ABSTRACT
The first case study is a story of failed efforts to understand and solve one of the oldest environmental problems known to humankind with one of the most promising modern environmental management technologies. Increased interest in nonpoint source (i.e. from geographically diffuse sources) pollution control in the US has revived discussion about the management and regulation of agricultural drainage over the past couple of decades. Adequate drainage is necessary to maintain irrigated agriculture over time. The purpose of drainage management, also known as return flow management, is to ensure adequate leaching of water and salts from the soil. Without drainage agriculture is impossible as soil becomes waterlogged and saline (National Research Council 1989; San Joaquin Valley Drainage Program 1990; US Committee on Irrigation and Drainage 1987). Computerized water quality modelling has played a central part in efforts to solve large-scale agricultural water and salt management problems in the Arkansas River Basin of southern Colorado since the 1970s. The use of models in the design of policy and management intensified in the early 1990s. Computer models can provide a credible scientific basis for the management and regulation of irrigation-induced drainage by formalizing for management purposes the causal relationships believed to be underlying the observed natural and social phenomena.
