Untangling the Factors Governing the Catchment-Scale Impacts of On-Site Stormwater Infiltration in Shallow Groundwater Contexts

Abstract

Urban stormwater management increasingly relies on decentralized infiltration systems to mitigate the adverse effects of soil sealing. At the catchment scale, the hydrological impacts of such practices however remain poorly understood, especially in shallow aquifers settings where interactions between infiltrated volumes, groundwater and underground infrastructures can occur. This study examines the hydrological response of a small shallow groundwater urban area to the implementation of stormwater infiltration, based on numerical modeling. The influence of climate, soil conditions, hydrogeology, urban context, and infiltration strategy is assessed. Results show that the concentration of runoff within infiltration systems causes a large increase of groundwater recharge, often leading to water-table rise. Where initial groundwater depth or low subsurface transmissivity is low, seepage into sewer pipes and underground drainage structures increases and potentially undermines the runoff volume reduction benefits of infiltration systems. Occasionally, an increase in transpiration from green spaces may also occur. For remaining settings, the additional recharge is mainly dissipated by downstream groundwater flow, without generating notable interactions with the surface or underground structures. Overall, this study illustrates the variety of stormwater infiltration outcomes and demonstrates the inability of this strategy, alone, to restore pre-development hydrological conditions.