Case study - River Exe, Devon

Question 1

What is the location of the River Exe?

Answer 1

• flows through Exmoor National Park
• southwest England
• enters the English Channel

Question 2

What is the length of the River Exe?

Answer 2

It is 82 kilometres long

Question 3

What is the average annual rainfall in the River Exe catchment area?

Answer 3

Around 1,200 mm of rainfall annually

Question 4

How does the soil in the River Exe influence the water cycle?

Answer 4

Soil (particularly in peat bogs) helps store water, impacting infiltration and soil moisture

Question 5

How does the River Exe contribute to the carbon cycle?

Answer 5

• carbon absorption by vegetation
• storage in soil
• transport of organic carbon downstream

Question 6

What role do peat bogs play in the carbon cycle of the River Exe?

Answer 6

Peat bogs store large amounts of carbon, but disturbance can release this stored carbon

Question 7

How do human activities affect the carbon cycle in the River Exe?

Answer 7

Deforestation, agriculture and urbanisation reduce carbon storage and increase emissions

Question 8

What are the main carbon fluxes in the River Exe?

Answer 8

• photosynthesis (carbon uptake)
• respiration (carbon release)
• decomposition (carbon release)

Question 9

How does climate change affect the water cycle in the River Exe?

Answer 9

It may increase rainfall, leading to more runoff and flooding, altering evapotranspiration

Question 10

How do wetlands impact the carbon cycle in the River Exe?

Answer 10

Wetlands act as carbon sinks, storing carbon in vegetation and soil and influencing the water cycle by filtering water

Question 11

What are the key management strategies for the River Exe?

Answer 11

• flood risk management
• sustainable land use practices
• conservation of wetlands and peat bogs

Question 12

How does flood management work along the River Exe?

Answer 12

Flood defences:
- floodplain zoning
- river channel modification
- flood-warning systems

Question 13

How does agricultural management help protect the River Exe?

Answer 13

• reduced use of fertilisers
• buffer zones
• erosion control
• helps minimise pollution and runoff into the river

Question 14

What role do wetlands play in the management of the River Exe?

Answer 14

• natural flood defences, absorbing water during heavy rainfall
• provide habitats for wildlife
• help regulate water quality and store carbon

Question 15

How much carbon do Exmoor’s peat bogs store?

Answer 15

Approximately 3 million tonnes of carbon

Question 16

How much funding was allocated for flood risk management along the River Exe in 2020?

Answer 16

The UK government allocated £4.7 million

Question 17

How does topography influence runoff?

Answer 17

Steep upland areas such as Exmoor leads to rapid surface runoff

Question 18

How does geology affect infiltration and runoff in the River Exe basin?

Answer 18

Around 84% of the River Exe catchment is underlain by impermeable sandstone, which leads to reduced infiltration

Question 19

How does land use in the River Exe basin impact the drainage system?

Answer 19

• predominantly agricultural (67%) with some woodland (15%)
• grazing compacts soil, reducing infiltration and increasing surface flow

Question 20

What is the impact of the Wimbleball Reservoir on the River Exe’s hydrology?

Answer 20

• built in 1979
• holds 21 billion litres of water and regulates flow by reducing peaks and maintaining steady discharge during dry periods
• helping manage flood risk downstream

Question 21

What is the Exmoor Mires Project and how does it impact the River Exe?

Answer 21

• since 2010, over 1000 hectares of Exmoor’s peatland have been restored to increase water retention
• enhances infiltration, slowing down the flow into the river and improving quality (as slower throughflow means less sediment is transported)
• more water stored in the upper catchment slows transfers creating a yearly steady supply of water, which improves grazing for animals

Question 22

What are the key outputs from the River Exe drainage basin?

Answer 22

Evapotranspiration and streamflow (river discharge) are the major outputs

Question 23

How does vegetation influence outputs in the River Exe basin?

Answer 23

• areas with woodland and moorland increase interception and evapotranspiration
• grazing land reduces vegetation cover and leads to greater runoff

Question 24

How does drainage of peatlands affect the carbon cycle?

Answer 24

Draining peat exposes it to oxygen, accelerating decomposition and releasing CO2, converting it from a sink to a source

Question 25

How does urbanisation affect the water cycle in the Exe basin?

Answer 25

Urban areas like Exeter increase impermeable surfaces, reducing infiltration and increasing surface runoff and flood risk

Question 26

How is the water balance effected?

Answer 26

- run-off accounts for 65% of the water balance - drainage ditches reduce amount of soil water storage