African Water Development Report 2006 - United Nations Economic ...

Case Study: Sediment Control andAquatic Weeds in the Nile Basin – IntegratedWatershed ManagementNeededAt present, a limited number of sediment monitoringstations are operating. These are at ElDeim, Wad Alais and Sennar on the Blue Nileand, Gawisi and Hawata on rivers Dinder andRahad, respectively. The high sediment loads ofthe Main Nile, Blue Nile and Atbara rivers havea major influence on the design and operation ofany river control and storage works on these rivers.The sediment which originates in the Ethiopianhighlands is concentrated during the floodseason, which lasts from about July to October.The highest sediment concentrations occur onthe rising flood from about late July to the firstten days of August.It can be noted from table 6.11 that there is ahuge reduction in the original capacities of thereservoir in the Sudan due to sedimentation.This is because rain in the Ethiopian highlandsfalls on bare lands at the beginning of the rainyseason in July, and brings high sedimentationload before the maximum runoff occurs in thearea. The Sennar has lost 66 per cent, the Girba60 per cent and the Roseires 30 per cent. FiguresProtecting Ecosystems in AfricaTable 6.11: Sudan’s Water Storage CapacityDAM Date of commissionRiver Ci Cg Vg Purpose of storageMm 3 Mm 3 Mm 3Sennar 1925 Blue Nile 930 370 560 Irrigation & powerElGirba 1966 Atbra 1300 560 740 Irrigation & powerRoseires 1964 Blue Nile 3354 2227 1127 Irrigation & powerJebelAuilia 1937 White Nile 3500 3500 - Irrigation & powerTOTAL 9084 6657 2427C i= original storage capacity, C g= present storage capacity, V g= Volume of sediment deposits.Source: AWDR National Report; Ahmed,2005Fig. 6.14: Comparison of Rainfall, Discharge and Sediment Yield in the Blue NileFig. 6.14: Comparison of Rainfall, Discharge and Sediment Yield in the Blue NileSource: AWDR National Report, 2005Source: AWDR National Report, 2005153