The Influence of Sea Level Rise and Changes in Fringing Reef Morphology on Patterns of Coastal Sediment Transport

Climate change can strongly influence coral reef ecosystems, affecting species composition, growth rates, and reef morphology, potentially leading to altered wave energy dissipation across reefs. Sea level rise can also alter wave dissipation, which may lead to shifts in alongshore sediment transport gradients, thereby altering erosion and accretion patterns on tropical coastlines. Delft3D was used to simulate the effects of reef degradation for two schematized profile models based on the southern coast of Molokai, Hawaii. Two representative end-member reef flat widths were modeled and anthropogenic modifications to the reefs, including incremental degradation of the fore reef and reef crest structure, were combined with potential sea level rise scenarios. Findings indicate that over a wide reef flat, sea level rise has a greater relative effect than reef degradation on wave energy and alongshore sediment transport rates. In contrast, both reef degradation and sea level rise exert similar influence over a narrow reef flat. Results suggest that reefs having alongshorevariable widths are most likely to experience changes in alongshore sediment transport gradients, and therefore shifts in patterns of erosion and accretion, than more uniform reef systems.