W + C: The River Exe Flashcards
Where is the River Exe?
The River Exe flows for 82.7 km from its source in the hills of Exmoor, through Tiverton and Exeter, to the sea at Exmouth on the south coast of Devon. It has an extensive network of tributaries and a high drainage density.
- the upper catchment of the River Exe above a long-term gauging station at Thorverton, eight miles north of Exeter.
What are the physical characteristics of the rivers upper catchment?
the area of the upper catchment is just over 600km2. Its maximum elevation of 514 m is in the north. The land is much flatter in the south - the lowest elevation is 26 m.
What are the geological characteristics of the rivers upper catchment?
an estimated 84.4% of the catchment is underlain by impermeable rocks, predominantly Devonian sandstones, which accounts for the extensive drainage network.
What is the land use for the upper catchment of the river?
most of the land is agricultural grassland (67%), with some woodland (15%) and arable farmland. On the high ground of Exmoor, there are moors and peat bogs (3%).
What is the water balance of this river?
Rainfall is high, particularly over Exmoor. Much of it is absorbed by the peaty moorland soils. However, if saturated or where drainage ditches have been dug, water can flow off the hills rapidly. Runoff accounts for some 65 per cent of the water balance, which is quite high compared with other UK rivers. There are 2 main reasons for this.
- The impermeable nature of the most of the bedrock reduces percolation and baseflow.
- Drainage ditches on Exmoor reduce the amount of soil water storage.
—> annual hydrograph shows that the Exe responds relatively slowly to rainfall events. After flooding, discharge recedes slowly reflecting the rural nature of the lower catchment - 82% of the land use is either woodland or grass.
What is the Wimbleball Reservoir?
In 1979 the River Haddeo, an upland tributary of the River Exe, was dammed to create Wimbleball Reservoir. The reservoir has a surface area of 150 hectares
How did the Wimbleball reservoir affect the water cycle?
The reservoir supplies water to Exeter and parts of East Devon. 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.
Why are peat bogs bad in Exmoor and affect the water cycle?
For decades, drainage ditches have been dug in the peat bogs of Exmoor to make it suitable for farming. This has increased the speed of water flow to the Exe, which reduces water quality as more silt is carried downstream. Peat has also been dug as a fuel, leaving behind ugly scars in the landscape. As the peat surface has dried out, decomposition has occurred, releasing carbon from this important carbon store in the form of CO2 and methane.
What’s the Exmoor Mires project and how will it help the peat bog problem?
The Exmoor Mires Project works to restore the peat bogs (mires) by blocking the drainage ditches with peat blocks or moorland bales. This increases water content and returns the ground to the saturated, boggy conditions that would naturally occur in this moorland environment. These conditions help to retain carbon stored within the peat.
