Novel techniques for designing hydrodynamically scaled kelp mimics for use in laboratory wave tank experimentsMacroalgal Traits

Jack Duffy¹, Robert Houseago², Pippa Moore¹, Heather Sugden¹

¹Newcastle University, UK - ²Loughborough University, UK

The use of natural habitats for coastal protection, so called nature-based solutions (NBS), is increasing in prevalence globally. Kelp forests, and the complex three-dimensional habitats they form, are promising candidates for NBS. Forests of Laminaria hyperborea, through their large biomass and surface area, are believed to generate considerable drag on waves propagating over them, potentially resulting in a significant reduction in wave energy reaching kelp dominated shorelines, leading to reduced coastal erosion. However, evidence supporting this ecosystem service is limited and further research is required to justify the use of kelp forests as an NBS for coastal protection. Hydrodynamically-scaled artificial kelp mimics in laboratory wave tanks can provide unique insights into the role of kelp forests in attenuating wave energy. The degree of environmental control and experimental replication that wave tanks and mimics provide is not possible with field studies. There are though distinctive challenges to such work, most notably ensuring the behaviour of the mimics under wave conditions is consistent with nature. To provide meaningful instruction on kelp forest wave attenuation requires careful choice of material properties and design to ensure geometric, kinematic and dynamic similarity with their natural counterparts. We outline how these conditions can be achieved through precise matching of dimensionless parameters governing kelp hydrodynamics between mimics and nature, and the use of novel construction techniques. Hydrodynamically important kelp biomaterial and morphological characteristics were identified, measured for collected kelp samples and used to inform kelp mimic design. Silicone moulds were made from 3D printed kelp, fabricated to exact measurements determined by the matching of the dimensionless parameters governing kelp wave behaviour. Kelp mimics were cast from these moulds using a liquid polyurethane rubber, selected to ensure the correct rigidity and density of the mimics. The polyurethane kelp mimics produced possessed the requisite material and geometric properties to hydrodynamically mimic a kelp forest in a laboratory wave tank.