Estimating runoff volumes and flood hydrographs in the Colorado River Basin, southern Utah

Hydrographs of 364 floods from 18 continuous-record gaging sites in the Colorado River basin in southern Utah were used to define a single relation of flood volume to peak discharge; the standard error of estimate of that relation . is 82 percent. Using the same data, a mean dimensionless hydrograph was pre-pared. Synthetic hydrographs may be derived for basins of 5 to 300 square miles (13 to 780 square kilometers) and flood peaks of 1 to 7,000 cubic feet per second
(0.03 to 200 cubic meters per second) using that mean dimensionless hydrograph. Design flood peaks may be estimated from other reports. A method is presented to estimate the reduction in culvert or bridge size resulting from use of storage above the structure. Reduction of structure capacity of 25 percent may be achieved by storing 4 percent of the total flood volume.