Environmental Engineering Reference
In-Depth Information
Figure 17.11
Barrier and estuarine coast, northern Cardigan
Bay, Wales. Dominant waves from the south-west help
redistribute terrestrial and offshore late Quaternary
sediments via longshore drift, diverting or blocking river
mouths (Aber-). Most sand dune systems are of medieval age.
process continues once wave action has removed the debris. Wave action may account
directly for up to 25 per cent of cliff erosion. Mass wasting triggered indirectly by wave
action and other erosion accounts for the remainder. Net evacuation of eroded debris and
any longshore sediment influx is an important requirement for continuing erosion,
without which
effective
wave energy is reduced to zero. Cliff retreat leaves behind a
rock
platform
. Its extent is determined by effective wave depth and the degree of water layer
and biotic weathering, particularly during exposure at low tide. Platforms may be
horizontal, or slope gently seaward, controlled either by gently dipping structures or by
higher tidal ranges, with the seaward margin receiving most wave energy. Slow
