Coastal Defence Scheme nearshore data monitoring service for Pevensey Bay

Tender description

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 (many built at the crest) 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 (Sutherland and Thomas, 2011). The spatial and temporal variations in beach volume, erosion and rollback remain poorly understood, and interventions to redistribute beach material are continuous. Moreover, the beach experiences lowering of the sandy foreshore, though the exact drivers for this remain unknown. A better understanding of the dynamics of this barrier beach is thus needed to inform future management. The aim of the project is to apply 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 CD water depth at low water). Lot 1- A synoptic radar system or accepted equivalent capable of delivering wave field data (including wave heights, periods, direction, and spectral properties) and surface current data for a duration of 12 months at a recording frequency of 15 minutes. The system must store and provide access to raw data such that further data service products may be derived if needed in the future. The system must be able to provide data to a distance of at least 2 km from the shoreline (defined as the high water line at the site normal to the shore at the location of the array lines); and preferably 4-6 km from power supply/set up location at PCDL office. The directional wave/current data must be gridded to a spatial resolution no more than 60 m Cartesian grid. Lot 2- Data on wave progression across Pevensey Bay with vertical velocity and suspended sediment profiles.Two cross-shore transects, 1.8 km long and 200 m apart, will be set up across the sandy foreshore (in shallow waters with a tidal range of 6.1 m). Each transect will comprise an instrumented array to define a 'sediment flux curtain' (Figure 2). Each array should comprise up to 5 stations (locations of seabed mounted instruments) to be deployed concurrently for a minimum of 1 year. The provider will be responsible for maintenance and operation of the arrays throughout their deployment, and the recovery and demobilisation process. These will allow the measurement of wave progression across the beach and vertical velocity and suspended sediment profiles (including a near bed point). The seaward-most station should be an acoustic wave and current profiling system (600 kHz or higher) capable of measuring directional (spectral). A near bed measurement of velocity and backscatter (acoustic/optical) is also required (no higher than 0.5 m above sea bed).