SEDIMENT RATING CURVES FOR A CLEAR-CUT PONDEROSA PINE WATERSHED IN NORTHERN ARIZONA

Data from a 455-acre clearcut ponderosa pine forest watershed in northern Arizona were used to identify relationships between suspended sediment concentration and streamflow discharge. Sediment rating curves were derived by geometric least-squares regression using 515 paired suspended sediment concentration and streamflow discharge measurements obtained from 1974 through 1982. Scatter about the straight line relationship was found when all available pairs of suspended-sediment-concentration and streamflow measurements were used together. The effect of some of the variation was offset by subdividing the data set on the basis of streamflow generation mechanisms. Improved descriptive power also was achieved when separate rising- and falling-stage data sets were considered in deriving the sediment rating curves. Most noticeable was the improvements within low-intensity, frontal rainfall events. There was no significant improvement in descriptive power when separate rising- and falling-stage data sets were considered in deriving the sediment rating curves for snowmelt-runoff events. Higher suspended sediment concentrations were observed during the rising stage of hydrographs than for similar flows on the falling stage, mainly for winter-rainfall with insignificant snow accumulation on the ground and rain-on-snow events.