Island wakes, headland eddies and sandbank formation

Strong tidal flow past headlands and islands leads to the generation of intense eddy systems and, in the case of headland eddies, the formation of associated headland sandbanks. The eddies themselves play an important role in larval dispersal and sediment dynamics, and the sandbanks (which are several miles in length) are important as a source of marine aggregates and for coastal defence (due to wave refraction and breaking). Through in situ observations and numerical modelling, I am trying to understand the 3D hydrodynamic mechanisms within such eddy systems and the processes which lead to the formation of associated headland sandbanks. My main tools are the 3D POLCOMS model and in situ measurements using ADCP and LISST profiles. Funding for ship time (RV Prince Madog) has been provided by NERC (NE/E011268/1) and the School of Ocean Sciences.

Our latest modelling of headland sandbank formation (Neill and Scourse, 2009) demonstrates why there are four large sandbanks in the vicinity of Portland Bill, English Channel (see figures, left and below). A series of morphological modelling experiments, parameterised by relative sea-level data and validated by in situ observations, have demonstrated that two of the major sandbanks (West Shoal and Adamant Shoal) may have been formed c. 9–7 ka BP, when the Isle of Portland was isolated from the mainland by a navigable strait. After the closure of the strait (due to sedimentation), these two sandbanks were no longer actively maintained, and subsequently migrated towards the two dominant present-day headland sandbanks of the region (Portland Bank and Shambles Bank). Determining the role of such sandbanks in wave-related processes throughout the Holocene contributes to an improved understanding of inter-related coastal processes such as beach evolution. In addition, understanding the response of such sandbanks to changes in sea level will be important for effective future management of the coastal zone, including exploitation of marine aggregates.

Relevant publications:

Neill, S.P., Jordan, J.R. and Couch, S.J. (2012) Impact of tidal energy converter (TEC) arrays on the dynamics of headland sand banks. Renewable Energy 37, 387-397.
Neill, S.P. and Scourse, J.D. (2009) The formation of headland/island sandbanks. Continental Shelf Research 29, 2167-2177.
Neill, S.P. (2008) The role of Coriolis in sandbank formation due to a headland/island system. Estuarine, Coastal and Shelf Science 79, 419-428.
Neill, S.P., Hashemi, M.R. and Elliott, A.J. (2007) An enhanced depth-averaged tidal model for morphological studies in the presence of rotary currents. Continental Shelf Research 27, 82-102.
Neill, S.P. and Elliott, A.J. (2004) In situ measurements of spring-neap variations to unsteady island wake development in the Firth of Forth, Scotland. Estuarine, Coastal and Shelf Science 60, 229-239.
Neill, S.P. and Elliott, A.J. (2004) Observations and simulations of an unsteady island wake in the Firth of Forth, Scotland. Ocean Dynamics 54, 324-332.
Abstract of paper presented at AGU Ocean Sciences 2010 meeting in Portland, Oregon: The structure of headland eddies and their role in sandbank formation: an in situ and modeling study.