Estimating Flood Frequency in Gaged and Ungaged Watersheds
Pruitt, Bruce A.
Nutter, Wade L.
Ainslie, William B.
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Estimation of flood frequency is important in jurisdictional wetlands determination and functional assessment, stream classification and restoration, and in assessing urban and agricultural risk in flood prone areas. For example, in utilizing the hydrogeomorphic approach (HGM) for wetland functional assessment for riverine wetlands, the flood frequency variable is required in seven of the suite of fifteen functions. However, site-specific determination of flood frequency has been difficult, especially in ungaged watersheds. One promising method is development of regional dimensionless rating curves. The curves are derived from stage/discharge and channel geometric relationships associated with gaged watersheds. Once the curves are constructed and calibrated to a specific region, flood frequency and channel geometry can be estimated at any point within ungaged as well as gaged watersheds within that region. This method was employed to calibrate the flood frequency variable in the low gradient, riverine HGM guidebook applicable to Western Kentucky. Flood frequency and discharge were determined at several riverine reference wetlands for the purpose of assessing wetland function throughout the Western Kentucky Coalfield Physiographic Region.