Silting-up of High Aswan Dam: Design, investigation and removal of deposits

摘要

The main two tributaries of the Nile, Atbara and the Blue Nile, when in flood carry along, solid matter which has been washed by the rains off the catchment area, and transported by the Nile water. Since 1964, the year of the Nile diversion, and due to the formation of the huge Artificial Lake upstream the dam, the majority of the transported sediments was trapped in the reservoir (Nasser Lake). Nasser Lake, southern Egypt, one of the largest man-made reservoirs in the world, extends over about 350 km in the Egyptian territory and about 150 km inside Sudan. Max. water depth in the dam site area is about 100 m. The total capacity of the lake (162 milliard m~3), is divided into 3 capacities, the dead capacity (31 milliard m~3), the live capacity (90 milliard m~3), and the flood control capacity (41 milliard m~3). Therefore the dead capacity that designed for sedimentation represents a ratio of 1/5 from the total lake capacity and a ratio of 1/3 from the total live storage capacity. The High Dam Lake is a good example as an artificial lake can receipt, average annually 135 million tons of sediments. The average annual rates of sedimentation in the Egyptian borders partly less than that in the Sudanese borders and represents about (15―20%) from the total ratio of the sediments in the lake per year. So, High and Aswan Dams Public Authority (HADA) sent many annual surveying missions starting from 1973 to the sedimentation area for researches and investigations related to that phenomena. Selected stations were fixed. The form of the collected data are on, velocity measurements, suspended sediment samples, hydro-graphical survey, freshly deposited sedimentation samples, and chemical analysis of water samples. It's noticed that the majority of sediment deposition occurs at the tail zone of the reservoir, and movement of sediment deposition will be along the lakebed in the downstream direction towards the Egyptian borders (North). So, HADA begins to establish the pre-feasibility studies about extraction of the sediments, transportation and utilization, with research institutes that belongs to the Ministry of Water Resources and Irrigation in Egypt. Two extraction methods have been suggested and studied to use in the highly sedimentation sectors in the lake inside Egyptian borders. The first method by using mobile dredges. The second one by sacking the sediments using sack pumps.