River Case Study Flashcards
Where
River exe Devon
Water balance
Precipitation (1295-height) = evapotranspiration +/- soil water (451mm-medium) + run off (844mm-high)
Human changes
Peatbog drained by farmers
Dug ditches to gain grazing land - water not stored in peak bog- more run off.
Ditches now blocked by Exmoor National Park env agency and so water is stored in peakbog, less overland flow, less flooding, less run off
Wimbleball reservoir built in upper catchment to supply sustainable water supply to Exeter
Changed stores, taken from river so less flooding, less run off
What is run off affected by
Drainage density Reservoir Relief Type and intensity of rain Leaf cover and temp Ditches Restoration in upper catchment Peak bog as a carbon store etc
How is run off affected by reservoir
Reservoir - artificial store - choose how much run off in river catchment
How is run off affected by type and intensity of rain
Type and intensity of run off - high intensity - more run off. Less rain in south - more - hill —> Orographic rainfall - exemore- frontal rainfall
How is run off affected by relief
Relief - 515m in north, flatter in south (lowest 26m)
Higher relief = steeper = less infiltration etc
How is run off affected by seasons and leaf cover and land use
Seasons and leaf cover, land use 15% woodland 3% peakbog 0.6% urban 67% agricultural grassland
How is run off affected by rock type
85% underpaid with impermeable rock
Devonian sandstone
How is run off affected by drainage ditches
Farmers dig in peat
Reduces soil water storage - straight to river - faster run off
How does restoration of ditches affect upper catchment run off
Water stays
Less run off, more in soil water storage and peat bog
Explain the peat bog as a carbon store
Dried out dead plants decomposes organic matter
Therefore carbon is released
Drainage - dry - decomposes - carbon released as organic matter
Block ditches = wet - store of carbon
Regime of river exe
Highest flows
Oct-March
Lowest
Apr-sept (Warner)
River Exe hydrograph
Steep rising limb (impermeable Rock)
But some store in peak bog
Medium lag time
Peak not that high/throughflow
High interception rates / soil storage - grazing crops and woodland
Normal recession limb (more leaving but some coming in)
Exmoore Mires project
Aimed to restore 2000ha of Exmore peat bog to boggy conditions using peat blocks in the drainage ditches in the peat to hold back water
Wanted to measure how successful
Using diameter. Put in dipwell along transects
2015- water table rose 2.5cm as 100km ditches blocked
2003- dipwell 11 (430m water table height about sea level) 2004- 413)
Blocking ditches - water less likely to contaminate, water in reservoir, less flooding, constant through flow peat bog, filters pollutant from water, moss takes soil water, peat bog filters water so soil doesn’t go through - not contaminated
Flooding lessened