Summary

This project aims to create a method for predicting the mesoscale (10 – 100 years and 10 – 100 km) evolution of managed sandy shorelines that accounts for sea-level rise and complex planform morphologies (e.g. coral reef systems). This aim originates from the growing need to predict the evolution of managed sandy shorelines over meso time and space scales for guiding the management of sandy coastal systems. Extensive use of hard defences for coastal management presents the biggest threat to the continued existence of sandy coastal systems, limiting their ability to migrate under sea-level rise. Sandy coastal systems are the primary socio-economic resource for most small island states in the Caribbean and Pacific, which are likely to be severely challenged by sea-level rise this century. Sea-level rise and hard defences can together influence the evolution of sandy coastal systems over decades to centuries across tens to hundreds of kilometres. Models that simulate mesoscale shoreline evolution assume an equilibrium active coastal profile, therefore cannot account for sea-level rise. An equilibrium active coastal profile implies a fixed closure depth and shore-parallel depth contours. The closure depth is the depth beyond which there is no significant sediment transport. Sea-level rise is known to change the closure depth and will likely be endogenous in meso timescale coastal evolution. The equilibrium active coastal profile assumption also limits the applicability of existing mesoscale shoreline evolution models in complex planform morphologies, defined by non-parallel depth contours and a spatially variable closure depth. Such morphologies characterise sandy coastal systems in many Caribbean and Pacific small islands where shoreline evolution models are, arguably, most needed to guide coastal management. Accounting for sea-level rise and complex planform morphologies in mesoscale shoreline evolution predictions are thus novel scientific challenges facing coastal managers. 

Novel contributions

To better account for sea-level rise and complex planform morphologies in mesoscale shoreline evolution models, I re-schematised an existing hybrid 2D/one-line shoreline model (MIKE21) to handle temporal and spatial variations in the closure depth, respectively.  

Outputs

• A new approach for handling complex planform morphologies in hybrid shoreline evolution models (Seenath, 2023).

• A new approach for incorporating sea-level rise in hybrid 2D/one-line shoreline models (Seenath, 2022a). 

• On simulating shoreline evolution using a hybrid 2D/one-line model (Seenath, 2022b). 

• Modelling mesoscale evolution of managed sandy shorelines with particular reference to Caribbean small island states (Seenath, 2021).