Rivers in Coastal Landscapes Summary

Rivers as a Sediment Source

  • Rivers serve as a major input into the coastal Sediment Cell through Fluvial Deposition.

  • The Nile: Historically a prograding delta; the Aswan Dam now traps sediment, leading to coastal erosion of up to 200 m/year200\,m/year.

Estuaries and Salt Marshes (Haloseres)

  • Flocculation: A chemical process where saltwater causes river clay particles to clump together and sink.

  • Succession: Mudflats are colonized by salt-tolerant plants like Salicornia, trapping sediment to form a Salt Marsh.

Submergent Landforms: Rias

  • Formation: Drowned V-shaped river valleys caused by eustatic sea-level rise.

  • Description: Wide at the mouth and narrow inland; unlike a Fjord, a Ria is purely fluvial/river-shaped.

  • Example: Kingsbridge Estuary in South Devon.

Deltas

  • Condition: Formed when river sediment supply exceeds the rate of removal by waves and tides.

  • Arcuate Delta: Fan-shaped, such as The Nile.

  • Cuspate Delta: Tooth-shaped, such as The Tiber in Italy.

  • Bird’s Foot Delta: Sediment fingers extend outward, such as The Mississippi.

The Drainage Basin Link

  • Hjulström Curve: Explains how river velocity dictates the transport of sediment, from large boulders to fine silts.

  • Deforestation: Increases soil erosion and river sediment, causing Spits and Deltas to grow.

  • Dams: Lead to "sediment starvation" and rapid coastal recession downstream.