扬水灌区渠道泥沙冲淤时空分布特性及临界条件

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

【目的】探究镫口扬水灌区总干渠泥沙淤积特性、影响因素及冲淤平衡的渠道边界和临界水力条件。【方法】对2010-2012年各灌水期总干渠不同监测断面进行水力特性测试,分析泥沙颗粒级配、含沙量、泥沙来源、渠道冲淤时空特征。计算不同流量下各监测断面的水流挟沙力,对比现状渠道和渠道整治后水流挟沙力与实测含沙量大小关系。【结果】(1)造成总干渠淤积的泥沙主要为粒径大于75μm的推移质泥沙,泥沙来源包括水中悬移泥沙和停泵后淤积在取水口周围泥沙。(2)泥沙淤积主要发生在总干渠上游泵站出水口-东富桥断面之间,各灌水期中夏灌二水淤积最严重。(3)现状渠道在流量小于30 m^(3)/s时水流挟沙力明显小于含沙量,导致总干渠整体处于淤积状态。(4)增大渠道底坡坡降至1/7 000,结合渠道整治与衬砌,可以显著提高水流挟沙力,总干渠多年平均含沙量下不淤临界流量为24 m^(3)/s。【结论】渠道冲淤平衡的临界流量条件为24 m^(3)/s,灌区可根据冲淤平衡矩阵来指导渠道的防淤管理。

【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】(1)Sediment 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.(2)Sediment deposition appeared at the outlet of the station in the upstream channels at the Dongfuqiao section, and the second summer irrigation caused serious sedimentation.(3)Sediment carrying capacity of the current channels under discharge rate less than 30 m^(3)/s was lower than sediment concentration, leading to sediment deposition in the whole channels.(4)Combined 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 m^(3)/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 m^(3)/s, and it can be used by the authority of irrigation districts for management.