River Exe, Devon Case Study

Question 1

What are the physical characteristics of the river catchment (relief)?

Answer 1

Maximum elevation is 514m in the north and a low of 26m in the south

Question 2

What is a geology of the river catchment?

Answer 2

84% of the river catchment is impermeable rock, mainly Devonian Sandstone

Question 3

What is a predominant land use?

Answer 3

Most of the land is used for agriculture grassland (67%) with some woodland (15%) and arable farmland.

Question 4

How much of the land use of the river catchment accounts for the peat bogs and moors?

Answer 4

3%

Question 5

What is a water balance of a river Exe?

Answer 5

1295mm = 451mm + 844 mm
Precipitation = evaporation +- soil water storage + runoff

Question 6

How much runoff accounts for in the water balance?

Answer 6

Runoff accounts for 65% of the water balance

Question 7

What are the 2 reasons for high surface runoff in river Exe?

Answer 7

1.The impermeable nature of most of the bedrock reduces percolation and base flow
2. drainage ditches on Exmoor reduce amounts of soil water storage

Question 8

How rainfall is precipitated and infiltrated/percolated?

Answer 8

Rainfall is high, particularly over Exmoor.
Most rainfall is absorbed by the peaty moorland soils but if soils are saturated or drainage ditches have been dug, water can flow off the cliffs rapidly

Question 9

Why does discharge recedes slowly in aftermath of rainfall/flooding event?

Answer 9

it reflects the rural nature of the lower catchment - 82% woodland and grass.

Question 10

Which 2 recent major developments have affected the water cycle and water balance of the River Exe?

Answer 10

1. Construction of a Reservoir at Wimbleball
2. Restoration of peatland in Exmoor

Question 11

When was the reservoir constructed?

Answer 11

In 1979 on the River Haddeo

Question 12

What surface area does reservoir have?

Answer 12

150 hectares

Question 13

What is the role of the reservoir in water balance?

Answer 13

It regulates water flow, ensuring a steady flow regime during the year.
This prevents the peaks and troughs of water discharge that make flooding or drought more likely

Question 14

Why was drainage ditches dug in the peat bogs and what were the effects of it?

Answer 14

To make it suitable for farming, which has increased the speed of water flow to the Exe, reducing water quality as more silt is carried downstream

Question 15

How much of peat bogs area is aimed to be restored by Exmoor Mires project?

Answer 15

2000 ha

Question 16

How is the Exmoor Mires project conducted?

Answer 16

by blocking drainage ditches with peat blocks and moorland bales

Question 17

Outline the benefits of Exmoor Mires project for water balance (2)

Answer 17

More water storage in upper catchments - water transfer is slowed, increasing storage capacity and ensuring a steady supply of water throughout the year
Improved water quality - slower thoughflow means that less sediment is carried into the rivers so water is cleaner

Question 18

outline the benefits of Exmoor Mires project for carbon cycle

Answer 18

Dry peat releases carbon dioxide thorough oxidation so the encouragement of the re-wetting of peat and active peat growth ensure that carbon dioxide is naturally absorbed from the atmosphere and stored

Question 19

How much of the peat moorland was restored by 2015 and what effect it had on water tables?

Answer 19

1000 ha of peat moorland, and 100km of ditches blocked, raising the water table by 2.65 cm

Question 20

By how much did the amount of water draining from moorland decreased?

Answer 20

By 2/3

Question 21

What was the impact of completion of Exmoor Mires project on a flood hydrograph?

Answer 21

Storm flow and flood peaks have been reduced and base flow has increased

Question 22

How much of river catchment is urbanized?

Answer 22

Only 0.6%