Rivers

Upper course

• vertical erosion

• large bedload

• low velocity

• V shaped valley

• Shallow and narrow

Middle course

• lateral erosion

• Wider

• Higher velocity

• Smoother bedload

Lower course

• wide and flat

• Deposition

• smooth bed channel

• High velocity

Estuary

• At the mouth of the river

• Tidal water

• When high tide - water floods over the land, carries slit and sand onto the valley floor

• When tide is at its highest point - water loses energy and slows down - deposition

• Overtime more mud builds up - mudflats

Levees

• during a flood material is deposited

• Heaviest material - deposited closest to the river’s channel as it gets dropped first when river slows down and looses its energy

• Builds up over time

Flood plains

• Wide valley floor that often floods

• Flood - water slows down and looses energy

• This builds up flood plain

• Migration of meanders also leads to formation of flood plains

Waterfalls

1. When river falls over area of hard then soft rock

2. Softer rock is eroded more than hard rock - step

3. Water flows over the step erodes soft rock further - steep drop is created (waterfall)

4. Hard rock is eventually undercut by erosion and collapses

5. Waterfall retreats upwards, leaving behind a gorge

Interlocking spurs

• Upper course - erosion is vertical - steep sided valleys

• Areas of hard rock that are harder to eroded - river bends around them

Meanders

• Outside bend - current is faster because it is deeper - more erosion - river cliifs

• Inside bend - current is slower because it is shallower - deposition - slip off slopes

Ox bow lakes

1. form from meanders

2. erosion - outside bends get closer until small bit is left

3. flood - river flows through the neck

4. deposition then cuts off the meander

Discharge

volume of water flowing per second measured in cumecs

Hydrograph

relation of rainfall to discharge

Flood factor - Physical

1. Precipitation - prolonged rainfall/heavy rainfall

2. Geology - impermeable rocks

3. Relief - steep sided valley

Flood factors Human

• Urbanisation - roads covered in tarmac

• Deforestation

• Farming

• Climate change - extreme weather

HE - damn

• Barriers in the upper course

• store water - HEP

• expensive

• habitat destruction

Embankments

• raised walls along a river bed

• more capacity

• expensive

• if flood, water cant drain back

Channel straightening

• meanders removed by building a straight channel

• water leaves quickly

• risk of flooding downstream

Flood Relief Channels

• Diverts water to increase capacity

• expensive

• risk of downstream flooding

SE - flood warning

• less impact - gives people time to prepare for the flood

• does not prevent floods

SE afforestation

• more interception less soil erosion

• takes long time

Plain zoning

• restrictions to prevent building on the flood plain

• less impermeable surfaces

• too late in urban areas

River restoration

• making it more natural

• increases capacity

• little maintenance

• local flood risk and angry farmers