Sandbar breakwaters
Analysis of the effects of variations in wave climate on the morphological development of sandbar breakwaters by using the Lekki Sandbar Breakwater case study
N. Moesker (TU Delft - Civil Engineering & Geosciences)
Stefan G. J. Aarninkhof – Mentor (TU Delft - Coastal Engineering)
RJ Labeur – Graduation committee member (TU Delft - Environmental Fluid Mechanics)
A. Antonini – Graduation committee member (TU Delft - Coastal Engineering)
L. de Wit – Coach
Antoon J.H. Hendriks – Coach (Royal Boskalis Westminster)
Bart-Jan van der Spek – Coach
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Abstract
Many coastlines feature a sediment transport in a dominant direction, possibly burying a traditional breakwater in sand in several years. The sandbar breakwater concept uses this sediment supply to its benefit to make the use of vast amounts of rocks abundant. During this research the morphological development of the worlds first sandbar breakwater built in Lekki, Nigeria, is analysed: The minimal amount of sand used for construction of the Lekki breakwater is placed such that the combination of the adaptation of the initial
profile and the natural supply of sediment results in a smooth coastline at the end of the first year. This development is in turn used to setup a calibrated model to study the influence of the wave climate on the development of the sandbar breakwater concept. The wave climate at Lekki is characterised by a single dominant wave direction (called unidirectional) and has a narrow direction bandwidth (yearly standard deviation of the wave direction is about 5 degrees). This ideal wave climate is altered to research the influence of the mean wave direction, directional variation and the sequence of waves (seasonality). The study showed the sandbar breakwater concept to be mainly influenced by the mean wave direction and to lesser extent by the directional variation and the seasonality. These results can be used to make a first assessment on the possibility of applying a sandbar breakwater for a wave climate somewhere around the world.