Recharge of valley-fill aquifers in the glaciated northeast from upland runoff

Channeled and unchanneled runoff from till-covered bedrock uplands is a major source of recharge to valley-fill aquifers in the glaciated northeastern United States. Streamflow measurements and model simulation of average steady-state conditions indicate that upland runoff accounted for more recharge to two valley-fill aquifers in moderately high topographic-relief settings than did direct infiltration of precipitation. Recharge from upland runoff to a modeled valley-fill aquifer in an area of lower relief was significant but less than that from direct infiltration of precipitation. The amount of upland runoff available for recharging valley-fill aquifers in the glaciated Northeast ranges from about 1.5 to 2.5 cubic feet per second per square mile of drainage area that borders the aquifer. Stream losses from tributaries that drain the uplands commonly range from 0.3 to 1.5 cubic feet per second per 1,000 feet of wetted channel where the tributaries cross alluvial fans in the main valleys. Recharge of valley-fill aquifers from channeled runoff was estimated from measured losses and average runoff rates and was represented in aquifer models as specified fluxes or simulated by head-dependent fluxes with streamflow routing in the model cells that represent the tributary streams. Unchanneled upland runoff, which includes overland and subsurface flow, recharges the valley-fill aquifers at the contact between the aquifer and uplands near the base of the bordering till-covered hillslopes. Recharge from unchanneled runoff was estimated from average runoff rates and the hillslope area that borders the aquifer and was represented as specified fluxes to model-boundary cells along the valley walls.