Hydrologic performance of a transitioned infiltration basin managing highway runoff

Infiltration basins are widely used stormwater control measures (SCMs) for urban stormwater runoff management. However, these SCMs can experience progressive failure to hydrologically perform as originally designed (i.e., primarily infiltration-based runoff control) and the functionality of such failed infiltration basins in managing stormwater runoff is unknown. In this field-scale research study, the hydrologic performance of a failed stormwater infiltration basin was investigated over 3 years. Visual indications of wet pond/wetland like conditions on-site suggested that the infiltration basin had evolved or transitioned to an alternate type of SCM. The transitioned infiltration basin mitigated runoff flows by providing dynamic flow attenuation, total volume and peak flow reductions, and reduced discharge durations. Performance of the transitioned basin can be classified into the following three hydrologic regimes: 100% volume reduction due to complete capture for small storm events; variable volume reductions (4-100%) for most medium and some large storm events depending on the season; and small or no net impact on the largest and extreme events. Although the original infiltration capacity was found to be diminished, detention, retention, and evapotranspiration promoted by the presence of open water and vegetation in the transitioned infiltration basin enabled effective management of runoff.