Environmental Engineering Reference
In-Depth Information
Fig. 2.2
Microcliff (erosional scarp) on Collaroy-Narrabeen Beach, NSW, Australia, cut by a
number of late summer storms in 2013. © Nick Lewis
14. Increased scour by wave reflection from an artificial structure
15. Extraction of sand and shingle from the beach
Erosion on a particular beach is generally due to more than one of these causes,
although one cause is often dominant.
2.1 Reduction in Sediment Supply from Eroding Cliffs
A common cause of beach erosion is the reduction of the supply of sand or gravel
from erosion of nearby cliffs. Stabilisation of a cliff to halt erosion usually takes
the form of building a solid wall or boulder rampart along the base of a cliff to
prevent wave attack. Beach erosion also occurs when the sediment supply from
an eroding cliff by runoff, seepage and slumping is reduced by inserting drains or
introducing vegetation or a geotextile carpet.
As cliffs are stabilised their sediment yield to the shore diminishes, and may
cease altogether. Beach erosion ensues as sediment lost offshore (mainly during
storms) or alongshore (when waves arriving at an angle to the shore generate long-
shore drift) is no longer replenished from an eroding cliff. This happened on the
