Modelling and managing runoff processes in peri-urban area
Résumé
Nowadays, a deeper knowledge of the extreme runoff generation requires more inclusive and interactive understanding of its numerous determining factors. This includes not only a better estimation of meteorological extremes under changing climate conditions, but also a better evaluation of infiltration and saturation excesses, of subsurface return flows, as well as, of human impacts on surface runoff. This communication presents a physically based and spatially distributed numerical model for simulation of the hydrologic interactions between the surface and subsurface flows. Further particularities of this model correspond to: (1) a new methodology for the estimation of the precipitation input; and (2) a new modelling methodology to design Sustainable Urban Drainage Systems (SUDS) in urban and peri-urban areas. The multifractal frequency analyses have been used to evaluate the maximum precipitation rate for several durations with the design return period. This method has the advantage to rely on a few robust exponents that are physically meaningful and can be evaluated on discontinuous and/or low frequency samples. The design of Sustainable Urban Drainage Systems (SUDS) in urban and peri-urban areas with low permeability soils as well as with high groundwater levels can be used to decrease the floods risk in the inundated zones. Our model was particularly oriented towards the retention in ponds and swales, infiltration into the ground and drainage through perforated pipes to manage the storm water runoff. The methodology explicitly takes into account the interactions with the water table, the evolution of the latter with infiltration and the soil profile. Using GIS, we visualise the resulting runoff processes together with the evolution of water table levels for the two case studies: a county contiguous to Paris (France) and in the Panola Area (USA). The obtained results demonstrate the effectiveness of SUDS in urban and peri-urban areas and fluvial retention measures to attenuate floods in small urban catchments. Comparisons with natural catchments with low urban development illustrate the impact of climate change and urbanisation on extreme runoff characteristics.