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Relations between total-sediment load and peak discharge for rainstorm runoff on five ephemeral streams in Wyoming

January 1, 1994

Total-sediment loads transported by ephemeral flows are a function of rainstorm energy and peak discharge. Rainstorm energy, estimated by rainfall intensity, is the primary mechanism for soil-particle detachment. Vegetation, soil cohesiveness, and land slope also are related to the amount of sediment detached, but these factors remain nearly constant, except for seasonal or human-induced changes in vegetation. Thus, the largest variability in total-sediment loads is the result of variability in rainstorm energy. The magnitude of the peak discharge in a stream from a runoff-producing rainstorm is a function of the intensity and volume of rainfall. The greater the rainfall intensity for the same volume of rainfall, the larger the peak discharge. Therefore, for each drainage area a relation exists between the total-sediment load for a rainstorm and the peak discharge for the rainstorm, because both are a function of rainstorm energy.

Total-sediment loads for runoff-producing rainstorms were computed from sample data collected at five ephemeral streams in semiarid areas of Wyoming. Regression analyses were used to develop equations relating total-sediment load to the peak discharge. Coefficients of determination ranged from 89 to 97 percent. Average standard errors ranged from 35 to 94 percent. The slopes of the lines defined by the equations were not different at the 95-percent level of significance, but the intercepts were significantly different for the five streams.