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Field and flume studies of heterogeneous sediment transport on an upper-flow regime bed

上部流态床上非均质沉积物输送的现场和水槽研究

基本信息

批准号：
62460235
负责人：
TAKAYAMA Shigemi
金额：
$ 2.62万
依托单位：
The University of Tsukuba
依托单位国家：
日本
项目类别：
Grant-in-Aid for General Scientific Research (B)
财政年份：
1987
资助国家：
日本
起止时间：
1987 至 1989
项目状态：
已结题

项目摘要

The Higashi-Gochi is a small torrential grave-bed tributary. The catchment got an intense rainstorm in 1982. A 900-mm- rainfall released abundant sediment. In torrential streams of headwaters regions, deposition or erosion depends mostly on the sediment supply, not on the magnitude of flow discharge. This project describes the 1982 Higashi-Gochi deposits and uses three different flumes to discuss the depositional mechanism of heterogeneous sediment at high aggrading rates and at an extremely high boundary shear stress.Transverse and longitudinal trenchings of one of 1982 terraces schematized the sedimentary structure into two basic units. The lower half was massive, in which boulders, sands, and mud accumulated with few internal structures. In the upper half, a matrix-supported gravel layer and an open-work gravel layer repeated ultimately. Both the thickness and the grain size of each layer became smaller toward the top. Some lenses of cobble gravels, a few grains thickness, also char … More acterized the tipper half.Precise mapping of micro stratigraphy on the terrace surface and many pictures at the study reach that were taken only one day after the rainstorm suggested that the deposits were caused by fluvial processes, never by debris flows as usually expected in those torrents with steep slopes and large sediment supply. A flume experiment which modeled the flow of the Higashi-Gochi successfully created the deposits similar to those of the 1982 deposits. Next three would be critical mechanisms. 1) Where and when does the bed aggrade? : Deposition occurred only when the bed was covered with excess sediment supply or the thalweg that had extremely high concentration of bedload. The flow never covered the entire floor bottom at once, and the thalweg braided and wandered. As the local bed aggraded, the thalweg moved laterally to lower bed surface and thus raised there then moved continually. 2) Grain sorting between coarse and small: Large grains never stop within an intense bedload layer. As the bed aggrades localy, smaller grains thus selectively deposit. Imagine a margin where the thlaweg began to occupy a local bed, large grains that traveled quickly from the upstream bedload layer deposited first, and then covered with smaller grains. 3) Longitudinal time lag for deposition: The lower half sequence of the deposits would be produced at the initiation of sediment supply from the upstream, when bedload tongues gradually filled the stream bed. Less

东高内河是一条小的湍急的墓床支流。1982年，该集水区遭遇了一场暴雨。一场900毫米的降雨释放了大量的沉积物。在源区的急流中，泥沙淤积或侵蚀主要取决于泥沙供给量，而不是流量大小。本项目描述了1982年东高地沉积物，并使用三种不同的水槽来讨论高沉积速率和极高边界剪切应力下非均质沉积物的沉积机制。1982年阶地之一的横向和纵向沟将沉积构造划分为两个基本单元。下半部分是巨大的，里面堆积着巨石、沙子和泥浆，内部结构很少。在上半部分，基质支撑的砾石层和开放式砾石层最终重复出现。每一层的厚度和晶粒尺寸都是越往上越小。一些透镜状的鹅卵石砾石，几粒厚度，也烧焦了……更活跃了一半的倾斜度。阶地表面微地层的精确测绘和研究河段的许多仅在暴雨后一天拍摄的照片表明，这些沉积物是由河流作用引起的，而不是通常认为的在坡度陡峭、沉积物供应充足的激流中由泥石流引起的。一个水槽实验模拟了Higashi-Gochi的流动，成功地创造了与1982年沉积物相似的沉积物。接下来的三个将是关键的机制。床在什么地方、什么时候变质？只有当河床被过量的泥沙供应或极高浓度的床质所覆盖时，沉积才会发生。水流从来没有一次覆盖整个地板底部，而塔韦格则编织在一起，四处游荡。随着局部床层的淤积，塔身向下部床面横向移动，在下部床面抬升后继续移动。2)粗粒分选与小粒分选：大粒在强质层内从不停止。随着河床的局部沉积，较小的颗粒选择性地沉积下来。想象一下，在一个边缘，泥沙开始占据当地的河床，从上游的河床层迅速移动过来的大颗粒首先沉积下来，然后被较小的颗粒覆盖。3)沉积纵向滞后：沉积物的下半层序形成于上游输沙开始时，此时床质舌逐渐填满河床。少