1.4- The River Exe

Question 1

Describe the location of the River Exe

Answer 1

A river in the South-West of England that rises in the moorland of Exmoor and travels to reach the sea at Exmouth on the South coast of Devon flowing through the towns of Tiverton and Exeter on Route

Question 2

what are the characteristics of the catchment (drainage basin)?

Answer 2

• area of catchment is 600km (squared)
• the river’s source is on Exmoor, an upland area of moorland and peat bogs rising to over 500m above sea level and used for sheep farming and shooting game birds
• the catchment is largely underlain by impermeable sandstones which leads to a high drainage density

Question 3

the majority of the catchment is rural with grasslands accounting for over __% of the land use in the catchment

Answer 3

60

Question 4

rainfall is high for the catchment as it lies in the South-West of the UK- how many mm annually?

Answer 4

1000+

Question 5

based on the rural nature of the catchment, it may be expected that much of this rainfall will infiltrate, but actually

Answer 5

much forms run-off due to the impermeable nature of the underlying rocks, already saturated peat, and drainage ditches which have been dug to drain the moorlands and make them more suitable for farming and shooting

Question 6

why is the regime of the River Exe not as flashy as perhaps expected?

Answer 6

although there is a clear response to rainfall events, this occurs relatively slowly- one reason for this is the rural nature of the catchment as over 80% of the catchment is either woodland or grassland

Question 7

there is a reservoir on the the River _____, a tributary of the Exe

Answer 7

Haddeo

Question 8

what is the significance of Wimbleball reservoir to the river Exe?

Answer 8

Wimbleball Reservoir supplies supplies water to Exeter and elsewhere in East Devon, but it also regulates the flow of the river smoothing out more flashy peaks and troughs which otherwise may have been expected

Question 9

what human factors affect the regime?

Answer 9

water is abstracted at a couple of locations and used for agriculture- in some places effluent (liquid waste) is also returned to the river

Question 10

the River Exe has experienced some significant flooding in the past and is projected to experience more in the future as ______ _____ makes extreme weather events more likely

Answer 10

climate change

Question 11

__% of houses in the Exe catchment are at risk of a 1 in 100 year flood which is quite high

Answer 11

10

Question 12

what provides justification for blocking drainage ditches on Exmoor in order to attenuate more water in the upper catchment rather than allowing it ti enter the river channel and become flood water

Answer 12

10% of houses in the Exe catchment are at risk of a 1 in 100 year flood

Question 13

the very upper catchment of the River Exe is moorland with large amounts of

Answer 13

peat

Question 14

peat should be a carbon sink as

Answer 14

dead,organic matter is compacted in saturated conditions and is therefore unable to decompose much due to the anaerobic conditions

Question 15

Since the ______ ____ ___ , in attempt to make the UK more agriculturally more productive, large areas of what peat been drained by digging drainage ditches in the peat evident in Yorkshire Dales and also on Exmoor

Answer 15

Second World War

Question 16

What have been the impacts of digging draining ditches in the peat?

Answer 16

• dried peat out and made it more suitable for conversion to farmland or for grazing more sheep on
• also meant that water entered the river channel more quickly, reducing lag time and increasing flood risk downstream
• dried peat was susceptible to erosion and the carbon within it was dissolved in water and transported downstream creating problems for water as dissolved organic carbon (DOC) makes water brown and so water companies have to spend money removing the brown colour
• also means carbon is no longer being sequestered in peatlands but is free to exchange from water with the atmosphere and become atmospheric carbon

Question 17

Because of water quality problems, and to a lesser extent, the loss of carbon on Exmoor there has been a shift away from drainage and a move towards

Answer 17

Blocking up these drainage ditches and restoring the peat to its original saturated state in which it is able to sequester carbon

Question 18

Why do landowners have to be convinced of the benefits in order to invest in blocking drainage ditches?

Answer 18

May potentially lose money from agriculture as their land becomes saturated and boggy once again

Question 19

On Exmoor, what project has done some research into the effects of blocking drainage ditches between 2000 and 2015?

Answer 19

Exmoor Mires Project

Question 20

What’s the aim of the Exmoor Mire’s Project?

Answer 20

Aims to restore 2000 ha of Exmoor to the boggy conditions that would naturally be present by blocking drainage ditches with peat blocks and moorland bales

Question 21

What are the benefits of Exmoor Mires Project?

Answer 21

• 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 throughflow means less sediment is carried into the rivers. Water is cleaner, less expensive to treat and good for wildlife like salmon
• more carbon storage- peat is essentially water and carbon so is an important carbon store. Dry peat however releases carbon dioxide through oxidation so by encouraging the re-wetting of peat, carbon dioxide is naturally sequestered from the atmosphere and stored

Question 22

What’s a potential limitation of Exmoor Mires Project?

Answer 22

It is thought that blocking ditches does reduce carbon transfers however the ditches haven’t been blocked for long enough to show conclusive evidence of this