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