11.4 River erosion and deposition landforms Flashcards
What are meanders?
➢ Wide bends of a river found mainly in lowland areas
What are the processes responsible for meanders?
➢ Lateral erosion and deposition in the river channel
What is the thalweg?
➢ Line of fastest flow within the river
How does a meander form?
➢ When water in the stream channel erodes the sediments of an outer bend of a streambank and deposits this and other sediment on subsequent inner bends downstream.
What are pools?
➢ Alternating deep sections
What are riffles?
➢ Alternating shallow sections
Where are pools usually found?
➢ Outside bends of the meanders where there is a faster flow of water
How are ox-bow lakes formed?
➢ Over time as meanders migrate across the valley floor, they may start to erode towards each other
➢ Gradually the neck of the meander narrows until it is completely broken - usually by hydraulic action and abrasion
➢ Then when it is completely broken a straighter channel is formed where water takes the shortest route
➢ The meander is cut off by deposition sealing of the old meander
What is a floodplain?
➢ A wide - flat area of marshy land on either side of a river - found in the middle and lower courses
Why are floodplain useful?
➢ As they are very fertile
How are floodplains formed?
➢ Meanders migrate across the floodplain due to lateral erosion.
➢ When they reach the edge of the floodplain they erode the valley side (bluff)
Or:
➢ When the river floods it deposits silt creating a very flat floodplain
How are levees formed?
➢ Levees are formed by the repeated flooding of the river.
➢ When the river floods, the biggest, most coarse material will be dumped close to the river banks due to the low velocity of the river here
➢ This will continue to build up the levee over time
What is a levee?
➢ A raised river bed found alongside a river ints lower course
What are estuaries?
➢ Transitional zones between the river and coastal environments and are affected by wave action as well as river processes
How are salt marshes formed?
➢ During a rising tide river water is unable to be discharged into the sea
➢ The river’s velocity falls and sediment is deposited
➢ At low tied these fine deposits form extensive mudflats
➢ Overtime plants and habitats start to grow and a saltmarsh is formed
