CS(AR)-18/99-2000 : Reservoir sedimentation study of Bargi dam using satellite data

Abstract

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 process going on in a reservoir, remedial measures can be undertaken well in advance and reservoir operation schedule can be planned for optimum utilisation of water.

With the deposition of sediments in the reservoir, the waterspread area at an elevation keeps on decreasing. Using the remote sensing techniques, the revised waterspread area can be determined for different reservoir levels and the revised elevation-capacity curves can be prepared. By comparing the original and the revised elevation-capacity curves, the amount of capacity lost to sedimentation can be assessed. Further, for the different reservoir elevations, revised contours can be obtained from the periphery of the waterspread.

In the present study, the revised capacity was assessed in the Bargi reservoir in the Narmada basin. This reservoir was first impounded in the year 1989. The post-monsoon period of the year 1996-97 was chosen for analysis. The remote sensing data of IRS-1C satellite and L1SS-III sensor were acquired for nine different dates and the revised water spread areas have been extracted. The original elevation-area-capacity curves and the reservoir levels on the nine dates of pass of satellite were obtained from the dam authorities. Using the trapezoidal formula, the revised capacity in between the maximum (421.45 m) and minimum (406.00 m) observed levels was obtained. The results of the study demonstrate that the available capacity in the zone of study (406.00 m to 421.45 m) has reduced by 26.67 M Cum from the original capacity (2585.56 M Cum). The sedimentation rate in the zone of study comes out to be 0.023 ha-m/Sq. km/year. As per the CWC report of Bargi project sedimentation, the total sedimentation in the entire reservoir for this period was estimated at 85.74 M Cum. The height of the zone of study is about one third of the height of the dam from bed level to the FRL. This reservoir has significant tail portion as compared to its main body.

From the waterspread areas obtained using remote sensing analysis, the revised contours were derived and plotted. The procedure for deriving the continuous waterspread areas from the remote sensing image was also automatized to a considerable extent.