Rivers (unknown only) Flashcards
What is a hydrograph, and what are the different features on it?
A hydrograph shows how the discharge in a river changes in relation to rainfall.
- Peak rainfall - highest point of rainfall
- Rising limb - as discharge increases
- Peak discharge - highest point of discharge
- Lag time - time between peak rainfall and peak discharge
- Falling limb - as discharge decreases (this is slower than the rising limb)
What are the factors affecting flood risk?
- Heavy rainfall
- Geology (rock type)
- Prolonged rainfall
- Relief (changes in land height)
- Land use (cities have many impermeable surfaces, increasing runoff; trees intercept rainfall on leaves, which evaporates, and also take up water in roots).
What hard engineering methods deal with flood risk?
Dams and reservoirs:
- Reservoirs store water
- Can generate hydroelectric power
- Expensive
- Reservoir may flood existing settlements
- Material deposited in reservoir - less fertile land downstream
Channel straightening:
- Meanders are removed
- Water leaves the area quickly, minimising flood risk
- May flood areas downstream
- Increased erosion
Embankments:
- Raised walls along river banks
- The river can hold more water; less frequent flooding
- Expensive
- Severe flooding if water rises above embankments
Flood relief channels:
- Divert water if levels get too high
- Increased discharge where the rivers join back up again: potential for flooding
What soft engineering methods deal with flood risk?
Flood warnings and preparation:
- Gives time to evacuate and protect possessions; reduced impacts
- Preparation doesn’t guarantee safety
Flood plain zoning:
- Prevent building on parts that are likely to be flooded
- Fewer impermeable surfaces
- Limits expansion of an urban area
Planting trees:
- Increased interception
- Reduces soil erosion
- Less land available
River restoration:
- Removing man-made levees for natural flooding
- Better habitats for wildlife
- Local flood risk can increase
Where is the River Tees?
The River Tees is in the north-east of England, and its source is in the Pennine Hills.
What features are in the upper course of the River Tees?
- Steep-sided V-shaped valley (vertical erosion)
- Large, rough load
- Bogs, marshland
- Interlocking spurs
- Cow Green Reservoir
- High Force Waterfall (hard windstone over soft limestone)
What features are in the middle course of the River Tees?
- Wider, curving U-shaped valley (lateral and vertical erosion)
- Meanders
- Oxbow lakes
what features are in the lower course of the River Tees?
- Very wide, flat valley (lateral erosion)
- Larger meanders
- Human industry, ports and settlements in Yarm, where two meanders were artificially cut off to straighten the channel to allow boats to sail inland quicker.
- Flood plains
- Levees
Why were flood defences needed in Oxford?
- Oxford is at the confluence of the River Thames and the River Cherwell.
- In July 2007, there was intense flooding, causing over 250 homes to be evacuated, and later flooding occurred in 2014 too.
What was the flood management scheme in Oxford?
- Excavating a flood relief channel outside the city centre.
- Using excavated material to build new flood walls and embankments.
- Planting 20,000 trees and shrubs around the excavated area
- Increasing water storage in the floodplain, and increasing capacity of bypass channel.
What were the social impacts of the scheme?
- Compulsory Purchase Orders were sent to land owners whose land was needed to widen the flood plain.
- Construction disrupted residents’ lives, such as through noise pollution and large vehicles.
- The scheme improved public footpaths, providing more opportunities for recreation.
- Residents felt more confident their homes were flooded.
What were the economic impacts of the scheme?
- Cost over £120 million in total, not all funding secured.
- Over 1000 homes and businesses better protected, so less risk of expensive damage and rising insurance costs.
What were the environmental impacts of the Oxford flooding scheme?
- Over 2000 trees and 2 hectares of rare grassland were removed, although they were replanted.
- The scheme created over 20 hectares of new riverside habitats, improving biodiversity.
