UM-1/97-98 : Reservoir sedimentation study for Ukai dam using satellite data

Abstract

India is a vast country with high spatial and temporal variability of rainfall. In order to tap the available water resources and to utilise the water in accordance with the requirements, more than 3000 river valley projects have already been constructed in this country. To determine the useful life of a reservoir and to assess the sedimentation rate in a reservoir, it is essential to periodically conduct the surveys. With the correct knowledge of the sedimentation processes going on in a reservoir, remedial measures can be undertaken well in advance and reservoir operation schedule can be planned for optimum utilization of water. Present conventional techniques of sediment quantification in a reservoir, like the hydrographic surveys and inflow-outflow methods, are cumbersome, costly and time consuming. Remote sensing, through its spatial, spectral and temporal attributes, can provide synoptic, repetitive and timely information regarding the revised water spread conditions in a reservoir. With the deposition of sediments in the reservoir, the waterspread area at an elevation keeps on decreasing. By comparing the decrease in the water spread area with time. the sediment distribution and deposition pattern in a reservoir can be determined indirectly. This information can be used to quantify the rate of reservoir sedimentation.

In the present study, the sedimentation rate and volume has been determined in the Ukai reservoir using the remote sensing data. The post-monsoon period of the year 1993-94 was chosen for the analysis. The remote sensing data of IRS-1B satellite and LISS-II sensor was acquired for eight different dates and the revised water spread areas were extracted. The original elevation-area-capacity curves and the reservoir levels on the eight dates of pass of satellite were obtained from the dam authorities. Using the trapezoidal formula, the revised capacity in between the maximum (104.446 m) and minimum (92.196 m) observed levels was obtained. The loss of capacity (324.6 M Cum) was attributed to the sediment deposition in the zone of study of the reservoir. The results of this study have been compared with the results of hydrographic survey which was carried out in the year 1992-93.