UK Physical landscapes- Rivers Flashcards
What is a Water Table
- Upper level of saturated rock/soil where no more water can be absorbed
What is groundwater flow
Water flowing through the rock layer parallel to surface
What is through flow
- Water flowing through soil layer parallel to surface
What is surface runoff
- Water flowing on top of the ground
What is evaporation
- Water lost from ground/vegetation surface
What is transpiration
- Water lost through pores in vegetation
What is groundwater storage
- Water stored in rock
What is percolation
- Water seeping deeper through rock
What is soil moisture
- Water held in the soil layer
What is infiltration
- Water sinking into the soil/rock from ground surface
What is surface storage
- Water held on the ground surface eg. puddles
What is interception
- Water being prevented from reaching surface by vegetation or trees
What is precipitation
- Any source of moisture reaching the ground e.g rain
What is the source
- Start of river
What is a drainage basin
- Area of land drained by a river and its tributaries
What is a confluence
- Where a tributary joins a larger river
What is the mouth of a river
- end of a river- usually where it meets the sea
What is the watershed
- The edge of a river basin
What is a tributary
- A small stream that joins a larger river
How many courses of the river are their
- 3
-Upper, middle, lower
How does relief of river valley change from source to mouth
- Starts steep and becomes flatter
Characteristics of upper course of river
- Steep, V shaped valley
- Narrow channel
Characteristics of middle course of river
- Less steep, more U shaped valley
- Wider channel
Characteristics of lower course of river
- Flat valley
- Very wide channel
What does fluvial mean
- To do with rivers
What is erosion
- the wearing away of the river’s banks and beds
Type of erosion in upper course of river
- Vertical erosion
Why does vertical erosion happen
- Higher up and steep gradient means higher gravitational store, therefore water cuts through the land in order to get down
Type of processes in middle course of river
- Lateral erosion
- transportation
- (some) deposition
Why does lateral erosion happen
- A more gentle gradient means the water moves from side to side, eroding the side of bank
What process occurs in lower course of river
- Deposition
- transportation
Why does deposition occur
- happens in lower courses of river, as river loses its energy and drops material that has been eroded
What is hydraulic action
- When force of the river compresses air trapped in cracks in the banks, meaning increased pressure with gradually wears away the bank
What is abrasion
- When rocks carried buy river scrape and rub along the bed and bank of river, wearing them down
What is solution (erosion)
- Where water is slightly acidic, and dissolves certain types of rock on river bed
What is attrition
- When rocks carried by the river collide with each other and break into smaller pieces
What is a river’s load
- Material carried by a river
What is a river’s discharge
- Amount of water in a river at a given time
What is traction
- Large boulders and rocs being rolled along the river at times of high discharge
What is saltation
- Small rocks and sand particles bounced along the river
What is suspension
- Fine clay and sand particles suspended in the water even at low discharges
What is solution (transportation)
- Some minerals dissolving in water
Reasons for deposition
- Flooding
- Meanders
- at river mouth
How does flooding cause deposition
- Friction with the land slows water down and so material deposited
How do meanders cause deposition
- on the inside of the bend, the river is moving at a slow speed, and so material deposited
How do river mouths cause deposition
- River slows down as it reaches large body of water
What is a floodplain
- The land that gets flooded when the river overflows
Upper course of severn landforms
- Waterfalls
-Severn breaks its neck
Middle course of severn landforms
- Meanders near Welshpool
- Oxbow lake near Caersws
Lower course of severn landforms
- Levees near Minsterworth
- Floodplain in Tewkesbury
- Severn estuary
- Mudflats in Chepstow
What are interlocking spurs
- Steep sided hills which interlock with each other as river winds round them
How are interlocking spurs formed
- Vertical erosion
-cuts into landscape at angles
How is a waterfall formed
- Water running over hard rock on the top, and softer rock on the bottom
- soft rock erodes faster due to hydraulic action and abrasion, causing the soft rock to undercut the hard rock
- hard rock left unsupported, and so collapses into river bed
How are gorges formed
- When a waterfall retreats, it causes a steep sided gorge to be left behind
What is Thalweg
- Fastest flow of river
What is a meander
- A large curve in river
Characteristics of meander
- Thalweg on outside bends, leading to erosion of bank- undercut ledge
- Slow water flow on inside bend, leading to deposition
What is an Oxbow lake
- An old meander that’s neck has been cut through as river has taken fastest course and not gone around meander
What is a levee
- A raised embankment next to a river
How does a levee form
- During a flood, water passes over surface causing deposition of material due to friction, causing areas around the river channel to have raised embankments
How does a floodplain form
- A build up of sand, silt and clays which have been deposited around a river due to a flood, resulting in a flat piece of land around river
What is an estuary
- When the river meets the sea
What are mudflats
- When there is less water at a river estuary, causing the river to deposit silt forming a mudflat
What is flooding
- When amount of water in a river exceeds capacity of river channel, causing banks to burst
Physical factors effecting flood risk
- Relief of land
- Rainfall
- Basin size
- Rock type
- Saturation of soil
Human factors effecting flood risk
- Urbanisation
- Deforestation
How does urbanisation increase flood risk
- More impermeable rock means water flows over roads and into drains to rivers
How does deforestation increase flood risk
- Less interception means water is transferred more rapidly to river channels
How does rock type effect flood risk
- Impermeable rocks don’t allow water to pass through them, meaning water will not seep into rock and so increases flood risk
How does basin size effect flood risk
- Small river basins cannot store as much water meaning more likely to overflow, increasing flood risk
How does soil saturation effect flood risk
- When soil cannot absorb any more water it becomes over saturated and causes flow of water over land
How does relief effect flood risk
- Steep slopes allow for water to run over land quickly leaving little time to seep into soil, therefore more water enters river channels
How does precipitation effect flood risk
- Torrential rainstorms can lead to sudden flash floods as channels cannot contain volume of water falling into them
What is lag time
- Number of hours between peak rainfall and peak discharge
What is the rising limb
- The increase of Discharge in comparison to time
What does steep rising limb mean
- Short lag time- flood happened quickly as discharge increased rapidly
What are hard engineering strategies
- Involves manmade structures to control flow of river and prevent flooding and erosion
What are soft engineering strategies
- Involves managing a river using natural materials and mimicking natural processes to protect more vulnerable areas
Examples of hard engineering strategies
- Dams
- Channel straightening
- Embankments
- Flood relief channels
Examples of soft engineering strategies
- flood plain zoning
- planting trees
- river restoration
- flood warning and preparation
How do dams prevent flooding
- Large concrete barrier built to create a reservoir
- The amount of water released is monitored to control the amount flowing downstream
How does channel straightening prevent flooding
- Meandering areas are made more widened, straightened and deepened meaning more water can be carried
How do embankments prevent flooding
- Increasing height of river banks means more water is contained in the channel
How does flood relief channel prevent flooding
- another channel built to move water away from human settlements at times of high discharge
- essentially a back-up channel for a river that frequently floods
What are the 3 levels of flood warnings
- Flood watch
- Flood warning
- Severe flood warning
What is ‘flood watch’
- Expectance of people in low-lying areas to watch river channels and be prepared
What is ‘flood warning’
- When there is a threat to homes and businesses
- People advised to move valuables upstairs and turn of electricity and water
What is ‘severe flood warning’
- Extreme danger to life and property expected-
- proper informed to turn of electricity and water, and leave property
What is flood plain zoning
- Restriction of land uses in high flood risk areas to prevent damage to high value land uses such as housing
Positives of flood plain zoning
- Low cost
- reduces insurance costs
Negatives of flood plain zoning
- Restricts economic development
- hard to implement where urban areas already in flood plains
- contributes toward UK housing crisis
Where is Jubilee river relief channel
- Flows through old Windsor, Eton and Wraysbury
Average house price in Windsor
- £547,000
Average house price in Wraysbury
- £430,000
Cost of Jubilee river
- £330 Million- exceeded budget
Length of Jubilee river
- 11.7 Km
Cost of repairing jubilee channel after flooding
£680,000
When was Jubilee river completed
2002
Width of Jubilee river
- 50m
How many homes does Jubilee river protect from flood risk
- 3,200 Approx
Issues with Jubilee river relief scheme
- Increases risk of flooding downstream in less wealthy areas such as Wraysbury and Old Windsor due to merging to two channels, shown in intense flooding in 2014
- Means insurance more expensive in these areas- Business insurance costs £500m in Wrasybury in 2014
Positives of Jubilee scheme
- protects 3,200 homes from flooding
- 38 hectares of reed bed created as part of landscape corridor
- 193 hectares of native woodland created
- 326 hectares of wildflower grasslands planted
Length of River severn
- 354KM
