Abstract:
Periodic surveys of the reservoirs are essential to evaluate the decrease in storage
capacity due to inflow and trapping of sediment. Conventional hydrographic
surveys are time-consuming, labor-intensive and expensive. Satellite remote sensing
techniques provide time and cost-effective approach for the periodical capacity
surveys. Water-spread area estimated from the satellite data at different storage
levels in a hydrologic year provides an important input for the estimation of the
revised capacity of a reservoir. Comparison of previous and revised survey yields
the loss in storage due to sediment deposition. In this study, the Somasila reservoir,
located on the Pennar river that flows through the Nellore district of Andhra Pradesh,
has been chosen for evaluating the capacity loss using Indian Remote Sensed
Satellite image data. Digital satellite data pertaining to the water year 2002 were
acquired for seven different water levels of the reservoir, which ranges from minimum
draw down level (MDDL) to full reservoir level (FRL), and the revised water-spread
areas were extracted. Using trapezoidal formula, the revised volume between the
water level 83.17 m and 94.39 m was computed. Analysis of the results showed
that the loss in capacity is 23.96 M cum during the period 1987 to 2002. If uniform
rate of sedimentation is assumed in 15 years of operation of the reservoir, then the
sedimentation rate is 1.597 M cum per year.
