Study of overland flow with uncertain infiltration using stochastic tools

The effects of spatial and temporal scales in uncertain infiltration processes are investigated within overland flow models. The saturated hydraulic conductivity is considered as the uncertain input parameter. The probabilistic model for this parameter relies on a spatial organization of the watershed into fields. In each field, the saturated hydraulic conductivity is assigned a distribution function and is assumed to be independent of those of the other fields. Four rainfall events are considered to explore various temporal scales leading to different soil saturation levels. Our results show the important impact of soil saturation on overland flow variability and the moderate impact of grass strip localization on runoff variability. Moreover, the most influential input parameter, determined by sensitivity analysis, depends on its localization in the watershed and the duration of the rainfall event. Finally, smaller probabilities of extreme discharges are observed with three grass strips instead of just one located near the field outlet.