Design method for multi-functional artificial reefs in a coastal environment

Natural reefs are important habitats for a wide range of species. Furthermore, they attenuate waves and thereby protect the leeside, functioning as coastal protection. Many reefs are however eroding or degraded, leading to a loss of these ecosystem services. Artificial reefs can reverse this negative trend. The artificial reefs in this context are meant to restore or complement rocky reef environments in temperate to sub-tropical coastal waters. Such reefs can be created by 3D printers, providing a variety of possible shapes and local topographies. The design of a successful artificial reef is however not straightforward. The interaction between the complex topography and the flow is an important physical property of a reef, determining the success of habitability for certain species. In this study, we aim to develop tools/guidelines to design the reefs in order to increase the success rate of artificial reefs. A modelling sequence is developed to translate offshore wave data to detailed velocity profiles near the face of the structure, for a given design. Modelling is done in a 2DV environment. MET-ocean wave data is used as input for the SWAN wave model, to translate offshore wave conditions to a near shore wave climate. SWAN output is analysed by means of an extreme value analysis, creating input for large-scale computations with XBeach. In XBeach a first order approximation of location and dimensions of the reef, taking into account wave attenuation. SWASH is used to model the reef setup in detail. The model is calibrated with data collected in an experimental setup The 3D printed structure has been simplified to a steel plating with fixated rock, which resembles the porosity and cavity size of the 3D printed surface. From literature study it was established that velocity profiles over potential habitat is an important physical property of a reef which determines the success of habitability for certain species. An easy to interpret, visual result is obtained, linking ecological habitability to velocity patterns in the vicinity of the structure. The numerical model was able to reproduce detailed hydrodynamic motion with high correlation. Case study results indicate that the method developed is functional with restricted applicability. The tool can be used to design habitat in the cross section of a reef, or used as a decision support tool when existing structures are enhanced with habitat elements.Environmental fluid mechanicsHydraulic EngineeringCivil Engineering and Geoscience