Effect of input uncertainties upon scenario predictions for the river vecht

Within the restoration plan for the river Vecht, the linked flow-water quality model DUFLOW has been applied to describe the behaviour of heavy metals. The model has been used to predict the effects of a number of scenarios for improvement of water quality. In this paper an analysis of the input uncertainty and the effect upon the resulting uncertainty in the output is presented. Both the influence of parameter uncertainty and the uncertainty in the other input variables as: boundary conditions, loading from point and non-point sources, and initial conditions, has been studied. From reported ranges in literature an estimate of the parameter uncertainty has been made. The uncertainty within the other input variables has been assessed from available data. Through Monte Carlo simulation, using Latin Hypercube sampling the resulting uncertainty in the model predictions has been determined. From the uncertainty analysis it appeared that it was not possible to discriminate between the predicted impacts of some of the scenarios. Both the uncertainty in the parameters and in the loading of the system contributed to the overall model uncertainty, although their relative contribution differed going from south to north in the system.