Estimation of reservoir discharges from Lake Nasser and Roseires Reservoir in the Nile Basin using satellite altimetry and imagery data
Research output: Contribution to journal › Article
This paper presents the feasibility of estimating discharges from RoseiresReservoir (Sudan) for the period from 2002 to 2010 and Aswan High Dam/Lake Nasser(Egypt) for the periods 1999-2002 and 2005-2009 using satellite altimetry and imagerywith limited in situ data. Discharges were computed using the water balance of thereservoirs. Rainfall and evaporation data were obtained from public domain data sources.In situ measurements of inflow and outflow (for validation) were obtained, as well. Theother water balance components, such as the water level and surface area, for derivation ofthe change of storage volume were derived from satellite measurements. Water levels wereobtained from Hydroweb for Roseires Reservoir and Hydroweb and Global Reservoir andLake Monitor (GRLM) for Lake Nasser. Water surface areas were derived from LandsatTM/ETM+ images using the Normalized Difference Water Index (NDWI). The watervolume variations were estimated by integrating the area-level relationship of eachreservoir. For Roseires Reservoir, the water levels from Hydroweb agreed well with in situwater levels (RMSE = 0.92 m; R2 = 0.96). Good agreement with in situ measurements werealso obtained for estimated water volume (RMSE = 23%; R2 = 0.94) and computeddischarge (RMSE = 18%; R2 = 0.98). The accuracy of the computed dischargewas considered acceptable for typical reservoir operation applications. For Lake Nasser,the altimetry water levels also agreed well with in situ levels, both for Hydroweb(RMSE = 0.72 m; R2 = 0.81) and GRLM (RMSE = 0.62 m; R2 = 0.96) data. Similaragreements were also observed for the estimated water volumes (RMSE = 10%-15%).However, the estimated discharge from satellite data agreed poorly with observeddischarge, Hydroweb (RMSE = 70%; R2 = 0.09) and GRLM (RMSE = 139%; R2 = 0.36).The error could be attributed to the high sensitivity of discharge to errors in storage volumebecause of the immense reservoir compared to inflow/outflow series. It may also be relatedto unaccounted spills into the Toshka Depression, overestimation of water inflow anderrors in open water evaporation. Therefore, altimetry water levels and satellite imagerydata can be used as a source of information for monitoring the operation of RoseiresReservoir with a fairly low uncertainty, while the errors of Lake Nasser are too large toallow for the monitoring of its operation.
|Research areas and keywords||
Subject classification (UKÄ) – MANDATORY
|Number of pages||24|
|Publication status||Published - 2014 Jan 1|