The hydrologic outcome of a Low Impact Development (LID) site including superposition with streamflow peaks

Hydrology plays a key role in mitigating environmental impacts with Stormwater Management (SWM). Site-level Low Impact Development (LID) is a promising approach but impeded by a lack of experience, performance metrics and comprehensive analysis. This study investigated the hydrologic performance of a small LID site (0.15 km(2)) including superposition with high flows of the receiving stream by monitoring precipitation, discharge and streamflow for 30 months. The results (73% event capture, 66-87% volume reduction, 39 L/ha/s peak discharge, 4.5% streamflow amplification) implied that site-level LID provides an alternative to conventional SWM even for unfavourable conditions. Weak performance related to underground storage, antecedent conditions, storm characteristics and freezing periods occurred seasonally; and a minimum storm capture volume could not be observed, but a maximum retention capacity. Future LID site designs should consider these characteristics and limitations, together with a differentiated analysis of a set of metrics for deducing environmental implications.