A study was conducted to determine the low-flow frequency of freshwater flow in the Atlantic Intracoastal Waterway (AICW) near Myrtle Beach, South Carolina and to determine the effects of proposed freshwater withdrawals of 45 cu ft/sec at the location of the saltwater-freshwater interface. Discharges simulated in the AICW for 1982-86 using BRANCH one-dimensional flow model were used to establish a relation of 7-day average flows in the AICW to summed 7-day average flows of four tributary streams. This relation was used with the tributary records for 1954-86 climatic years to generate 7-day minimum flows of the AICW, which were then used to develop a low-flow frequency relation. The relation indicated that the 7-day, 10-year flow of the Atlantic Intracoastal Waterway is 192 ct ft/s. A relation of the mile position of the saltwater-freshwater interface to recorded specific conductances at Vereen 's Marina was established. The 1982-85 period of record of specific conductance was used to simulate interface positions which were then used to establish a relation of 7-day average interface position to 7-day average discharge of the AICW. This relation indicated that the 7-day average interface position would be at mile 355.5 for the 7Q10 and at mile 356.2 if 45 cu ft were withdrawn during the 7Q10. The analysis indicates that the AICW can provide a reliable supply of freshwater at the proposed withdrawal location at mi 363.3 in the vicinity of Myrtle Beach, even during the 7Q10 low-flow conditions. (USGS)
