MEASURING DEPOSED SEDIMENT IN SMALL RESERVOIRS, CASE STUDY: GRADOCE RESERVOIR

Abstract

Reservoir sedimentation is a serious consequence of soil erosion with large environmental and economic implications. On the other hand, reservoir sedimentation also provides valuable information on erosion intensity and sediment transport within a drainage basin. A reservoir can be considered as a large scale experiment, as the outlet of a giant erosion plot. With the application of the global navigation satellite system (GNSS), the bathymetric measurements of the sediment in the reservoirs became much easier. The measurements done with GNSS supported echosounder are completed much faster with considerable accuracy. Because the time needed for the measurements is much shorter then besides the measurements of the established profiles also some additional measurements can be done. Namely this new method gives the opportunity for total measurement of the reservoirs on profiles and contour measurement. The case study was done on the reservoir “Gradče” which is a small reservoir with total storage of 1.8 106 m3.The reservoir siltation was measured twice (1984 and 1991) while the latest measurement was done in 2013 with echo-sounder with GPS support. Then the total deposited sediment was calculated and the deposition rates were calculated. It was concluded that until 1984 the deposition rate was 2.5 time higher than the later period (1984-2013).The used measuring method, combination of contour and cross-profile measurement, showed promising results.