Spatiotemporal Distribution and Critical Hydraulic Condition for Erosion-deposition of Sediment in Channels in Pumping Irrigation District

Abstract

【Objective】 The purpose of this paper is to study erosion-deposition of sediment, its influencing factors, as well as its critical hydraulic condition in channels in pumping irrigation districts. 【Method】 Hydraulic characteristics were tested at different sections during each irrigation even from 2010 to 2012 to analyze the gradation of sediment grains, concentration, source, as well as its spatiotemporal distribution. We calculated sediment carrying capacity at different discharge rates, which was used to determine the relationship between sediment carrying capacity and the measured sediment concentration under current situation and after the channels are improved. 【Result】 ①Sediment deposition in the channels was mainly caused by the bed load with grain sizes >75μm, formed from the suspended load and sediment deposition around the intake after the pump was stopped. ②Sediment deposition appeared at the outlet of the station in the upstream channels at the Dongfuqiao section, and the second summer irrigation caused serious sedimentation. ③Sediment carrying capacity of the current channels under discharge rate less than 30 m3/s was lower than sediment concentration, leading to sediment deposition in the whole channels. ④Combined with channel improvement, increasing the bed slope to 1/7 000 can increase sediment carrying capacity significantly. The non-silting critical discharge rate is 24 m3/s for the main canal under the multi-year average sediment concentration. 【Conclusion】 The critical hydraulic flow for channels scouring and silting balance is 24 m3/s, and it can be used by the authority of irrigation districts for management.

Keywords

• irrigation district
• sedimentation
• erosion-deposition
• sediment carrying capacity
• critical discharge