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

摘要

Coastal defences have long been employed to halt or slow coastal erosion,and their impact on local sediment flux and ecology has been studied indetail through field research and numerical simulation. The non-local impactof a modified sediment flux regime on mesoscale erosion and accretion hasreceived less attention. Morphological changes at this scale due todefending structures can be difficult to quantify or identify with fielddata. Engineering-scale numerical models, often applied to assess the designof modern defences on local coastal erosion, tend not to cover largestretches of coast and are rarely applied to assess the impact of olderstructures. We extend previous work to explore the influences of sea wallson the evolution and morphological sensitivity of a pinned, soft-cliff,sandy coastline under a changing wave climate. The Holderness coast of EastYorkshire, UK, is used as a case study to explore model scenarios where thecoast is both defended with major sea walls and allowed to evolve naturallywere there are no sea defences.Using a mesoscale numerical coastal evolution model, observed wave-climatedata are perturbed linearly to assess the sensitivity of the coastalmorphology to changing wave climate for both the defended and undefendedscenarios. Comparative analysis of the simulated output suggests that seawalls in the south of the region have a greater impact on sediment flux dueto increased sediment availability along this part of the coast. Multipledefence structures, including those separated by several kilometres, werefound to interact with each other, producing complex changes in coastalmorphology under a changing wave climate. Although spatially and temporallyheterogeneous, sea walls generally slowed coastal recession and accumulatedsediment on their up-drift side.