curving concave beaches.
face is orientated parallel to the fronts of the dominant waves.
which face the waves are termed swash aligned.
beaches show oblique alignments to the dominant wave fronts.
occurs where the beach gradient is steep and the wavelength is short.
is because the crest breaks at different times along the beach.
in beach alignment;
transport of sediment can determine the orientation of beaches.
most effective direction of wave advance for long shore sediment movement
is between 40-50°.
the angle of wave advance is less that this, transport can longer take
place, and deposition occurs.
accumulation continues until the angle narrows to the optimum of 40-50°.
usual result of this is that a spit is built out from the coast in a continuation
of the line of the best orientation for drift in relation to the waves.
the cost turns such that the angle of wave approach increases, deposition
occurs again and the angle continues to become greater.
swash alignment is acheived, accretion build the beach seawards at a constant
SMALL SCALE LANDFORMS ON BEACHES
when a swell approaches a beach with almost perfect refraction, beach
cusps are a series of small arcuate embayments between 5 and 50m across.
The sides of the cusp channel swash in to the centre of the arc. The backwash
in the centre is stronger, and deepens the cusp.
piles water up in the surf zone. Water tries to escape laterally, but
is opposed by the water flowing in the oposite direction. The two together
have sufficient energy to break through the surf as a well defined zone
of high velocity water. They can scour channels, and be as fast as 8m/s.
ripples are produced when a wave oscillates back and forth in shallow
water. They are elongated in the direction of the crest. They are small
scale, perhaps 10-50 cm.Asymmetrical ripples are produced where there
is a resultant directional flow. The current moves particles up the gentle
stoss slope, and then deposits them in the eddy zone in the lee side of
features are named after their shape, as opposed to their origin.
Spits;e.g. Spurn Head, Holderness,
Yorkshire.Dominant waves push material along the coast in longshore drift.
Coast turns inwards, and the material continues to be deposited in line
with the coastal trend. Finer materials are deposited in the sheltered
side of the spit. Marshes can build up, and this forces the river to the
other side of the estuary.
Proximal end of the spit - the bit that meets
the land.Distal end of the spit - the tip,
As spits build further in to deeper water, they require more sediment
to build above the HWM. The waves have greater energy to attack the distal
end, turning it inwards. Sometimes, the curves are due to the changing
of the predominant wind direction to another, causing waves, and thus
deposition to occur an a different angle. These recurves are sheltered
by the spit and become prominent features, e.g. Hurst Castle Spit, The
Double Spits; Both Poole Harbour,
and Christchurch harbour have spits which have grown from both sides.
Both show attributes which indicated that they are swash and drift aligned.
Forelands; Low lying triangular areas
of coarse deposits. The updrift side traps sediment and slowly builds
forward, whilst the downdrift side is eroded. The balance between erosion
and deposition determines the size of the foreland.e.g. Dungeness, Hastings-Dover,
SE England. Benacre Ness, Suffolk. Nr. Southwold.
Barrier beachesBeach which stretches
across from one embayment to the other, and encloses a lagoon behind it,
e.g. Loe Bar, near Porthleven, Cornwall. Feature is swash aligned, and
has probably been driven landwards from the offshore zone.
of sediment parallel to the coast and submerged during the tidal cycle.
Assumed to be the precursor of barriers and being driven landwards.