陡坡河段变动回水区推移质运动特性的试验研究
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摘要
基于物理模型试验,探讨典型河段变动回水区推移质的运动特性,分析在库水位消落及来流增大过程中,淤积体平面形态及淤积体推进轨迹变化等特性。试验结果表明,由于河段比降较大,水库回水尖灭点上下游呈现不同的流态,从急流变为缓流的过程中,输沙能力会陡然下降。在库水位消落过程中,保持上游来流不变,泥沙淤积体输移的距离大致与水库回水尖灭点前行的距离相当,且下游水位降至875 m时,淤积体在河道湾顶附近被水流切割分成上下两部分,两级淤积体间泥沙颗粒级配差异较为明显,反映出水流的分选作用。在来流增大过程中,当推移质来沙量不变时,保持下游库水位不变,增大上游来流量,推移质淤积体向下游推进的幅度相对较小,表明研究河段变动回水区内的推移质运动受下游回水作用影响较大。对于陡坡性变动回水区,在给定上游来沙总量的前提下,泥沙淤积体前沿的推进幅度主要受到库水位降低的影响,而受上游流量的影响相对较小。
The characteristic motion of the traction load in typical fluctuating backwater area, including the plane conformation, the promotion track of the sedimentation during the drawdown process of the reservoir, and the increasing process of the upstream flow, were studied based on the physical model tests. The results indicated that due to the large specific drop in the reach, the upstream and downstream flow patterns of the reservoir pinch-out point were different, and the sediment transport capacity would drop sharply in the course of the water flow changing from a jet to a slow flow. During the drawdown process of the reservoir, keeping the upstream water at a constant level until sediment transport distance was similar to the advancing distance of reservoir pinch-out point and the downstream level fell to 875 m, the siltation near the top of river bay would be cut into the upper and lower parts separately. The difference of sediment gradation between two grades of silt was more obvious, reflecting the separation effect of water flow. Comparatively, increasing the upstream flow while keeping sediment supply and the downstream level unchanged, the bed-load sediment of the downstream propulsion was relatively small,which showed that the bedload transport in the area of fluctuant backwater was greatly influenced by the backwater action in the lower reaches of the river. Under the premise that the total amount of the upstream sediment was given, the promoting of the frontier sedimentation was mainly affected by the decreasing water level of the reservoir, and the effect by the upstream flow was relatively small.
The characteristic motion of the traction load in typical fluctuating backwater area, including the plane conformation, the promotion track of the sedimentation during the drawdown process of the reservoir, and the increasing process of the upstream flow, were studied based on the physical model tests. The results indicated that due to the large specific drop in the reach, the upstream and downstream flow patterns of the reservoir pinch-out point were different, and the sediment transport capacity would drop sharply in the course of the water flow changing from a jet to a slow flow. During the drawdown process of the reservoir, keeping the upstream water at a constant level until sediment transport distance was similar to the advancing distance of reservoir pinch-out point and the downstream level fell to 875 m, the siltation near the top of river bay would be cut into the upper and lower parts separately. The difference of sediment gradation between two grades of silt was more obvious, reflecting the separation effect of water flow. Comparatively, increasing the upstream flow while keeping sediment supply and the downstream level unchanged, the bed-load sediment of the downstream propulsion was relatively small,which showed that the bedload transport in the area of fluctuant backwater was greatly influenced by the backwater action in the lower reaches of the river. Under the premise that the total amount of the upstream sediment was given, the promoting of the frontier sedimentation was mainly affected by the decreasing water level of the reservoir, and the effect by the upstream flow was relatively small.
引文
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[2]Geng Xu,Mao Jixin,Chen Xujian.Study on scour and armor in the downstream of Three Gorges reservoir[J].Journal of Sediment Research,2017,42(5):19-24.[耿旭,毛继新,陈绪坚.三峡水库下游河道冲刷粗化研究[J].泥沙研究,2017,42(5):19-24.]
[3]Fan Shugang,Zhu Daichen,He Yanjun,et al.Stepped navigation regulation structures design of Hujiatan beach in fluctuating backwater area of the Three Gorges reservoir[J].Port&Waterway Engineering,2016(1):134-138.[樊书刚,朱代臣,何艳军,等.三峡水库变动回水区胡家滩滩段阶梯状整治建筑物设计方案[J].水运工程,2016(1):134-138.]
[4]Liu Qingquan,Li Jiachun.Sedimentation and optimal operation of Three Gorges reservoir in Yangtze River[J].Mechanics in Engineering,2000,22(6):1-10.[刘青泉,李家春.三峡水库的工程泥沙与优化运行[J].力学与实践,2000,22(6):1-10.]
[5]Yin Weiqing,Dai Changjun,Qian Jun.Strategy study on waterway and port regulation in fluctuation backwater area of Three Gorges reservoir[J].Yangtze River,2011,42(23):10-13.[尹维清,戴昌军,钱俊.三峡水库变动回水区航道与港口治理对策研究[J].人民长江,2011,42(23):10-13.]
[6]Shu Anping,Huang Jintang,Ding Junsong.Experimental study on the transformation to the braidedchannel pattern in the fluctuating backwater zoneof the reservoir[J].Journal of Sediment Research,1992(4):54-62.[舒安平,黄金堂,丁君松.水库变动回水区分汊河型转化问题的试验研究[J].泥沙研究,1992(4):54-62.]
[7]Chen Li,Wang Xin,Zhang Jiong,et al.Evolutionprocess of Tunaozi shoal at the fluctuating backwater area of the Three Gorges project[J].Port&Waterway Engineering,2007(1):70-74.[陈立,王鑫,张炯,等.三峡变动回水区典型淤沙浅滩土脑子河段河型变化特点分析[J].水运工程,2007(1):70-74.]
[8]Lin Yunfa,Luo Yuan,Ye Zhixiong,et al.Regularity of recent sedimentation in Danjiangkou reservoir area of mainstream Hanjiang river[J].Journal of Yangtze River Scientific Research Institute,2014,31(7):7-12.[林云发,罗媛,叶志雄,等.丹江口水库汉江干流库区近期淤积规律分析[J].长江科学院院报,2014,31(7):7-12.]
[9]Zhang Houyu,Lin Yunfa,Yang Dean,et al.Deposition analysis on Danjiangkou reservoir area in Han river[J].Journal of Yangtze River Scientific Research Institute,2010,27(9):1-5.[章厚玉,林云发,杨德安,等.丹江口水库汉江干流库区淤积分析[J].长江科学院院报,2010,27(9):1-5.]
[10]Xu Cheng,Chen Li,Tang Rongjie,et al.Fluvial processes of Dagushan braid reach in the Danjiangkou reservoir after construction of reservoirs inthe upstream[J].Journal of Sediment Research,2016(1):19-23.[徐程,陈立,唐荣婕,等.丹江口库区大孤山分汊段冲淤变化及趋势分析[J].泥沙研究,2016(1):19-23.]
[11]Jiang Ling,Li Yitian,Zhang Wei.Research on trend of the Shashi channel evolution in the middle reachof Yangtze River[J].Journal of Sediment Research,2006(3):76-80.[江凌,李义天,张为.长江中游沙市河段演变趋势探析[J].泥沙研究,2006(3):76-80.]
[12]Zhang Wei,Li Yitian,Jiang Ling.Fluvial process change of the typical multi-branched meandering reach in the middown Yangtze River after Three Gorges dam impoundment[J].Journal of Sichuan University:Engineering Science Edition,2008,40(4):20-27.[张为,李义天,江凌.三峡水库蓄水后长江中下游典型分汊浅滩河段演变趋势预测[J].四川大学学报:工程科学版,2008,40(4):20-27.]
[13]Yao Shiming,Zhang Chao,Wang Long,et al.Study on thecharacteristics of flow movement in branching river[J].Journal of Hydroelectric Engineering,2006,25(3):49-52.[姚仕明,张超,王龙,等.分汊河道水流运动特性研究[J].水力发电学报,2006,25(3):49-52.]
[14]Zhao Jinqiong.Analysis of influences on riverpattern change of braided channel in reservoir fluctuated backwater area[J].Yangtze River,2013,44(17):52-55.[赵瑾琼.水库变动回水区分汊河道河型转化影响因素分析[J].人民长江,2013,44(17):52-55.]
[15]Li W,Wang J,Yang S,et al.Determining the existence of the fine sediment flocculation in the Three Gorges Reservoir[J].Journal of Hydraulic Engineering,2015,141(2):05014008.
[16]Beylich A A,Laute K.Sediment sources,spatiotemporal variability and rates of fluvial bedload transport in glacierconnected steep mountain valleys in western Norway(Erdalen and B?dalen drainage basins)[J].Geomorphology,2015,228:552-567.
[17]Jin Zhongwu,Zhang Xiaofeng.Preliminary study on bedload sediment transport rate in the presence of backwater flow[J].Journal of Yangtze River Scientific Research Institute,2014,31(2):1-7.[金中武,张小峰.壅水条件下推移质泥沙输沙率变化规律初步研究[J].长江科学院院报,2014,31(2):1-7.]
[18]Ziegler A D,Sidle R C,Phang V X H,et al.Bedload transport in SE Asian streams-Uncertainties and implications for reservoir management[J].Geomorphology,2014,227:31-48.