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

BackShore – 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, Hurricane Hugo

Hurricane Sandy