Coral Mitigates High-energy Marine Floods: Numerical Analysis on Flow–Coral Interaction

Abstract

This paper investigates the effect of coral reef roughness on mitigating marine floods by using numerical analysis. The study includes two ocean bathymetries – idealised bathymetry with 1% gradient and real bathymetry – for Gold Coast, Australia. The results indicate that characteristics of the marine flood (wave height and period), coral roughness, and shape of the bathymetry are key to the mitigation of marine floods. Wave height reduction behind the reef and at the shore increases with the incident wave height of the marine flood. The maximum reduction behind the reef is around 60% for both bathymetries for the incident wave height of 4 m. When the incident wave period increases from 10 min to 20 min, the wave height reduction increases to 60% but increases from 20 min to 40 min, decreasing the reduction to as little as 3% behind the reef for the ideal bed condition. However, the marine floods caused by longer period waves can be slowed by higher coral roughness compared to the floods caused by relatively shorter period waves. The wave force reduction behind the reef increases with the incident wave height of the marine flood. The wave force reduction is greater than the wave height reduction behind the reef. KEYWORDS Marine flood; roughness; coral; numerical modelling; long-period waves