Geography Reference
In-Depth Information
narrow seaways connecting the sea to the main ocean such as the
Bay of Fundy, Canada (17 metre tidal range) or the Irish Sea (13
metre tidal range in the Severn Estuary) or where there are wide
continental shelves, such as off the east coast of China. On coasts
facing the wide, open ocean, tidal ranges are usually less than 2
metres.
As the tide rises and falls against the coastline it produces a flow
of water. This is a
tidal current
. If you throw an orange into the
water at the shoreline during a rising tide the orange is pushed up
the beach. However, if you throw it in at the same point on a
falling tide the orange will float out to sea as the tidal current takes
it away from the shore and you will lose your orange. The geome-
try of the coastline can control the tidal current which is most pro-
nounced in river mouths, estuaries and where flow is squeezed
through inlets.
Coastal landforms
There are a number of driving forces behind coastal landforms.
These can be grouped into waves, tides and rivers, although obvi-
ously the nature of the land material at the coast is also important
(e.g. hard rock or erodible loose sediment). There are different
landforms that are characteristic of locations where waves, tides or
riverine processes dominate.
For example,
a common feature of
wave-dominated coasts is a beach perhaps with coastal dunes.
Beaches are formed by deposits of sediment brought by waves
and are typically shaped with a concave profile. Towards the top of
the beach is the
berm
which is where the slope steepens and then
flattens off. Within the beach there can often be cusps of sand or
gravel at the shoreline which are repetitive features a few metres
apart formed by swash action. Beaches respond to changing wave
energy conditions. When it is calm and wave energy is low then
the net sediment transport is in an onshore direction resulting in
steepening of the beach and a pronounced berm. In stormy con-
ditions net offshore sediment transport occurs with the destruction
of the berm and flattening of the beach. This then helps to dissipate
the wave energy over a wider area.
Coastal dunes protect the coastal area behind them by providing
a buffer to extreme waves and winds. Dune formation requires
