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

最近，从各种野外观测中可以清楚地看到，下游河系面积的减少在很大程度上是由粗碎屑的选择性沉积造成的。然而，在可控条件下，选择性沉积分选从未被系统地研究过。考虑到最近提出了许多解释这一现象的理论，缺乏一套关于下游分选的参考数据更加令人震惊。拟议项目的主要目标是在分选较差的砾石沉积物中进行一系列选择性输送和沉积的基本实验。大多数实验将在圣安东尼瀑布水力学实验室的一条大水道中进行。在那里，我们将在大约50米的距离内从分选不佳的砂砾混合物中产生沉积物。主要变量将是泥沙进给率(因此是沉积)和河道形态(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泥沙输送和表面纹理进行详细测量。这些数据将被用来开发基于表面的传输公式，该公式将用于模拟在大型水槽中观察到的分类。

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.