Predicting the Hydraulic and Morphological Conse- quences of River Rehabilitation

Decisions about flood protection and river rehabilitation require prediction of the consequences of each possible management alternative. To provide such predictions, an integrative model is required that represents the cause-effect relations between revitalisation measures and morphologic, hydraulic and ecological consequences. This paper describes the hydraulics submodel of such an integrative model. This submodel is subdivided into four modules predicting channel morphology, gravel transport, velocity distribution, and riverbed clogging. The channel morphology module predicts natural channel form based on a simple regression model of its dependence on easily available influence factors (valley slope, annual discharge, and median gravel size). Morphology predictions are then corrected by considering width constraints. The gravel transport module tests whether sufficient gravel is available for the development of gravel bar features or if a straight, incising river will result. A parameter describing the spatial velocity distribution is again estimated with a simple regression on relevant influence factors. Finally, estimates of the extent and severity of bed clogging are based on a model estimating the retention of fine particles carried by water infiltrating the gravel bed. This estimate is currently very uncertain as it depends on a number of uncertain input parameters. A preliminary application of the hydraulics submodel to a reach of the Thur River in Switzerland demonstrates its utility for predicting important consequences of river channel widening. The full integrative model will be used, together with quantitative assessments of stakeholder preferences, for decision support concerning revitalisation alternatives.