2B.8A - Human Activity and Coastal Recession
Rapid coastal recession is caused by physical factors (geological and marine) but can be influenced by human factors (dredging or coastal management) (The Nile Delta of the Guinea coastline or Californian coastline) (A: actions of different players may alter natural systems)
Rapid coastal erosion is caused by physical factors when geological and marine characteristics combine to promote erosion.
Geological factors include:
Human activity can increase rates of coastal recession by interrupting the operation of the sediment cell. The construction of major dams of rivers can trap river sediment behind the dam wall. This then starves the coast of a sediment source, leading to serious consequences.
The construction of the Aswan High Dam on the River Nile in 1964 reduced sediment volume from 130 million tonnes to about 15 million tonnes per year. Erosion rates jumped from 20-25 m per year to over 200 metres per year as the delta was starved of sediment.
Dredging
This is the removal of sediment from a beach, sea or river.
Rapid coastal erosion is caused by physical factors when geological and marine characteristics combine to promote erosion.
Geological factors include:
- Lithology - soft rock type, weak cohesive bonds, porous rocks
- Geological structure - well jointed rocks, rocks with seaward dipping beds, heavily faulted rocks
- long wave fetch promoting large, destructive waves
- strong longshore drift that quickly removes collapsed sediment allowing erosion to restart
Human activity can increase rates of coastal recession by interrupting the operation of the sediment cell. The construction of major dams of rivers can trap river sediment behind the dam wall. This then starves the coast of a sediment source, leading to serious consequences.
The construction of the Aswan High Dam on the River Nile in 1964 reduced sediment volume from 130 million tonnes to about 15 million tonnes per year. Erosion rates jumped from 20-25 m per year to over 200 metres per year as the delta was starved of sediment.
Dredging
This is the removal of sediment from a beach, sea or river.
- Sands or gravels scooped/sucked up for use by construction industry
- Dredging of river mouths and estuaries often to maintain navegable channel for ship transport