Environmental Engineering Reference
In-Depth Information
Plate 1
Expensive and often strategic coastal infrastructure, such as
the Llandarcy oil refinery and Port Talbot steelworks complex in
Swansea Bay, South Wales, will require hard defences against
rising sea level. They, in turn, will threaten the soft natural sand
dune defences of Crymlyn Burrows (foreground).
during storm events, when large volumes of sand may extend sand plains seaward.
Waves with weak backwash and low swash impedance from previous waves, commonly
at 8-10 s intervals, are responsible for net beach construction. By contrast, plunging
waves with short (4-5 s) intervals often have a strong backwash and transfer sediment
seaward. Longshore drift rates increase with wave power and angle of wave approach.
They are often the principal transfer process and the only net transport mechanism on
equilibrium coastlines. The nature and orientation of
bed forms
exposed on the foreshore
at low tide ('ripples') illustrate tidal sediment mobility.
COASTAL LANDSYSTEMS
DELTAS
Deltas develop by
progradation
or seaward extension of river flood plains. Most large
deltas are located on trailing-edge or other passive-margin coasts, fed by trunk rivers
draining substantial continental areas - often sedimentary or cratonic basins. Many have
foundations 10
5-7
a old but their modern configuration is essentially mid to late Holocene
in age, postdating the Flandrian transgression. Low Quaternary sea levels drew flood
plains across the continental shelf, delivering sediment closer to shelf slope margins and
the ultimate oceanic sink. Transgression trimmed flood plains back towards the modern
