Beaches Beach Profile A beach environment consists of
Beaches
Beach Profile A beach environment consists of several zones
Not every feature is found at all beaches Scarp of a sandy beach may simply be high tide mark shown by seaweed
3 Beach Zones Back. Shore – From the High Tide mark and beyond Foreshore – Between the High Tide and the Low tide Offshore – From the Low tide out REMEMBER The Benthic Zones: The Littoral Zone is from the low tide mark to the shelf break
Coastal Water Movement • As waves enter shallow water they interact with the sea bottom where their – Speed slows – Height increases – Wavelength decreases • Most waves encounter the shoreline at an angle and are refracted. • In very shallow waters waves oversteepen and form breakers.
Coastal Water Movement • Longshore currents flow parallel to the shoreline. – This is due to the release of energy when waves strike the beach at an angle. – Their strength depends on the angle of wave approach. – Their direction depends on the incoming waves.
Longshore Currents
• Longshore currents can also be generated by wave setup which forms pressure gradients – just like sand, water can build up on the coast, but it must get back to the sea. – Where waves are higher, more water piles up and flows longshore in the direction of “lower water” – Longshore currents converge in the regions between piles of water and as a result water is forced away from the shoreline forming a rip current.
Nearshore currents due to parallel waves Rip currents tend to be in areas of lower wave height – troughs/depressions
Beaches • Beach profiles delineate the shape of the beach surface along a set of transects. By comparing profiles over time it is possible to determine the sand budget. There are two basic profiles. – Swell profile • Occurs during calm weather due to deposition. • A broad berm forms at the high-water mark. • The beach face is steep.
Beaches • Beach profiles (cont. ) – Storm profile • Caused by steep waves due to storms which cause erosion. • Sand is moved seaward to form longshore bars. • Grain size of the beach increases because the wave action and rip currents carry the fine particles offshore.
Beaches Beach profiles.
Storm Effects • Storm surges are extreme high water events caused by high winds that pile water up along the shoreline. They are most severe when they coincide with spring tides. – They lead to flooding of low lying coastal areas and contribute to the overwash of barrier islands.
Storm Surge
S. Carolina, 1989. Hurricane Hugo
Hurricane Sandy
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