Dam Submergence Flows: An Environmental Flow Prescription Designed to Aid Migratory Fish Passage

ABSTRACT As part of a holistic ecosystem‐focused set of unified flow prescriptions, natural spring flood events were enhanced with releases from an upstream reservoir on the Cape Fear River in North Carolina (USA) to submerge a series of low‐use, low‐head lock‐and‐dam structures for anadromous fish to move upstream. We termed this novel environmental flow (e‐flow) prescription as dam submergence flows . This approach involved releasing water from an upstream reservoir to temporarily submerge three low‐head dams located 130 to 219 rkm downstream, facilitating fish passage by creating smooth, laminar flow conditions over the low‐head dams. From 2020 to 2023, when traditional fish passage methods were unavailable due to inoperable lock chamber gates, this method was essential for maintaining connectivity to upstream spawning areas. A comparative analysis of time‐lapsed camera images time‐synced to discharge rates from nearby stream gages revealed that low‐head dams were completely submerged at approximately 496 m 3 /s. Flows were designed to enhance the natural pulse magnitude above 496 m 3 /s during low flows and to extend the natural pulse duration during high flow. Dam submergence flows were successful in supplementing and lengthening natural floods to inundate the low‐head dams. Flow manipulation experiments emphasized the potential of adaptive management approaches to reconcile ecological objectives with socio‐economic demands and the importance of tailored e‐flow prescriptions to support fish migration and ecosystem health. Long‐term sustainability requires further research into the potential impacts of low‐head dams on migratory delay, early life stage survival, and juvenile downstream migration. Dam submergence flows were successfully implemented with the goal of enhancing fish passage success and population sustainability in the absence of alternative management strategies.