Regional sediment transport study in Poole and Christchurch Bays, UK

Lewis, R. and Sutherland, J. and Knaapen, M. and Simm, J.D. (2019) Regional sediment transport study in Poole and Christchurch Bays, UK. In: ASBPA 2019 National Coastal Conference, 22-25 October 2019, Myrtle Beach, USA.

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The beaches of Poole and Christchurch Bays in the south of England are important to their local communities for protection against erosion and flooding as well as the recreational space they provide. These beaches are extensively managed through beach nourishment or recycling, combined with construction and maintenance of groynes and seawalls. Three local councils are jointly considering the management of beaches between Swanage and Hurst Spit as a whole. They recognise the complexity of sediment transport within their shared area and the benefits in identifying how that resource could be managed holistically to optimise beach management. The councils have commissioned a detailed numerical model of sediment transport in Poole and Christchurch bays to facilitate a joined approach. Previous studies of sediment transport and erosion along this frontage have tended to use one-line models of wave-driven beach plan-shape elevation (such as Beachplan or Genesis). These models allow the user to run a long time series of wave conditions from an established hindcast simulation. The use of a long time series allows seasonality and inter-annual variations in longshore transport and sediment budget to be determined. However these models only simulate wave-driven longshore transport along gently-curved beaches. The bathymetry here is too complicated for such an approach to cover the entire region. Moreover, offshore sediment transport pathways and sinks are of interest as potential sources of sand for beach nourishment. Therefore the model developed is a fully-coupled coastal area model of wind, tide, waves and sediment transport, created using the open source, finite element TELEMAC modelling suite. It has a high resolution of 5m in the surf zone, expanding out to 5,000m outside the bays. The model has been set up using the latest data on bathymetry and seabed composition. It has been calibrated and validated against different periods of deployment of nine measurement frames, which recorded waves, currents and suspended sediment concentrations over periods of two months. A representative year and a 20-year simulation have been run and provide information on sediment pathways and transport rates. A morphological speed-up factor was used for the 20-year simulation. This approach simulates many more processes than a one-line modelling approach and is much more computationally demanding. The model was run on 108 cores and took several weeks to run. A huge amount of information is available from the model at each timestep, but shorter durations can be simulated than with a one-line model. This presentation will discuss the model set-up and calibration, the simulations undertaken the and information from them (including contributions).

Item Type: Conference or Workshop Item (Paper)
Subjects: Coasts > Sediment transport and scour
Divisions: Coastal
Depositing User: Unnamed user with email
Date Deposited: 02 Apr 2020 09:54
Last Modified: 02 Apr 2020 09:54

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