Impact of water withdrawals and releases on the parameters of a bucket-type rainfall-runoff model

Water management practices (dam management, uptakes for irrigation, industry and domestic water supply or water sanitation) can strongly influence river flow at the catchment scale. If water withdrawals and releases are important (for example in the case of a large dam), this influence can strongly impact the performance of bucket-type rainfall-runoff models whose structure do not explicitly consider water management practices. However, the influence of water management can also be compensated by the calibration of parameters, which is difficult to perceive when the model is conceptual, as the performance may not necessarily be negatively affected. This work aims at evaluating the effect of these compensations over the parameters of the GR4J bucket-type rainfall-runoff model over an influenced catchment. To do so, the model was applied in a semi-distributed way over the rainfed Sèvre Nantaise catchment in Western France. For this catchment, we used uptakes, sanitation and reservoir management data estimated at a daily time step, as well as a dense network of daily flow measurement stations. Water management practices were explicitly taken into account in the GR4J model through the airGR and airGRiwrm R packages that allow injecting or removing water from the river depending on water management practices. The model was calibrated on the different flow stations both with and without taking water withdrawals and releases into account. The obtained parameter values were compared in terms of reliability, robustness, plausibility and spatial homogeneity.