The Role of Gate Operation in Reducing Problems with Cohesive and Non-Cohesive Sediments in Irrigation Canals

Abstract

Sediments cause serious problems in irrigation systems, adversely affecting canal performance, driving up maintenance costs and, in extreme cases, threatening system sustainability. Multiple studies were done on the deposition of non-cohesive sediment and implications for canal design, the use of canal operation in handling sedimentation problems is relatively under-studied, particularly for cohesive sediments. In this manuscript, several scenarios regarding weirs and gate operation were tested, using the Delft3D model, applied to a case study from the Gezira scheme in Sudan. Findings show that weirs play a modest role in sedimentation patterns, where their location influences their effectiveness. On the contrary, gate operation plays a significant role in sedimentation patterns. Reduced gate openings may cause canal blockage while intermittently fully opening and closing of gates can reduce sediment deposition in the canal by 54% even under conditions of heavy sediment load. Proper location of weirs and proper adjusting of the branch canal’s gate can substantially reduce sedimentation problems while ensuring sufficient water delivery to crops. The use of 2D/3D models provides useful insights into spatial and temporal patterns of deposition and erosion but has challenges related to running time imposing a rather coarse modelling resolution to keep running times acceptable.

Challenges and prospects to reduce sedimentation in small-scale irrigation schemes in the Great Rift Valley Basin, Ethiopia

“…Operations and maintenance aspects, particularly operating gates, also were found to affect sediment transport. The current study is consistent with evidence from previous observations (e.g., (Depeweg and Paudel, 2003;Munir, 2011;Osman et al, 2016;Paudel, 2010;Theol et al, 2019b). Arata-Chufa, for example, was designed with two gates at DB 1, where the main canal divides, forming a T-shape.…”

“…To reduce the sedimentation problem, farmers use their indigenous knowledge to avoid withdrawal of water during times of high sediment concentration (beginning of the cropping season) and deflect surface runoff to prevent its entrance into the main canal. This tacit operation of the irrigation scheme by the farmers to reduce sediment deposition load is similar to the suggestion by previous studies (Depeweg and Paudel, 2003;Munir, 2011;Osman et al, 2016;Paudel, 2010;Theol et al, 2019b). However, the principal difference between the suggestion of these studies and that of farmers' practice is that the suggestion of these studies only is helpful to reduce sediment deposition that comes from the river source.…”

“…Beyond design, irrigation scheme O&M is another key factor in determining the extent of sedimentation problems. Inadequate O&M is said to be responsible for more than 50% of sediment deposition in feeder canals (Osman et al, 2017;Theol et al, 2019b). The O&M rules set for an irrigation scheme need to clearly state the required frequency of desilting campaigns to maintain canal transport capacity.…”

Effect of Gate Selection on the Non-Cohesive Sedimentation in Irrigation Schemes

“…From these studies, it is clear that canal operation and the operating method have an effect on sediment transport. Theol et al [8] found that proper location of weirs and proper adjusting of the branch canal's gate can substantially reduce sedimentation problems while ensuring sufficient water delivery to crops.…”

“…The direction of the bedload transport is in first order equal to the direction of the depth-averaged velocity in a 2D simulation and equal to the direction of the velocity at the reference height (a) in a 3D simulation [38]; secondary flow correction is applied in 2D simulations, and adjustments due to bed slope are applied in both 2D and 3D simulations. Running the model in 2D mode is to ensure better representation of the sediment processes and the large scale behavior with an acceptable simulation time period [8]. Running the model in 3D mode (5 layers) provides information about flow and sediment parameters in the vertical direction and gives more details near structures [39].…”