CHAPTER 8: FLUVIAL PROCESSES, PATTERNS AND LANDFORMS
3. Flood plains Main processes: flooding, deposition Example: River Suir, CountyWaterford Aflood plain is a flat area of land either side of the river. Flood plains are created by river deposition. They may be found in the mature and old stages of a river.
IN DEPTH – Flood plains
Meanders swinging across the valley floor remove interlocking spurs as they migrate downstream. Doing this, they create a flat area in the centre of the valley. This is the flood plain. During a flood the river overspills its banks and the flood water flows across the flood plain. As the river spreads out across the flood plain it loses some of its energy. This causes the river to slow down. The flood water gradually soaks (percolates) into the ground, depositing a thin layer of sediment known as alluvium onto the flood plain. This is very fertile. These sediments may be many metres deep representing centuries of repeated flooding. Because of their flat and fertile nature, flood plains are heavily populated. The edges of flood plains are known as bluffs. One of the flattest flood plains in Ireland is that found on the River Suir near Clonmel. Flood plains are a river’s safety valve. In times of heavy rain the river has to
overflow its banks onto its flood plain. The flat ground slows the river down and encourages deposition. This reduces the damage caused by erosion.
Bluffs: low hills created by meanders as they remove interlocking spurs
Flood plain
Alluvium
During flood: flood plain area covered with water
Percolation of flood water
Fig. 35 Exam Diagram: An uncovered and covered flood plain 121