Environmental Engineering Reference
In-Depth Information
HELWICK BANK
The Helwick Bank, a linear sandbank aligned east-west, lies to the west of Port-Eynon Point, about 4
kilometres south of Worms Head. The Reverend J. D. Davies in his history of West Gower (1894) noted
that'Atlowwaterduringextraordinaryspringtides,Ihavebeentoldthatpilotshavebeenknowntojump
from a boat on these sands and that these have been seen almost dry.' He goes on to record an ancient
tradition with respect to the 'Helwicks', 'that there was once a road along these sands and that pieces of
iron horse's shoes have been dredged up'. Davies also notes that 'Hele is an old Anglo Saxon word still
in use and means to cover something up: to “hely potatoes” is a very common expression in Gower, also
“to hely up the head”, i.e. to cover it up with a whittle (a woollen shawl) or handkerchief.'
Subtidal sandbanks such as Helwick Bank are the result of relatively high energy conditions. As such
they will be naturally disturbed by large changes in sea state, caused for example by storms. The animal
communities found in and on Helwick Bank reflect the exposed conditions, being generally tolerant of
high levels of disturbance. The first biological sampling of the Helwick Bank occurred during the late
1970s (Tyler & Shackley, 1980). This study was an investigation of the biology of the linear sandbanks
onthenorthcoast oftheBristol Channel andwasnotaspecific studyoftheBank,although samples were
taken from it. It was not, however, a survey of an undisturbed environment, but represented a study of an
area which at that stage had already been subjected to between 20 and 30 years of aggregate extraction.
Unfortunately there are no biological data for the Helwick Bank and the adjacent seabed before dredging
began. A very limited field survey was carried out in 2000, as part of the monitoring of dredging opera-
tions,toidentifyseabedhabitatsandthetypesandnumbersofanimalspresent.In2001anewjointsurvey
involving the Countryside Council forWales, the National Museum ofWales and the University ofWales
at Bangor provided the first quantitative data on the invertebrate life associated with Welsh sandbanks,
including Helwick Bank (Darbyshire et al ., 2002). Although the 2001 survey found that the range of in-
vertebrates in the sandbanks was generally lower than that of the coarser sediments nearby, the animals
associated with the sandbanks often formed distinct groupings.
The seabed sediments of the Helwick Bank area are uniform, medium-grained sands with little or no
fine or organic material. Sand-waves are present along its flanks, indicating that sand transport is occur-
ring. To the south an area of megaripples (large ripples of sand on the seabed surface) merges to the west
with an area of sand-waves and gravelly sand. Extensive research over the past 30 years has shown that
the predominant sand transport pathway under the normal tidal regime south of the Gower coastline is
towards the west. At the eastern end there is a link with the Port-Eynon subtidal area. Under particular
weather conditions, for example during southwesterly storms, sediment will travel into the embayment,
and into Port-Eynon Bay. Normally, however, sediment will tend to move out from the bay towards the
south and west.
Theshallowsandysedimentsarecolonisedbyaburrowingfaunaofworms,crustaceans,bivalvemol-
luscs and echinoderms. Mobile animals at the surface of the sandbank include shrimps, gastropod mol-
luscs, crabs and fish. Sandbanks such as Helwick are also important nursery areas for fish such as sand
eels Ammodytes spp., which are an important component of marine food webs. They prey on the eggs
and larvae of other fish and crustaceans and themselves form a significant part of the diet of many of the
commercially important fish species harvested in and around the Helwick Bank, including sea bass Di-
centrachus labrax , and a number of species of flatfish. They also provide food for a number of seabirds
and the Bank is therefore a key feeding ground for species such as puffins Fratercula arctica and razor-
bills and especially common scoter Melanitta nigra .
Studies have shown that large numbers of molluscs, echinoderms and crustaceans can be killed or
damaged by dredging operations, together with extremely large numbers of the burrowing sand eel. The
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