Assessment of Sedimentation in Gilgel Gibe 1 Reservoir Project Using Remotely Sensed Data
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Date
2018-02
Authors
Journal Title
Journal ISSN
Volume Title
Publisher
AAU
Abstract
A reservoir is an integral component of a water resources system. Periodic evaluation of the
sediment deposition pattern and assessment of available storage capacity of reservoirs is an
important aspect of water resources management. The conventional techniques of quantification
of sediment deposition in a reservoir, such as hydrographic surveys and the inflow-outflow
methods, are cumbersome, costly and time consuming. Further, prediction of sediment
deposition profiles using empirical and numerical methods requires a large amount of input data
and the results are still not encouraging. There is a need for developing simple methods, which
require less time and are cost effective. Due to sedimentation, the water-spread area of a
reservoir at various elevations keeps on decreasing. Remote sensing, through its spatial, spectral
and temporal attributes, provides synoptic and repetitive information on the water-spread area of
a reservoir. By use of remote sensing data in conjunction with a geographic information system,
and Envi software the temporal change in water-spread area can be analyzed to evaluate the
sediment deposition in a reservoir.
In this study, a remote sensing approach has been attempted for assessment sedimentation in
Gilgel Gibe 1 hydropower Reservoir, the reservoir located on the upper parts of the Gilgel Gibe
catchment. Multi date remote sensing data (Landsat 8) provided the information on the waterspread
area of
the reservoir,
which was
used
for computing
the sedimentation
rate. The
revised
capacity
of
the
reservoir
between
maximum
and minimum
levels
was
computed
using
the
Trapezoidal
formula.
The current capacity of Gebi 1 reservoir estimated using remote sensing techniques becomes
809.216 Mm3. The original capacity during planning was 827.439 Mm3 at the same level, the
loss in reservoir gross capacity due to sediment deposition for a period of 27 years since the
construction of the dam in 1990 to 2017 was determined to be 18.223 Mm3 which translate to
2.2 % gross capacity loss. The specific sediment yield over Gibe 1 was calculated to be 204.147
tones / km2 / year. The result of the sedimentation analysis is typical of medium reservoirs. The
sedimentation results or Gibe 1 reservoir using the remote sensing approach for 2017 are
comparable with the sedimentation results from the 2013 Swat model and hydrological survey
method (during planning and design phase) . The results further confirm the applicability of
remote sensing for sedimentation analysis for medium reservoirs in Gibe 1. Assuming a uniform
sedimentation rate, current trends suggest that Gibe 1 reservoir may be filled up in the next sixty
eight years from 2017, however the useful capacity of the reservoir may be lost in much less
time.
Description
Keywords
inflow-outflow methods, reservoir sedimentation rate, storage capacity; reservoir, remote sensing, hydrographic survey