The influence of sea level rise and changes in fringing reef morphology on gradients in alongshore sediment transport

Abstract

Climate-change-induced alterations to coral reef ecosystems, in combination with sea level rise, have the potential to significantly alter wave dissipation across reefs, leading to shifts in alongshore sediment transport gradients and alterations to tropical coastlines. We used Delft3D to model schematized profiles of two reef flat widths based on the south Molokai, Hawaii coast. Simulated anthropogenic modifications include incremental degradation of the reef structure as well as sea level rise. Our findings indicate that sea level rise has a greater relative effect on wave energy flux and alongshore sediment transport over a wide flat, whereas both reef degradation and sea level rise exert similar influence over a narrow flat. These results suggest reefs that vary in width alongshore are more likely to experience changes in alongshore sediment transport gradients, and therefore shifts in shoreline erosion and accretion patterns, than more uniform reef systems. Key Points Non-uniform reef flat width leads to gradients in alongshore sediment transport Shoreline change is most likely where reef degradation outpaces sea-level rise Rates of shoreline change potentially linked to coral reef health ©2013. American Geophysical Union. All Rights Reserved.