WC12 - local River Catchment Case Study
The River Exe, Devon
Where is the river Exe?
Flows for 82.7km from its source in the Exmoor hills
Through Trueton and Exeter to the sea at exmouth, on south coast of devon
Extensive network of tributaries and high drainage density
Charcteristics of the Exe's upper catchment
physical
geology
land use
water balance
Area 601km^2
maximum elevation of 514m in the north
lowest elevation of 26m in the south
84.4% Catchment is underlain by impermeable rocks
4 devonian sandstones, accounts for extensive drainage network
rainfall is high, much absorb by peaty moorland soils (if saturated or where drainage ditches are dug, can flow off hills rapidly)
67% agricultural grassland
15% woodland and arable farmland
3% high ground is moors and peat bogs
Runoff accounts for 65% of water balance
impermeable nature most bedrock reduces percolation and baseflow
drainage ditches on exmoor reduce the amount of soil water storage
The drainage ditches were dug to drain the peat moorland of water, allowing it to be farmed
types of cloud formation and precipitation
Orographic
frontal
has to go over hills. the warm air condenses, forms cloud and rains
Prevailing winds bring in warm air, which is forced over the cold air, it condenses, forms clouds and then rains.
wimbleball reservoir
1979, river haddeo, upland tributary of River Exe, dammed to create a reservoir.
surface area of 150km
Supplies water to Exeter and parts of East Devon
regulates water flow, steady flow regime during the year
prevents peaks and troughs of water discharge, making floods less likely
Peatland restoration on Exmoor
drainage ditches have been dug in peat bogs to make it suitable for farming
increased speed of water to flow to river exe
reduced water quality, more silt carried downstream
also been dug as fuel, leaving ugly scars. As dried out, decomposition happened, releasing carbon
project works to restore peat bogs (mires) by blocking drainage ditches with peat blocks or moorland bales
Increases water content and saturated soil (what moorland should be)
helps carbon stores within the peat
Exmoor mires Project
Social - improved opportunities for education, lesuire and recreation
Environmental - improved grazing and water supply for animals
water cycle - more water storage in upper catchments - water transfer slowed. improved water quality, less sediment, cleaner
Carbon cycle - More carbon storage - rewetting peat means CO2 stored
by 2015, 1000ha peat moreland were restored, 100km ditches blocked.
data collection
scientists established 3 experimental stations (pools), involving installation of dipwell transects (surveys along a line) across newly blocked ditches.
electronic contact dipmeter records depth of water table.
inserted into a dipwell, when electrodes make contact with water, buzzer or light activated, depth of measurement taken.
results
water tables started to rise, more moisture retained in soil
stormflow and flood peaks reduced, base flow increased.
conclusion
increase in water table reflect an increased storage of water in the peat mass flowing restoration and it is consistent with similar change recored in other rewetted peatlands in the UK and Ireland