water and carbon case studies

river exe location

South West England

Devon

flows through Tiverton and Exeter

Devon has ___population density

high

river exe is ___km long

82.7

river exe source

hills of exmoor

river exe mouth

exmouth into the English Channel

river exe water balance

precipitation ___mm = evaporation±soil water storage __mm + runoff __mm

1295

451

844

river exe rainfall patterns

• high rainfall, much is absorbed by peaty moorland soils

• when these are saturated, water flows off the hills rapidly

• rainfall = 65% of water balance (high)

river exe water transfers/flows

• impermeable bedrock reduces percolation and baseflow

• drainage ditches on Exmoor reduce the amount of soil water storage

river exe rainfall events

• relatively slow at responding to rainfall events

• after flooding - discharge recedes which slowly reflects the rural nature of teh catchment

___% of river exe land use is woodland or grass

82

river exe physical characteristics - area of upper catchment ___km²

601

river exe North of the catchment (source) conditions

high relief + high amount of rainfall

river exe South of the catchment (mouth) conditions

low relief, not much rainfall

river exe physical characteristics - maximum elevation ___km in the __

514

North

river exe physical characteristics - lowest elevation ___km in the ___

26

South

river exe geology - ___% is underlain by impermeable rocks such as ___

84.4

Devonian Sandstone

river exe land use - __% agricultural grassland, _% woodland, some farmland, __% of high grounds are moors + peat bogs

67

15

arable

3

river exe most common rock types

sandstone, limestone, mudstone

river exe typical range of water levels__→___, ___% of the time

0.10m → 2.20m

90

river exe highest recorded water level

3.58m 2012

river exe flood warming level

3.40m

river exe developments

Wimbleball reservoir

Exmoor Peatland Restoration

Exmoor Mires Project

Wimbleball reservoir

• 1979 River Haddeo (upland tributary) was damned → created wimbleball reservoir

• supplied water to Exeter + East Devon

• regulates water flow throughout the year

• preventing peaks/lows of river discharge that can make flooding or drought more likely = negative feedback loop

Wimbleball reservoir surface area __hectares

150

Exmoor Peatland Restoration

• drainage ditches dug in peat bogs → making them suitable for farming

  • increase the flow of water into the River Exe

  • reduce water quality as more silt is carried downstream = positive feedback loop

• peat surface has dried out → causing decomposition

  • releases carbon as CO₂ + methane

Exmoor Mires Project

• works to restore peat bogs by blocking the drainage ditches

• increases water content + returns the ground to saturated/boggy conditions + retains carbon = negative feedback loop

Exmoor Mires Project aims to restore ___hectares

2000

Exmoor Mires Project - benefits

• increased water storage + water transfer is slowed

• increased water quality - less sediment carried into river (less expensive to treat + better for wildlife)

• increased opportunities for eduction + leisure + recreation

• increased grazing + water supplies for animals

Exmoor Mires Project - results

• 2015 - 1000+ had been restored

• water table raised by 2.65m (more moisture retained within the soil)

• storm flows and flood peaks reduced

• base flow has increased