River Exe - W&C

Question 1

Where is the river exe

Answer 1

South-West England, it 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

Where is all the data being used collected

Answer 2

On the upper area of catchment upstream of an Environment Agency level monitoring station at Thorverton

Question 3

How long do the river travel

Answer 3

82.7km

Question 4

What are the physical characteristics of the catchment area

Answer 4

Area of upper catchment is 601km^2.
Maximum elevation at 514km at river source (Exmoor).
Land is flatter in south, by the time it reaches Thorverton it’s elevation is 26km.

Question 5

What is the geology of the catchment area

Answer 5

84.4% of catchment is underlaid by impermeable rock, usually Devonian sandstone, which accounts for extensive drainage network

Question 6

What is the land-use of the catchment area

Answer 6

Source - used for sheep farming and shooting game birds.
67% of land is agricultural.
15% is woodland.
High group or Exmoor - 3% of land is peat bog and moor.

Question 7

What is the water balance for the exe catchment

Answer 7

Precipitation (1295mm) = evaporation +/- soil water storage (451mm) + run off (844mm)

Question 8

Why is the hydrological element of rainfall high for the river

Answer 8

Bc it lies in the wet south-west

Question 9

What is much rainfall absorbed by

Answer 9

Peaty moorland soil. However if it is saturated or there are drainage ditches dug, water call flow off the hills rapidly.

Question 10

Why does alot of rainfall form runoff in the exe catchment

Answer 10

Becsuse of the impermeable underlying rocks

Question 11

How much of the water balance does runoff account for

Answer 11

65%

Question 12

Why does rainfall run off in the catchment

Answer 12

Bc of impermeable rocks reduces percolation and base flow.

Drainage ditches on Exmoor reduces amount of soil water storage.

Question 13

What is the regime of river exe

Answer 13

Not as flashy as expected but there is a clear response between rainfall events as this occurs relatively slowly and discharges recedes slowly following an event

Question 14

What is a reason for the subdued regime of river exe

Answer 14

Becsuse of the rural natural of the catchment - 82% is either woodland or grassland

Question 15

What is the reservoir

Answer 15

Wimbleball Reservoir

Question 16

Where is the Wimbleball reservoir

Answer 16

On the River Haddeo - an upland tributary

Question 17

Where does Wimbleball supply water

Answer 17

To Exeter and elsewhere in East Devon

Question 18

What does Wimbleball regulate

Answer 18

The flow of the river smoothing out the more flashy peaks and troughs which may otherwise have been expected

Question 19

What are human hydrological factors afecting the regime or the river

Answer 19

Water is abstracted for agriculture.

In some places, effluent is also returned to the river.

Question 20

The river exe has experienced significant flooding in the last, why is it projected to experience more in the future

Answer 20

Climate change makes extreme weather events more likely

Question 21

When were the last major floods

Answer 21

1960

Question 22

What percentage of the houses in the Exe catchment are at risk of a 1 in 100 year flood

Answer 22

10% (this is quite high)

Question 23

Why is blocking drainage ditches on Exmoor used to reduce flooding

Answer 23

It attenuates more water in the upper catchment rather than allowing it to enter the river channel and become flood water

Question 24

What is the current amount of properties at risk from a 1 in 100 year flood (taking existing flood defences into account) in Exeter

Answer 24

Around 3500

Question 25

What is the predicted (2100) amount of properties at risk from a 1 in 100 year flood (taking existing flood defences into account) in Exeter

Answer 25

Around 4500

Question 26

What is the very upper catchment of the River Exe

Answer 26

Moorland with large amounts of peat

Question 27

Why should peat be a carbon sink

Answer 27

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

Question 28

Why have large areas of peat been drained

Answer 28

Since the Second World War, it was an attempt to make the UK more agriculturally productive

Question 29

How have large areas of peat been drained

Answer 29

By digging drainage ditches

Question 30

How did digging drainage ditches help

Answer 30

It dried the peat out and made it more sustainable for conversion to farmland or for grazing more sheep on

Question 31

How was digging drainage ditches a bad thing

Answer 31

It meant that water entered the river channel more quickly, reducing lag time and increasing flood risk downstream.
Dried peat was also susceptible to erosion and the carbon contained within it was dissolved in water and transported downstream.

Question 32

Why is dissolved carbon in water bad

Answer 32

Creates problems with water quality. Dissolved organic carbon (DOC) makes water brown (DOC is what you’re seeing in Dales river when they’re the colour black tea) and therefore water companies have to spend money removing the brown colour.
It means carbon is no longer being sequestered in peat lands but is free to exchange from water with the atmosphere and become atmospheric carbon.

Question 33

Due to the water quality problems and the loss of carbon on Exmoor, what has there been a move towards

Answer 33

Blocking up these drainage ditches and restoring the pest to it original saturated state in which it is able to sequester carbon. However, landowners have to be convinced of the benefits in order to invest in blocking drainage ditches and potentially lose money from agriculture as their land becomes saturated and boggy once again

Question 34

Who did research into the effects of blocking drainage ditches between 2000 and 2015

Answer 34

On Exmoor the Exmoor Mires Project

Question 35

What are the key findings of the Exmoor Mires Project into the effects of blocking drainage ditches

Answer 35

Restoration of peat bogs on Exmoor has resulted in a third less water leaving the moorland during heavy rainfall compared with three years ago.

By blocking up drainage ditches, the moorland can now hold more water and release it more slowly, reducing potential flooding elsewhere.

Extrapolated across the whole 2000 hectares of restored moorland - which was the 2015 target for the Exmoor Mires Project - the results indicated that the amount of storm water running off the moorland has reduced by a third, the equivalent of more than 6,630 Olympic size swimming pools less water entering downstream rivers.

It also indicates increased water storage in the peat of 260,000 cubic metres. Put another way, that’s 104 Olympic-sized swimming pools of water removed from the river system flowing down to major population centres like Exeter.

Prof Brazier (the lead academic) said: “across the experimental site we are seeing a rise in water table levels of up to 2.65cm that can be attributed to the ditch blocking and moorland restoration. This enhanced water storage could, when replicated across the whole of Exmoor, provide a significant buffer against downstream flooding in rivers like the Exe.”

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.