Groynes

Introduction

A groyne is an active structure extending from shore into sea, most often perpendicularly or slightly obliquely to the shoreline. Adequate supply of sediment and existence of satisfactorily intensive longshore sediment transport are the sine qua non conditions of groynes efficiency. Catching and trapping of a part of sediment moving in a surf zone (mainly in a longshore direction), as well as reduction of the sediment amount transported seawards, are the principle functions of the groyne. As revealed by experiments, during weak and moderate wave conditions, the groynes partly dissipate energy of water motion and lead to sand accumulation in the vicinity of a shore, thus causing its accretion. Under storm waves, mainly approaching the shore perpendicularly, the role of the groynes decreases and a beach is partly washed out.

Effect of groynes on seashore

Intensity and character of groynes influence on shore behaviour depend on sea water level, parameters of waves, currents and sediment supply in the surf zone, as well as a shape and inclination of the cross-shore profile. Protection of the shore by use of one groyne only is most often inefficient. Therefore, shore protection by groynes is designed as a group comprising from a few to tens of individual structures. A scheme of a system of interacting groynes is given in Fig. 1.

Wooden groynes

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