The effect of navigation on the flow in a river trained with groynes

Abstract

The study deals with the investigation of flow structures in groyne fields interacting with the flow generated by navigation. Groynes are traditionally constructed to ensure adequate water depth for navigation, so the interaction of navigation and groyne fields is nearly guaranteed. The Hungarian Danube section – which is part of the 7th European transport corridor – has a great importance, however, there are several places where the minimum 25 dm navigational water depth is not available in low water regime. As the River Waal (a branch of River Rhine), which falls in the same category of navigable waterways as River Danube, in my TU Delft based research I used that particular Dutch river as case study. The goal of this graduation project is formulated as follows: What kind of effects does navigation have on river morphology? This was investigated on physical basis by means of a numerical model. First, the influence of push towing on morphology is investigated by analyzing the bed shear stress distributions, then the impacts on groyne fields. It could be concluded that primary waves caused by push tows increase the bed shear stresses around the ship, moreover, groyne fields are also affected, especially their zone close to the main stream. The impact of different ship sets on shear stresses was also studied. It was found that the most significant effect was caused by the ship velocity, the sailing distance between ship and groynes, a moderate one by the ship’s width and a minor one by the ship’s length. A numerical morphological model could offer a more detailed insight in the morphological changes than analyzing the bed shear-stress distribution, only, a recommendation for future studies is therefore the implementation of such a model. FINEL2D’s capability of predicting the flow changes at groyne fields caused by navigation have been shown, although FINEL2D only uses advective momentum transport (but suffering from some numerical viscosity) to predict the flow, while in the groyne fields inhomogeneous turbulent processes are supposed to be dominating. Nevertheless, FINEL2D showed a sufficient match with physical model results.