Donald R. Nielsen

2001 Robert E. Horton Medal Winner

Donald R. Nielsen was awarded the Robert E. Horton Medal at the AGU Spring Meeting Honors Ceremony, which was held May 31, 2001, in Boston, Massachusetts. The medal recognizes outstanding contributions to the geophysical aspects of hydrology.


“The Horton Medal is the highest honor a hydrologist may receive. Today we add another giant, Donald R. Nielsen, to this most impressive list of recipients.

“As Don’s career at the University of California, Davis, parallels my own life, I hereby provide a brief overview to bring into perspective his many achievements. By 1958, as I was a toddler, Don was appointed assistant professor of irrigation. Ten years later, as I struggled to learn algebra, Don was already a full professor of water science, having authored over 65 articles. By 1973, when I entered college, Don served as associate dean of research and his publications exceeded 100 papers. By 1980, when I came to the United States to study hydrology, he had already served as department chair and as director of the Kearney Foundation; and his publications surpassed 140. By 1986, when I met him when joining the faculty at Davis, Don’s exceptional stature had advanced him beyond the highest rank conferred to a professor. Today, as I have the honor to write these words and as I am in the midst of my own academic career, I am no less than humbled by Don’s continued achievements for, even though officially retired from the university, his contributions continue and his publications have exceeded 300. But substance is not measured by numbers alone, as these by themselves may just lead to chaos on one’s career.

“Don’s outstanding contributions to the geophysical aspects of hydrology are many. Particularly noteworthy are his innovative achievements in the understanding of chemical transport through soils and the quantification of spatial variability of subsurface materials. In the early 1960s, Don, together with Jim Biggar, initiated basic research work on solute transport through soils. Via a comprehensive set of controlled laboratory experiments, they studied materials under unsaturated conditions and their observations led to a miscible displacement theory that first used advective-diffusive concepts, in a manner that is now taken for granted in the literature. As research moved to the field scale in the 1970s, Don became interested in the spatial variability of soils and, together with Jim, he carried the first comprehensive study that demonstrated the highly heterogeneous and scale-dependent nature of soil hydraulic properties and solute transport characteristics. Such seminal work established new and lasting directions in subsurface hydrologic research. It unequivocally revealed the relevance of research at the field scale and triggered an active development, even to this day, of probabilistic solute transport models capable of capturing the observed log-normal statistics and able to bridge the scale gap, from the laboratory to the field. But Don Nielsen’s achievements extend beyond these fundamental topics in hydrology and also include fundamental advancements in the study of nitrogen pollution and soil management.

“Via the lectures, courses, and workshops he has given in more than 30 countries around the world, Don has inspired many. As remarked by Art Warrick, ‘He is one of the strongest and most extraordinary mentors I have experienced in my career; this in spite of the fact that he was never a formal instructor or even a member of the faculty where I studied or worked.’ Don’s uncompromising standards, coupled with his unusual passion, propelled him to serve on numerous boards and committees that have shaped the course of hydrology. Within the American Geophysical Union, he served as president of the Hydrology Section and as editor of Water Resources Research. As swift action has followed Don’s words, he has been one of the most eminent flag bearers of hydrology as a science, leading to the promotion and implementation of NRC’s Opportunities in Hydrologic Sciences. And all of these accomplishments have been achieved while raising a family of five with his beloved wife, Joanne.

“For his fundamental and pioneering work in hydrology, combined with his uncanny love for the profession, it is my honor to present the most deserving recipient of the 2001 Horton Medal, Donald R. Nielsen.”

—CARLOS E. PUENTE, University of California, Davis


“Thank you, Carlos, for your kind and most generous words. I am deeply appreciative of being one of those to receive the Horton Medal. Their achievements continue to inspire me. Some of them I knew personally and better than others.

“For example, Walter Langbein nurtured my interest in written scholarship about hydrology. He sparked my initial commitment to the first volume of Water Resources Research in 1965.

“I also acknowledge John Philip. He informed my colleagues at U.C. Davis that I was really not very talented in mathematics. Thanks to him, I made a special effort to improve my mathematical awareness, and eventually, my colleagues approved my tenure, but not on the basis of my mathemetical ability. Pete Eagleson gave me the opportunity to learn from others when he led the development of the NRC book, ‘Opportunities in Hydrologic Sciences.’

“My major professor in soil physics was Don Kirkham–he and his wife Betty stimulated Joanne and me to concentrate on science, education, and on the lives of others. Ignacio Rodrequez-Iturbe taught me to stretch my imagination-to dream while I attempted to explore hydrology and other facets of life. And Wilfried Brutsaert, a student at U.C. Davis where I was a newly-appointed faculty member 40 years ago, helped me recognize the tremendous academic contributions made by students in addition to those expected of faculty members, scientists, and engineers.

“I am grateful to Wallace H. Fuller, who served as my M.S. advisor in soil microbiology at the University of Arizona. Through his advice, I switched from chemistry to microbiology, and eventually to soil physics with Don Kirkham. And after that, on my arrival at U.C. Davis, I was indeed fortunate to meet Jim Biggar–a colleague and friend who contributed as a partner to virtually every study I have made during my career.

“Having started my studies in agricultural sciences, I was challenged and helped by my colleagues in AGU to continue to learn and to explore uncharted avenues of hydrology. I especially thank Steve Burges–he remains my most valued mentor in AGU. I also wish to acknowledge the superb resources and academic environment of the University of California during my career.

“I was always blessed with bright students from many reaches of the world, eager to explore approaches to soil hydrology that I had yet to contemplate. I am indebted to each of them for advancing knowledge in soil hydrology, and now appreciate them as close friends and honored colleagues. Wilfried Brutsaert was correct: students were and continue to be the life of any scientific discipline.

“A very special acknowledgment goes to my wife Joanne, for without her support, I would not be here this evening. She is also the one who writes personal letters each and every day to previous students and colleagues throughout the world.

“Indeed, I am pleased to accept this wonderful medal. For me, it is a tribute for all of my colleagues who contributed their help and knowledge to improve my understanding of the vadose zone.”

—DONALD R. NIELSEN, Davis, Calif.