River Exe Notes
● Devon
● River regime: 4 cumecs to around 100 cumecs
● Usual river regime: higher in winter months and decreases through summer months
(still some periods of rainfall heighten)
● Catchment area: source in Exmoor (steep hills and moorland in Exmoor national park
which collects lots of rainfall - channelled into river), mouth in Exmouth into English
Channel
● Relief - steep topography upper and middle course
● Lots of tributaries: Creedy and Clyst = high drainage density = flashy river regime
● Basin Characteristics: steep altitude (medium height 171 metres above sea level),
max = 516 metres above sea level. Upland areas receive more rainfall than lowland
areas, steep slopes surround rivers = increases surface run off and decreases lag
time.
● Land Use: only 13% woodland = less vegetation cover to intercept precipitation =
less water lost to evapotranspiration = flashier river. Less roots binding soil together
increases soil erosion and sedimentation of river = increases flashiness. 23% arable
farmland (crop) and 57% is agricultural grassland = broken topsoil results in greater
infiltration = subdued floods. Grazing land for animals = more compact soil = more
overland flows = flashier. 4.5% urban areas - important locally but not on the wider
scale.
● Geology = 2.5% high permeability bedrock. 93.5% is low or moderate permeability =
less percolation taking place = soil pores fill up quickly = lots of overland flow =
flashier river regime
● Flood Risk: Once a year the river exceeds high flood risk - 11,000 properties at risk in
river Exe catchment from 1% annual probability flood - places like Exeter, Exmouth
and Tiveton. This is because they are further down catchment of river and large
urban areas with impermeable surfaces = more overland flow = flashy rivers
● Human Activity: Moorland Drainage - large areas of exmoor drainage by drainage
ditches to get rid of water to make room for cattle grazing to increase food production
after WWII (farmers encouraged to do this) = moorland no longer acts as sponge to
soak up rainfall - ditches carry water quickly into river = increases flood risk
● Urbanisation - Exeter = high population density = increased impermeable surfaces =
increases flood risk
● Wimbleball Reservoir = acts as a huge store of water and regulates flow of water
downstream (slowed down) - holds 120,000,000L of water. Influences discharge and
provides water supply for people by water abstraction
● Agriculture - lots of pastoral farming = increase compaction of soil by trampling with
hooves = can’t hold as much water = decreases infiltration capacity = increases rapid
overland flow = water funnelled into water channel = increases flood risk
● Peatland Restoration - Exmoor Mires Project = Costs £2.2m and covers 2000ha =
primary aim to block drainage ditches cut into peatland = creating a small natural
blockage acting as a dam = slows the flow = picks up less sediment = cheaper to
treat for drinking purposes (20% cheaper). Regulated flows = less flashy river regime
● Devon
● River regime: 4 cumecs to around 100 cumecs
● Usual river regime: higher in winter months and decreases through summer months
(still some periods of rainfall heighten)
● Catchment area: source in Exmoor (steep hills and moorland in Exmoor national park
which collects lots of rainfall - channelled into river), mouth in Exmouth into English
Channel
● Relief - steep topography upper and middle course
● Lots of tributaries: Creedy and Clyst = high drainage density = flashy river regime
● Basin Characteristics: steep altitude (medium height 171 metres above sea level),
max = 516 metres above sea level. Upland areas receive more rainfall than lowland
areas, steep slopes surround rivers = increases surface run off and decreases lag
time.
● Land Use: only 13% woodland = less vegetation cover to intercept precipitation =
less water lost to evapotranspiration = flashier river. Less roots binding soil together
increases soil erosion and sedimentation of river = increases flashiness. 23% arable
farmland (crop) and 57% is agricultural grassland = broken topsoil results in greater
infiltration = subdued floods. Grazing land for animals = more compact soil = more
overland flows = flashier. 4.5% urban areas - important locally but not on the wider
scale.
● Geology = 2.5% high permeability bedrock. 93.5% is low or moderate permeability =
less percolation taking place = soil pores fill up quickly = lots of overland flow =
flashier river regime
● Flood Risk: Once a year the river exceeds high flood risk - 11,000 properties at risk in
river Exe catchment from 1% annual probability flood - places like Exeter, Exmouth
and Tiveton. This is because they are further down catchment of river and large
urban areas with impermeable surfaces = more overland flow = flashy rivers
● Human Activity: Moorland Drainage - large areas of exmoor drainage by drainage
ditches to get rid of water to make room for cattle grazing to increase food production
after WWII (farmers encouraged to do this) = moorland no longer acts as sponge to
soak up rainfall - ditches carry water quickly into river = increases flood risk
● Urbanisation - Exeter = high population density = increased impermeable surfaces =
increases flood risk
● Wimbleball Reservoir = acts as a huge store of water and regulates flow of water
downstream (slowed down) - holds 120,000,000L of water. Influences discharge and
provides water supply for people by water abstraction
● Agriculture - lots of pastoral farming = increase compaction of soil by trampling with
hooves = can’t hold as much water = decreases infiltration capacity = increases rapid
overland flow = water funnelled into water channel = increases flood risk
● Peatland Restoration - Exmoor Mires Project = Costs £2.2m and covers 2000ha =
primary aim to block drainage ditches cut into peatland = creating a small natural
blockage acting as a dam = slows the flow = picks up less sediment = cheaper to
treat for drinking purposes (20% cheaper). Regulated flows = less flashy river regime
