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

东口河是一条小型的湍急的河床支流。1982年这个集水区下了一场大暴雨. 900毫米的降雨释放了大量的泥沙.在源头地区的急流中，淤积或侵蚀主要取决于泥沙的供应，而不是流量的大小。本项目描述了1982年的Higashi-Gochi矿床，并使用三个不同的水槽来讨论高加积速率和极高边界剪切应力下的非均质沉积物的沉积机制。1982年的一个阶地的横向和纵向沟槽将沉积结构示意为两个基本单元。下半部分是巨大的，其中堆积着巨石、沙子和泥土，内部结构很少。在上半部分，基质支持砾石层和开放工作砾石层最终重复。各层的厚度和晶粒尺寸都随着向上逐渐变小。一些卵石砾石的透镜体，几粒厚度，也烧焦了 关于我们 阶地表面的微地层精确绘图和暴雨后仅一天在研究河段拍摄的许多照片表明，这些沉积物是由河流过程造成的，而不是通常预期的泥石流，因为这些泥石流具有陡峭的坡度和大量的沉积物供应。一个水槽实验模拟了东高知河的流动，成功地创造了类似于1982年矿床的矿床。接下来的三个是关键机制。1)河床在何处及何时发生淤积？只有当床面被过量的泥沙供应或具有极高的推移质浓度的深线覆盖时，才会发生沉积。水流从来不会一下子淹没整个地板底部，谷底线编织着，游荡着。当局部床面加积时，深泓线侧向移动到下床面，并在那里上升，然后继续移动。2)粗颗粒和小颗粒之间的分选：大颗粒在强烈的推移质层中从不停止。当河床局部加积时，较小的颗粒因此选择性地存款。想象一下，在一个边缘，thlaweg开始占据局部床，从上游推移质层快速移动的大颗粒首先沉积，然后被较小的颗粒覆盖。3)沉积的纵向时滞：沉积的下半序列将在上游泥沙供应开始时产生，当推移质舌逐渐填满河床时。少

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