Physical Modelling of 3D-Printed Artificial Reefs with Complex Shapes in the Wave Flume

Abstract

Coral reefs are considered to be a crucial ecosystem and form of natural coastal protection. They owe their effectiveness to their high structural complexity. This complexity, which positively influences aspects like species richness, coral recovery, live coral cover, and coastal protection, is often quantified using parameters such as porosity and rugosity as has been done in this thesis. However, coral reefs are currently facing decline due to both natural processes and human activities. To address this issue, artificial reefs (ARs) have been proposed as a potential solution. Coastruction, a start-up specializing in 3D printing, has developed a 3D printer capable of creating artificial reefs in any shape. In this thesis, biomimicry-inspired complex ARs were designed and printed to examine the impact of structural complexity on wave attenuation.

Data was collected through physical model tests in a wave flume at Deltares, using Froude scaling with a length scale of nL=4. The experiments involved 1 to 2-meter-long reefs composed of three distinct structures with different geometrical complexity levels: design 1 (medium complexity), design 2 (maximum complexity), and cubes (low complexity). These structures were tested under similar, primarily non-breaking wave conditions. The aim was to determine if the dissipation observed resulted from friction rather than wave breaking.

The results of the conducted experiments showed that structural complexity does not significantly affect wave transmission. Overall, high transmission coefficient were observed across the different structures, ranging from 0.96-0.99. Additionally, no significant differences in dissipation were found among the three structure types, with dissipation ranging from 5.5% to 13.5% of the incoming wave energy. However, increased reef coverage positively impacts transmission reduction and spectral wave dissipation, exhibiting a linear decrease in transmission coefficients and a simultaneous increase in dissipation.

In summary, the various artificial reefs examined in this study demonstrated minimal effectiveness in wave attenuation, with negligible differences among reefs featuring different degrees of structural complexity. Despite the similar wave attenuation effects, the environmental benefits of a highly structurally complex reef suggest that it should be considered a viable solution.