Drainage basin- River Exe

Question 1

Case study for the drainage basin:

Answer 1

River Exe, Devon.

Question 2

What are the characteristics of the river Exe’s basin in the upper course (near simonsbath)?

Answer 2

• Land use - town, hotel, housing (concrete)
• Little vegetation (few areas of forest)
• Steep sloping land around the river - average 350m

Question 3

What are the characteristics of the middle course (near dulverton)?

Answer 3

• Lots of vegetation (large areas of forest)
• Rural - not many buildings - caravan park, farmland, castle
• Not as steep as upper course, average approx. 250m

Question 4

What are the characteristics of the lower course (near Exeter)?

Answer 4

• High density buildings
• Barely any vegetation (only golf course)
• Low lying land - approx. 40m

Question 5

What are the characteristics of the wimbleball reservoir and whats its job?

Answer 5

The dam impounds water from the river Haddeo to form a reservoir. 150 hectares.

The reservoir supplies Exeter and parts of East Devon by releasing water into the river exe.
The water is then abstracted at Tiverton and Exeter.
Also supplies water by pipeline to Wessex waters Maundown water treatment works.

Question 6

What happens as a result of the wimbleball reservoir?

Answer 6

Peak discharge lowered, regulates and controls discharge throughout the year, helps meet demand and decreases likelihood of flooding.
River Haddeo no longer supplies as much water, but will mean the supply is regulated year round.

Question 7

How does rock type affect run off in the upper catchment?

Answer 7

• 88.4% Of underlying rock is impermeable, therefore water is unable to percolate and become groundwater.
• Increases the amount that becomes run off as through-flow reaches the river much quicker.

Question 8

How does the type/density of vegetation affect run off?

Answer 8

• Mostly grassland, therefore won’t be dense in vegetation. This means little evapotranspiration so more precipitation as runoff.
• 15% is woodland in these areas evapotranspiration will be much higher.

Question 9

How does the land use affect run off in the catchment?

Answer 9

• Grassland/farmland are likely to have high infiltration rates so little becomes run off.
• 0.6% urbanised, in these areas will stay as overland floe due to impermeable surfaces and will become run off much quicker as it does not go through natural processes instead goes through purpose built drains.

Question 10

What is the water balance for the river Exe?

Answer 10

P (1295mm) = E +/- Soil water (451mm) + Run off (844mm)

• Run off accounts for 65% of the water balance.
• Due to little soil water storage due to drainage ditches built to make land suitable for farming.
• High precipitation potentially caused by high relief (514) which may be causing orographic rainfall.

Question 11

How do the drainage ditches affect run off in the upper catchment?

Answer 11

• Built to make land suitable for farming.
• Have increased the speed of the water flow to the river Exe as they mean little can be stored in the soil.
• Also reduces water quality.

Question 12

How has the restoration of peatland affected run off?

Answer 12

• Involves blocking drainage ditches, increases water content and returns the ground to saturated and boggy conditions.
• Increases soil water store = less run off.

Question 13

The Exmoor Mires project:

Answer 13

Aimed to restore 2000 hectares of Exmoors peat bog to its boggy conditions by using peat blocks in the drainage ditches to hold back the water.

• By 2015 the blocking of the drainage ditches had resulted in the water tables rising by 2.65cm after 100km of drainage ditches blocked.
• Reduced water being drained by 2/3
• Also improves water quality in the area as water is filtered by natural processes.