The Influence of Soil Stochastic Heterogeneity and Facility Dimensions on Stormwater Infiltration Facilities Performance

The progressive increase of impervious surfaces induced by urbanization altered significantly the natural hydrological cycle of urban catchments. To face the need of more sustainable and effective solutions for stormwater management and planning, Low Impact Development (LID) practices have been frequently proposed to support existing urban drainage systems. Among LID infrastructures, design and management of stormwater infiltration facilities are still characterised by a high degree of uncertainty. Since the stochastic heterogeneity of the soil may affect significantly their hydraulic performance, it is crucial to understand whether it should be accounted for in the design process. To this aim, numerical experiments under transient variably water saturated conditions were performed. Four infiltration facilities of different bottom length subjected to the same spatial variability of the intrinsic permeability field were considered. Simulations showed that the effects of stochastic heterogeneity on the hydraulic performance are dependent on the dimensions of the facility and on the correlation lengths of the intrinsic permeability field. These effects may potentially undermine the capacity to capture stormwater. To be reduced, the bottom dimensions of the facility should be higher than the horizontal correlation lengths of the intrinsic permeability field. Most strikingly, whether the stochastic heterogeneity is considered or not, the volume infiltrated through the bottom follows an increasing power law with increasing bottom length, while the average infiltration rate at the bottom follows a decaying power law.