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Last modified
1/25/2010 6:28:14 PM
Creation date
10/5/2006 12:03:39 AM
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Template:
Floodplain Documents
County
Statewide
Basin
Statewide
Title
Comparison of Flood Hydrologic Estimates in Colorado
Date
5/1/1990
Prepared For
CWCB
Floodplain - Doc Type
Flood Documentation Report
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<br />~11ERATURE SEARCH <br /> <br />Flood f~equency methods can be divided into two catego~ies based on <br /> <br />thei~ unde~lying assumptions. The~e a~e those methods that use ~ainfall data <br /> <br /> <br />and those methods that use st~eam gaging station data in developing <br /> <br /> <br />hyd~og~aphs fo~ the d~ainage basin unde~ conside~ation. The ~ainfall-~unoff <br /> <br /> <br />methods fi~st assume that the~e is a ~elationship between p~ecipitation and <br /> <br /> <br />~unoff, that this ~elationship is desc~ibable, and p~ovides mo~e pe~tinent <br /> <br /> <br />info~mation to make bette~ hyd~og~aphs fo~ the d~ainage a~ea unde~ <br /> <br /> <br />conside~ation. <br />The ~ainfall ~unoff models assume that because of limited data in the <br /> <br />st~eamflow gaging ~eco~ds, the p~ecipitation data fo~ an a~ea can be <br /> <br />inco~po~ated and an imp~oved estimate of flood f~equency flows achieved. <br /> <br /> <br />Statistical models, calculating mean, standa~d deviation and skew fo~ ~ainfall <br /> <br /> <br />data a~e p~epa~ed and a ~ainfall ~unoff ~elation developed fo~ the wate~shed <br /> <br /> <br />based on the climatic conditions p~esent fo~ the basin. Data f~om simila~ <br /> <br /> <br />climatic basins can be inco~po~ated into the models and the enti~e model <br /> <br /> <br />calibrated based on actual runoff data. <br /> <br />There are three basic steps in the rainfall runoff models: the <br />determination of rainfall and resulting excess, conversion of rainfall excess <br />to runoff and computation o.f the hydrograph and routing of the hydrograph. <br />The determination of ~ainfall and ~esulting excess ~equires the assessment of <br />rainfall distribution, depth and areal extent. The rainfall may be determined <br /> <br />from actual rainstorms, t~ansposed rainstorms or may be a design sto~m <br /> <br />~ecommended by regulatory agencies. Precipitation statistics can be obtained <br /> <br /> <br />f~om statistical analysis of ~eco~ded ~ainfall data. This has been completed <br /> <br /> <br />fo~ most a~eas by the National Oceanic and Atmospheric Administration (NOAA). <br /> <br />5 <br />
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