Ten-and 1-percent chance exceedance flows from the previous South Carolina flood-frequency investigation and from the current flood-frequency investigation .......29 12. Ten-and 1-percent chance exceedance flows from the previous South Carolina flood-frequency investigation for regression curves relevant to sites in North Carolina and Georgia and from the current flood-frequency investigation ..........29 13. Variance of prediction values for rural streamgaging stations in South Carolina

No abstract

Reliable flood-frequency estimates are an important factor for hydraulic structure design and floodplain management. Annual peak streamflows (hereafter, referred to as peak flows) measured at 965 U.S. Geological Survey (USGS) streamgages were used to compute flood-frequency estimates with annual exceedance probabilities (AEPs) of 50, 20, 10, 4, 2, 1, 0.5, and 0.2 percent. These AEPs correspond to flood-recurrence intervals of 2, 5, 10, 25, 50, 100, 200, and 500 years, respectively. A subset of these streamgages (801) were used to develop equations to predict the flood-frequency estimates (hereafter, referred to as AEP streamflows) at ungaged stream locations. This study was completed by the USGS in cooperation with the Georgia, South Carolina, and North Carolina Departments of Transportation and the North Carolina Department of Crime Control and Public Safety; the results are summarized in this fact sheet. Complete results and the supporting data are presented in the companion scientific investigations report and data release (Feaster and others, 2023; Kolb and others, 2023).

Transportation, as well as John Dorman (retired) and Krzysztof (Chris) Koltyk of the North Carolina Floodplain Mapping Program within the Emergency Management Division of the Department of Crime Control and Public Safety. The foresight and leadership of these individuals in areas of flood-frequency issues, as well as their assistance and support in the completion of this study have improved the understanding of flood-frequency characteristics in Georgia, South Carolina, and North Carolina.The peak-flow data used in the analyses described in this report were measured throughout Georgia, South Carolina, North Carolina, and adjoining States at streamgages operated by the U.S. Geological Survey (USGS) in cooperation with a variety of Federal, State, and local agencies. The authors also acknowledge the dedicated work of the USGS field-office staff in measuring, processing, and storing the peak-flow data necessary for the completion of this study.