A System for Measuring Total Sediment Yield from Small Watersheds

Design and calibration data are presented from eight sediment measuring installations that have been constructed and tested by the U.S. Forest Service on the Beaver Creek pilot watershed in Arizona. Each installation includes a low dam and basin to trap coarse sediments and a series of splitters that collect a representative portion of the suspended sediment leaving the basin. The first splitter, a Barnes runoff sampler, is a sharp edged slot extending downstream from the dam spillway. With a 12-foot-wide spillway it extracts a theoretical split of 1/600 of the total volume of flow. The second splitter, an inclined slot mounted at the lower end of the Barnes sampler, extracts a theoretical 0.1 sample. This sample, 1/6000, enters an intermediate storage tank that leads from the middle of the stream channel to a final storage tank on the bank. The third splitter is a single slot, extracting a 0.1 sample, mounted below a small rectangular weir in the end of the intermediate tank. The slot, which carries a 1/60,000 sample, enters the final storage tank. Calibration data are presented to characterize sampler performance, and a procedure is outlined for calculating total sediment yield. Errors in estimating total sediment are usually less than 18%.