Environmental Engineering Reference
In-Depth Information
that it would have been better to renourish the whole of the Sandringham beach
compartment without inserting any groynes. It would indeed be possible to do this,
given a sufficiently large quantity of sand, but the effects of seasonal longshore
drift must be taken into account. Each winter sand drifts northward and would
accumulate alongside Picnic Point, spilling round into Sandringham Harbour (in
the same way that the renourished beach between New Street and Green Point
Sandringham Harbour already has a problem of excessive sand accretion, and each
summer southward drift of sand would widen the beach towards Red Bluff until
sand spilled round into the next bay. These losses from the extremities of the
Sandringham beach compartment would in due course deplete the renourished
beach until storm waves resumed their attack on the base of the backing bluff.
Seasonal alternations of longshore drift thus make it difficult to maintain a ren-
ourished beach in an elongated beach compartment, and it is necessary to intro-
duce groynes to divide the compartment into manageable sections.
These projects have demonstrated the importance of renourishing and maintain-
ing a wide, high and persistent beach to prevent cliff recession. Such a beach is
a means of absorbing wave energy and protecting the coastline from further ero-
sion. It is important that a sufficient volume of beach material be maintained to
protect the backshore, because a small quantity of sand or shingle that can be
mobilised by storm waves can actually accelerate abrasion of cliffs or solid struc-
tures. This was the cause of severe erosion when the shingle beach was depleted at
Hallsands in south-west England. Increased abrasion occurred on the sea wall at
Aberystwyth in Wales after much of the sediment used in a beach renourishment
project quickly weathered and dispersed, leaving small quantities of hard granitic
gravel that were hurled at the wall by storm waves (So
1974
).
Reference
So CL (1974) Some coast changes around Aberystwyth and Tanybwlch, Wales. Trans Inst Brit
Geogr 62:143-153
