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<br />H!TERMEDIATE REGIOf>lAL FLOOD <br /> <br />The Intermediate Regional Flocd Is one that could occur about once <br />In 100 years on the average, although It may occur In any year. Its <br />magnitude was determined from statistical analysis of streamflow <br />records, characteristic climatic conditions as they relate to snowmelt, <br />and the runoff characteristics of stream basin, taking Into account <br />losses from infi Itratlon and other factors. Due to lack of adequate <br />streamflow and precipitation data for cloudburst runoff from the <br />creeks In the study area, a characteristic convective-type storm Iso- <br />hyetal developed from similar drainaGe areas was transposed to the <br />Rifle, Government, and Hubbard Gulch drainage areas, and the most <br />critical area of contribution and the ralnfali over that area were <br />found. Peak flows thus developed for the Intermediate Regional Flood <br />at selected locations in the study area are shown in Table 4. Synthe- <br />sized stage hydrographs of the Intermediate Regional Flood at various <br />locations in the study area are shown on Plates 2-4. <br /> <br />STANDARD PROJECT FLOOD <br /> <br />Peak flows for the Standard Project Flood on the Colorado River <br />were determined In the same manner as peak flows for the Intermediate <br />Regional Flood. For the purpose of determining peak cloudburst flows <br />for the Standard Project Flood on the creeks In the study area, an <br />Isohyetal pattern for a Standard Project Storm(a) was developed and <br />appl led in the same manner as described for the IntermedIate Regional <br />Flocd. Peak flows thus derived for selected locations on the Colorado <br />River and Rifle, Governmen~ and Hubbard Gulch Creeks are shown in <br />Table 4. <br /> <br />(a) The most severe combination of meteorological conditions reasonably <br />characteristic of the geographical region. excluding extremeZy rare <br />combinations. <br /> <br />20 <br />