ESTIMATION OF SEDIMENT YIELD OF RESERVOIR USING CATCHMENT CHARACTERISTICS

Abstract

Storage reservoirs are inevitable, to meet the vagaries of nature and to serve the community. Whenever we think of storage reservoir, immediately we have to think of its attendant evil- silting. 'Rivers can be said to be the mortal enemies of Lakes'. A reservoir is an artificial lake and begins to fill with sediment the moment it is formed and gradually dies from loss of its capacity caused by the deposition of sediment, most of which is transported by the inf lowing water. Reservoir silting may have both long range and short range impact. It may so happen in a project that the rate of silting may be so rapid and its service value received so small as to amortise the cost of development. Therefore, as a part of any economically sound project development, the probable rate of silting needs be forecast with some degree of accuracy. Presently at the planning stage provision is made for silting of reservoir, but due to complex nature of the phenomenon of soil erosion, its transportation and finally deposition in reservoir area, many a times the rate of silting has been observed 2 to 5 times more than the assumed rate of silting. Consequently the dead storage provided is silted up much quicker than anticipated,. and the encroachment of the live storage takes place. This necessitates the realistic assessment of the sediment yield from a catchment based on various climatic, watershed and geological characteristics. (iv) (v) In India systematic and scientific observations of the sedimentation rate in reservoirs were taken during the Second Five Year Plan period and are still continued. These reservoirs are spread over throughout the country and re-present various climatic, watershed and geological character-istics. The various parameters of these reservoirs represen-ting various characteristics have been collected from various publications and have been analysed to yield realistic sedi-ment produced from a catchment and deposited in reservoirs. The resulting sediment yield is compared with the observed one. It is found that it has compared well with a standard error of 26.32/ and high correlation coefficient. The relationship so developed can be used for any type of catchment and - climatic conditions, of course addi-tional data,for some more reservoirs especially for Himalayan rivers may further improve the estimation of sediment yield from catchments.