Modelling morphological processes in the vicinity of shore-parallel breakwaters

A coastal area morphological modelling system is used to investigate the planform development (tombolo or salient) behind a single surface-piercing detached breakwater. A quasi three-dimensional (Q3D) description of the flow and the sediment transport, together with a revised bed level update scheme, were incorporated recently in the morphological modelling suite applied in the present investigation. The Q3D sediment transport formulation used allows simulating beach profile evolution and planform development simultaneously. Several breakwater layouts were investigated in a series of tests, in which the incident wave condition was taken as constant in time. The investigation was done for surface-piercing, shore-parallel breakwaters in a non-tidal environment. The morphological simulation results for the planform shape agree qualitatively with field observations and predictions from empirical rules. Using the simulation results, simple design curves for surface-piercing breakwaters are derived. The importance of properly accounting for the influence of wave diffraction when modelling sediment transport and morphology in the vicinity of shore-parallel structures is also investigated. The present paper summarises much of the work performed at DHI Water & Environment over the past 10 years within the field of coastal area morphological modelling. (C) 2002 Elsevier Science B.V. All rights reserved.