Environmental Engineering Reference
In-Depth Information
Fig. 2.13
Sand is moving inland from a beach as drifting (transgressive) dunes on the shore of
Encounter Bay, South Australia. The lowered backshore is then cut back quickly because of the
diminished volume of sand to be removed by wave attack. © Geostudies
beach are not compensated by the arrival of fresh supplies of beach sediment from
offshore, alongshore or hinterland sources the beach profile is lowered and the
coastline recedes. Overwash during successive storm surges has eroded beaches
on sandy barrier islands on the Atlantic coast of the United States. At Rockaway
and Long Beach on the New York coast overwash during Hurricane Sandy in 2012
swept large amounts of beach sediment shoreward into residential areas.
2.11 Beach Weathering, Including Attrition of Beach
Sediment
Beaches no longer receiving a sediment supply lose volume as the result of weath-
ering, which reduces the size of beach particles and hence the volume of the
beach, beach profile and so allowing larger waves to attack the shore and further
erode the beach. Chemical weathering includes the decay and removal of ferro-
magnesian minerals from sediments of volcanic origin and the dissolving of car-
bonate beach sand grains or limestone gravels in rainwater, stream seepage or sea
spray. Physical weathering occurs as the result of agitation of the beach by wave
action and consequent gradual attrition of sediment particles.
Four Mile Beach, in North Queensland, Australia, has been eroded because its
fluvial sand supply from the adjacent Mowbray River was cut off by coral reef
