology, I met a colleague who confided to me that he was having trouble modeling a dam-breach failure1 using a well-known model. He mentioned that his results appeared to be off by a factor of two.

I asked him what value of discharge coefficient was he using.

He responded: "Greater than 3, as given in Chow." 2

I said: "You must be using SI units."

To which he responded: "Of course."

Then I said: "That is your problem. You are using a discharge coefficient applicable to U.S. customary units. You should be using the SI equivalent, which is roughly about one-half."

1 Ponce, V. M., A. Taher-Shamsi, and A. V. Shetty. (2003). Dam-breach flood wave propagation using dimensionless parameters.   Journal of Hydraulic Engineering, ASCE, Vol. 129, No. 10, October, 777-782.

2 Chow, V. T. (1959). Open-channel hydraulics. McGraw-Hill, New York.

Number 50, July 2006, Level 1


In the late 1980's, I visited Itaipu Dam on the Parana River, along the border between Brazil and Paraguay, accompanied by my friend Newton Carvalho, hydrologist of ELETROBRAS. During the visit, I noticed intently that the three emergency spillways were gated. Curious about this, I asked my host what were they planning to do in the event of a flood. I added: "What if they were caught by surprise, and the flood came when the gates were closed?"

He looked at me, smiled, and pronounced: "This is the Parana. When we have a flood, it has a way of announcing itself several weeks in advance. It would be unthinkable to have so many people at the damsite caught by surprise!"

I then learned that hydrology has many facets, and that local experience is paramount.

Number 51, August 2006, Level 0


I attended Colorado State University, in Fort Collins, from Fall 1968 to Spring 1970, precisely at the height of the student unrest. I obtained a master's degree in civil engineering. The student movement. which started in Europe in early 1968, reached a peak in the spring of 1970 with the unfortunate Kent State massacre.

While at school, one day I went to the Lory Student Center to a political gathering of international students. My interest was to see just what was going on. I got there early and sat in the back of the room. As I was beginning to relax, a student from a newly independent African country suddenly approached me in a direct and forthright manner, and said: "Where are you from?"

I said: "I am from Peru."

He said: "Oh, we are friends... you are too far away."

It was then that I began to realize that politics and geography can make strange bedfellows.

Number 52, September 2006, Level 0


In December 1993, I took a UNDP consulting assignment at the Indian National Institute of Hydrology Ganges Plains Regional Centre, in Patna, India. On the first night at the Guest House at the Water and Land Management Institute (WALMI) Complex, I found myself unable to eat the potatoes with chili because the dish was too hot for my taste. So, I told the waiter to instruct the cook to cut down the amount of chili for the next day's meal.

The next day, finding the food equally hot, I repeated the admonition to the waiter. On the third day, when the situation didn't change, I decided to take matters into my own hands. I entered the kitchen to explain to the cook that I was going to starve if he insisted on adding too much chili to the potato curry.

Great was my suprise to find the cook preparing the dish, not in a pot as I had expected, but directly on the floor, as is apparently the tradition in Patna. He had piled a mountain of chili and other seasonings and was adding a few potatoes in the middle. I knew then why he could not comply with my order; I should have instructed him to add more potatoes rather than to reduce the amount of chili. Thus, the moral of the story: Different cultures lead to different perspectives.

Number 53, October 2006, Level 1


The difference between hydrology and hydraulics continues to confuse laypersons. Even engineers are often fuzzy about the subject.

Several years ago, at a conference in San Francisco, I met a colleague who was employed with a leading engineering firm. He had gotten his doctorate in hydraulic engineering at a reputable school, and had eventually risen to become section head at his firm. Yet, the title in his business card read: "Chief Hydrologic Engineer." Knowing that he was a good hydraulics man, I could not help but to ask him how much he knew about hydrology.

He responded, smiling: "Not much, but it sells better than hydraulics."

Number 54, November 2006, Level 1


In the 1990s, I attended a conference convened to examine the environmental impact of the Parana-Paraguay waterway on the Pantanal of Mato Grosso. The day before the conference, I had dinner with an engineering colleague. Among other topics, we discussed the subject of free-surface instability, and I came away from the meeting greatly impressed by his grasp of the subject.

Later, we traveled to the city where the conference was to take place. The presentation given by my colleague was highly technical and was delivered in a monotonous voice. When my turn came, I summarized the findings of my work on the hydrologic and environmental impact of the Parana-Paraguay waterway.

The last talk of the day was by a person who spoke in a very clear and engaging style, leaving no doubt that his was the best presentation. Pleasantly surprised, and seeing that his style was quite different from what I had observed earlier, I was curious to find out what he had majored in college. He said: "Communications." That explained it, but I could not help but wonder whether we had again been caught in the age-old predicament between form and substance.

Number 55, December 2006 2006, Level 1


Global warming is one of the most important issues of our time. Several years ago, I wrote a piece on global warming and submitted it to the Opinion section of the San Diego Union-Tribune. The article was rejected and returned to me unpublished.

Disappointed but not undaunted, I sought the advice of a friend, who recommended that I submit the article to the Science section of the paper instead. Here again, the article ran into trouble: It was too straightforward, too simple, to constitute a veritable scientific piece.

By now, the issue of global warming has made it to the mainstream of public discourse. Yet, sorting through the myriad facts and opinions remains a challenge for many people. Nevertheless, the world continues to warm up.1

1 According to NASA, the year 2005 was the warmest year of record.

Number 56, January 2007, Level 0


In the early 1990s, I went to Patna, in Bihar, India, on a consulting assignment at NIH's Ganga Plains Regional Center. The assignment included a visit to the Kosi project, in Eastern Bihar and neighboring Chatra, Nepal. I was accompanied by three staff engineers from the center.

The trip to the Kosi river valley took our party to the town of Birpur, where we settled down for lunch at a place conspicuously labeled "Hotel DeLuxe". To my surprise, I noticed that there were no eating utensils, so I made a point of requesting them. In the meantime, my companions proceeded to eat without the utensils.

Ten minutes later, I again requested the utensils. The person in charge told me very politely that he had sent somebody to look for them. It took another ten minutes for them to produce the utensils; apparently, they had looked for them all over town.

I later realized that there are four ways of eating in this world: (1) using a knife and fork, as in most of the Western world, (2) with chopsticks, as in China and other Asian countries; (3) with a tortilla or flatbread, as in some parts of Mexico, the Arab world, and Africa, (4) with the fingers, as in many parts of India.

Number 57, February 2007, Level 2


Kinematic waves are simplified models of unsteady free-surface flow. Dynamic waves solve the complete equations of continuity and motion, i.e., the St. Venant equations. Based on this fact alone, it would seem that dynamic waves must be altogether better than kinematic waves, yet, experience indicates otherwise. In their classical paper on the theory of kinematic waves, Lighthill and Whitham concluded the following: "Under the conditions appropriate for flood waves... the dynamic waves rapidly become negligible, and it is the kinematic waves, following at a slower speed, which assume the dominant role."

Woolhiser, the developer of the kinematic flow number, recalls how he and Liggett started their joint research at Cornell University in 1964, with the intent of showing that the St. Venant equations without simplification were required for the overland flow problem. Yet, to their surprise, they came to quite different conclusions.1

Theory tells us kinematic waves do not attenuate. We reckon that many flood waves either do not attenuate, or attenuate very little. Therefore, it follows that most flood waves must be kinematic, or, at the very least, diffusion, and not necessarily dynamic.

1 Woolhiser, D. A. 1996. Search for physically based runoff model - A hydrologic El Dorado? ASCE Journal of Hydraulic Engineering, Vol. 122, No. 3, March, 122-129.

Number 58, March 2007, Level 0


In January of 1992, I spent three weeks in Belgaum, Karnataka, India, on a UNDP assignment with the Hard Rock Regional Centre of India's National Institute of Hydrology. That spring, back in the United States, I shared my observations with my undergraduate hydrology students. I told them that I had not seen many fat people in India, certainly not in Belgaum.

The last day of the semester, I decided to do a review of the class in an unconventional way: I would have every student tell me in a nutshell what he/she had learned.

The students sitting in the front rows, usually the better students, had a favorite topic that they particularly remembered, such as the runoff curve number, the unit hydrograph, or the kinematic wave.

As I reached the students sitting in the back of the classroom, one of them said: "I learned that there are no fat people in India." That was certainly not hydrology, but it was a lesson nevertheless.

Number 59, April 2007, Level 2


In the middle 1980s, I was advisor to the ASCE Student Chapter at San Diego State University. The group met weekly and we invited an engineer from the local community to share his/her experiences with our students.

For one of the talks, a well known hydraulic engineer came and spoke to us about a project that he had been involved with. Sometime during the course of the presentation, he said that he had done routing with HEC-2. Being an unsteady flow expert, I know that you cannot route with HEC-2. So, I felt a little uncomfortable having to correct our guest on a matter of concept.

In 1998, HEC-2 was replaced by HEC-RAS, which remained a steady flow model through its versions 1 and 2. However, version 3, released in 2002, has the capability to perform unsteady flow computations. Thus, now we can properly say that we can "route with HEC-RAS," while a similar statement was not correct in regard to HEC-2.

Number 60, May 2007, Level 0


In July of 1997, I attended a horse clinic at Rancho Chahuchu, in Solvang, California. I had a personal invitation from the trainer, and was eager to learn more about horses. The clinic was an all-day event featuring demonstrations on how to deal with problem horses. The attendance was low, about 20 people. As we settled down to our seats, I was surprised to find, among the attendees, a famous Hollywood star who had a keen interest in horses. She was accompanied by a friend, a distinguished lady who was visiting from Europe. I was dressed properly for the occasion, with jeans, a western-style shirt, boots, a belt, and a cowboy hat which I had purchased recently, and we sat down to enjoy the experience.

I did not strike up a conversation with the movie star, but, given the low attendance, everybody's presence was apparent to everyone else. We moved around, trying not to miss any details. At times, I tried out my cowboy stroll, where you walk bowing your legs to show that you are a well seasoned horseman.

Toward the end of the day, our movie star broke the ice and approached me, pointedly, and said: "You are a true Mexican cowboy."

I smiled at the compliment, but could not help to think that she had missed it on all three counts: I was neither true, nor Mexican, nor a cowboy.