Jet behaviour in longitudinal deepening shallow flows

Abstract

In the proximity of the Eastern Scheldt storm surge barrier (ES-SSB), one of the largest hydraulic structures of the Dutch Delta Works, scour holes have developed that potentially threaten the stability of the structure. Although, these scour holes were anticipated in the design phase recent bathymetry measurements show that they are growing deeper than initially predicted. Uncertainties in the predictions of the equilibrium dimensions partially arise from the presence, thickness and erodibility of clay layers, but first and foremost from a lack of understanding of the flow conditions in the vicinity of the scour holes. High flow velocities are still observed near the bed in the scour holes, that can be associated with high bed shear stresses. This implies that an equilibrium state has not yet been reached and that the scour holes still become deeper. The presence of these high flow velocities is not fully understood, making predictions on the development of the scour holes and mitigation strategies difficult. As a result, the risk of geotechnical instabilities increases, which may potentially endanger the stability of the ES-SSB.

The objective of this master thesis is to obtain more fundamental understanding of the flow patterns and turbulence structure in the vicinity of tidal barriers, such as the Eastern Scheldt storm surge barrier, and how these may contribute to ongoing scour. In this thesis, we experimentally investigate the development of a shallow jet that experiences a streamwise increase in depth, with and without the effect of grid turbulence. The aim of this thesis is to obtain additional insights into the fundamental processes in scour holes using experimental results, that can contribute to the improvement of equations and models that estimate scour near hydraulic structures.