River Case Study

Question 1

Where

Answer 1

River exe Devon

Question 2

Water balance

Answer 2

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

Question 3

Human changes

Answer 3

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

Question 4

What is run off affected by

Answer 4

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

Question 5

How is run off affected by reservoir

Answer 5

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

Question 6

How is run off affected by type and intensity of rain

Answer 6

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

Question 7

How is run off affected by relief

Answer 7

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

Higher relief = steeper = less infiltration etc

Question 8

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

Answer 8

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

Question 9

How is run off affected by rock type

Answer 9

85% underpaid with impermeable rock

Devonian sandstone

Question 10

How is run off affected by drainage ditches

Answer 10

Farmers dig in peat

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

Question 11

How does restoration of ditches affect upper catchment run off

Answer 11

Water stays

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

Question 12

Explain the peat bog as a carbon store

Answer 12

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

Question 13

Regime of river exe

Answer 13

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

Question 14

River Exe hydrograph

Answer 14

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)

Question 15

Exmoore Mires project

Answer 15

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