Coastal Processes l Understanding coastal processes is important

Coastal Processes l Understanding coastal processes is important when trying to preserve and protect beaches l In Florida, 75% of the population (10. 5 million) live within 10 miles of the coast

l Waves are present along all coastlines, and are created by wind blowing over the ocean – Wave action is responsible for the presence of well- sorted, well-rounded sands along the beach. Waves are often the main agent of erosion – As waves approach the shoreline they grow in height and eventually break. The zone where they break is termed the surf zone

– As a wave crest approaches an irregular coastline it bends. This is called wave refraction, which causes wave energies to be concentrated at headlands and dispersed at bays

– Waves approaching a shoreline at an angle cause two important processes l l Longshore Drift – the gradual lateral movement of sand along the beach Longshore Current – a shallow-water current parallel to the shore

l Tides are another process that occurs along every shoreline – Tides are the twice daily rise and fall of the sea, and are caused by the gravitational attraction of the Moon, and to a lesser degree the Sun

l Coastal Setting and terminology

Beach Profile

l Accretion or erosion of a beach is dependent on its sand budget. There are several inputs and outputs of sand to a beach

– When the total inputs equals the total outputs, the beach is said to be in equilibrium. If the beach is not in equilibrium either erosion or deposition will occur – Often see interesting erosional and depositional formations Erosion of a cliff to form a wave-cut terrace Deposition of sand at Cape Cod to form a spit

l When sand outputs is greater that sand inputs beach erosion occurs – Humans have tried to slow beach erosion by stabilizing the beach. There are two types of stabilization techniques 1) Hard Stabilization – Emplacement of hard structures, including groins, jetties , and sea-walls, to protect the beach. Often involves significant construction and coastal engineering 2) Soft Stabilization – Replace lost (eroded) sand with new sand. New sand can either be sediment picked up from dredging, pumped from offshore, or from sand deposits on shore. Costs roughly $1 million/ mile

Two examples of the use of groins. These structures trap sand that is being moved along by longshore drift, causing a build up of sand on one side and a depletion along the other. This is a dangerous practice and could lead to “New Jerseyization” of the shoreline

l Sea-level rise is another problem facing coastal communities. – Global warming may lead to increased rates of sea-level rise. – Most models expect a rise of 1 -1. 5 meters within 50 years