On the correspondence between morphological and hydrodynamical patterns of groyne fields

摘要

This paper examines a variety of recirculation flow patterns that develop in the groyne fields on rivers. A comprehensive data set was obtained from flume experiments at Delft University of Technology and field measurements performed on the Elbe River in Germany. The analysis focuses on patterns of velocity, scour and deposition, and corresponding change of riverbed morphology. The results show that velocity patterns in the groyne fields depend mainly on the aspect ratio between groyne length and length of groyne field. When the aspect ratio is greater than 0.5, a one-gyre pattern of recirculation develops, while at groyne fields with aspect ratios less than 0.5 a two-gyre recirculation pattern emerges. The spatial distribution of fine-sediment deposition between the groynes coincides with the locations of gyres. Moreover, the thickness of the fine-sediment layer decreases toward the gyre margins where recirculation velocities are greatest. Although the total concentration of suspended sediment in the river does not change considerably as the flow moves through the groyne field, the biological and gravimetrical composition of the suspended material changes substantially within the groyne field. These changes are due to preferential deposition of coarse mineral particles and the replacement of those minerals with finer organic material.