Effective use of non-erodible layers for improving navigability

摘要

By constructing a non-erodible layer in the pool of a river bend, the distribution of flow and sediment discharge can be modified such that the shallow inner bend will degrade to a certain extent. This results in a larger width for navigation. The approach has been successfully applied in two river bends in the Waal River in the Netherlands. We analyzed the governing processes to estimate the effectiveness of these non-erodible layers. We also applied a 2-D morphological model to laboratory experiments and to the Waal River with a special sub-model for simulating the effect of non-erodible layers. The results have been compared with measurements of bed development, water motion and bed form propagation. A conceptual analytical approach verifies the answers from the more advanced 2D model. From the analysis of field data and model approaches it is concluded that in most conditions the non-erodible layer can be used effectively to reduce the bed level in the inner bend. However, in certain situations such as narrow rivers like the Ussel River in the Netherlands, the flow re-distribution in the cross-section is such that the net degradation of the point bar does not occur.