Collaborative Research: Experimental Study of Downstream Fining in Coarse-grained River Channels

最近，从各种实地观察中可以清楚地看出，泥沙淤积的河流水系的下游尺寸减小在很大程度上是由粗碎屑的选择性沉积引起的。然而，在受控条件下，对选择性沉积分选的系统研究从未进行过。考虑到最近提出的解释这一现象的大量理论，缺乏一组关于下游分选的参考数据就更令人吃惊了。拟建项目的主要目标是开展一系列在差分选砾石沉积物中选择性迁移和沉积的基础实验。大部分实验将在圣安东尼瀑布水力实验室的一个大河道中进行。在那里，我们将在大约50米的距离上从一种分类不良的砂砾混合物中开采矿床。主要的变量将是泥沙进给量（以及因此产生的沉积）和河道形式（直的、弱弯曲的、辫状的）。此外，我们将在约翰霍普金斯大学的一个较小的水槽中对沉积物运输和表面结构进行详细测量。这些数据将用于开发基于地表的运输公式，该公式将用于模拟在大水槽中观察到的分选。

Recently it has become clear from a variety of field observations that downstream size decrease in aggrading river systems is caused in large part by selective deposition of coarse clasts. However, sorting by selective deposition has never been studied systematically under controlled conditions. The absence of a set of reference data on downstream sorting is even more striking in light of the number of theories that have been advanced recently to explain it. The main goal of the proposed project is to carry out a series of basic experiments on selective transport and deposition in poorly sorted gravelly sediments. Most of the experiments will be conducted in a large channel at the St. Anthony Falls Hydraulic Laboratory. There we will produce deposits from a poorly sorted sand-gravel mix over a distance of about 50 m. The main variables will be rate of sediment feed (and hence deposition), and channel form (straight, weakly sinuous, braided). In addition we will make detailed measurements of sediment transport and surface texture in a smaller flume at Johns Hopkins University. These data will be used to develop surface-based transport formulas that will be used in modeling the sorting observed in the large flume.