Estimation of predictive uncertainties in flood wave propagation in a river channel using adjoint sensitivity analysis

This paper applies adjoint sensitivity analysis to flash flood wave propagation in a river channel. A numerical model, based on the St-Venant equations and the corresponding adjoint equations, determines the sensitivities of predicted water levels to uncertainties in key controls such as inflow hydrograph, channel topography, frictional resistance and infiltration rate. Sensitivities are calculated in terms of a measuring function that quantifies water levels greater than certain safe threshold levels along the channel. The adjoint model has been verified by means of an identical twin experiment. The method is applied to a simulated flash flood in a river channel. The sensitivities to key controls are evaluated and ranked and the effects of individual and combined uncertainties on the predicted flood impact are also quantified.