COASTAL EROSION

COASTAL EROSION (Acronym: CASH)

1. Corrasion / abrasion
   As waves break, sediments carried by the waves such as sand and rocks are hurled against the coast. The loosened sediments knock and scrape against the coastal cliffs. This weakens the surface and breaks down the coast. Over time, the impact of corrasion is powerful enough to erode resistant rocks and undercut a cliff.
2. Attrition
   When rock particles carried by waves rub or hit against one another, they break down into smaller pieces and become more smoother and more rounded over time.
3. Solution / corrosion
   Sea water reacts chemically with water-soluble minerals in coastal rocks and dissolves them. For example, limestone rocks are easily eroded by carbonic acid. When solution of minerals occurs, rocks are weakened and eventually disintegrate.
4. Hydraulic action
   When waves strike against a rock surface, the waves trap air in the rock joints. This air is compressed by the oncoming waves, exerting pressure in the joints. As the air is repeatedly compressed, the joints weaken and the rocks shatter.

SEDIMENT TRANSPORT

Sediments are transported along coasts through two related processes: beach drift and long shore drift. These processes are the result of waves approaching the coast at an angle. As waves approaching the coast at an angle break on the beach, the sediments move up the beach as swash and move perpendicularly down the beach as backwash. The resultant zigzag movement along the beach is known as beach drift.

When waves approach the coast at an angle, they generate longshore currents in the nearshore zone and move sediments along the shore. Long shore currents are ocean currents that flow parallel to a coast. The combined effect of sediment movement by longshore currents and beach drift is known as longshore drift. Longshore drift is most
rapid when waves approach a straight coast at an angle of 40° to 50°

SEDIMENT DEPOSITION

Sediments eroded from the coast are transported away and deposited elsewhere. When wave energy decreases, the waves are unable to carry these sediments. Large sediments are deposited first, followed by smaller sediments. Deposited sediments vary in type and
size, resulting in a variety of beaches.

The location of Coasts influences the deposition of sediments. In areas where coasts are sheltered from strong winds, destructive waves are less common. Fine sediments are deposited along sheltered coasts with calm waters such as mangrove coasts. In large sheltered bays, sandy beaches are common. On the other hand, coarser sediments are likely to settle in small bays.