Modelling shelf morphodynamics and resulting shoreline evolution of mesotidal uninterrupted sandy coasts - free behaviour and response to construction of artificial islands
Many low-lying coastal areas around the world experience beach erosion and flooding to the ongoing rise in mean sea level and changes in wave and storm climate. This poses a threat to safety of humans living in these areas. One option to protect such coasts, is the construction of artificial islands offshore of coastal areas. The idea is that those islands will reduce the risk of flooding, resulting from an increasing mean sea level enhanced wave forcing. The overall aim of this study is to gain fundamental insight into the natural hydro- and morphodynamics (free behaviour) of a mesotidal coastal zone and its response to the presence of offshore artificial islands (forced behaviour). To this end, the coupled Delft3D-SWAN numerical model is used, which accounts for flow, waves, sand transport and bed level update. An idealized modeling approach is applied by choosing a rectangular model domain of 75 by 50 km, which crudely mimics the Belgian continental shelf. For the sake of minimizing computation times, a relatively coarse grid (resolution ∼ 700 m) is used, implying that processes in the nearshore zone are not explicitly resolved by this model. Instead, from the wave conditions, the longshore sand transport in the breaker zone and the resulting coastal accretion and erosion patterns are determined.
The methodology employed is that, first, the free behavior of the continental shelf is studied by conducting spin-up runs for a period of 1000 years, thereby starting from an initially linear bottom profile in the cross-shore direction. Subsequently, one or more islands are created and the response of the system to these perturbations is studied. During the presentation results will be shown of the time evolution of waves, tides and bathymetry at the shelf, as well as results of the longshore sand transport and coastal evolution for different configurations of the islands (number, size, location, etc).