River Exe, Devon Case Study Flashcards
What are the physical characteristics of the river catchment (relief)?
Maximum elevation is 514m in the north and a low of 26m in the south
What is a geology of the river catchment?
84% of the river catchment is impermeable rock, mainly Devonian Sandstone
What is a predominant land use?
Most of the land is used for agriculture grassland (67%) with some woodland (15%) and arable farmland.
How much of the land use of the river catchment accounts for the peat bogs and moors?
3%
What is a water balance of a river Exe?
1295mm = 451mm + 844 mm
Precipitation = evaporation +- soil water storage + runoff
How much runoff accounts for in the water balance?
Runoff accounts for 65% of the water balance
What are the 2 reasons for high surface runoff in river Exe?
1.The impermeable nature of most of the bedrock reduces percolation and base flow
2. drainage ditches on Exmoor reduce amounts of soil water storage
How rainfall is precipitated and infiltrated/percolated?
Rainfall is high, particularly over Exmoor.
Most rainfall is absorbed by the peaty moorland soils but if soils are saturated or drainage ditches have been dug, water can flow off the cliffs rapidly
Why does discharge recedes slowly in aftermath of rainfall/flooding event?
it reflects the rural nature of the lower catchment - 82% woodland and grass.
Which 2 recent major developments have affected the water cycle and water balance of the River Exe?
- Construction of a Reservoir at Wimbleball
- Restoration of peatland in Exmoor
When was the reservoir constructed?
In 1979 on the River Haddeo
What surface area does reservoir have?
150 hectares
What is the role of the reservoir in water balance?
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 was drainage ditches dug in the peat bogs and what were the effects of it?
To make it suitable for farming, which has increased the speed of water flow to the Exe, reducing water quality as more silt is carried downstream
How much of peat bogs area is aimed to be restored by Exmoor Mires project?
2000 ha
How is the Exmoor Mires project conducted?
by blocking drainage ditches with peat blocks and moorland bales
Outline the benefits of Exmoor Mires project for water balance (2)
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 thoughflow means that less sediment is carried into the rivers so water is cleaner
outline the benefits of Exmoor Mires project for carbon cycle
Dry peat releases carbon dioxide thorough oxidation so the encouragement of the re-wetting of peat and active peat growth ensure that carbon dioxide is naturally absorbed from the atmosphere and stored
How much of the peat moorland was restored by 2015 and what effect it had on water tables?
1000 ha of peat moorland, and 100km of ditches blocked, raising the water table by 2.65 cm
By how much did the amount of water draining from moorland decreased?
By 2/3
What was the impact of completion of Exmoor Mires project on a flood hydrograph?
Storm flow and flood peaks have been reduced and base flow has increased
How much of river catchment is urbanized?
Only 0.6%
