Coasts

• Over 1 billion people live on the coast
• About 50% of the world's population live within 200 km of the coast
• The littoral zone is a dynamic area of high risk that includes coastal flooding and coastal erosion
• Littoral zone


  • Coast land adjacent to the sea and often heavily populated and urbanised
• Backshore zone

  • Above high tide level and only affected by waves during exceptionally high tides and major storms
• Foreshore


  • Where wave processes occur between the high and low tide marks
• Nearshore

  • Shallow water areas close to land and used extensively for fishing, coastal trade and leisure
• Offshore


  • The open sea
• Classifying coastal landscapes

  Coasts can be divided into two main types:

  1 rocky (or cliffed) coastlines with cliffs varying in height from a few metres to hundreds of metres

  2 coastal plains (with no cliffs) where the land gently slopes towards the sea across an area of deposited sediment, often in the form of sand dunes and mud flats.

  Cliffs create a sharp distinction between land' and 'sea' whereas coastal plains gradually transition from land to sea.
• Primary coasts

  Dominated by land-based processes, such as deposition at the coast from rivers or new coastal land formed from lava flows
• Emergent coasts

  Where the coast is rising relative to sea level, for example as a result of tectonic uplift
• Tidal range on coastlines

  • Microtidal (tidal range of 0-2 m)
  • Mesotidal (tidal range of 2-4 m)
  • Macrotidal (tidal range greater than 4 m)
• Low energy sheltered coasts


  With limited fetch and low wind speeds resulting in small waves
• Secondary coasts

  Dominated by marine erosion or deposition processes
• Submergent coasts

  Being flooded by the sea because of sea level rise and/or subsiding land
• High energy exposed coasts

  Facing prevailing winds with long wave fetches resulting in powerful waves
• Rocky coasts

  Many coastlines consist of rocky cliffs that vary in height from a few metres (low relief) to hundreds of metres (high relief). High relief cliffs are composed of relatively hard rock. There are two main cliff profile types:

  Marine erosion dominated: wave action dominates and cliffs tend to be steep, unvegetated and there is little rock debris at the base of the cliff.

  Subaerial process dominated: not actively eroded at the base by waves; shallower, curved slope and lower relief; surface runoff erosion and mass movement are responsible for the cliff shape.
• Coastal plains

  Low-lying, flat (low-relief) areas close to the coast are called coastal plains. Many contain estuary wetlands and marshes, being just above sea level and poorly drained because of the flatness of the landscape.
• Erosion rate

  Variations in erosion rate
• Rates of erosion are not constant and are influenced by different factors
• On the Holderness coast in East Yorkshire, average annual erosion is around 125 m, but there are wide variations in this rate, from 0 m per year to 6 m per year
• Reasons for variations in erosion rate on Holderness coast

  • Coastal defences at Hornsea, Mapleton and Withensea have stopped erosion, starving places further south of sediment
  • Erosion rate generally increases from north to south
  • Some areas of boulder clay are more vulnerable to erosion than others
  • Some cliffs are more susceptible to mass movement
• Erosion of Holderness varies over time

  1. During winter, 2-6 m of erosion is common when storms, combined with spring tides, increase erosion rates

  2. Summer erosion, during periods when constructive waves dominate, is much lower
• Northeasterly storms cause most erosion because of the long wave fetch of 1500 km from the north Norwegian coast
• Shape of the beach on Holderness

  • Ords are deep beach hollows parallel to the cliff which concentrate erosion in particular locations by allowing waves to directly attack the cliff with little energy dissipation
  • Ords slowly migrate downdrift by about 500 m per year so the location of most erosion changes over time
  • Ord locations erode four times faster than locations without ords
• Rapid coastal retreat

  Rapidly eroding coasts
• Physical features of rapidly eroding coasts

  • Long wave fetch
  • Large destructive ocean waves
  • Soft geology
• Human stone can make the situation worse

  Usually interfering with the coastal sediment cell
• How human interference can worsen coastal erosion

  1. Construction of major dams on rivers

  2. Trapping river sediment behind dam wall

  3. Starving the coast of a sediment source

  4. Serious consequences
• Examples of dams causing coastal erosion

  • Aswan High Dam on the River Nile in 1964
  • Akosombo Dam in Ghana in 1965
• Aswan High Dam reduced sediment volume from 130 million tonnes to about 15 million tonnes per year
• Erosion rates jumped from 20-25 metres per year to over 200 metres per year as the Nile delta was starved of sediment
• Akosombo Dam reduced the flow of sediment down the River Volta from 70 million cubic metres per year to less than 7 million
• Submergent coastlines

  Coastlines that were never altered as a result of glacial sea level rise
• Submergent coastlines were submerged (drowned) when present glacial sea level rose
• Submergent coastlines

  • Found in southern England and on the east coast of America
• Major impacts on longshore drift and coastal erosion in Ghana and even in neighbouring countries due to Akosombo Dam
• Ria


  The most common coastal landform
• Fjords

  • Drowned valleys, but they differ from rias in that the drowned valley is a U shaped glacial valley and the fjord is often deeper than the adjacent sea, some are more than 1000 m deep
  • At the seaward end of the fjord there is a submerged lip, representing the former extent of the glacier that filled the valley
• Barrier island landforms

  • Found on the east coast of the USA (Figure 49)