This study examines stream flow conditions across North Carolina and makes recommendations for environmental flow guidelines to conserve and protect riverine ecosystems. Monthly stream flow percentile metrics (90th, 75th, 50th, 25th, and 10th percentiles) were compared over two time periods (1955-1980 and 1984-2012) for 63 gages distributed statewide. The results showed that stream flow changes varied spatially by flow magnitude, ecoregion, basin, and temporally by months. The greatest changes occurred with decreases to the 10th, 25th, 50th, and 75th percentiles and the least amount of change was associated with 90th percentile flows. The spring and summer months of February through August experienced the greatest flow reductions, while September, November, and December experienced magnitude increases for the 75th and 90th percentile flows. The Blue Ridge experienced the least amount of change, whereas the Piedmont and Coastal Plain have experienced much greater change. The few gages that did not show significant magnitude decreases to the 10th percentile flow were below major dams on the Neuse, Cape Fear, and Roanoke rivers. These same dammed rivers exhibited increases to the 90th percentile flows. The Tar River Basin, which is free of dams, showed opposite effects, with significant decreases to the 10th percentile flows and minimal changes to the 75th and 90th percentile flows. This study elucidates the importance of establishing different sets of environmental flow criteria that apply statewide across North Carolina. Sustainable environmental flow criteria need to be established that conserve seasonal patterns of flows, sustain low flows (from increases and decreases), and protect headwater and tributary accumulation areas from over-abstraction.
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