Measurement of Sedimentation in Small Reservoirs

Measurements of the volume of sediment in reservoirs provide a basis for determining the extent of sedimentation damages, for periodically correcting the capacity curve to assure more efficient operation, for evaluating the effects of watershed and climatic factors on rates of sediment production form watersheds, and for developing sediment production indexes useful in the design of reservoirs. Sediment volumes may be determined by comparison of original contour maps with maps showing, the present, topography of the sediment surface or by direct measurement of sediment thicknesses. Two methods of survey are used by the Soil Conservation Service (SCS), United States. Department, of Agriculture–the contour method and the range method. Water depths are measured by use of a lead line, sounding pole, or echo sounder. Sediment thicknesses are determined by use of a spud, sounding pole, Or soil auger. The specific weight of sediment is determined in conjunction with reservoir sedimentation surveys. Water capacities and sediment volumes are computed for contour surveys by a modified prismoidal formula and for range surveys by the Dobson prismoidal formula.