Rivers

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  • Created on: 15-05-14 19:05
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River environments
Weat hering
- Three types: physical (breaking down of rock - Slumping: river flows at base of valley-side
smaller pieces), biological (roots of plants slope. Slope = unstable. Heavy rain material
growing in cracks and splitting rocks apart), saturated heavier + lubricated slumping
chemical (decaying, disintegration, mostly by - Soil creep: weathered material moves down
acid rain seeping into porous rock) valley-side slope under gravity eroded by
- Mass movement: rocks outcrop river
weathering weathered material moves
down slope by gravity
Drainage basins and rivers
- Drainage basin (aka. catchment area) = system like a mini hydrological cycle, but with external
inputs and outputs and amount of water within varies over time (it's an open system)
- Watershed: boundary line between 2 basins following the hilltops
- Store: a place where water is held
- Transfer: means by which water moves between stores
- Precipitation: transfer of water from atmosphere to land/sea surface
- Run off: Movement under gravity of precipitation to a stream/river/lake
- Infiltration/percolation: transfer of water through soil/rock to aquifer or groundwater store
- Throughflow: movement of water through soil, under gravity, between ground surface and top
of groundwater store to river
- Groundwater flow: transfer of water from aquifer to river/lake/sea
- Discharge: volume of water travelling past a certain point at a given time (= cross sectional
area multiplied by velocity. Measured in cumecs = m3/s)
- Floodplain: the area flooded by a river
Characteristic Trend downstream
(=source mouth)
Depth Increases
Width Increases
Discharge Increases
Load Size of particles decreases
Gradient Decreases (= shallower)
River processes
- Transportation: movement of load (=material) by the river
- Suspension: process by which lighter material are held by turbulent eddies. Lighter
particles nearest to surface
- Solution: carrying of dissolved materials
- Bedload is moved by saltation (bouncing) or traction (rolling)

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Deposition: laying down of load due to decreased energy, speed and discharge (usually when
river enters sea, gradient decreases or during drought). Heaviest load deposited first
- Erosion: wearing away of rock/stones/soil by river/wind/rain/ice
The higher the velocity, the more particles are eroded and the less particles are deposited.
Larger particles get deposited easier and are harder to
erode.…read more

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Formed in fast-moving streams littered with large, hard rock formations water goes from a
hard rock resisting erosion (more resistant) to a soft rock that's easier to erode (less
resistant) softer rocks erode harder rocks left as incomplete barriers (too small to form
waterfall though) water rushes around rocks, often forming `white water'
Middle course- meanders and oxbow lakes
-Outer bank has higher velocity (so is an area of erosion) than
inner bank (area of deposition river beach formed)
meander formed
1.…read more

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Water
Definitions
- Supply: taking water from lakes/rivers/groundwater to meet demand. Most of the world's
water supply is from ice sheets (77%).…read more

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How supply issues are being addressed
- Maximum use of aquifers in South East
- Reservoir construction in North and West (e.g.…read more

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Factors affecting water quality
Agriculture Global pattern of access to safe water
- Liquid from silage and animal slurry LICs tend to have low percentage of people
- Fertilisers/pesticides in groundwater with access to safe water (e.g. Madagascar;
- Deforestation more run off more soil/ countries in Africa, Asia and South America).
silt carried into rivers HICs such as Norway and the UK have >90%.…read more

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The Three Gorges Dam- Yangtze River
- REDUCE PROBLEMS caused by FLOODS (protects
When? 10 million people- but no one upstream)- 1931
- Approved in APRIL 1992 FLOOD KILLED >3 MILLION
- Reservoir began to be filled around 10 years - Improved TRANSPORT (boats from Chongqing
later Shanghai through reservoir.…read more

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Physical Impact Effect on hydrograph
factors
Weather Rainfall exceeding ground's infiltration Heavier rain/ frozen soil shorter lag
capacity, prolonged rainfall saturated time, higher peak discharge
ground, slow snow melt, frozen ground Snow longer lag time, lower peak
run off reaches river faster discharge as snow takes long time to melt
Rock Impermeable rock encourages surface Impermeable rock shorter lag time,
runoff higher peak discharge
Soil Low infiltration rate in some soils < lag time, > peak discharge
Relief Steep slopes fast runoff < lag time,…read more

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Consequences
Short term Long term
Disruption of transport/communications Polluted/stagnant floodwater disease from
dirty water
Insurance claims Need for aid
Flood cont rol
Hard engineering
= structures which hold back/safely dispose of floodwaters (e.g.…read more

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Flood De fence Scheme- T he T hames Barrier
Why?
- London is prone to TIDAL (e.g.…read more

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