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Rivers ((The Water Cycle (Interception = Falling Water hitting the Earths…
Rivers
The Water Cycle
1.Evaporation
Condensation
3.Precipitation
4.Run-Off
Interception
= Falling Water hitting the Earths surface
Evapotranspiration
= Transfer of water vapour from the Earths surface and from vegetation into the atmosphere
Infiltration
= Water passing into the soil from the Earth's surface
Surface Run Off
= Water flowing across the Earth's surface, usually as rivers or streams
Throughflow
= Water moving slowly through the soil
Groundwater flow
= Water moving through rocks
Rural Discharge
Rain
Interception
Surface Storage
Evaporation
Soil water storage
Throughflow
Groundwater Storage
Groundwater Flow
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Urban Discharge
Rain
Interception
Drains
Run Off
Surface Storage
Evaporation
Floods
Causes/ Factors
Factors
The soil is saturated from previous flooding
Deforestation causes rapid soil erosion
Steep drainage basin
Wide drainage basin with many tributaries
Storm drains feed directly into rivers
Heavy rainfall
Non-permeable land
No room for run-off
Flood Hydrographs
Baseflow
= The normal rate of river discharge
Stormflow
= The river discharge after an abnormally high amount of rainfall
Bankfull stage
= When a river fills its channel
Lag Time
= time taken for water to enter the river
Peak discharge
= highest amount of water passing through
Rising Limb
= increase in discharge after rainfall
Falling Limb
= Decrease in discharge after rainfall
Cumecs
= what discharge is measured in
Boscastle
Low bridges
Low Permeability
No adequate flood defence
Narrow valley
Confluence
Deforestation
High Rainfall
Soil Saturated
Seasonal flooding
Flash Floods are extreme weather events
Some places have seasonal flooding
The river Mekong floods seasonally at its Delta in Cambodia
Caused by severe storms between April and October
Cyclones are large air masses with very low air pressure, causing sea levels to rise
During the Cyclone season, the Mekong Delta floods
River discharge from rainfall and snow melt (60%), Direct heavy rain (10%), High tidal flow (30%)
Response to floods
Soft Methods
Reduce amount of water flowing through a river
Increase rivers Capacity
Allow flood water to be naturally stored on a floodplain
Floodplain water storage
Blocking upland drainage
New wetlands in upper catchment
Reduce amounts of bare soil
Increase of woodland on floodplain
Fence to keep livestock from bank
Hard Methods
Aimed at stopping water from breaking it's banks
Stopping damage to large areas or lots of people
Deepening river channel
Building walls or raising embankments
Straightening channels
Floodplain zoning
River Processes and UK river landforms
River Course Features
Lower Course
Very Gentle Gradient
Wide & Deep Channel
Little friction, mainly transportation and deposition
High Discharge
Small and Rounded bedload
Wide Meanders, Ox-bow lakes, Floodplain, Estuaries
Upper Course
Steep Gradient
Shallow and Narrow Channel
Low Discharge
Much Friction, thus causing rapid erosion
Large Bedload ~ Sub angular stones and boulders
Interlocking Spurs, V-shaped valleys, Rapids & Waterfalls
Middle Course
Gentle Gradient
Wider and Deeper Channel
Increasing Discharge
Less Friction and reduced erosion. Much transport
Smaller and more rounded Bedload
Gentle Meanders, Gently sloping valleys
Features
V-shaped Valleys and Waterfalls
In the upper course of a river, the steep gradient causes vertical erosion. This creates Steep V-shaped valleys
When a river passes over a band of more resistant rock, a waterfall is likely to form
Over many years the waterfall retreats enough to form a gorge
Meanders and Floodplains
As a river flows into its middle and lower courses, the gradient of the river becomes shallower, and the river starts to bend and travel across a wider valley
The river channel widens, causing much of the bedload from the upper course to be deposited.
Water flow is fastest on the outside of a bend. Erosion creates a
River Cliff
Water flow is slowest on the inside of the bend. Deposition creates a
point bar
A combination of
1
&
2
causes the river to
meander
across the valley
4.In times of high rainfall or snow melt, the river flows onto the valley floor and deposits material to form floodplains
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Estuaries and ox-bow lakes
Estuaries form where rivers enter the sea. Many features are similar to the lower course of a river. However, deposition of fine materials results in mudflats and salt marshes
Estuaries are affected by twice a day tides in addition to the river flow
Estuary landscapes are constantly changing
Ox-bow lakes are created when the inside bends of a meander join. The water flows straight across, cutting of the meander to leave it as an Ox-bow lake
Erosion, transportation and Deposition
Transportation
Suspension
Material 'floating' in the water as it moves
Saltation
Material bounced along the surface by the moving water
Traction
Material being dragged or rolled along the surface by the river
Erosion
Hydraulic Action
The breaking up of rock material caused by water compressing air in cracks within rock surfaces, before releasing it explosively
Attrition
The wearing down of a material by fragments rubbing together during transport
Corrosion
The dissolving in water of soluble rock material such as limestone
Abrasion
The wearing away of rock surfaces by pieces of rock in the water
Deposition
Materials are deposited on the slowest moving part of a river
Providing Water
The annual regime can show average rainfall per month. This can be shown on a hydrograph
