The study assesses sedimentation rate, water spread area and volume of the Bhakra reservoir in Satluj basin using remote sensing data of IRS-1B satellite and LISS-II sensor data of the years 1988-89 and 1996-97. The original elevation-area capacity curves and the reservoir levels on the eight dates of pass of the satellite were obtained from the Bhakra Beas Management Board, Nangal.
Using the trapezoidal formula, the capacity in between the maximum (513.904 m) and minimum (450.436 m) observed levels was assessed for the year 1996-97. The loss of capacity till 1988-89 was 491.315 mcum and till 1996-97 was 807.354 mcum. These could be attributed to the sediment deposition in the zone of study of reservoir.
The results of the study have been compared with the results of hydrographic survey, which was carried out in the year 1989-90. As per the survey, the estimated capacity of the zone of the study comes out to 4949.237 mcum with an average capacity loss rate of 12.65 mcum per year. This value is appreciably lower than that determined through the remote sensing analysis. The possible reasons for this difference have been discussed.
It is observed that the remote sensing method of determining sedimentation is highly sensitive to interpretation of the water spread area. The study estimates that one percent change in interpretation of the water spread area can result in change in sedimentation volume by about 48 mcum.
Conventional techniques of sediment quantification in reservoir like the hydrographic surveys and inflow-outflow methods are cumbersome, costly and time consuming. With the introduction of remote sensing techniques, it has become very convenient to quantify sedimentation in a reservoir.
With the deposition of sediments in the reservoir, the water spread 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 the reservoir can be determined directly. This information can be used to quantify the rate of reservoir sedimentation.
Satellite remote sensing based survey gives the information of the capacities in water level fluctuation zone (live storage zone) of the reservoir. In the dead zone, the information on capacity could be taken from the most recently concluded hydrographic survey. Hydrographic surveys conducted at longer interval may well complement the remote sensing based sedimentation surveys carried out at shorter intervals.
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