Gravel barrier resilience in a changing climate (#gravelbeach)

Project context

The #gravelbeach project is funded by a £3m Natural Environment Research Council (NERC) Special Highlight Topic grant and is led by Dr Jenny Brown of NOC Southampton, involving a consortium of academic and non-academic partners, with researchers from the Coastal Processes Research Group playing a key role.

This NERC Special Highlight Topic was originally proposed in 2021 by Professor Gerd Masselink (Topic F: ‘Building understanding of natural coastal protection by gravel barriers in a changing climate’), which addresses the following six research questions:

Aim

It is generally accepted that gravel barrier shorelines offer widespread, critically important natural flood protection to many coastal communities. Moreover, their creation and enhancement are increasingly seen as sustainable and nature-based adaptation options that boost natural capital. But these assets must be well managed to ensure they continue serving such functions in the face of increased risk of coastal erosion and flooding. Our understanding and modelling capability of gravel beach and barrier dynamics significantly lags behind that of their sandy counterparts.

The principal aim of #gravelbeach is therefore to enhance understanding of gravel barrier systems and improve predictive capability to support more sustainable coastal management, increase overall coastal zone resilience and reduce vulnerability to climate change.

Activities

Classify and characterise all UK gravel barriers

Analysis of gravel barrier topography and shorelines over annual to decadal time scale

Observe barrier stratigraphy through sediment sampling, coring and ground-penetrating radar

'Storm chasing' on six gravel barrier sites to collect morphodynamic data under extreme conditions

Physical laboratory experiments to study fundamental sediment transport processes

Develop, validate and calibrate numerical models of gravel barrier morphodynamics over range of time scales

Apply new numerical models to inform management at several sentinel gravel barrier sites

workshop for practitioners and project partners

Training of post-docs and PhD's

Outputs

Database of all UK gravel barrier sites

Contextualisation of gravel barrier morphodynamics and sediment stratigraphy

New sand-gravel sediment transport equation

Numerical modelling capability for gravel barrier morphodynamics over multiple scales

Peer-reviewed publications

Conference presentations

Unique hydro- and morphodynamic data sets from the field and laboratory for future model development

Predictions of future coastal dynamics for several sentinel gravel barrier sites and evaluation of adaptation strategies

Skill enhancement amongst researcher staff and trained PhD students

Outcomes

Improved understanding and modelling capability of how gravel barriers respond to changing sea level, storminess and sediment supply (Q1)

Evaluation of how natural protection by gravel barriers will be compromised by climate change, potentially triggering management interventions (Q2)

Quantitative consideration of the unique aspects of sediment transport of sand-gravel mixture and how this influences barrier morphodynamics (Q3)

Characterisation of the internal structure and spatial variability in sediment composition, and how this impacts on gravel barrier morphodynamics (Q4)

Insight into the role of hydraulic conductivity in influencing barrier behaviour (Q5)

Appreciation of the fundamental difference between constructive overtopping and destructive overwash, and how this influences the back-barrier (Q6)

Gravel barriers extend along a fifth of the non-estuarine coastline of England and Wales, and are also common in Scotland and Northern Ireland. At many locations they act as natural coastal defences and are unique ecosystems, especially in association with back-barrier marsh or lagoonal systems. In offering physical protection from coastal flooding and erosion, they represent critical natural capital. For example, over 30 coastal frontages (> 180 km) in SE England have a mixed sand-gravel barrier as the main coastal defence.

Acknowledging the socioeconomic value of gravel barriers, significant sums are spent annually on engineering structures and management practices to maintain and enhance their capacity for coastal protection. Gravel barriers also represent valuable morpho-sedimentary niches, supporting internationally important biodiversity (e.g., ‘vegetated shingle’) and providing back-barrier conditions that enable carbon storage. Yet, given the vital functions played by gravel barrier systems, our understanding of their resilience to climate change is alarmingly poor.

Approach

The over-arching aim is underpinned by five Work Package objectives:

(1) develop a GB-wide gravel barrier typology encompassing morpho-sedimentary structure and dynamics; (2) collect and analyse field data of event-scale gravel barrier dynamics; (3) collect and analyse laboratory data, and derive new equations for key processes; (4) develop new predictive capability for gravel barrier dynamics over short- to long-term time scales, accounting for cross-shore and longshore sediment transport; and (5) apply new understanding and enhanced numerical capability to project future dynamics of gravel barriers.

All work packages involve use and implementation of innovative measurement, analysis and modelling methods and tools: use of AI for sediment size analysis; installation of LiDAR towers for recording waves, runup and beach change; deployment of UAV and USVs for topographic and bathymetric surveys; storm surveys; state-of-the art physical modelling of mixed sand-gravel sediment transport modelling; and novel equilibrium-based numerical modelling of gravel barrier dynamics.

Involvement of an Impact Advisory Board at the outset ensures that the new science and tools emanating from this project will find application in the real world.

An international Scientific Advisory Board will enable inclusion of expertise from outside UK, as well as facilitating international reach of the research impacts.