Prediction of storm sediment yield from a small watershed.

The R-5 catchment is an experimental plot within the Washita river experimental Watershed. It occupies an area of 0.1 km2 and is located near Chickasha, Oklahoma, in rolling prairie grassland. Precipitation, suspended sediment concentration and discharge records covering the 9-year period were availed for use in this study. The mobilised sediment during a storm was related to excess rainfall depth and the parameters of the model were estimated from observed events. The relationship between the two was found to be approximately linear on a log-log paper. The sediment rating equation was used in power form: C=aQB. The values of the parameters were found to be a=145.01, b=0.05. A conceptual model of the IUSG was developed for sediment graph prediction by routing mobilised sediments through a series of linear reservoirs. The sediment graphs generated by convolution of the IUSG compared reasonably well with the observed ones for the seven verification events. A model for an IUSG based on time-area sediment histogram routed through a single linear reservoir was also developed and applied on R-5 catchment. The IUSG was convolved with mobilised sediment for generation and prediction of sediment graphs. The predicted sediment graphs generally showed close agreement with their observed counterparts. The IUSG model based on the multireservoir cascading concept predicted the sediment graphs more accurately than that based on the time-area sediment histograms routed through a single linear reservoir concept. For the seven verification events the total sediment yield was 137.500 and 114.465 Kilogrammes by IUSG (based on multireservoir cascading concept) and IUSG (based on time area sediment histograms routed through a single linear reservoir concept) methods respectively. The mean sediment yield of the R-5 catchment was found to be approximately 0.158 tonnes/ha/yr. Such a low estimate of the sediment yield signifies the high level of conservation practices prevalent in the catchment and shows that soil erosion due to rainfall is not rampant in this area.