Reservoir sediment assessment of Wabbale Valley Dam in Nakasongola District, using remote sensing and ARC-GIS software.

Abstract

Sedimentation results in the annual loss of 0.5 to 2.0 percent of world reservoir capacity, which makes it a big threat since it reduces the live and dead storage of the reservoirs. This leads to the reservoir failing to serve its intended purpose of storing the water runoff for community use.

The sedimentation rate of the reservoirs needs to be determined for proper surface water resource management but the traditional methods of assessing reservoir sedimentation are typically timeconsuming, labor-intensive, weather-dependent, and so costly. Reservoir capacity surveys may now be carried out quickly, regularly, and cost-effectively thanks to geospatial technologies like remote sensing and Arc-GIS. The bathymetric field data obtained was used to calculate water surface area and reservoir capacities, resulting in an empirical link between water surface area and reservoir capacity. The accuracy of this geospatial technology improves (volume and area) when employed in conjunction with an empirical relationship between the parameters of the reservoirs like depths and surface areas. This study generated a water surface area-storage capacity equation for the Wabbale reservoir and its sedimentation rate.

Field work and satellite image analysis of Wabbale reservoir were used to build the reservoir capacity empirical equation ( 𝑆𝑡𝑜𝑟𝑎𝑔𝑒 𝑐𝑎𝑝𝑎𝑐𝑖𝑡𝑦 = 1.67𝑥10−10∗ 𝐴𝑟𝑒𝑎3.2593 ). The study's validation process yielded accuracy of 99.52 percent for water surface areas and 98.47 percent for reservoir capacity, respectively. The study concluded that the Wabbale reservoir had lost 324,043 m3 of its capacity for a period of 8 years from 2013 to 2021 due to sedimentation in the reservoir.

Therefore the sedimentation rate of Wabbale reservoir is 40,505.4 m3/year which is an alarming rate so some drastic interventions need to be done to save the live storage of the reservoir and further study can be done on the quality of the water as the community was directly using the water for their domestic needs.