Beaches

• A beach is an area of sediment deposition on a coastline. They are formed by constructive waves.
• 𝙄𝙉𝙋𝙐𝙏𝙎:

  • erosion
  • weathering
  • seabed
  • estuaries
  • rivers
  • tides
• 𝙊𝙐𝙏𝙋𝙐𝙏𝙎:

  • destructive waves
  • storm surges
• A beach acts as a large sediment store.
• 𝙁𝙇𝙊𝙒𝙎:

  • longshore drift
  • wave refraction
• Beach accretion is the building up of a beach via constructive waves. Input is greater than output (deposition is greater than erosion).
• Beach excavation is the removal of sediment from a beach via destructive waves. Output is greater than input (erosion is greater than deposition).
• 𝙎𝙒𝘼𝙎𝙃-𝘼𝙇𝙄𝙂𝙉𝙀𝘿:

  Sediment moves up and down the beach with little lateral transfer. This is caused by wave refraction and typically occurs in bays.
• 𝘿𝙍𝙄𝙁𝙏-𝘼𝙇𝙄𝙂𝙉𝙀𝘿:

  Sediment is transferred along the coast by longshore drift.
• SWASH-ALIGNED BEACHES:

  • form in low-energy environments such as bays
  • found between two headlands
  • crescent-shaped due to wave refraction
  • waves approach roughly parallel to shore
  • can be sand, shingle, or mud
• DRIFT-ALIGNED BEACHES:

  • usually end in spits
  • longshore drift moves sediment along the beach
  • waves usually approach the shore from an angle caused by prevailing winds
  • are typically 'graded' - large pebbles are dropped first and fine sediment travels further along the beach
  • can be sand, shingle, or mud
• A beach ends where waves break during low tide.
• Beaches often extend out quite a way offshore (continental shelf).
• The backshore is above the influence of waves.
• The foreshore is influenced by waves.
• Offshore is beyond the influence of breaking waves.
• Burms are a flat strip of land, raised bank, or terrace, bordering a river or canal.
• Cusps are shoreline formations made up of various grades of sediment in an arc pattern.
• Runnels are channels in the sediment that look like ridges.
• A longshore bar is a ridge of sand, gravel, or mud built on the seashore by waves and tidal currents, generally parallel to the shore and submerged by high tides.
• A storm beach is a ridge composed of the biggest boulders thrown by the largest waves. It is above high tide.
• Burms mark the successively lower high tides below the storm beach as the cycle goes from spring to neap. They are beach ridges built up by constructive waves.
• Cusps are semi-circular-shaped depressions which form when waves break directly onto the beach and swash and backwash are strong.
• The idea of equilibrium is especially significant for drift-aligned beaches as without a continual supply of sediment, the longshore drift would remove it faster than it was deposited.
• Explain why larger, more angular pebbles tend to be found higher up the beach.

  During storm conditions, larger material can be thrown up the beach by the high-energy waves, settling on the storm beach. This is located above high tide and therefore is unreachable by incoming waves under normal conditions. This explains why they are angular as they are not eroded via hydraulic action or attrition by the waves.
• Describe the differences between summer and winter beach profiles.

  High-energy destructive waves dominate during the stormier winter months, whereas low-energy constructive waves are more common in the calmer summer months. Sandy beaches are eroded in the winter when the destructive waves excavate the beach sediment via strong backwash. As smaller particles require less energy to be transported, beaches can be depleted quickly, creating a lower, steeper, narrower beach. A beach profile during the summer would be higher, wider, and more gradual as beach accretion would replenish the sediment.
• A spit is a long and narrow finger of sand or shingle jutting out into the sea. They form where there is an estuary, and as a result of longshore drift.
• Spits are determined by the prevailing wind direction and form on coasts where there is significant longshore drift. If the coast changes orientation it bends sharply. Sediment is then deposited out at sea and forms an extension to the land. Strong winds or tidal currents may bend the spit further.
• 𝙎𝙄𝙈𝙋𝙇𝙀 𝙎𝙋𝙄𝙏𝙎:

  • straight or recurved
  • do not have minor spits or recurved ridges along their landward edge
• 𝘾𝙊𝙈𝙋𝙊𝙐𝙉𝘿 𝙎𝙋𝙄𝙏𝙎:

  • have a number of recurved ridges or minor spits along their landward edge
  • e.g. Hurst Castle
• Bars form when spits develop across a bay where there is no strong flow of water from the landward side and the sediment reaches across the other side.
• Bars trap fresh water behind them to form lagoons.
• An offshore bar forms further out to sea. Waves approaching a gently sloping coast deposit material due to friction with the seabed. This causes mounds to form on the seabed and waves break out at sea instead.

  E.g. Chesil Beach, Dorset.
• Tombolos occur when a spit joins an island to the mainland.
• Barrier islands are long, thin islands that run parallel to the coast.