Citation Speech by Alf-Goran Dahlberg,
Chairman of the Nomination Committee
at the
Stockholm City Hall, 13 August 1998
Groundwater is an essential resource for mankind, not only for drinking water supply, but also for the sustainability of many natural ecosystems. As population pressures have increased, so groundwater has become increasingly subject to pollution, for example from accidental discharge of industrial contaminants, from widespread application of fertilizers and pesticides and from poorly managed waste repositories. Groundwater systems are particularly vulnerable to contamination given their long residence time and their protection is hindered by the problems of describing contaminant transport processes in a subsurface medium which is difficult to characterise and to observe. Nevertheless, their protection is vital to sustain human needs and ecosystems.
The conventional approach in groundwater hydrodynamics is borrowed from fluid mechanics, where media are treated as homogenous, either globally or locally. However, as anyone who has looked at the walls of an open ditch can attest, the geologic formations that store and carry the water we need are anything but homogenous. Their properties vary at scales large and small. The general tendency was to hush up about the impact of heterogeneity and to shun issues of scale (e.g.: that a parameter measuring the rate of spreading in a small tube in the laboratory may not describe the rate of spreading of a km-long contaminant plume in the field).
Dr. Dagan tackled these problems head-on, by advancing stochastic approaches that recognise heterogeneity and the inherent uncertainty associated with geological formations. He developed scientific and yet practical methods for evaluating macroscopic or effective parameters of heterogeneous media. In particular, in the study of solute transport in heterogeneous media, he advanced his trademark Lagrangian approach. Although the roots of this method are in classical fluid mechanics, Dr. Dagan adopted it to ground wather problems, complemented it with appropriate approximations and applied it to practical problems. It is important to emphasise that Dr. Dagan has taken this approach much further than anyone thought possible and certainly much further than classic Lagrangian methods in the study of turbulence. Using this theory he has been able to predict large-scale rates of spreading, to mention one of the practical applications. The predictions of the theory have been verified through field observations and through laborious computations.
Dr. Dagan has also recognised that site characterisation is a challenge facing groundwater professionals and he advanced methods for parameter estimation, also known as inverse problems. An example of an inverse problem is the determination of aquifer conductivity from measurements of head pressure at various observation points. Such methods are of tremendous practical significance because the hydrogeologic parameters of natural formations are generally not directly measurable. It is also a pleasure to mention the connection Dr. Dagan has to Sweden and the Royal Institute of Technology (KTH) in Stockholm. This collaboration has helped in the development of an internationally recognised research group in the area of stochastic subsurface hydrology. The ongoing challenging task is related to comprehensive field investigations of transport properties of crystalline rock. These investigations are unique in the world and are expected to contribute significantly to our understanding of pollutant transport in crystalline rocks. Dr. Dagan's work can also be described in keywords and they would be:
Characterisation of aquifers and soil properties
Monitoring of groundwater quality
Predicting the uncertainty related to subsurface pollution and restoration as well as to risk assessment and cost-benefit analysis .
Design criteria for pollution prevention and control measures.Behind the scientist is also a human being. Born in Rumania, where he got his basic engineering background, Professor Dagan emigrated to Israel in 1962, when he was 30 years old, starting the academic career and became 1976 Professor at the Tel Aviv University, and since 1994 as the Raquel and Manuel Klachky Chair in Subsurface Hydrology. When he is not there he will be found as visiting Professor somewhere in the world: University of California at Berkeley, Imperial College in London, Ecoles des Mines in Paris, Princeton University in New Jersey or Delft University in the Netherlands.
In 1996 Dr. Dagan was made Doctor Honoris Causa at Univeristy "Pierre et Marie Curie", Paris-6, a very prestigious appointment.
The letters of support from colleagues in connection with the nomination of Dr. Dagan have one thing in common. They did not only talk about the scientific part but also about the person Gedeon Dagan. I want to give a few citations:
"Professor Dagan is a gentleman and scientist of the highest calibre. He is the model of a humane devoted scientist and engineer".
"He is always willing to explain, to use his quick wit to gain insight and to help others in their work".
"He has a wonderful sense of humor that is one aspect of his charming personality"
Years of abuse and ignorance have resulted in contaminated groundwater throughout a great part of the world, endangering the health and economic development for millions. Society is now in the midst of finding a remedy for those mistakes of the past and developing practices that will prevent damage in the future. Professor Dagan's work gives us the tools and the hope to succeed in this endeavour.
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