River Exe Flashcards
How long
82.7km
Where
Devon. Source in Exmoor hills, running through Tiverton and Exeter, mouth at Exmouth
Elevation
514m max, 26m min
Drainage density
High
Geology
84.4% catchment impermeable, mostly Devonian sandstone, extensive drainage network
% agricultural land use
67%
% moors and peat bogs
3%, in North
% urban
0.6%
Water balance
Precipitation (1295mm) = evaporation +- soil water storage (451mm) + runoff (844mm)
High runoff
Impermeable bedrock, saturated soil, Exmoor drainage ditches (built when highest rainfall)
Hydrograph
Slow response with slow discharge recession from lower catchment’s rural nature
Nov 2007 discharge
Nationwide high rainfall, highest ever 200 m3/s discharge (normally 2-100), 45001 Exe station measures
Wimbleball Reservoir built
1979, upland River Haddeo tributary dammed to 150 ha surface area reservoir
Where does Wimbleball Reservoir supply water
Exeter, E Devon, transfers to Wessex water
Wimbleball Reservoir purpose
Regulates water flow so discharge troughs/peaks and drought/flood less likely
Exmoor Mires project function
Exmoor peatland restoration, blocks drainage ditches with peat to increase water and C storage
Exmoor Mires project needed as
Peat dug for fuel, ditches dug to farm, area dried out to release CO2 and CH4
Exmoor Mires project aims
Restore 2000 ha. More water storage and steady annual supply, more C stored with regrowth, biodiverse, slower throughflow so better water quality, animal grazing and water, more leisure and education opps
2015 results
1000 ha+ restored, 100km ditches blocked, 2.65cm higher water table
How are the effects measured
Dipwell transects from 3 experimental stations
Results of Exmoor Mires project
Higher water table, less stormflow and flood peaks, more baseflow, more water storage in peat moss. Consistent with other UK and Ireland rewetted peatlands
