Remote sensing to assess reservoir sedimentation
Management of water resources in a country often requires construction of dams across rivers for creating storages and regulating flows. This practice is widely prevalent in the country due to variations of the rainfall distribution with respect to time and space. Water flowing into a dam from surface run-off always carries sediments, which settle down on the bed of the reservoir due to variation of flow velocity. Continued deposition of sediments in course of time leads to reduction in the storage capacity of the dam. In some of the reservoirs constructed in earlier periods it is found from capacity surveys that the design assumption of sedimentation rate was quite low causing reduction in the useful life of reservoir (Rajan,1982)Timely assessment of sedimentation in a reservoir is required to determine the useful life of a reservoir and for downstream planning. The conventional method of reservoir capacity survey is laborious, time consuming and costly in comparison to the capacity survey based on remote sensing techniques. The water-spread area of the reservoir reduces with the sedimentation at a given level and this fact is utilized in estimation of reservoir capacity. In remote sensing based reservoir survey, water-spread area at the time of satellite pass is mapped and used to calculate the incremental reservoir capacity between two levels. The use of this technique has been many attempted by many researchers (Mohanty et al, 1986; Vibulshresth et al., 1988; Manavalan, 1991 ; Goel and Jain, 1996; Bryant et al., 1999; Goel et al., 2002; Jain et al, 2002; Bothale et al, 2003; Durbude et al, 2005).
The results obtained by remote sensing technique have been found to be all most similar to that obtained from conventional method. This technique has the limitation of estimating sedimentation below the dead storage levels, as measurement of water spread area below this level using satellite imagery is not possible
Management of water resources in a country often requires construction of dams across rivers for creating storages and regulating flows. This practice is widely prevalent in the country due to variations of the rainfall distribution with respect to time and space. Water flowing into a dam from surface run-off always carries sediments, which settle down on the bed of the reservoir due to variation of flow velocity. Continued deposition of sediments in course of time leads to reduction in the storage capacity of the dam. In some of the reservoirs constructed in earlier periods it is found from capacity surveys that the design assumption of sedimentation rate was quite low causing reduction in the useful life of reservoir (Rajan,1982)Timely assessment of sedimentation in a reservoir is required to determine the useful life of a reservoir and for downstream planning. The conventional method of reservoir capacity survey is laborious, time consuming and costly in comparison to the capacity survey based on remote sensing techniques. The water-spread area of the reservoir reduces with the sedimentation at a given level and this fact is utilized in estimation of reservoir capacity. In remote sensing based reservoir survey, water-spread area at the time of satellite pass is mapped and used to calculate the incremental reservoir capacity between two levels. The use of this technique has been many attempted by many researchers (Mohanty et al, 1986; Vibulshresth et al., 1988; Manavalan, 1991 ; Goel and Jain, 1996; Bryant et al., 1999; Goel et al., 2002; Jain et al, 2002; Bothale et al, 2003; Durbude et al, 2005).
The results obtained by remote sensing technique have been found to be all most similar to that obtained from conventional method. This technique has the limitation of estimating sedimentation below the dead storage levels, as measurement of water spread area below this level using satellite imagery is not possible
The Computations of reservoir capacity at various Elevations have been made using the following prismoidal formula.
V = h/3 (AI+A2+ Sqrt(Al*A2)) ----------------- eq 01.
Where,
V = Reservoir Capacity between two successive elevations hl and h2.
H = Elevation difference (hl - h2)
AI&A2 = Water spread area at elevation hi& h2.
The difference between the original and revised cumulative capacities represents the loss in capacity of the reservoir.
V = h/3 (AI+A2+ Sqrt(Al*A2)) ----------------- eq 01.
Where,
V = Reservoir Capacity between two successive elevations hl and h2.
H = Elevation difference (hl - h2)
AI&A2 = Water spread area at elevation hi& h2.
The difference between the original and revised cumulative capacities represents the loss in capacity of the reservoir.
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