Use of a submerged wall in controllin sedimentation at El Nasr canal intake structure

摘要

Right angle canal intakes suffer from sedimentation problems and unequal distribution of flow velocities through the intake openings (vents). Two main methods are used to overcome the sedimentation problem. The first one is periodically dredging the accumulated sediment from the intake while the second is to improve the approach flow conditions in the source canal to bypass and minimise or exclude the entering sediment to the intake of the branch canal. E1 Nasr Canal, one of the irrigation canals in Egypt, which irrigates an area of around 40,000 hectares, takes its water from El Nobaria canal. The canal has a right angle intake, which suffers from sedimentation problem. El Nasr Canal authority used to dredge the accumulated sediment from the downstream channel regularly. This process proved to be very expensive. Therefore, searching for another more sound solution becomes necessary. The present paper aims at finding the optimum solution to enhance the flow pattern and to bypass the sediment at the intake area. A physical model of scale 1:25 was constructed at the Hydraulics Research Institute, Egypt, to test the different alternatives that may be used to solve this problem. The sediment transport was studied by applying the flow velocity measurements in the well-known sediment transport equations. These measurements were also used to check the approach flow pattern in addition to track the surface current by floats and dye. The obtained results have shown that the use of a bottom wall has improved the flow distribution through the intake vents and that the construction of a sediment trap in the main channel upstream of the intake structure prevents the sediment from entering the canal.