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Abstract:
Lateral flow L is a major process during flood events, which can represent either a gain for the reach such as surface runoff from hillslopes or water table drainage, or a loss such as overbank flow during extreme floods or infiltration into the aquifer. Despite recent progress in measurements, lateral flow cannot be measured and experiments cannot be carried out in situ due to the difficulty of controlling all exchanges along a river (river – hillslope – aquifer – overbank flow).This work aims at evaluating L and the corresponding solute concentration in a channel using the inverse model of the Diffusive Wave Equation DWE. Three applications are shown. First we realize 62 experimental flood scenarios on a novel experimental channel in the laboratory where the inflow, the outflow and the lateral exchanges are highly controlled, and we validate the hypotheses of the DWE inverse model and its ability to reproduce complex shapes of lateral flow hydrograph and solute concentration dynamics. Second, we apply the methodology on two French karst rivers in order to establish a scheme for surface-subsurface exchange during flood events. Third, application was carried on a physical scale model of the Var river Southern France to model the stage-discharge and concentration-discharge hysteresis relationships during flood events. Results are encouraging to extend this approach to a variety of sites, notably those affected by significant surface-subsurface-overbank flow interaction. The coupled experimental-modelling approach, for water and conservative solutes, opens promising perspectives regarding the evaluation of lateral flow on real channels.
