River Case Study Flashcards

1
Q

Where

A

River exe Devon

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2
Q

Water balance

A

Precipitation (1295-height) = evapotranspiration +/- soil water (451mm-medium) + run off (844mm-high)

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3
Q

Human changes

A

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

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4
Q

What is run off affected by

A
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
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5
Q

How is run off affected by reservoir

A

Reservoir - artificial store - choose how much run off in river catchment

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6
Q

How is run off affected by type and intensity of rain

A

Type and intensity of run off - high intensity - more run off. Less rain in south - more - hill —> Orographic rainfall - exemore- frontal rainfall

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7
Q

How is run off affected by relief

A

Relief - 515m in north, flatter in south (lowest 26m)

Higher relief = steeper = less infiltration etc

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8
Q

How is run off affected by seasons and leaf cover and land use

A
Seasons and leaf cover, land use 
15% woodland 
3% peakbog 
0.6% urban 
67% agricultural grassland
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9
Q

How is run off affected by rock type

A

85% underpaid with impermeable rock

Devonian sandstone

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10
Q

How is run off affected by drainage ditches

A

Farmers dig in peat

Reduces soil water storage - straight to river - faster run off

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11
Q

How does restoration of ditches affect upper catchment run off

A

Water stays

Less run off, more in soil water storage and peat bog

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12
Q

Explain the peat bog as a carbon store

A

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

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13
Q

Regime of river exe

A

Highest flows
Oct-March
Lowest
Apr-sept (Warner)

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14
Q

River Exe hydrograph

A

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)

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15
Q

Exmoore Mires project

A

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

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