COLLABORATIVE RESEARCH: Experimental Study of the Effect ofSediment Sorting on Bed Forms, Bed-Surface Texture and Fractional Transport Rates in Coarse, Mixed-Size Sediments

当单向水流通过粗混合粒度泥沙的床面时，会产生多种床面形态，泥沙、床面层和底面之间的颗粒大小会发生分离。在河床形态、输送的泥沙和底质之间存在着强烈而复杂的相互依存关系。许多在实验室和野外对分选好的沙子进行的研究，已经使人们对常见沙丘床型的行为以及床型和输运之间的相互作用有了相当好的了解。最近，各种描述为推移质垫层、砾石波和碎石堵塞的特征在分选较差的砂砾混合物上的流动中已有报道。这些看似不同的床特征之间的关系，以及它们对床上大小分离的依赖，目前尚不清楚。本文对单向流中床面特征随水流强度和泥沙分选的性质进行了实验研究，涉及几种平均粒径约为4 mm的泥沙混合物，但分选差别很大，并在每种泥沙混合物上以几个平均流速连续运行。目的是对在这些流动中产生的各种床面特征的基本特征和相互关系进行统一的描述。这项工作将与筑波大学环境研究中心的池田宏教授、高山茂美教授和石谷藤子博士合作完成。这项提议包括国际和平研究所和一名研究生研究助理为期两年的薪金和旅费。彼得·R·威尔科克教授(约翰·霍普金斯大学)正在提交一份具有相同科学文本的配套提案。这家日本集团已经拥有建造实验设备和进行实验的资金。

When a unidirectional current passes over a bed of coarse mixed-size sediment, a variety of bed forms are generated, and there is segregation of particle sizes among the load, the bed surface layer, and the substrate. There is a strong and complex interdependence between the bed forms, the transported sediment, and the substrate. Many studies in well sorted sands, both in the laboratory and in the field, have led to fairly good understanding of the behavior of the familiar dune bed forms and the interaction between bed forms and transport. More recently, features variously described as bed-load sheets, gravel waves, and clast jams have been reported in flows over poorly sorted sand-gravel mixtures. The relationships among these seemingly diverse bed features, and their dependence on size segregation in the bed, is unclear. This is an experimental study of the nature of bed features in unidirectional flows as a function of flow strength and sediment sorting involving several sediment mixtures with the same mean size of about 4 mm but with widely varying sorting and making series of runs at several mean flow velocities over each sediment mixture. The objective is a unified picture of the fundamental characteristics and interrelationships of the various kinds of bed features produced in these flows. The work will be done in cooperation with Prof. Hiroshi Ikeda, Prof. Shigemi Takayama and Dr. Fujiko Iseya of the Environmental Research center at the University of Tsukuba. This proposal covers salary and travel for the PI and a Graduate Research Assistant for two years. A companion proposal with identical scientific text is being submitted by Prof. Peter R. Wilcock (The Johns Hopkins University). The Japanese group already has funds for building the experimental apparatus and conducting the experiments.