Laserfiche WebLink
<br />In the second method, flood frequency estimates are calculated through <br /> <br /> <br />rainfall-runoff modeling. Rainfall and runoff data are collected at a <br /> <br /> <br />site, and the hydrologic response of the basin (in terms of loss rates, <br /> <br /> <br />unit-hydro graph coefficients, and routing) is established. Then, by using <br /> <br /> <br />the modeled basin and long-term rainfall records, long-term runoff records <br /> <br /> <br />and, subsequently, flood-frequency relations can be determined. <br /> <br />Flood-frequency estimates are used for flood-plain management and the <br /> <br /> <br />design of structures in the flood plain. For example, current practices <br /> <br /> <br />for the design of high-hazard dams include protection against severe <br /> <br /> <br />short-term precipitation of approximately 1 to 72 hours in duration, termed <br /> <br /> <br />probable maximum precipitation (PMP). The basic guideline used in estab- <br /> <br /> <br />lishing these criteria for design of dams in Colorado is a publication of <br /> <br /> <br />the U.S. Bureau of Reclamation (1973). The PMP magnitudes are based on the <br /> <br /> <br />hydrometeorological processes that generate extreme floods, Careful <br /> <br /> <br />consideration is given to the meteorology of storms that produce these <br /> <br /> <br />major floods in the United States and include features, such as quantity of <br /> <br /> <br />rainfall, dew-point temperatures, and depth-area-duration (D-A-D) values, <br />produced by these storms, The D-A-D values for different areas then can be <br /> <br /> <br />maximized hypothetically by maximizing the factors affecting rainfall to <br /> <br /> <br />estimate an appropriate PMP value, A recent report establishes revised PMP <br /> <br /> <br />values in the Front Range of Colorado (Miller et aI" 1984). <br /> <br />7 <br /> <br />