Author(s): W. S. J. Uijttewaal Wallast; A. Van Mazijk
Linked Author(s):
Keywords: Exchange processes; Shallow flows; Groyne fields; Dead-zone-models
Abstract: The exchange of dissolved matter between groyne field and main stream influences the transport and distribution of a pollution cloud in a river. Forecasting models include the global effects of the exchange process on the transport of a solute, but little research has been done on the exchange process between groyne field and main stream itself. Therefore this study is aimed at examining this exchange process and validating of a prediction model, which treats the exchange process as a first order system. A schematised model of the Waal including groynes was built in a laboratory flume. The exchange process was visualised quantitatively with a dye and with floats in a few subsequent groyne fields. These visualisations represent the exchange over the entire depth and the exchange at the surface layer respectively. A camera recorded the exchange of floats and dye in time after realising a certain groyne-field concentration. The experiments showed differences in two ways i. e. between experiments with dye and floats, and between the experiments carried out in successive groyne fields. Both effects can be ascribed to the flow pattern in the groyne field and the development of three-dimensional structures in the mixing layer both depending on the downstream position of the groyne field. Despite the fact that variations in the flow patterns as well as three dimensional effects could be observed, the overall exchange of matter could be characterised as a first-order process, in accordance with the dead-zone-theory. The corresponding exchange coefficient agreed reasonably well with the results of earlier experiments.
Year: 1999