Morphological behaviour of the Scroby (East Anglian) near-shore sandbank system
Scroby Sands, a major nearshore sandbank on the East Anglian coast of the
U.K., is constantly changing its configuration and alignment with the surrounding
sandbanks and nearby coastline. This study investigates the hydro dynamical and
morphological processes occurring over this complex area and provides an insight
into the future morphological development of the Scroby sandbanks region.
Numerical modelling, using the TELEMAC finite element system (version
5.5), is used to investigate the relative importance of waves, tidal currents, and storm
surges in modifying this sandbank system and to understand the sand transport
pathways and bed-evolution under a variety of hydrodynamic conditions around the
sandbanks. To enhance model's performance, calibration and validation tests were
conducted; field measurements of waves and tidal currents in the study area are
analysed to help understand the spatial distribution of the hydrodynamic
characteristics of the area. Analyses of recent and historical charts, and recentlysurveyed
swathe bathymetries, are conducted to validate the morphodynamic model
and to improve understanding for the morphology evolution of the study area.
The model demonstrates that waves, especially northerly waves associated
with a storm surge, enhance the net sand fluxes and the bed-evolution by 'stirring'
the sand, while the asymmetrical tidal currents play an important role in transporting
the sand. The model identifies Caister Ness as an area of sand flux convergence and
a source of sand for the nearshore sandbanks (McCave, 1978), and suggests that the
sand is moving to the sandbanks along features < 10 m in water depth (Caister Shoal
to Cockle Shoal to Scroby Sands to Corton Sand to South Cross Sand). The relatively
stable position of the -10m ODN contour on the historical charts since 1846
indicates that the regional tidal current stream dynamically maintains Scroby in its
present configuration, although the exact configuration and central position of the
shallowest part of Scroby varies over the time due to waves and storms. A steady
increase in the area and volume of Scroby above -5 m ODN, where the major sand
transport occurs, suggest a linear morphological trend rather than the recurrent cycles
which were proposed by Robinson (1966) and Reeve et al. (2001a; 2001b).