Laserfiche WebLink
<br />MANUAL FOR ESTIMATING FLOOD CHARACTERISTICS <br /> <br />39 <br /> <br />P I a ins Reg i on <br /> <br />The Plains Region, comprising almost one-half of the total area of <br />Colorado. consists of the eastern foothills of the Rocky Mountains and the <br />adjoining High Plains to the east (fig. 2). The western edge of the region <br />corresponds to the approximate upper 1 imit of floods resulting from wide- <br />spread, high-intensity rainfall. In the South Platte River basin, the bound- <br />ary corresponds to a line drawn along an elevation of 7,500 ft. The boundary <br />in the Arkansas River basin corresponds to an elevation of 9,000 ft. The <br />transition between the two elevations was made along the Rampart Range west <br />of Palmer Ridge which forms the boundary between the two river basins. The <br />western boundary was based on an interpretation of flood-discharge data for <br />gaging stations in the foothill areas of both basins. <br /> <br />The flood-producing rainfalls occur from April through September each <br />year during which period about two-thirds of the mean annual precipitation <br />falls. Because of the absence of snow accumulat ion, snowmel t floods do not <br />occur on streams which originate in the Plains Region. Streams in general <br />are ephemeral but respond quickly to intense rainfall resulting in short- <br />duration, small-volume floods. <br /> <br />Records for 83 gaging stations were initially used in the regression for <br />Plains streams. Preliminary results indicated that most gaging stations in <br />northeast Colorado and areas to the north and east plotted highly negative on <br />the regression relations. This area, commonly referred to as the Sand Hills, <br />is characterized by numerous permeable closed depressions and discontinuous <br />stream channels. The major difficulty appears to be the inability to ac- <br />curately define the contribllting drainage area of basins within the area. <br />Because of this problem, the gaging stations ir, the Sand Hi lls area were <br />el iminated from later regression trials. The final regression equations for <br />the Plains Region are applicable to the contributing parts of drainage basins <br />within the Sand Hills area. <br /> <br />l <br /> <br />The equations relating flood characteristics to basin parameters and <br />the standard error of estimate for each equation are 1 isted in table 1. The <br />equations for the 100-year flood discharge and depth are depicted graphically <br />in figures 3 and 4, respectively. <br /> <br />1 <br />