Physical Landscapes in the UK : Rivers Flashcards
Drainage Basin
An area oif land drained by a river and its tributaries
Source
Start of a river
Tributary
A smaller stream that joins a larger river
Confluence
Where a tributary joins a larger river
Watershed
Edge of a river basin
Mouth
End of a river, usually where it joins the sea
How does the cross profile of a river change as you go downstream?
Start - V-shaped valley, steep sided valley, narrow, shallow and turbulent river
Middle - Wider valley, flat floor, wider and deeper river
End - Very wide valley, flat, very wide and deep river with large sediment load
How does the long profile of a river change as you go downstream?
Upper course - Source, steep gradient, shallow but turbulent waters, slower rivers except for rapids (friction)
Middle course - Gentle gradient, deeper water with increased velocity
Lower course - Very gentle gradient, deep water with high velocity
Vertical Erosion
Erosion downwards
Lateral Erosion
Erosion sideways
Hydraulic Action
The force of the water hitting river banks and beds, causing erosion
Attrition
When stones carried byu the river collide against each other, gradually making them smaller and rounder
Abrasion
When load carried by river repeatedly hits the bed or banks dislodging particles into the flow of the river
Solution (process)
When river flows over limestone or chalk, the rock is slowly dissolved, because the water is mildly acidic
Traction
Large boulders and rocks are rolled along river bed
Saltation
Small pebbles and stones bounce along river bed
Suspension
Small particles are carried along by the water
- Silt or clay
Solution (physical)
Dissolved load
Typical Landforms in the upper course of a river
- Interlocking spurs
- V-Shaped valley
- Gorges
- Waterfalls
Typical Landforms in the middle course of a river
- Meanders
- Ox-Bow lakes
Typical Landforms in the lower course of a river
- Levees
- Flood plains
- River estuaries
Deposition
When the velocity of a river decreases, it no longer has enough energy to transport sediment, so it is deposited
Deposition across courses of river
Upper course - Larger rocks get deposited
Finer sediment tends to be carried further downstream, via suspension
Downstream, the river’s gentle gradient decreases velocity, so more sediment is deposited
Interlocking Spurs Formation
- V shaped valley created by vertical erosion
- Rivers are not powerful enough to erode laterally, not enough velocity
- So wind around the hillsides in the way
- Hillsides interlock as river winds around them
- Interlocking spurs is formed
Waterfall formation
- River flows over hard rock lying on top of soft rock
- River erodes soft rock faster, developing a vertical drop where hard rock and soft rock meet
- Plunge pool forms from hydraulic action of falling water
- Rock above plunge pool is undercut and left hanging
- Overhanging hard rock eventually collapses due to force of gravity
- Erosion continues to undercut underneath hard rock
- Process repeats and the waterfall retreats over time, forming a gorge
Gorge formations
- Waterfall retreats upstream
- This leaves a narrow, steep sided valley called a gorge
- Can also be formed at the end of glacial periods when the ice melts
Meander
- Wide bend in river found mainly in lowland areas
- Most efficient course of a river in gentle slopes
Meander Formation
- Thalweg is the line of fastest velocity in the river
- This shifts from side to side, causing greater rates of lateral erosion on river banks via hydraulic action
- Which widens meanders
- Deposition occurs on the insides of bends, and erosion on the outside
Pools and Riffles
Pools formed from erosion of outside of bends
Riffles formed from deposition of sediment on the inside of the bend
Ox-Bow Lake formation
- A meander is created
- Erosion through hydraulic action bends river so that meanders travel towards each other
- The neck of meander eventually breaks creating a straight river
- Old meander is blocked from main river by deposition
- Forming an Ox-Bow lake
Floodplain
Wide flat area of marsh, wet land which lies on either side of the river
- occurs mainly in middle and lower courses
Levee
An enlarged bank built up on each side of the river by deposition during river flooding
Estuary
- Tidal mouth of a large river, where tide meets stream
- A transition zone between fluvial and coastal processes
River Tees
.
Physical Factors causing flooding
- Precipitation (rivers cant contain volume of water, river basins may flood too over consistent rain for days)
- Geology (impermeable rocks, eg. Clay, encourage water to flow overland and into river channels, WHICH INCREASES LAG TIME and increases water volume because it does not absorb water and is likely to cause flooding)
- Steep slopes (mountain environment with steep slopes encourage a rapid transfer of water to rivers, increasing risk of flooding)
Human Factors causing flooding
- Urbanisation (roads are impermeable so can cause flooding due to decreased lag time)
- Deforestation (lack of trees means decreased lag time and aids water flow)
- Agriculture (increased surface runoff in unused soil, decreasing lag time)
What are hydrographs
Graph plotting river discharge measured in CUMECS, against time after a storm
Learn HYDROGRAPHS
.
Hard engineering strategies
- Dams and reservoirs
- Straightening
- Embankments
- Flood relief channels
General Costs of hard engineering schemes
- Temporarily environmentally damaging
- Expensive
- Socially impacting
- Climate change
General benefits of hard engineering schemes
- Financial savings from potential floods
- Lives saved from potential floods
How are Dam’s and reservoirs useful hard engineering strategies?
- Prevent flooding (storage of water)
- Irrigation
- Water supply
- Hydroelectric Power generation
Channel Straightening
- Cutting through meanders to speed up water flow
- Concrete lines inside of river
Pros of Channel Straightening
- Reduces chances of flooding in desired areas
Cons of Channel Straightening
- Expensive
- Destroys riverside habitats
- Ugly
- Causes increased flood risk further downstream
Flood relief Channels
- Man made river channels constructed to by-pass an urban area
- Activated when a river is close to its maximum discharge
Eg. Jubilee River
(110 million to construct)
(11km channel)
(Reduces flood risk for 3000 properties)
Pros of Flood Relief Channels
- Reduce flood risk
Cons of Flood Relief Channels
- Expensive
- Environmentally damaging
- Climate Change
Embankments
- Raised riverbank
- Reduces chances of river overflowing, because it increases its maximum discharge
- Can be through concrete embankments, or dredging rivers
Soft engineering strategies
- Afforestation to increase interception of surface runoff, INCREASES LAG TIME
- Wetland areas used for water storage
- River bank conservation, eg. Planting trees
- Flood warning / preparation
- River restoration
River Restoration
- Changing back to original course of a river
- Slows river and reduces likelihood of flooding
Floodplain Zoning
- Reduces overall costs from flood damage
- Involves avoiding areas which would be affected by flooding, eg. Areas on same relief as rivers
What has been done to reduce the effects of flooding in Banbury?
- Raising A361 road in the flood storage area
- Improvements to drainage beneath roads to prevent flooding
- New earth embankments and floodwalls to protect property
- New pumping station to transfer excess rainwater to a river away from town
- Creation of new habitats to absorb and store excess water
Social costs / benefits of Banbury flood management schemes?
- Raised A361 road reduces impact on local lives
- Quality of life for locals is improved with new footpaths and green areas
- Reduced anxiety through fear of flooding
- Noise pollution
Economic costs / benefits of Banbury flood management schemes?
- £18 million in costs
- Benefits are estimated over £100 million
- Over 500 properties will be protected from flooding
Environmental costs / benefits of Banbury flood management schemes?
- 100,000 tonnes of earth were required to build the embankment, creating a small reservoir
- Habitats were created, eg. Ponds, trees, hedgerows
