Adaptation of Salt Marshes in a Changing Climate

Introduction:

Aim:
Salt marshes form a living shoreline, which acts as a natural buffer to wave impact reducing flood hazard at the coast. These environments can laterally migrate, and accrete vertically but they are suffering from ‘coastal squeeze’ due to a combination of fixed sea-defence, rising sea level, and storm action. Can salt marshes survive climate change? This PhD will study salt marsh resilience to future changes in wave climate and sea level rise and will inform decisions associated with adaptive coastal management strategies (e.g. Knight et al., 2015).

Winter 2013/2014 saw repeated storm impacts, bringing large waves close to the coast. These extreme events lead to coastal erosion, and to the modification of beach profiles. Under projected sea level rise scenarios, extreme wave events are reaching the shoreline more frequently, and are becoming more powerful. Salt marshes are very effective in dissipating wave energy as well as high surge-induced water levels. For these reasons, many coastal protection schemes are considering the use of these vegetated surface, rather than traditional engineering structure to protect coastal communities and mitigate the impact of violent storms and extreme water levels on coastal areas (e.g. Leonardi et al., 2016).

Coastal Risk
Coastal risk is closely related to land use, coastal type, and sediment characteristics. Combined with rising sea level, extreme wave events lead to even larger impacts at the coast, including overtopping, inundation, and coastal erosion. After the extremity of the UK’s 2013/2014 winter, many coastal systems have already undergone a change in state and reached ’tipping points’ which are critical thresholds possibly corresponding to irreversible changes in the state of the system (Brown et al 2016).
Salt marshes can very effectively:
i) Dissipate wave energy and extreme water levels thanks to vegetation-induced bottom friction;
ii) Prevent coastal erosion thanks to the stabilizing effect of root-mat and sediment trapping by leaves.
Salt marshes really are living sea defences but under a climate change scenario, how effective will salt marsh be as flood defences, and what change will they undergo?

Project Summary:

Approach
This PhD will focus on two contrasting sites: Southport (where a large tidal range is combined with a natural / unprotected marsh), and Minsmere (where the tidal range is smaller, and the marsh is protected by a gravel barrier). Both sites form nature reserves that are considered as sites of special scientific interest (SSSI) and are low lying, thus are at risk of flooding. Flood risk management is concerned with community safety at
Southport and nuclear power generation near Minsmere. In collaboration with the BLUEcoast project, beach samples and profiles will be collected at the two study sites and engagement activities with the local stakeholders will enable the new scientific findings to inform shoreline management planning. Fieldwork and Aerial images will be used to collect information on grain-size, local vegetation, lateral migration and accretion rates.