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Unit Hydrograph Peaking Analysis for Goose Creek Watershed in Virginia: A Case Study

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Technical Report

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U.S. Army Engineer Research and Development Center Vicksburg United States

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Existing U.S. Army Corps of Engineers USACE policy suggests unit hydrograph peaking factor UHPF, the ratio of an observed event unit hydrograph peak to the modeled one for a catchment, ranges between 1.25 and 1.50 to ensure dam safety. It is pertinent to investigate the impact of extreme flood events on the validity of this range through physically based rainfall-runoff models not available during the planning and design of most USACE dams. The UHPF range was analyzed by deploying the Gridded Surface Subsurface Hydrologic Analysis model in the Goose Creek, VA, watershed to develop a peaking factor relationship with excess rainfall for National Oceanic and Atmospheric Administration rainfall depths across various return-period events as well as the National Weather Service probable maximum precipitation event. The effect of statistical uncertainty on UHPF at Goose Creek was determined by applying the 5 and 95 confidence interval precipitation depths to the watershed in addition to the 50 value. This study concluded that a design event with a return period greater than 5-year is required for the unit hydrograph to ensure dam safety. Goose Creek unit hydrograph was designed from 25-year return period rainfall and therefore ensures dam safety given the current UHPF guidance.

Subject Categories:

  • Hydrology, Limnology and Potamology
  • Civil Engineering

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