Sediment transport characteristics in cannal irrigation district

Abstract: 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. In this paper, the transport characteristics of the suspended sediment in the irrigation canals in the irrigation system are mainly studied. Based on the field data sampled in Jinghuiqu irrigation district during the summer and autumn irrigation period in 2013, the temporal and spatial variation laws of sediment concentration and gradation of the suspended load will be researched and the transport characteristics of the suspended load of different size will be described quantitatively 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. The laser particle size analyzer is used to measure the particle size of the sediment sample. The vertical distribution of sediment concentration of the total load and sediment particles with different size are further analyzed. It shows that the vertical distribution of sediment concentration of the total load basically obeys Rouse formula and the Z value ranges 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 shows certain randomness. Meanwhile, the variation laws of vertical distribution of sediment concentration in sedimentation condition have been verified. 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 0.05mm. 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. So sedimentation in irrigation canals is mainly caused by coarse particles. Besides, the movement laws of sediment laden flow and the transport characteristics of the suspended sediment of different size near canal nodes in irrigation canal system are very complicated, and the content ought to be further researched. Muddy water sampling and flow measuring work in Jinghuiqu irrigation district will be carried out sequentially, and the transport characteristics of the suspended sediment in different scouring-deposition process in irrigation canal system will be further studied.