Low-flow frequency and flow duration of selected South Carolina streams in the Broad River basin through March 2008

In 2008, the U.S. Geological Survey, in cooperation with the South Carolina Department of Health and Environmental Control, initiated a study to update low-flow statistics at continuous-record streamgaging stations operated by the U.S. Geological Survey in South Carolina. This report presents the low-flow statistics for 23 selected streamgaging stations in the Broad River basin in South Carolina, and includes flow durations of 5-, 10-, 25-, 50-, 75-, 90-, and 95-percent probability of exceedance and the annual minimum 1-, 3-, 7-, 14-, 30-, 60-, and 90-day mean flows with recurrence intervals of 2, 5, 10, 20, 30, and 50 years, depending on the length of record available at the streamgaging station. The low-flow statistics were computed from records available through March 31, 2008. In addition, flow duration information is presented for one streamgaging station 021556525, Pacolet River below Lake Blalock near Cowpens, SC, where recurrence interval computations were not appropriate.
Of the 23 streamgaging stations for which recurrence interval computations were made, 14 had low-flow statistics that were published in previous U.S. Geological Survey reports. A comparison of the low-flow statistics for the minimum mean flow for a 7-consecutive-day period with a 10-year recurrence interval (7Q10) from this study with the most recently published values indicated that 8 of the 14 streamgaging stations had values that were within plus or minus 25 percent of the previous value. Ten of the 14 streamgaging stations had negative percent differences indicating the low-flow statistic had decreased since the previous study, and 4 streamgaging stations had positive percent differences indicating that the low-flow statistic had increased since the previous study. The low-flow statistics are influenced by length of record, hydrologic regime under which the record was collected, techniques used to do the analysis, and other changes, such as urbanization, diversions, and so on, that may have occurred in the basin.