Quantifying Runoff Reduction When the Fate of Infiltrated Stormwater is Unknown

Abstract Submission: Due to increasing precipitation frequency and intensity, green infrastructure stormwater control measures (GI SCMs) have become one of the preferred methods for managing the impacts of wet weather. GI SCMs like biofilters, bioretention, and bioinfiltration are desirable because they are reported to improve water quality, reduce flooding by infiltration, and contribute positively to community goals. As precipitation patterns are changing, a focus on managing runoff by infiltration has emerged via a desire to mimic the natural hydrology of undeveloped land in urban settings. In such settings, space is a limiting factor for stormwater management and proprietary systems like high rate biofiltration devices have been used to integrate GI components where it would commonly be challenging to do so. However, in an urbanized environment, the fate of infiltrated water is often unknown. This presentation will include a review of data collected for a multi-year monitoring study of runoff reduction by a high rate biofiltration practice, in which the fate of the infiltrated water was unknown. While infiltration is generally assumed to occur locally around a GI SCM and recharge the groundwater, recent studies suggest that macro pores around sub-surface infrastructure like storm sewer pipes may provide potential flow paths for infiltrated water. These pathways, termed “urban karst,” can divert infiltrated water away from the catchment area and impact the capacity for runoff reduction. A discussion on the quantification of runoff reduction when the fate of infiltrated stormwater is unknown and recommendations for future monitoring of GI SCMs will also be presented.

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