Estimation of Reservoir Sediment by using Satellite Remote Sensing for Legedadi Dam Reservoir
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Date
2021-04
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Addis Ababa University
Abstract
Reservoir sedimentation is the gradual accumulation of inward sediments from upstream catchment that has driven the decrease in useful storage volume of the reservoir. Enumerating the reservoir sedimentation amount is vital for improved water resources management. The conventional methods to estimate sediment deposition in a reservoir, such as hydrographic surveys and the inflow-outflow approaches, are bulky, costly, and time-consuming. Further, forecasting of sediment deposition outlines using empirical and numerical methods needs a large quantity of input data and the outcomes are still not inspiring. It is necessary to develop a precise approaches, which need less time and cost-effective. Because of sediment deposition, the water-spread area of a reservoir at different levels keeps on decreasing.
The Satellite Remote Sensing (SRS) method for estimation of reservoir sediment uses the fact, that the water spread area of reservoir at different elevations keeps on decreasing due to the sediment accumulation takes the area of the water. The remote Sensing technique gives us directly the water spread area of the reservoir at a particular elevation on the date of pass of the satellite. This helps us to determine sedimentation over a specified time. By using remote sensing data in combination with a geographic information system and Envi 5.3 software the chronological variation in the water-spread area can be investigated to assess the sediment deposition in a reservoir. The revised capacity of the reservoir for available satellite image and at fluctuation levels was computed using the Simpsons 1/3 Rule formula.
In this paper, a remote sensing method has been tried to estimate sedimentation in Legedadi Dam Reservoir, the reservoir placed on the upper part of Awash Basin, the outflow is joining Akaki river. Multi-date remote sensing data level 1 Landsat 8 and 7 gives the information on the water spread area of the reservoir, which will be used for calculating the sedimentation amount.
The current (2018/19 GC) live storage capacity of Legedadi reservoir estimated using remote sensing approach is 36.087 Mm3 at an elevation of 2465.16 m.a,m,s,l. According to 1979Gc study result the capacity was 41.610 Mm3 at the same level. The loss in reservoir capacity due to sediment deposition for a period of 39 years since the 1979 hydrographic survey to 2018/19 Gc is determined by deducting the 1979 and 2018/19 GC value it gives 5.523 Mm3 which is 13.27 % capacity loss between 2465.16 and 2460.98 m.a,m,s,l. At the live storage zone, Therefore, the result shows that there is a need to give a serious attention for reservoir sedimentation. To protect the reservoir from sedimentation problem we need to protect the upstream and downstream catchment by means of integrated environmental protection.
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Keywords
hydrographic survey, inflow-outflow methods, remote sensing, reservoir sedimentation amount, storage capacity, water-spread area