WCC: River Catchment Case Study - River Exe Flashcards
Case study of a river catchment at a local scale to illustrate and analyse key themes in water and carbon cycles and their relationship to environmental change and human activity, engage with field data and consider the impact of precipitation upon drainage basin stores and transfers and implications for sustainable water supply and flooding.
How does the relief of the River Exe drainage basin impact on its hydrology?
Steep slopes increase the speed water gets to the river
How does the area of the River Exe drainage basin impact on its hydrology?
Small area means water has less distance to travel to get to the river so runoff is faster
How does the geology of the River Exe drainage basin impact on its hydrology?
Impermeable rocks reduce infiltration, increasing runoff and therefore the speed the water reaches the river
How does the land use of the River Exe drainage basin impact on its hydrology?
Rural nature means more infiltration - relatively slow reaction to rainfall events
What are the benefits of using a proportional circle map to display data?
It’s easy to interpret
Gives you a scale and location
What are the problems of using a proportional circle map to display data?
Large margin of error - numbers aren’t exact
Hard to tell the difference between the sizes of circles
Why were drainage ditches originally dug in the UK?
In an attempt to make the UK more agriculturally productive after WW2
What are the 3 problems with drainage ditches?
Increases flood risk downstream
Dried peat susceptible to erosion
Carbon from peat was dissolved in water
What are the key advantages of blocking drainage ditches?
The moorland can hold more water and release it more slowly, reducing potential flooding elsewhere.
Restoring the peat to its original saturated state means it can sequester carbon.
What other data would you want before recommending blocking drainage ditches on a wider scale?
How cost effective it is
What exactly the impact is on water quality, over a long period of time and in different catchments
Where is the River Exe?
Devon, SW England
Describe the route of the River Exe
It rises in the moorland of Exmoor, travels 82.7km and through two towns to reach the sea at Exmouth on the south coast of Devon
Which 2 towns does the River Exe flow through?
Tiverton
Exeter
How large is the River Exe catchment?
601km^2
Where is the River Exe’s source?
On Exmoor
Describe Exmoor.
It is an upland area of moorland and peat bogs
What is Exmoor used for?
Sheep farming and shooting game birds
Why does the River Exe catchment have a high drainage density?
It is largely underlain by impermeable rocks
What is the majority of the land use in the River Exe catchment?
Rural (grassland)
What percentage of the River Exe catchment is grassland?
67%
What is the elevation of the River Exe when it reaches the end of the upper course at Thorverton?
26m above sea level
How much rainfall does the River Exe catchment receive annually?
1295m
Why is rainfall high in the River Exe catchment?
It lies in the wet SW of the UK
What happens to much of the rainfall in the River Exe catchment?
It forms runoff
What are the 3 main reasons for the limited infiltration in the River Exe catchment?
Impermeable underlying rocks
Saturation of upland peat
Drainage ditches
Why have drainage ditches been dug in the River Exe catchment?
To drain the moorlands so they are more suitable for farming and shooting
Describe the river regime of the River Exe.
There is a clear response to rainfall events however this occurs relatively slowly and discharge recedes relatively slowly following rainfall events.
What percentage of the River Exe catchment is rural?
82%
What 4 factors reduce the flashiness of the River Exe’s regime?
Rural nature of the catchment
Wimbleball Reservoir
Water abstraction
Return of effluent
How does Wimbleball Reservoir affect the River Exe’s regime?
It regulates the flow of the river, smoothing out the more flashy peaks and troughs
Where is Wimbleball Reservoir?
On a tributary of the River Exe - Rivver Haddeo
What percentage of the River Exe’s drainage basin is underlain by impermeable rocks?
84%
What is the main rock underlying the River Exe’s drainage basin?
Sandstone
Describe the relief of the River Exe drainage basin
It ranges from 514m ASL in the north to 26m in the south.
It’s hilly in the north but much flatter in the south.
Describe the upper course of the River Exe.
Highest and steepest from 444m-330m.
There is a V-shaped valley in the centre due to vertical erosion, surrounded by flat moorland and bogs.
Describe the middle course of the River Exe.
Less steep, with a wider valley starting to develop into a floodplain.
Describe the lower course of the River Exe.
The least steep from 80m-35m.
Floodplain surrounded by remains of the valley sides
Describe the pattern of flood risk in the River Exe.
Risk is highest in the lower course of the river, with a cluster around the estuary area where the river meets the sea. The biggest towns are at the most risk of flooding.
What are the 2 major reasons flood risk in towns will increase in the future?
Climate change making extreme weather events more likely
Towns are likely to be larger in the future
What is the flood risk in the Exe catchment?
10% of houses are at risk of a 1 in 100 year flood
Quite high
Why does the high flood risk in the Exe catchment justify the blocking of drainage ditches on Exmoor?
It will attenuate more water in the upper catchment rather than allowing it to enter the river channel and become flood water.
How would drainage ditches increase agricultural production?
They dry out the peat which makes it more suitable for conversion to farmland or for grazing more sheep on
What are the 2 major problems with carbon from peat becoming dissolved in water?
DOC makes water brown so water companies have to spend money removing it
Carbon is free to become atmospheric carbon by diffusion
What was the project that researched the effects of blocking drainage ditches between 2000 and 2015?
Exmoor Mires Project
How much moorland has been restored on Exmoor?
2000 hectares
How have restoration of peat bogs and moorland on Exmoor affected the rates of runoff?
The amount of water leaving the moorland during heavy precipitation has reduced by 1/3
How much has the water storage of peat increased by due to blocking drainage ditches?
260,000 m^3
What 3 pieces of evidence show the success of blocking drainage ditches on Exmoor?
Reduced runoff
Increased water storage in peat
Rise in the water table
How much have water table levels risen by due to blocking drainage ditches?
Up to 2.65cm
