Step by step on forming an oxbow lake
- Meanders in river erode on the outside
- Outside erosion causes meanders to get closer together
- A flood causes a shorter route for the water to take
- Deposition on the edge of the new river cuts off the meander from water
Step by step on forming of a meander
- Flow of river swings side by side
- Erodes the bank, undercuts, steep, river cliff on outside of bend
- Deposition on inside of bend makes slip off slope
Step by step on forming a waterfall
- Soft rock erodes faster than hard rock
- Soft rock erodes upstream and undercuts the hard rock
- Bottom of waterfall is a plunge pool
- Undercut worsens then the overhang collapses due to gravity
- Retreats upstream, forms a gorge
What river landforms are found in the upper course?
V shaped valley
Waterfall
Gorge
Interlocking spurs
What river landforms are found in the middle course?
Meander
Oxbow lake
Flood plain
What river landforms are found in the lower course?
Mudflats
Natural levees
Estuary
How do the characteristics of the river change from the source to the mouth? (Include a case study)
CS: River Severn Land gradient goes from 30 degrees to 3 Width goes from 1m to 70m Depth increases from 15cm to 10m Velocity increases from o.25m/s to 10m/s
Define attrition
Rocks collide together and make them smaller, rounder and smoother
Define hydraulic action
Water and air get into cracks and make them larger
Define abrasion
Rocks are thrown at cliffs or banks from high energy water
Define corrosion
Water dissolves and wears away banks
What are the three steps to slumping?
1) Heavy rain lubricates the rock and makes it heavier
2) River erodes the bottom of the valley sides making them steeper
3) The steep slope slides down in rotational way
What is soil creep?
The movement of objects in the earth down hills from particles of soil moving downhill and being eroded away by rivers
Step by step on forming a natural levee
- Formed on a river that carries lots of sediment
- The river floods and the sediment is deposited on the edge of the river as the water has lost velocity
- More flooding causes higher levees
- Can be reinforced by humans to prevent floods
How are interlocking spurs formed?
River finds the fastest route by curving around mountain bases and then eroding into them to make the spurs interlock
How are floodplains formed?
A wide flat area of land around the river that has lots of sediment from rivers flooding and the water spreading over it
What are the physical causes of flooding?
Intensity of rainfall Length of rainfall Snow melt Relief Shape of drainage basin Size of drainage basin Vegetation Geology
What are the human causes of flooding?
Deforestation
Burning fossil fuels
Putting tarmac down instead of gravel
What is the HIC case study for floods, and the cause of flooding?
Boscastle, Cornwall, UK
16th August 2004
75mm of rainfall fell in 2 hours
Confluence of Rivers Valency, Jordan and Paradise
What are the key impacts of the HIC case study flood?
- £50 million damage to houses businesses and land
- 100 cars swept away
- 58 properties flooded and 4 swept away
- 300m of sewage pipe blocked
What is the LIC case study for floods, and the cause of flooding?
Mozambique, Africa January to 22nd of February 2000 3 days of heavy rain, then 5 weeks Cyclones hit in February Water levels rose 8m in 5 days from 6 rivers
What are the key impacts of the LIC case study flood?
- Many cases of cholera
- 250,000 peoples houses destroyed
- Cost £175 million to rebuild transport
- 83% of people work in agriculture- damaged crops
- Floods displaced rodents and snakes
Name four river management strategies and whether they are hard or soft engineering
Dams- HARD
Flood walls- HARD
Washland- SOFT
Straightening the river- HARD
What is one of the case studies for managing the effects of flooding, and why is it prone to flooding?
Khulna, Bangladesh
80% of Bangladesh is floodplains
Most land is under 10m above sea level
