Stormwater to Base Flow? Investigating Surface-Groundwater Interactions for Stormwater Management and Ecosystem Enhancement

Minnehaha Creek is among the most valued natural resources in the Minneapolis, MN metro area. However, frequent drought periods—which have left the creek dry in nine of the last 13 years—impair both the ecological and cultural value of the creek. Rapid rises and falls in streamflow due to stormwater runoff contribute further to flow-related impairments in Minnehaha Creek. We hypothesize that flow in the creek during low-flow periods could be augmented through strategic infiltration and storage of stormwater runoff in the shallow aquifer feeding the creek. Existing hydrogeologic data suggest sustained base flow in Minnehaha Creek is limited due to rapid vertical transmission of recharged groundwater to underlying bedrock aquifers, the vertical travel time of which is on the order of 0.5 years. A streamflow-based systems model applied to infer physical characteristics of the shallow aquifer system indicated that the area of the contributing aquifer system is less than 1% of the creek's watershed area. O-18 and dueterium isotope signatures likewise indicate limited groundwater inputs to the stream system. However, site-level field measurements of groundwater-surface water interactions—including thermal mapping, streambed seepage rate measurements, and monitoring of piezometric heads throughout the creek's riparian area—indicate there may be opportunities to augment base flow if infiltration occurs in select regions. The understanding of surface-groundwater exchanges in Minnehaha Creek gained through field measurements will be used to inform stormwater management efforts as to opportunities to capture stormwater for augmentation of base flow.