| Due to non-uniformity of precipitation distribution, irrigation plays an irreplaceable role in agriculture, and diversion channel is the main form in irrigation district. Water and sediment is always indivisible, so it’s always inevitable to divert water at the same time not to divert sediment into the irrigation system. Based on the field data sampled in Jinghuiqu irrigation district during the summer and autumn irrigation period in 2013, the transport characteristics of the suspended sediment in the irrigation canals in the irrigation system will be mainly researched in this thesis in order to provide basis for sediment treatment and the further research on the theory and technique on regulating the sediment in muddy flow in irrigation channels. The sampling and measurement work have been carried out along a selected typical channel-line from main canal to branch canal to lateral canal in Jinghuiqu irrigation district.Several sediment measuring lines are arranged in each testing station cross-section where muddy water sampling and flow measuring are carried out, and bed material sampling on the canal bottom is carried out respectively before and after muddy water sampling.Based on the measured data of water and sediment, the vertical distribution of sediment concentration of the total load and sediment particles with different size in different irrigation canals have been further analyzed. What’s more, adjustment and variation of erosion and deposition of sediment concentration and the gradation have been studied. Meanwhile, the variation laws of vertical distribution of sediment concentration in sedimentation condition has been verified and analyzed. The program composition with MATLAB language is used to solve steady one-dimensional non-uniform suspended sediment non-equilibrium sediment transport mathematical model and the deposition process is only studied. The computed results and the measured data of flow and sediment of the certain canal in Jinghuiqu irrigation district have been compared. Causes of sediment deposition in irrigation canals has been systematically analyzed so as to provide preliminary sedimentation reduction ideas and countermeasure for Jinghuiqu irrigation district. Based on field data in different canals, the vertical distribution of sediment concentration of the total load basically obeys Rouse formula and the value ranges of Z is from 0.001 to 0.015. But the vertical distribution characteristics of sediment particles with different size are different. The concentration of coarse particles decreases with the increase of relative water depth, while the vertical distribution of fine particles whose diameter is less than 0.001 mm show a certain randomness. In non-equilibrium super-saturation transportation condition, sediment concentration is well-distribution in vertical, and super-saturation degree increases with the increase of relative water depth. The vertical distribution of sediment concentration adjusts in the sedimentation process, and adjustment amplitude of upper water is stronger than lower water. The calculation results of the variation and adjustment of sediment with different grain sizes demonstrate that sediment with different grain sizes have different transport characteristics.Incoming sediment particles in Jinghuiqu irrigation district during the summer and autumn irrigation period are very fine and the upper limit diameter is 0.05 mm. Scouring-deposition variation of each size-group sediment is not completely consistent with the total load, but the coarse particles whose diameter is about larger than 0.015 mm located at the left end of the gradation curve within a certain range obey the same scouring-deposition laws with the total load. It indicates that coarse sediment is sensitive to scouring-deposition process and the adjustment amplitude of scouring-deposition is basically controlled by coarse particles.Causes of sediment deposition in irrigation canals has been systematically analyzed from several aspects such as canal design, actual running, characteristics of incoming flow and sediment of irrigation district, and so on. The results shows that sedimentation in irrigation canals is mainly caused by silting of the coarse particles during the summer and autumn irrigation period. |
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