Climate change and accelerated rates in sea-level rise are expected to increase flooding and eros... more Climate change and accelerated rates in sea-level rise are expected to increase flooding and erosion on the world's coastlines. Coastal managers and planners face the challenge of helping communities to adapt to the changing coast. Traditionally hard engineering has been used to defend communities on the coast, but as this option becomes unsustainable and financially unviable, coastal managers are increasingly employing planning policy to mitigate the risk posed by coastal change. Zonation of coastal change areas and delineation of erosion extents, such as setback lines, are used globally to restrict development in the coastal zone. In England there is policy in place to allow planning authorities to restrict certain development in areas expected to be affected by coastal change. This study aims to examine how coastal planning authorities in England have implemented coastal change adaptation policies, specifically Coastal Change Management Areas (CCMA). These areas should include sections of coast that will experience significant change over the next 100 years through erosion, accretion or flooding. Through an analysis of planning documents, we have found that since the policy was introduced in 2012, only 15% of coastal planning authorities have designated a CCMA, with just 5.7% of the coast of England designated as a CCMA. We have found that inadequate and ambiguous guidance has reduced the effectiveness of the national policy with coastal planning authorities unsure of which datasets to apply for delineating areas of coastal change. This has led to vulnerable coastal areas being omitted from CCMAs. The datasets that are available for mapping the coastal change areas are found to vary in erosion extent and do not account for expected increases in the rate of sea-level rise. We suggest that for coastal zonation and climate change adaptation policy to be successful, a robust methodology, including a classification of coastal typologies and their response to sea level rise, is needed to delineate the extent of erosion or coastal change over the next 100 years. Understanding and mapping coastal response to sea level rise will aid planning authorities to build more resilient communities on the coast.
Predicting change to shorelines globally presents an increasing challenge as sea level rise (SLR)... more Predicting change to shorelines globally presents an increasing challenge as sea level rise (SLR) accelerates. Many shoreline prediction models use the simplistic 'Bruun rule' for dealing with SLR profile translation, in-part due to alternative approaches being too complex and time-consuming to implement. To address this, we introduce ShoreTrans: a simple, rules-based, user-input driven, shoreface translation and sediment budgeting model, that applies the surveyed 2D-profile (not a parameterization), for estimating change to realistic coastlines, resulting from SLR and variations in sediment supply, while accounting for armouring, hard-rock cliffs and outcropping rocks. The tool can be applied to sand, gravel, rock and engineered coasts at a temporal scale of 10-100 years, accounting for shoreline trends as well as variability. The method accounts for: (1) dune encroachment/accretion; (2) barrier rollback; (3) non-erodible layers; (4) seawalls; (5) lower shoreface transport; (6) alongshore rotation; and (7) other sources and sinks. Uncertainty is accounted for using a probabilistic distribution for inputs and Monte Carlo simulations. We provide a first-pass assessment of two macrotidal UK embayments: Perranporth (sandy, dissipative, cross-shore dominant transport) and Start Bay (gravel, reflective, bi-directional alongshore dominant), then use idealised profiles to investigate the relative importance of forcing controls on shoreline recession and beach width. For the dissipative sandy site, the primary modes of coastal change are predicted to be short-term storm erosion and SLR translation while long-term trends may be important but are highly uncertain. For the reflective gravel site, the primary mode is multi-decadal longshore sediment flux, while shortterm alongshore rotation and SLR translation are secondary. Relative to the ShoreTrans approach, the Bruun rule under-predicts shoreline recession in front of cliffs, seawalls and for low barriers that rollback, and overpredicts where large erodible dunes are present. ShoreTrans directly addresses change in beach width, with beaches in front of seawalls and cliffs predicted to shrink, such that narrow beaches (<50 m width) may disappear under 1-m SLR. As a standalone tool, ShoreTrans is transferable to many coast types and will provide coastal practitioners with a simple first-pass estimate of how the 2D appearance of a complex profile may change under SLR. A future benefit will be to combine this approach with existing hybrid modelling techniques to augment SLR translation predictions.
Predicting change to global shorelines presents an increasing challenge as sea-level rise (SLR) a... more Predicting change to global shorelines presents an increasing challenge as sea-level rise (SLR) accelerates. Many shoreline prediction models use variations of the ‘Bruun-rule’, failing to account for relevant processes and morphologic complexity. To address this, we introduce a simple rules-based model (ShoreTrans) designed for complex, real-world profiles that predicts change across a wide variety of sand, gravel, rock and engineered coasts at a temporal scale of 10–100 years, accounting for shoreline trends as well as variability. The model translates 2D cross-sections of the shoreface, using the surveyed profile, then integrates these cross-shore shoreface changes across multiple alongshore profiles to assess a simplified 3D sediment budget. Uncertainty is accounted for using a probabilistic distribution for model inputs and Monte Carlo simulations. The model accounts for: (1) dune encroachment/accretion; (2) barrier rollback; (3) non-erodible layers; (4) seawalls; (5) lower sho...
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Papers by josie kirby