A Perspective of the More Recent USLE Development1

 

Mathias J.M. Römkens

 

 

            It is a distinct honor to have been invited to this Historic Landmark Dedication of the USLE and to share with you my limited experiences of the development of the USLE.  Since Don Meyer discussed the early stages of USLE-development, I will naturally emphasize the more recent developments and to reminisce about the person, Walt Wischmeier, who was at the heart of its development.

 

            I was privileged to work with Walt Wischmeier for 5 years while I was stationed on this campus.  I believe that I was the last one to be hired by him.  My tenure at this location was relatively brief because the research team, that Walt so diligently had built up over the years, was suddenly and unexpectantly disbanded for “managerial” reasons.  That is, an Agency-wide policy was implemented at the urging of Congress of housing ARS-people, now at university facilities in vacant federal facilities.  Don Meyer and I were transferred to Oxford, MS, Walt Wischmeier would retire if moved, and George Foster was allowed to stay for the time being to complete his Ph.D. degree.  It is noteworthy that after this move, politics took over.  The Administration of the Purdue University School of Agriculture became very active and through the offices of Senator Birch Bayh, the National Soil Erosion Research Laboratory, an idea that already had been in the planning stages for many years, was established.

 

            But let me first describe the USLE development in the later years of its formulation, at the end of Walt’s professional career and what has happened since.  Without any reservation I can not think of any relationship that has so profoundly impacted soil conservation programs nationwide, yes world wide.

 

            To me, the most profound accomplishment during the early years of the USLE development, as so eloquently described by Don, was the formulation of this simple relationship of six factors that embodied all of the relevant factors influencing soil erosion of this enormously complex system that we call nature.   One needs only to reflect on the tremendously complicated task of having to make sense of the thousands of data points of soil loss collected from all over the USA for a wide variety of land conditions, rainstorms, topography, soils, etc. to fully appreciate what a major feat its development was.

 

            With the completion of AH 282 in 1965, work did not end.  In fact, it expanded in scope.  Instead of exclusive field plot research, which inherently had to be statistical in nature, research in the 1960s began to shift to process oriented work in order to fill the gaps of knowledge for the many situations for which we did not have any information, let alone data.  This shift was facilitated by two new developments. (1) the development of the field-plot rainfall simulator or rainulator by Don Meyer and Don McCune, and (2) model development, a topic that also became part of the erosion research program first by Don Meyer and Walt Wischmeier, later by George Foster and others.  In those days, as we now more fully appreciate, modeling activities were enormously facilitated and in a way, propelled, by the rapidly developing computer technology.  Far more complex situations, involving soil detachment and transport relationships, their interactions, in combination with continuity and momentum equations could now be handled.  Data bases could be simulated and generated.  Soil erosion research of the process type benefited from this development.  Another development that impacted soil erosion research was the increasing public awareness and interest in erosion problems of non-agricultural land such as on construction sites and even on forest land.  With all these developments, it was a foregone conclusion that AH 282 needed to be updated to include newly acquired information.  And so, at the end of his career, in fact immediately following his retirement and at the request of our agency, Walt Wischmeier and with the assistance of Dwight Smith took it upon themselves to do just that.  As a result and in a couple of years time, the updated version, AH 537, was written by them and published in 1978.  At that point in time, almost no natural runoff plots were anymore in existence.  Field data, to the extent collected, were obtained from rainfall simulator research.  Walt had been at the pinnacle of all these developments.  In fact, he not only recognized the need for simulated-rainfall, and process-based erosion research, but also stimulated and guided it.

 

            Here I should stop discussing USLE matters for here is where USLE research as we knew it came to a conclusion.  But let me make a few remarks about what has happened since.  Erosion research did not end with the publication of AH 537 nor did the need to improve our soil erosion prediction capability.  It became more involved.  Besides erosion processes research, modeling processes became a major if not dominant activity.  Although modeling often tends to develop a life of its own, in soil erosion research modeling became through the USLE the quintessential instrument in farm planning and soil erosion control.  Today we are at the verge of completing the second generation of the Revised Universal Soil Loss Equation, the successor to the USLE.  RUSLE, as it is called, is a far more sophisticated and comprehensive soil conservation management tool than USLE developers ever had dreamed about.  It includes many science based routines for predictions, it includes sediment deposition on slopes and it has the potential to include gully erosion and issues related to off-site sediment movement such as TMDL.  I could keep on enumerating the new features that have or are being included in RUSLE, but we do not have time for that in this presentation.

 

            It is only fair and appropriate to point out as well as from personal knowledge and experiences, that the USLE was adopted and adapted by many other countries, including Australia, Indonesia, Malaysia, Thailand, Argentina, Brazil, China and many European nations.  It was seen by many as the most useful tool for guiding soil conservation planning practices.  Efforts were made to adapt the underlying factor relationships to local conditions and many inquiries were made.  This leads me to spend the few remaining minutes of my talk on the central person in USLE-development: Mr. Wischmeier.  While Dwight Smith laid the foundation for the USLE-development, was the ARS soil conservation program manager, and had the broad vision during the early stages of development, Walt Wischmeier was the implementer, did the day-to-day work, gave the USLE structure and physical meaning, and perfected it, based on the data base that nationwide was collected.  He also developed and maintained the indispensable contacts with SCS-personnel, the other pillar on which the success of the USLE rests.  Let me relate to you a few anecdotes about Walt.

 

            In 1978, I was visiting a close friend in Melbourne, Australia, who was working for the Victorian Soil Conservation Authority.  They were highly interested in predictions of soil erosion and conservation programs.  When I mentioned that Mr. Wischmeier had recently retired, a letter of invitation immediately went out to him from this Authority and the New South Wales Soil Conservation Authority and within 3 months Walt, who always was reluctant to travel overseas, was in Australia assisting them in among others calculations of the erosivity factor for Australian conditions.

 

            Another anecdote, which is testimony to the status and respect Walt enjoyed, was an incident in India during a visit of Mr. Edminster, the administrator of ARS at that time.  On one of his travel legs, as I was told, he was approached by a young man who wanted to strike up a conversation in English -- not an unusual phenomenon when you travel in foreign countries.  The discussion lead of course to the question, What Mr. Edminster was doing.  When he indicated that he was the administrator of ARS but that professionally he was an agricultural engineer interested in soil conservation, the man’s face brightened and he asked Mr. Edminster: Do you know Dr. Wischmeier?  When Edminster answered that he knew him very well, the young man was in awe.  Apparently, he never expected to meet someone who personally knew this famous man Wischmeier.  It is noteworthy to indicate that most people who contacted him, assumed that he had a Ph.D. degree.

 

            The esteem Walt enjoyed in the international community is perhaps best illustrated with the incident that occurred at the 10th International Soil Conservation Organization (ISCO) conference that was held here on the Purdue University campus.  Walt, though at first very reluctant, was persuaded by Don Meyer to attend at least part of a plenary session of this conference.  Unbeknownst to the participants, when they became aware of Walt’s presence, the audience stood up and gave him a standing ovation.

 

            These anecdotes illustrate the esteem, respect, and appreciation the international community had for him and what the USLE has meant to the world at large.  To be somewhat more complete in matters of distinctions, Walt received many honors including the induction in the ARS Science Hall of Fame, two USDA Superior Service Awards, the Hugh Hammond Bennett Award from the Soil And Water Conservation Society, etc. etc.  A special erosion conference was held in his honor here at Purdue University in 1976.  To me personally, Walt was the professional father, a man of utmost modesty, always willing to give you advice about erosion and conservation issues and Agency policies and politics.  Now, more than ever I have come to appreciate how fortunate I was to have learned from him and to have been associated with him.

 

            The USLE has had a major impact on soil conservation in this country and the world.  Its impact is still felt and will be felt for many years to come through its derivative, RUSLE.  It is safe and fair to say that the legacies of the USLE, Walt Wischmeier, Dwight D. Smith and all those who were at the beginning of its development and who were involved in perfecting it are here to stay.  They have endured.

 

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            1Presentation given at the Dedication of the American Society of Agricultural Engineers (ASAE) Historic Landmark of Agricultural Engineering for the Universal Soil Loss Equation, Purdue University, West Lafayette, Indiana, April 25, 2003.