River Exe Flashcards
Where is the River Exe located and where does it flow?
The river Exe is located on the south-west of England.
Follows 83km from its source is Exmoor through Tiverton and Exeter before entering the sea at Exmouth on South Coast around Devon
What is the geology of the River Exe?
84% of catchment impermeable Devonian Sandstone which reduces infiltration, percolation and surface run-off
What is the proportion of surrounding land use around the River Exe?
67% agricultural land, 15% woodland and 3% peat bog
What is an example of positive feedback for the River Exe?
Implementation of drainage ditches dries peat which causes it to release carbon, increasing greenhouse gasses and global warming which dries peat further
What is the Wimbleball Reservoir?
Dam built in 1979 on the river Haddeo which supplies water to Exeter and East Devon
What does the Wimbleball Reservoir do?
Regulates water flow to prevent peaks and troughs, making a more predictable storm hydrograph which helps to mitigate flooding
How large is the Wimbleball reservoir?
150 ha
What are the positives of the Wimbleball Reservoir?
- Helps regulate water flow all year round
- Reduces seasonal variation in discharge
- prevents flooding during wet seasons and ensures there is a supply of water during dry season
- creates more predictable storm hydrograph which benefits water resource planners and urban areas downstream
- Wimbleball Lake has achieved a “Good” ecological status, with high ratings in parameters such as acid neutralising capacity and salinity.
- Implemented into projects like the Water Supply GRID, which enhances the resilience and flexibility of water distribution across the region.
What are the negatives of the Wimbleball Reservoir?
- Reduces seasonal flooding which impacts floodplain ecosystems and biodiversity which rely on inundation cycles
- Can lead to sediment starvation further downstream which can cause increased degradation and erosion downstream due to more abrasion and attrition
- Reduces deposition of nutrient rich soil which is deposited during floods
- Increased sediment in water leads to flocculation at Exmouth which degrades water quality
What is the Exmoor Mires Project?
Project which aims to restore 2,000 ha of peatland by blocking 100km of artificial drainage ditches with peat blocks. It hopes to increase ground water content, returning it to dynamic equilibrium so peat can absorb more co2
Benefits of the Exmoor Mires Project
- Raised water table by 7cm, slowing surface run-off and reducing flood risk
- Promoted infiltration and water storage in upper catchment, increasing baseflow and stability
- Reduced stormflow peaks helping to manage extreme weather events
- Slower throughflow leads to less sediment and nutrient run-off, improving water quality and reducing the economic cost of treating water
- Helps biodiversity
- Re-wetting of peatland prevents oxidation of dry peat which releases co2. Peat bogs 50% of volume is carbon
Negatives of the Exmoor Mires Project
- Expensive, by 2020 £2.2 million spent
- rewetting of peat can lead to more variation in seasonal flooding etc which can significantly reduce the socio-economic value of the land for agriculture and farming
- disrupts local habitats and displaces species
- may be less visually appealing and more difficult to access
What is the flood risk around the River Exe?
around 11,000 properties at risk from 1% annual probability flood
Human impacts on River Exe
Urbanisation
Peat drainage ditches
Abstraction of water Wimbleball Reservoir
Exmoor Mires Project
How much water is held in the Wimbleball Reservoir?
120 million litres
Physical impacts on the River Exe
Geology
Relief/Topography (516m at highest point)
High precipitation
Peat
What type of hydrography does the River Exe have?
Flashy hydrograph which is why Wimbleball Reservoir aims to stabilize it
How does the relief affect the hydrological cycle?
- upland areas receive more rainfall than lowland areas
- steep slopes encouraging surface runoff and reducing lag time
What is abstraction?
when water is taken out of the river system for human use ie. drinking water
What does blocking drainage ditches do (Exmoor Mires Project)?
- creates dam across ditch
- causes water to back up behind the dam
- slows down the flow of water across the landscape
- as water is moving more slowly, it doesn’t pick up as much sediment
- when water is treated for drinking - 20% cheaper due to less silt within it
