Hierarchical modelling of the environmental impacts of river impoundment based on a GIS

The modelling of water management scenarios and their impacts on the environment has to dale been undertaken using separate models and often by different organizations. The building and operation of a dam induces a chain of interlinked responses in the environment and to capture this in an impact assessment a more integrated approach to modelling is needed. The mixed spatial and temporal characteristics of the different variables mean that using a single model development environment is difficult. This paper shows how an integrated, hierarchically structured set of model components may be developed using an object-oriented modelling language linked with a geographical information system (GIS). This supports the representation of the process dynamics and the spatial complexity of the riverine environment. The method was applied to the Roadford Dam project on the River Wolf in south-west England. Water resource and water quality model components were developed in the object-oriented language and simulations were run for release regimes during the filling and operation of the dam for the years 1976, 1978, 1986 and 1989, which represent respectively drought, normal, wet and dry conditions. The results, when compared with base-case conditions, showed the changes to the discharge, temperature, and chloride and nitrate-N ion values. The resulting flow values were an input to the third model component, that of the biotic system. These data were combined in a GIS with information on channel form and substrate, and known spawning and breeding sites of the Atlantic salmon (Salmo salar). Overlay analysis was used to determine the suitability of the new conditions for the species. Copyright (C) 2000 John Wiley & Sons, Ltd.