Entrapment of kaolin in a gravel bed: A flume study.

摘要

The management of gravel-bed streams requires more and more accurate and detailed knowledge of both cohesive and non-cohesive sediment transport processes to cope with various problems such as depletion of fish spawning grounds, issues associated with dam removals, adverse impacts related to water quality, etc. Detailed mathematical models are necessary tools for the development and application of this knowledge. The physical understanding and mathematical description of the processes, however, are still lagging behind, especially with respect to the effects of near-bed turbulence on the critical deposition shear stress value, fall velocities of cohesive sediments and the controversy regarding pure erosion or deposition processes.; In this study, the author used a recirculating two-meter flume to physically model the entrapment of kaolin in a gravel bed. The kaolins were injected into the two-dimensional flows at various rates. Instantaneous concentrations in the water column at different stations were measured. Observed quantities of entrapment between stations were recorded over two periods, i.e. during and post-injection.; The existing mathematical models were then examined. Modifications were made to the model to reflect the influence of near-bed turbulence on the deposition, erosion and flocculation processes. As a result, a general equation was derived to estimate the entrapment quantities. The equation has the form of D-E, in which D and E are the deposition and erosion rates, respectively. Moreover, factors affecting both the deposition and erosion processes were also investigated. Detailed discussions regarding these factors are important components of this document.