case study - The River Exe

Question 1

Location

Answer 1

South west England
Source in Exemoor
82.7km long

Question 2

Land use of the catchment

Answer 2

67% grassland
15% woodland
82% woodland and grassland
Makes hydrograph less flashy, less runoff

Question 3

Factors effecting the river exe hydrograph

Answer 3

Less flashy:
- land use, 82% grassland and woodland, less runoff
- wimbleball reservoir helps regulate water flow

More flashy:
- drainage ditches
- 84% impermeable rock
Both increase runoff

Question 4

Flood risk on River Exe

Answer 4

10% of homes in catchment at risk of a 1 in 100 year flood

Drainage ditches increased risk
Less water stored in peatland, more runoff, enter channel faster
Reduces lag time and increased risk

Question 5

Effects of drainage ditches on River Exe

Answer 5

Peat should act as carbon sink, stops decomposing
Dug in attempts to make UK more agricultural
Drainage ditches made to dry peat as better for crops

Question 6

Effects on water cycle

Answer 6

Less water stored/ drained faster -> more water enters channel faster -> decreased lag time -> increased flood risk
Reduces amount of water stored

Question 7

Effects on carbon cycle

Answer 7

Dried peat more susceptible to erosion
Carbon not stored and released into atmosphere

Carbon can be dissolved in water as DOC, decreases water quality, expensive to clean

Question 8

Exemoor Mires Project

Answer 8

Restoration of moorland
Led to 1/3 less water leaving catchment in heavy rainfall
Moorland can now hold more water and release it slower

• 260,000 cubic metres more water storage
• 2.65cm rude in water table

Decreased flood risk, may reduce future carbon emissions
but small scale

Question 9

human factors affecting flood risk

Answer 9

+ drainage ditches
+ replacement of woodland with livestock

• Exemoor Mires
• Wimbleball reservoir

Question 10

physical factors affecting flood risk

Answer 10

+ 84% impermeable rocks
+ many tributaries, shortens tag time

• 82% grassland and woodland, interception