Understanding flow structure in a groyne field.

Abstract

Groyne structures are widely used all over the world for the purposes of controlling longshore currents and slowing down the rate of sediment transport along coast lines. The limited previous studies in this area have led to unfit designs and installations of these structures. The history of the Durban coastline highlights challenges concerning the use of these structures that engineers have been faced with. The groynes along the Durban coast are not sufficient to stabilize the coastline and they are used in conjunction with a sand nourishment scheme. This research aims to elucidate the flow field characteristics and patterns around groynes in a groyne field. A parametric study of three impermeable groynes in a groyne field was developed using numerical modelling software. The DHI MIKE 21 Spectral Wave and Hydrodynamic models were used for the study. Various wave and groyne field parameters were varied systematically. The main focus of the study was on the groyne tips as this is an area most prone to scour failure, especially with impermeable groynes. The simulations reveal how the flow patterns within the groyne compartments change with variation in wave parameters. It was found that under certain wave conditions, recirculation patterns develop within the groyne compartments. Storm conditions can have devastating effects on coastlines. Therefore, this study also aimed to understand how these conditions may affect the functioning of a groyne field.