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River EXE case study
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- Water and Carbon
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- AQA
River EXE case study
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CASE STUDY OF A RIVER CATCHMENT AT A LOCAL SCALE : THE RIVER EXETHE LOCATION OF THE RIVER EXE
Describe the location of the River Exe. Be sure to reference:
● counties
● highland areas
● towns
● the source
● the mouth
Include statistics such as the length of the river and height above sea-level at the source, and describe the
direction of flow using compass points. Comment on the amount of tributaries and the size of the
catchment
The river Exe rises in Somerset near the village of Simonsbath and makes its way through the Exmoor
landscape flowing south. The main area of the source is to the north of the Exe Head which is 440m
above sea level- it is an upland area containing peat bogs rising to 514m and is predominantly farmland.
67% of the river Exe catchment is grassland with an overall catchment of 601km2. The overall river is 50
miles long and is located in Devon (South West England). It travels from Moorland in Exeter and finally
ends up at the Exmouth drainage basin (specifically Exe Estuary which is 8 miles long). Some tributaries
that flow into the river are the River Haddeo, River Clyst and River Creedy. The water discharges into the
English Channel at Lyme Bay at 15.89m3/s.
The overall main towns and villages the Exe flows through are: Topsham, Exton, Dawlish and Lympstone.
Exeter and Exmouth are the most at risk from flooding with 2000-5000 properties at risk. However, the
Wimbleball Dam was built to control the rate of water flow.
The River Exe responds slowly to rainfall events: short lag time and slow flood recovery time.
,THE CLIMATE OF THE RIVER EXE AT DULVERTON
Month J F M A M J J A S O N D
Temperature
3.6 4.1 5.5 8.2 11 14.4 16.2 15.6 13.3 10.2 6.5 4.6
(°C)
Precipitation
124 90 91 67 69 68 67 82 91 107 118 128
(mm)
Produce a climate graph for the River Exe at Dulverton
Calculate the total rainfall, average annual rainfall and average annual temperature. Compare these to
Birmingham using https://en.climate-data.org/
River Exe at Dulverton
Total rainfall= 1102mm
Average rainfall: 1102/12 =91.83mm
Average annual temperature: 113.2/12=9.43C°
, CHARACTERISTICS OF THE UPPER CATCHMENT
Most of the land in the upper catchment of the Exe is agricultural grassland (67%), with some
woodland (15%) and some arable farming. On the high ground of Exmoor, there are moors and peat
bogs (3%). An estimated 84.4% of the catchment is underlain by impermeable rocks, predominantly
Devonian sandstones.
84.4% of the catchment is underlain by impermeable rock such as Devonian sandstone. Water is
therefore unable to infiltrate through due to lack of pores. It has no other option but to travel as surface
runoff down to the river channel which increases lag time and flood risk. Due to the Exe being located in
one of the wettest areas of the UK, increased levels of rainfall travel faster to the river channel because
infiltration capacity has been reached too quickly and the soil is too saturated. More rain leads to faster
runoff and a larger quantity of it.
In the past, drainage ditches have been dug into the peat on Exmoor. Why?
Drainage ditches were dug in an attempt to make the UK more agriculturally productive after WW2.
They drain water away from low-lying areas to prevent them from flooding and are built near roads to
direct the storm water away from the road’s impermeable tarmac surface. The drained water stored in
ditches can be directed elsewhere or used for irrigation.
(This is a guess but I think the ditches were dug regardless of the peat because agriculture was needed
to help feed the nation after WW2 and food rations. They had to prioritise producing food over the
environmental effects of removing peat).
How would this have impacted on both the water cycle and the carbon cycle?
Drainage ditches being dug and peat cutting dries out the Exmoor mires which reduces the
water/infiltration capacity of the moors. There is therefore pressure on the local water cycle because
there would be increased surface runoff and less stored groundwater. Flooding is more likely if large
quantities of water can no longer be stored underground. These drainage ditches increase flooding
downstream and the carbon from the peat dissolves in the water which contaminates it.
Peatland destruction releases vast amounts of stored carbon as CO2 to the atmosphere. 10% of annual
fossil fuel emissions are due to the draining and burning of peatlands. Large amounts of released CO2
contributes to global warming and will speed up the rate of the carbon cycle. Peat bogs are also very
acidic and contain decomposing matter. Exposing the contents of the peat bog could cause
contamination of the surrounding area.
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