Coastal vulnerability of a pinned, soft-cliff coastline. Part II, assessing the influence of sea walls on future morphology

Coastal defences have long been employed to halt or slow coastal erosion, and their impact on local
sediment flux and ecology has been studied in detail through field research and numerical simulation. The nonlocal
impact of a modified sediment flux regime on mesoscale erosion and accretion has received less attention.
Morphological changes at this scale due to defending structures can be difficult to quantify or identify with
field data. Engineering-scale numerical models, often applied to assess the design of modern defences on local
coastal erosion, tend not to cover large stretches of coast and are rarely applied to assess the impact of older
structures. We extend previous work to explore the influences of sea walls on the evolution and morphological
sensitivity of a pinned, soft-cliff, sandy coastline under a changing wave climate. The Holderness coast of East
Yorkshire, UK, is used as a case study to explore model scenarios where the coast is both defended with major
sea walls and allowed to evolve naturally were there are no sea defences.
Using a mesoscale numerical coastal evolution model, observed wave-climate data are perturbed linearly to
assess the sensitivity of the coastal morphology to changing wave climate for both the defended and undefended
scenarios. Comparative analysis of the simulated output suggests that sea walls in the south of the region have
a greater impact on sediment flux due to increased sediment availability along this part of the coast. Multiple
defence structures, including those separated by several kilometres, were found to interact with each other,
producing complex changes in coastal morphology under a changing wave climate. Although spatially and
temporally heterogeneous, sea walls generally slowed coastal recession and accumulated sediment on their
up-drift side.