Green infrastructure and episodic groundwater recharge

The connection between infiltration-focused green infrastructure and groundwater recharge is not straightforward. Water infiltrated through stormwater facilities may be stored in soil moisture, taken up by evapotranspiration, or contribute to recharge and potentially stream base flow. One way to quantify the fate of infiltrated stormwater on a watershed-scale is to use water table fluctuations in wells. We focus on a 1.1 km2 suburban watershed in Clarksburg, Maryland which includes 73 infiltration-focused stormwater facilities. We use the episodic master recession method of analyzing water table fluctuations and perform time series analysis on the hydrographs of six wells to examine how the spatial pattern of recharge and timing vary across the watershed and across storms. We find that the well hydrograph response to storm events varies dramatically over this small watershed. In this fractured rock system, a well close to a series of dry wells had an increase in water table height greater than 1.5 m in response to some storms, whereas deeper wells and those further from green infrastructure had relatively small well hydrograph responses. This work may be used to evaluate the groundwater effects of watershed-scale green infrastructure implementation.