Sandscaping the coast: two approaches to large-scale beach nourishment in the UK

Sandscaping the coast: two approaches to large-scale beach nourishment in the UK.
Sutherland, J.and Blanco Lopez de San Roman, B. and Knaapen, M.
In: ASBPA National Coastal Conference 2017, 24-27 October 2017, Fort Lauderdale, USA. (Submitted) (2017)

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Abstract:The Sand Motor is an inspirational 21.5 million m3 Dutch beach nourishment, that was constructed in 2011. The possibility of applying the principles of the Sand Motor in the UK been explored since then by a team consisting of The Crown Estate, Royal HaskoningDHV, HR Wallingford, van Oord and Arup. We refer to this as sandscaping: coastal management that uses large volumes of sediment to achieve economies of scale, work with natural processes and provide multiple benefits. HR Wallingford has undertaken numerical modelling of potential sandscaping solutions at two contrasting sites on the east of England: • Slaughden: a narrow shingle (sand and gravel) barrier with wave-dominated sediment transport. • Bacton: a soft cliff and eroding shore platform with partial sand cover concentrated in the upper beach. Progressive tides produce relatively fast current speeds close to the shoreline. The contrasting nature of these coastal sites has required different modelling approaches to be undertaken in order to assess the required size and shape of possible sandscaping options. Slaughden lies just south of Alborough (Suffolk, UK) at the narrowest point of the shingle ridge between the river Alde and the sea. The area has suffered persistent erosion in recent decades, mitigated by re-cycling shingle from the south. The one-line model Beachplan has been employed to simulate the wave-driven evolution of the beach plan-shape, due to variations in longshore drift rates. The performance of a number of shingle nourishments, of varying volume and dimensions has been examined assuming a range of possible variation in the future wave climates. The results indicate that a Shingle Engine of approximately 1.2Mm3 would be required to provide a reasonable level of defence at the end of the 50year design life. The morphodynamic evolution of five beach nourishment options, intended to defend Bacton (Norfolk, UK) from erosion and supply sediment to down-drift villages, has been modelled using the TELEMAC coastal area modelling suite. A fully-coupled wind, wave, flow and sediment transport model was used as beach sediment is lost offshore at this location and a one-line model does not simulate these processes. At first order, the amount of protection provided is determined by the spread of the nourishment. A wide nourishment initially protects more coastline from erosion and leads to lower losses offshore, as there is less exposure to strong tidal currents, leaving more material available to be distributed along the shoreline. Different modelling approaches were applied to reflect the important physical processes at each site. A one-line model is relatively quick to run, so many variations can be explored, but simulates wave-driven longshore transport only (although sediment losses or gains can be imposed). In contrast, the coastal area model is computationally intensive, yet still does not include all relevant processes (such as undertow or the onshore transport of sand by waves) so still requires interpretation. The paper will explore the differences in the approaches and how the results were interpreted.
Item Type:Conference or Workshop Item (Paper)
Subjects:Coasts > General
ID Code:1434
Deposited On:09 Oct 2017 13:39
Last Modified:10 Oct 2017 06:59

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