FLOOD05157 - Laserfiche WebLink

Home Browse Search

MANUAL FOR ESTIMATING FLOOD CHARACTERISTICS 25 UNGAGED SITES Peak discharges and depths for selected recurrence-interval floods at un- gaged sites on natural-flow streams in Colorado can be computed by one of the following procedures, depending on the location of the basin and the elevation of the basin divide. If the basin I ies entirely In a single region, then Procedure I is used. If the basin I ies partly in the Mountain Region and partly in one of the other regions, then Procedure 2 'is used, ProcedW"e 1.--Computation of flood characteristics of streams which lie entirely in one flood-characteristic region. I. Identify the flood region of the drainage basin on figure 2 and select the appropriate equations for the basin from tables I through 4. 2. Compute the required basin and cl imatlc parameters using the defini- tions and instructions given on pages 5 and 6. 3. Solve the equations for the desired flood characteristics. Figures 3 to 10 provide graphical solutions for 100-year flood characteristics. Examples 3 to 6 illustrate the use of the equations and graphs contained in this report. Examp I e 3, --PZains Region Flood discharges and depths for the 10-, 50-, 100-, and 500-year recur- rence-interval floods are required at secondary road crossing of Hay Gulch, 11.6 mi east of Parker (lat 39030'46", long 104032'32", NE~ sec. 22, T. 6 S., R. 64 W.). The basin is shown on U,S. Geological Survey 7~-mrnute topographic maps (scale = I :24,000) as follows: Watkins SE quadrangle Cabin Gulch quadrangle. Using figure 2 and the topographic maps, Hay Gulch lies in the Plains Region and the basin divide is less than 7,500 ft in elevation, The equations for flood discharges and depths for the Plains Region are listed in table 1. The equations require that the following basin pal-ameters be computed: A =drainage area, in square miles, SB=basin slope, in feet per mile, and SS=streambed slope, in feet per mile.