Laserfiche WebLink
The following program was developed by Greg Levicki <br />to determine the peak flow from small watersheds. <br />~e procedures utilized were taken from the SCS TR-55 Manual. <br />Input drainage area in acres --> <br />150.3 <br />input average curve number --> <br />77 <br />input design precipitation in inches --> <br />2.77 <br />THE SCS TR-55 HETHOD IS, USED TO CALCULATE THE PEAK RUNOFF BY FIRST DETERMINING <br />THE LAG TIME FOR THE WATERSHED AND THE TIME OF CONCENTRATION. <br />THE TC IS THEN RELATED TO A PEAK DISCHARGE IN CSM/INCH OF RUNOFF. <br />lAG TIME IN HOURS=-- <br /> <br />1900 Y".5 <br />WHERE L=HYDRAULIC LENGTH OF WATERSHED IN FEET <br />Y=AVERAGE LAND SLOPE IN $ <br />S IS A CURVE NUMBER PARAMETER GIVEN BY (1000/CN)-10 <br />DOES LAND SLOPE NEED TO BE CALCULATED(Y/N) --> <br />Y <br />RAGE WATERSHED LAND SLOPE IN $ _ .25 Z(LC25+LC50+LC75)/DA <br />HERE Z = ELEVATION DIFFERENCE IN FEET. <br />LC25 LC50 AND LC75 ARE THE LENGTHS OF THE CONTOURS AT 25,50 AND 75 $ OF <br />THE ELEVATION DIFFERENCE. <br />DA = DRAINAGE AREA IN SQUARE FEET. <br />DA = 6547068 SQUARE FEET <br />INPUT ELEVATION DIFFERENCE IN FEET: --> <br />830 <br />INPUT THE SUN OF LC25,LC50 AND LC75 IN FEET: --> <br />7920 <br />AVERAGE LAND SLOPE IN $ 25.18131 PERCENT <br />INPUT HYDRAULIC LENGTH OF WATERSHED IN FEET --> <br />5900 <br />LAG TINS IN HOURS = .2677729 <br />TIME OF CONCENTRATION IN HRS = .2677729 <br />FROM THS SCS TR-55 CHARTS, THS PEAK DISCHARGE IN CSM/INCH = 541.0695 <br />PEAK FLOW 541.0695 CSM/INCH X .2398438 SQUARE MILES X .9148326 <br />INCHES RUNOFF <br />PEAK FLOW 116.2448 CFS <br />r1 <br />lJ <br />y~~~'i <br />