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Evaluation of functions of a check dam in consideration of characteristics of heterogeneous sediment transport and abrasion of sediment

考虑非均质泥沙输送和泥沙磨损特性的淤地坝功能评价

基本信息

批准号：
02660152
负责人：
MAITA Hideji
金额：
$ 1.47万
依托单位：
University of Tsukuba
依托单位国家：
日本
项目类别：
Grant-in-Aid for General Scientific Research (C)
财政年份：
1990
资助国家：
日本
起止时间：
1990 至 1991
项目状态：
已结题

项目摘要

In the field we carried out the surveying of ricer bed profiles and cross sections in the observed reach which extends about lkm which bas a gradient of 6 degrees, when the floods caused the river bed fluctuation of between 1979 and 1991. Over the period 1979 to 1987, no modification of the channel of the reach by the check dam had been taken. But in 1988, the check dam which was 13 meters in height was built at the end of the observed reach, after that the influence of the check dam appeared in profiles and cross sections of the reach.As a result of this investigation, we found the following fact. 1)If the check dam existed in the observed reach when enormous volume of sediment supplied from the upper stream, rotational aggradation occurred in the upper reach of the dam, the longitudinal profile extended linearly from the dam crown without being affected by the original channel form and shape, and according as the sediment supply from the upper stream increased, the longitudinal slope … More became steeper. When no sediment supplied from the upper stream by the flood after the large deposition, the deposit of the upper reach of the dam removed to the downstream decreasing its longitudinal slope. 2)lf the check dam did not exist, parallel aggradation occurred in the observed reach when enormous volume of sediment supplied from the upper stream, and in erosional process after the large deposition, the longitudinal profile returned to the former profile rapidly.In the laboratory, we carried out the sediment-feed experiment in a flume 500cm long, 20cm wide and 23cm deep which set the dam of 5cm in height at the end. A beltconveyor 150cm long was used for controlling the sediment feed rate into the flume. Two size material of sand(Imm)and gravel(5.3mm)was used In this study. As a result of this experiment, we got the following fact. I)Rotational aggradation occurred in the upper part of the dam. 2)ln the uniform sand or gravel, the higher the sediment feed was. the steeper the longitudinal slope was. 3)The longitudinal slope made by the uniform gravel was roughly twice as large as the slope made by the uniform sand to any sediment feed rate. 4)ln sand and gravel mixtures, the relation between the concentration and the slope was not so simple as in the uniform material. When sand was added into the flume, keeping the feed rate of gravel constant, In spite of the fact that the concentration of the mixtures was increased, the slope decreased. This is due to Increase the mobility of the mixtures. This mobility depends on the proportion of sand to gravel, but it is not in simple proportion to sand. As mentioned above, without the understanding of characteristics of heterogeneous sediment transport, we can not clarify the function of a check dam. Less

在1979-1991年洪水引起河床起伏时，在观测河段进行了河床剖面和断面的野外测量，该河段延伸约1KM，坡度为6度。在1979至1987年间，淤地坝没有对河段的航道进行任何改造。1988年，在观测河段末端修建了一座高13米的淤地坝，此后淤地坝的影响出现在河段的剖面和断面上。1)观测河段存在淤地坝时，上游来沙量大，上游发生旋转淤积，坝顶纵断面呈线性延伸，不受原有河道形态和形态的影响，随着上游来沙量的增加，纵向坡度…更多的地方变得更加陡峭。当大淤积后没有上游洪水提供的泥沙时，大坝上游的泥沙向下游移动，降低了大坝的纵坡。2)在没有淤地坝的情况下，上游来沙量大时，观测河段出现平行淤积，大淤积后的冲刷过程中，纵向剖面迅速恢复到原来的剖面。在实验室，我们在长500 cm、宽20 cm、深23 cm的水槽中进行了输沙试验，最终坝高为5 cm。采用150 cm长的带式输送机控制输沙进水槽的速度。本研究使用了砂(IMM)和砾石(5.3 mm)两种尺寸的材料。作为这个实验的结果，我们得到了以下事实。1)坝体上部发生旋转堆积。(2)在均匀砂砾中，输沙量越大。纵向坡度越陡。3)在任意输沙速率下，均匀砾石形成的纵向坡度约为均匀沙形成的坡度的两倍。4)在砂砾混合料中，浓度与坡度的关系不像在均匀材料中那么简单。在水槽中加入沙子，保持砾石的进料速度不变，尽管混合料的浓度增加，但坡度减小。这是因为增加了混合物的流动性。这种流动性取决于砂石的比例，但并不是简单地与沙子成比例。如上所述，如果不了解非均质输沙的特点，我们就不能明确淤地坝的作用。较少