Modelling Nature I

This study aims to quantify wave attenuation by a series of parallel submerged reef structures, representative for designs used in recent shellfish reef restoration efforts in Australia and the US. Experiments (1:10 scale) were carried out in a 54-m-long wave flume with a range of wave conditions, water depths and reef designs. Overall, the results of this study show that, while situated in relatively deep water, these reefs can reduce incident wave energy and orbital velocities considerably, in particular for relatively high waves in relatively shallow water, and have the potential to be considered in nature-based coastal defense strategies.

Hybrid artificial reef structures can be designed to promote the development of a self-sustaining habitat for reef organisms while simultaneously enhancing the extent to which they provide coastal protection. In this study we investigate the wave attenuation capacity of engineered porous oyster reef modules that have been designed through the DARPA initiative Reefense: A Mosaic Oyster Habitat for Coastal Defense. Reduced scale (1:2) physical model testing of numerous modular reef layouts was conducted in the wave flume at the University of Western Australia's Coastal and Offshore Research Laboratory. The attenuation of wave energy was dominated by dissipative processes, due to both drag forces associated with the porous modules and wave breaking. Wave transmission was strongly governed by the dimensionless relative freeboard, the mean water depth above the top of the reef relative to the offshore incident wave height.

The large bottom roughness typical of coral reefs can be effective at reducing wave energy incident to coastlines through the dissipation induced by how wave-driven oscillatory flows interact with the roughness. A physical understanding of these fluid-structure interaction processes is essential in designing coral reef restoration projects that can enhance coastal protection as well as deliver other beneficial ecosystem services. A detailed 1:3 scale physical modelling study using the coral reef restoration solution developed by Mars Sustainable Solutions was undertaken in the University of Western Australia Coastal and Offshore Research Laboratory 54-m wave flume. Wave heights, flow velocities and hydrodynamic forces were measured to develop predictive formulations to quantify wave attenuation over arbitrary coral reef canopies as a function of coral canopy properties, wave and water depth conditions. This model enables the inclusion of coastal protection into the design of coral restoration projects across varying site conditions.

Coastal forests are considered a sustainable and economical solution to mitigate inundations from tsunamis. Owing to the rare occurrence of tsunamis and reported local tsunami heights being small, the coastal forests are a potential solution to protect from tsunamis in the Arabian Sea. The potential of date palm trees to mitigate tsunami inundations was investigated in an experimental study. The experiments were conducted at a geometric scale of 1:100 with the Froude-Cauchy similitudes. It found that the canopy of the tree played a key role in flow energy reduction. If the tsunami height was higher than the canopy height a significant tsunami depth was reduced behind the forest compared to the case that the tsunami height was lower than the canopy height. The highest percentage reduction in the maximum flow depth behind the forest was 37% for the forest length of 180 m and tsunami height of 7 m.