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Specifying ecosystem flows for the Savannah River.
Meyer, Judy*,1, Alber, Merryl1, Duncan, William1, Freeman, Mary1, Hale, V. Cody1, Jackson, Rhett1, Jennings, Cecil1, Lutz, Kim2, Palta, Monica1, Richardson, Elizabeth2, Richter, Brian4, Sharitz, Rebecca 3, Sheldon, Joan1, 1 University of Georgia, Athens, GA2 The Nature Conservancy, Savannah, GA4 The Nature Conservancy, Charlottesville, VA3 Savannah River Ecology Laboratory, Aiken, SC
ABSTRACT- To balance human and ecosystem needs for water in a regulated river, it is essential to identify ecosystem flow requirements. We have been engaged in a collaborative project to identify a flow regime for Thurmond Dam that would sustain ecosystems in the Savannah River and its floodplain. Using existing information sources, we characterized the current flow regime and identified flow requirements for various life history stages of representative species and ecosystem components in the shoals, river mainstem, floodplain and estuary. The post-dam hydrologic regime is characterized by much lower flood peaks, 7-day low flows that are higher and more variable in timing, and higher baseflows during the driest months. In addition, channel morphology and floodplain access have been altered by dredging; and water movement and salinity in the estuary have been impacted by harbor deepening. We identified the magnitude and timing of flows needed for egg and larval development, juvenile growth and survival, adult foraging, and spawning migration for fishes such as robust redhorse, Atlantic and shortnose sturgeon, striped bass, and American shad. We documented the flow requirements for seedling recruitment and tree growth and survival for floodplain plant species such bald cypress and water hickory, and outlined the consequences of altered plant communities and flood regime for floodplain birds and mammals. We developed simple conceptual models linking hydrologic changes with their likely ecosystem consequences. The background information and conceptual models guided the development of recommendations on flow regime, which were formulated during a workshop with stakeholders.
Key words: natural flow regime, floodplain, dam, river