JOURNAL OF TILE AMERICAN WATER RESOURCES ASSOCIATION VOL. 35, NO.5 AMERICAN WATER RESOURCES ASSOCIATION OCTOBER 1999 A MULTI-TIER APPROACH FOR AGRICULTURAL WATERSHED MANAGEMENT' R. P Rudra, W. T Dickinson, M. J. Abedini, and G. J. Wall2 ABSTRACT: A multi-tier approach for agricultural watershed man- agement has been proposed. The approach involves identification of a watershed management issue/problem, selection or development of simple conceptual model suitable for the exploration of the issue/problem identified and appropriate to the database available, and application of the model th address the identified issue/prob- lem. The procedure is repeated by increasing the complexity in the conceptual model until the identified issue/problem has been addressed satisfactorily. An application of the procedure to an example watershed in southern Ontario conditions is shown. The application example has revealed that for identification of temporal pattern of runoff and sediment loads a simple conceptual model is adequate. For identification of spatial location of the sediment source areas and for the development of a monitoring program for the evaluation of remedial strategies a more complex distributed agricultural watershed model is necessary. (KEY TERMS: nonpoint source pollution; watershed management; erosion; fluvial sediment.) INTRODUCTION The development and selection of effective and eco- nomical agricultural watershed management strate- gies has become vital for the sustainability of soil and water resources. Computer models have become an integral part of this process. They have been used to represent significant processes occurring in agricul- tural watersheds, and to reflect impacts of manage- ment strategies selected for exploration. The thesis of this paper is that even more effective use can be made of models for agricultural watershed management purposes, particularly when the approach includes multi-tier procedure. One such approach is presented, along with an example application. Agricultural watershed management problems are typically addressed in the following manner. A prob- lem is identified; possible remedial strategies are explored and evaluated; and a "best management practice" is selected and implemented. Models have been introduced into this procedure to describe agri- cultural watershed processes related to the problem at hand, and to explore possible impacts of the vari- ous remedial strategies identified for consideration (Adamus and Bergman, 1995; Soranno et at., 1996; Ward, 1995; Knisel, 1980; Baven, 1989; Beasley et al., 1980). The use of models in this way has often been inappropriate because agricultural watershed management problems have often been identified at a regional or large basin scale; the models typically used have been validated for relatively small agricul- tural watersheds; and the management strategies of interest have often been related to field-scale activi- ties. An appropriate approach to agricultural water- shed management must indeed address incongruities associated with scale. The multi-tier approach advocated in this paper involves the following stages: 1. Selection or development of a conceptual model that is suitable for the exploration of the agricultural watershed problem identified and appropriate to the database available. 2. Clarification or redefinition of the identified problem, particularly with respect to time and space dimensions in the agricultural watershed. 3. Identification of plausible management strate- gies and evaluation of their possible impacts. 1Paper No. 98064 of the Journal of the American Water Resources Association. Discussions are open until June 1, 2000. 2Respectively, Professor, Emeritus Professor and Graduate Student, Water Resources Engineering, School of Engineering, University of Guelph, Guelph, Ontario N1G 2W1, Canada; and Research Scientist, Agriculture and Agri-Foods Canada, Guelph, Ontario, Canada (E-Mail/Rudra: rrudra@unguelph.ca). JOURNAL OF THE AMERICAN WATER RESOURCES ASSOCIATION 1159 JAWRA