The study attempts to determine the useful life of the Bargi reservoir and assesses the sedimentation rate in it using satellite data. Periodical surveys are essential to provide a correct understanding of the sedimentation process going on in a reservoir, so that remedial measures can be undertaken well in advance and reservoir operation schedule planned for optimum utilization 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 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 watershed.
In the present study, the revised capacity was assessed in the Bargi reservoir of the Narmada basin. The 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 data and LISS-III sensor was acquired for nine different days of pass of the satellite and the revised water spread areas extracted. The original elevation-area-capacity curves and the reservoir levels on these nine days were obtained from the dam authorities.
Using the trapezoidal formula, the revised capacity in between the maximum (421.45m) and minimum (406.00m) observed levels was obtained. The height of the zone of study is about one-third of the height of the dam from bed level to the FRL. The reservoir has a significant tail portion as compared to its main body.
From the waterspread area 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.
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 mcum from the original capacity of 2585.56 mcum. The sedimentation rate in the zone of study comes out to be 0.023 ha-m/sqkm/yr. As per the CWC report on Bargi project sedimentation, the total sedimentation in the entire reservoir for this period was estimated at 85.74 mcum.
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