Processes and Landforms of the Willamette River and Floodplain
5 - River Processes and Pressures
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Dynamic Planet - River Processes and Pressures - 5 River Processes and Pressures How do rivers change from source to mouth? Along a river’s upper course, near the source, ‘vertical erosion’ is dominant forming V-shaped valleys, waterfalls and gorges. In the middle course ‘lateral erosion’ and deposition result in meanders, ox- bow lakes and flood plains. The lower course (towards the mouth) sees large meanders, flood plains and deposition to form estuaries and deltas. Changes in cross and long profile
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5 - River Processes and Pressures
Transcript of 5 - River Processes and Pressures
Dynamic Planet - River Processes and Pressures - 5
River Processes and Pressures
How do rivers change from source to mouth? Along a river’s upper course, near the source, ‘vertical erosion’ is dominant
forming V-shaped valleys, waterfalls and gorges. In the middle course ‘lateral erosion’ and deposition result in meanders, ox-bow lakes and flood plains. The lower course (towards the mouth) sees large meanders, flood plains and deposition to form estuaries and deltas.
Changes in cross and long profile
Features: The upper course:E.g. The River Wharfe, N. England: source – Buckden Beck
Weathering: Biological (breakdown of rocks by plant roots and burrowing animals), Chemical (breakdown of rock due to slightly acidic rain dissolving limestones), Physical (breakdown of rock due to freeze- thaw process).
Mass movement: Carries weathered material, (scree) down slope.
Dynamic Planet - River Processes and Pressures - 5
Features: The middle course:
Features: The lower courseE.g. The River Wharfe, N. England: mouth – Humber Estuary, North Sea
Over time continued erosion can lead to the development of an ox-bow lake.
Estuaries:Estuaries are formed where the river meets the sea. As the river meets the sea it loses speed and deposits material. This forms mudflats. These can be colonised by plants and wildlife. These plants will be adapted to live in salty conditions because the tides make the area a ‘salt marsh’.
Dynamic Planet - River Processes and Pressures - 5
River Flooding
What are the causes of floods?
Physical Causes Human CausesProlonged rainfall: This saturates the soil until it can absorb no more water.
Deforestation: Cutting down trees means less water is intercepted and used by trees.
Hard Dry Soil: Soils baked hard by dry weather, rain can’t soak into it easily so will run over and flood instead.
Human Interference: Humans often try to prevent floods, (e.g. by levees) they may work in some cases but often make matters worse if they fail.
Weather Conditions: Hurricanes and storms can make problems worse with periods of intense rainfall.
Urbanisation: Building cities means water cannot be absorbed into soil; instead it flows over concrete and fills drains.
Snow melt: Temperatures can rise and melt snow.
Global Warming: Could cause more intense rainfall which can lead to flash floods
Flat Land: This can be a problem because flood water has no-where to drain.
What are the effects of flooding?
Dynamic Planet - River Processes and Pressures - 5
How can flooding be managed?
Hard Engineering: Are to control nature. They are usually expensive and can have a negative impact on the environment.Soft Engineering: A more sustainable approach, as it works with nature. It will also help the local environment and is cheaper.
1) River Sheaf, Loxley and Don –Sheffield: Generally hard engineering, these made flooding worse in 2007 when they where overwhelmed: 2 people drowned, 1200 homes flooded, 1000 businesses affected. – Drains and embankments overflowed.2) River Skerne – Darlington Soft engineering (flood plain zoning> no building on flood plain, so no damage, restoring meanders, to slow the river flow down), has prevented property damage and improved local ecosystems.
