PA Aquatic Resource Restoration Conference 2026: Past, Present and Future

More than a hundred thousand milldams were constructed across the northeastern U.S., fundamentally altering the landscape. Sediment trapped and accumulated behind these structures burying pre-settlement Holocene wetlands, like a valley bottom Pompeii. After milldam failure, eroded legacy sediment has become a significant source of pollution in the Chesapeake Watershed. A new restoration paradigm is taking shape through the removal of legacy sediments, allowing original wetland-stream ecosystems to re-emerge. 

Big Spring Run (BSR), located in Lancaster County, Pennsylvania, has served as a national pilot site for implementing and evaluating this restoration approach since 2008. Here, we examine Big Spring Run and test the hypothesis that floodplain wetland restoration via legacy sediment removal will: (1) Reestablish hydrological connectivity by increasing groundwater recharge and expanding floodplain capacity for more frequent overbank flow; (2) Moderate stream temperatures and reduce thermal sensitivity through enhanced hyporheic exchange between surface water and groundwater; (3) Reduce turbidity and improve water clarity by increasing residence time, decreasing flow velocity, and promoting frequent overbank flows that trap sediments on the floodplain; and (4) Enhance nutrient retention and removal by increasing water residence time and exposing organic rich wetland soils that function as biogeochemical hotspots for denitrification.