River Exe Case Study

Question 1

Describe location of the River Exe

Answer 1

Flows for 82.7km from its source in the hills of Exmoor to the sea at Exmouth on the south coast of Devon

Question 2

Physical characteristics of the River Exe

Answer 2

• 601km^2 area
• maximum elevation of 514m in the north
• lowest elevation of 26m in the south

Question 3

Human characteristics of the River Exe (land use)

Answer 3

• majority of land is agricultural grassland (67%)
• some woodland (15%)
• high ground of Exmoor = moors and peatbogs (3%)

Question 4

Characteristics of geology at the River Exe

Answer 4

• 84.4% of catchment underlain by impermeable rocks (predominantly Devonian sandstones)

Question 5

Factors affecting the water balance

Answer 5

High rainfall = runoff being 65% of the water balance
soil water storage is 35%

Two reasons for this;
- impermeable nature of most of the bedrock reduces percolation and base flow
- drainage ditches on Exmoor reduce the amount of soil water storage

Question 6

What does the storm hydrograph for the River Exe show?

Answer 6

• the Exe responds relatively slow to rainfall events
• after flooding discharge recedes slowly reflecting the rural nature of the lower catchment

Question 6

Describe the Wimbleball reservoir and how it reduces the risk of flooding

Answer 6

• 1979
• River Haddeo was dammed
• SA = 150 hectares
• supplies water to Exmoor and East Devon
• regulates water flow, ensures a constantly steady regime
• prevents peaks and troughs of water discharge; reducing flood risk

Question 6

History of the River Exe/Exmoor Mires

Answer 6

1960s - government subsidies paid to peatland owners to drain the land

Question 7

How did the drainage ditches affect the river?

Answer 7

Increased the speed of water flow to the river, reducing water quality as more silt was carried downstream

Question 7

What was the Exmoor Mires Project?

Answer 7

Aims to restore 2000ha of land back to peat bogs by blockage of drainage ditches

Question 8

How does the Exmoor Mires Project benefit the area?

Answer 8

• improved water quality; slower throughflow means that less sediment is carried into the rivers; water is cleaner, less expensive to treat and good for wildlife, e.g. salmon (= increased biodiversity)
• more carbon storage; dry peat releases carbon dioxide through oxidation. by encouraging the re-wetting of peat and active peat growth, carbon dioxide is naturally absorbed from the atmosphere and stored
• more water storage in the upper catchments; water transfer is slowed, increasing storage capacity and ensuring a steady supply of water throughout the year

Question 9

How were the effects of the Exmoor Mires Project measured?

Answer 9

Dipwells were installed to measure the depth of the water table

Question 10

What were the results of the Exmoor Mires Project?

Answer 10

By 2015, over 1000ha of peat moorland had been restored

Nearly 100km of ditches had been blocked
water table raised by 2.65cm