| Summary: | This body of research contributes to the planning of future coastal adaptation. The various studies that make up this thesis have been undertaken at different locations around the coast of the UK ranging from a regional study covering the Northwest UK to smaller site locations at Fleetwood, Dungeness, Bradwell and Sizewell. The research focuses on establishing an exploratory numerical model that simulates a range of plausible extreme events made up of a combination of different flood sources: storm surge, sea-level rise, high river flow and wave overtopping. In addition to examining the areal and depth extents of flooding, the physical impacts are converted into an economic cost to support cost:benefit analysis resource allocation for climate change adaption to extreme events. The simulations showed that the flood sources do not combine in a linear way and that relying on one source of flooding to estimate the impact of an extreme event can under-estimate the economic impact of said event by up to 7.7 times, and the physical extent by up 3 times. This also highlights the non-linearity in increasing flood inundation extent and resulting economic cost. Different ways of disseminating the inundation information have been explored, particularly for local stakeholders such as residents to see the impact of the extreme event. Moving on from flood water depths, further research has assessed the economic impact of potential future sea-level rise on coastal energy infrastructure. For this body of work the infrastructure considered is electricity distribution substations. These substations are assessed in a Real Options economic framework to determine when it is beneficial to invest in flood defences to protect that infrastructure. The research found a tipping point in 2030 in the number of energy distribution assets in NW England where the damage cost due to extreme events increased the benefit that would result from building demountable flood defences that can be deployed around the electricity substation during an extreme event enabling the substation to be resilient to that event. Here, investment achieves sufficient potential averted damage cost to make it cost-effective to invest in defences. This Real Options methodology is able to assess options for intervention across a large region at local spatial scales, supporting optimal allocation of when and where investment resources should be deployed or deferred to ensure the energy infrastructure remains protected against future climate change. Quantifying the uncertainty in flood risk assessments where different combinations of water level and significant wave height have the same annual joint probability of 0.5% is a further contribution of this research. It was found that combinations with the highest extreme water levels generated the largest flood extent for a gravel barrier coast. Therefore, increasing extreme water levels consequent upon future sea-level rise and climate change drive an increasing risk of extensive floodplain inundation. Extreme event combinations that comprise a large significant wave height will have a correspondingly lower extreme water elevation to maintain the 0.5% annual probability. This lower extreme water elevation means that the larger waves will break further offshore, reducing the impact of these waves. This will reduce the impact of the event leading to reduced wave run-up and lower overtopping rates. The use of the longest peak period associated with the relevant significant wave height, consistent with swell waves is important as re-simulating events with wind wave conditions rather than swell, resulted in no flood inundation. This research has shown that ensuring a coastline is resilient to a given annual joint probability extreme event needs to consider that many different combinations of wave height and extreme water level equally apply and give a wide range in overwashing rates and inundation extents. It also highlights that managers need to focus on extreme water levels combining with swell waves, as these lead to the greatest flood inundation. Using this method will allow the testing the range of extreme events that meet the criteria and give coastal managers and stakeholders more confidence that the defences are resilient to the standard of protection specified. Research has also examined the morphological resilience of saltmarsh and barrier beach coastlines. In the case of saltmarshes, numerical modelling examined how the ability to reduce wave run-up changes as it erodes. Two critical saltmarsh widths were discovered, one at 810 m and the other at 270 m. The wider width is a threshold where the linearly increasing wave run-up with decreasing saltmarsh width changes to a constant wave run-up value despite a further decrease in width. The narrower critical width denotes another threshold where the constant wave run-up value changes to a linearly increasing one, but at a rate three times faster than before the before first threshold width. The research shows that a saltmarsh is able to maintain the resilience it provides before the first threshold until the narrower threshold width is reached. As well as width, the height of the saltmarsh edge is also important, with heights below 2 m having much less resilience or greater wave run-up values.
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