Shoreface dynamics – a novel approach to establishing a sediment flux curtain

The mixed, shingle barrier beach at Pevensey Bay, East Sussex, represents a crucial asset in flood defence and coastal risk management along the East Sussex coastline, protecting the low-lying Pevensey Levels, with designated wetlands as well as thousands of vulnerable properties and coastal infrastructure. The 9km frontage is highly dynamic, and suffers a net loss of sediment due to littoral drift, partly blocked by the Sovereign Harbour breakwaters at the southern side. This is managed through continuous bypassing and recycling of beach material as well as regular beach nourishment following a major, capital recharge scheme in 2002. This is administered through a unique, private finance initiative to provide a 1:400 standard protection against breaching and maintaining a crest elevation. The spatial and temporal variations in beach volume, erosion and rollback remain poorly understood, and interventions to redistribute beach material are continuous. To complicate matters further, the beach experiences lowering of the sandy foreshore though the exact drivers remain unknown. A better understanding of the dynamics of this barrier is thus crucial to inform future management.

The aim of the project is to develop a novel method for measuring shoreface processes, with an emphasis on wave propagation/ transformation and sediment transport across the very-shallow nearshore (out to approximately 5 m water depth at low water). A second project will examine “Integrating local shoreface changes and regional hydrographic data to establish a regional sediment budget”.

Two cross-shore transects, 1 km long and 200 m apart, will be set up across the sandy foreshore. Each transect will comprise an instrumented array to define a ‘sediment flux curtain’. Each array will comprise up to 5 pressure transducers to define wave progression across the beach, an upward-looking AWAC system to measure vertical velocity and suspended sediment profiles and; and a novel, continuous bed-level monitoring array to quantify bedload transport and sediment fluxes in the near bed region. A wave radar will be installed to map the nearshore wave field and intensive surveys (from project 2) will be used to describe sediment movement under local hydrodynamic forcing. This will be supplemented with existing records from the CCO and CEFAS wave rider data buoys, a 4 month ADCP record of currents and suspended sediments, and CCTV images.

Objectives:
a) Define the wave energy flux within the surf zone and across the shoreface
b) Develop and apply a novel technique for measuring sediment fluxes in highly energetic conditions and link these to the hydrodynamic forcing
c) Develop a conceptual model linking spatial and temporal variation in wave energy and sediment transport to observed lowering of the sandy foreshore

All doctoral candidates will enrol in the Graduate School of NOCS (GSNOCS), where they will receive specialist training in oral and written presentation skills, have the opportunity to participate in teaching activities, and have access to a full range of research and generic training opportunities. GSNOCS attracts students from all over the world and from all science and engineering backgrounds. There are currently around 200 full- and part-time PhD students enrolled (~60% UK and 40% EU & overseas).

Specific Training: The student will receive training in the deployment of state-of-the-art survey and monitoring equipment and laboratory sediment analysis techniques within OES and from the Environmental Sensing @ Southampton (ES@S) facility, including acoustic wave sensors and current profilers, unmanned aerial vehicles, mobile laser scanning and multibeam echo sounding equipment. Further training will provide expertise in the processing of these large, complex data sets. Local context and application advice, a rich set of historical data and further background to coastal sediment systems will be provided by PCDL.