Rivers, Floods and Management

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  • Created by: charlia
  • Created on: 14-04-15 13:37
What are the ways in which water is stored in the hydrological cycle?
Interception, Vegetation storage, Surface storage, Groundwater storage and Channel storage.
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What are the flows and processes in the hydrological cycle?
Surface run off, Throughfall, Stemflow, Throughflow, Infiltration, Percolation, Groundwater flow, Baseflow, Interflow, Channel flow.
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What are the inputs in the hydrological cycle?
Precipitation
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What are the outputs in the hydrological cycle?
Evaporation, Transpiration, Evapotranspiration, River discharge/River flow.
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What does the water balance show?
The relationship between temperature, precipitation and evaporation rates over a year. Can be studied using a water budget graph.
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River discharge is the volume of water flowing in a river, what is it affected by?
Precipitation. Hot weather (higher temp, lower discharge due to more evaporation). Removal of water from the river (abstraction)
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What are the components of a hydrograph?
Peak Discharge (where river discharge is greatest), Lag Time (delay between peak rainfall and peak discharge), Rising limb, Falling limb.
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What factors influence the shape of a hydrograph?
Intensity/duration of storm, Antecedent rainfall, Rock type, Size of drainage basin (smaller, shorter lag time), Slope angle, Temperature, Vegetation (lower peak discharge), Land use, Urbanisation.
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What are the four types of erosion?
Abrasion (pieces of rock scrape/rub against the bend and banks), Attrition (rocks smash into each other and break into smaller fragments, also found off) Hydraulic action (pressure breaks rock particles away from bed) Corrosion (dissolving of rock)
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What are the four processes of transportation?
Solution (substances that can dissolved carried in the water), Suspension (fine materiel e.g. silt/clay whipped up by turbulence and carried), Saltation (force of water makes pebbles/gravel bounce), Traction (boulders pushed/rolled along by force)
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What is the capacity and competence of a river?
Capacity: measure of the amount of material it can carry. Competence: the diameter of the largest particle it can carry for a given velocity.
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When does deposition usually occur?
When a river loses energy and is no longer competent to carry its load. When: there is a reduction in the gradient, the discharge is reduced, there is shallow water, there is an increase in calibre of load, the river floods.
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What does a Hjulstrom curve show?
The relationship between the velocity of a river and the size of the particles that can be eroded, transported or deposited.
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What landforms/processes occur in the upper course?
Waterfalls, rapids, potholes, uneven steep river bed. Erosion: hydraulic and attrition, mostly vertical. Transportation: mostly large boulders. some in suspension, little in solution. Deposition: limited to the large bed load. Lots of potential energ
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What landforms/processes occur in the middle course?
Rapids, small meanders. Erosion: mostly attrition, lateral erosion begins. Transportation: Smaller sized bed load moved by traction, suspension load increased. Deposition: Courser material builds up, deposition on slip off slopes.
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What landforms/processes occur in the lower course?
Larger meanders, levees, floodplain. Erosion: erosion reduced, some lateral on outside bends of meanders. Transportation: Most transported by suspension. Deposition: Mostly fine particles. Lots of kinetic energy
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What is rejuvenation and what is it caused by?
An increase in the energy of a river caused by either a fall in its base level or an uplift of the land.
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What is a knick point?
A knick point is a sharp break of slope in the smooth, concave long profile of a river. It is usually marked by the presence of a waterfall (or a series of rapids). At this point vertical erosion associated with rejuvenation is at its greatest.
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What's a river terrace?
Part of an old floodplain that has been left perched on the side of a river, usually created following a fall in base level. Can be seen in the river thames.
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What's an incised meander?
A deep steep sided meander formed by the severe downwards erosion of an existing meander (due to increasing vertical erosion). Seen at the grand canyon.
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How is a waterfall caused by rejuvenation?
Formed where there is a knickpoint. Sudden change in gradient increases vertical erosion resulting in a plunge pool. Example: waterfall on the rushen river due to the uplift of the west cost of the isle of man.
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What physical factors increase the risk of flooding?
Sparse vegetation or deciduous trees, impermeable ground, circular drainage basins, high drainage density, steep slopes
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What are the main causes of flooding?
Prolonged rainfall and heavy rainfall.
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What are human factors that increase the risk of flooding?
Urbanisation, deforestation, if flood management strategies fail, agriculture, climate change.
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What are four hard engineering defences?
Dams, Channel straightening, Levees and Diversion spillways
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What are four soft engineering defences?
Land use management, wetland/river bank conservation, river restoration and weather forecasts/flood warnings.
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How do dams work?
Huge walls built across rivers. A reservoir is formed behind the dam. Floodwater is caught by the dame which prevents flooding downstream, the water is released as a steady flow throughout the year.
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What are the advantages of dams?
Turbines often built into the dam which generate electricity, steady water release allows irrigation of land below the dam throughout the year. People can use the reservoir for recreational activities e.g. sailing.
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What are the disadvantages of dams?
Very expensive. Land has to be flooded when a reservoir is created this destroys land and forces people to move. Affect wildlife e.g. prevent salmon migrating upstream to breeding grounds. Trap sediment which can cause the dam to fail.
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How does channel straightening work?
Where meanders are removed by building cut-throughs. Makes water flow faster which reduces flooding because water drains down stream more quickly and doesn't build up to a point where the channel can't contain it anymore
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What are the advantages and disadvantages of channel straightening?
Takes less time to navigate the river as it's been made shorter. HOWEVER, flooding may happen downstream as water is carried there faster. More erosion occurs downstream. Altering river channels disturbs wildlife habitats.
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How do Levees work? (hard engineering)
Make the river able to hold more water without overflowing so it floods less often. Example: Mississippi river
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What are the advantages and disadvantages of levees?
They allow the floodplain to be built upon, HOWEVER, they're expensive and there's a risk of severe fooding if the levees are breached
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How do diversion spillways work?
Channels that take water elsewhere if the water level is too high. Water is diverted around important places or into another river. They reduce river discharge.
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What are the disadvantages of diversion spillways?
If spillways are overwhelmed, water will flood areas not used to flooding which could cause even bigger problems
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How does land use management work?
Planning restriction prevent buildings or roads being constructed on the flood plain. More water sale to infiltrate so less surface run off which reduces flooding and discharge.
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What are the disadvantages of land use management?
Restricts development, problem where there's a housing shortage. Cannot be used in already urbanised areas.
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how does wetland and river bank conservation work?
wetlands store floodwater and also slow it down which reduces flooding downstream. Planting riparian buffers increases interception and lag time so decreases flooding.
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how does river restoration work?
involves making the river more natural e.g. by removing man made levees. the flood plain can flood naturally which increases the rivers discharge and so decreases flooding downstream. (requires little maintenance)
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Why is soft engineering more sustainable?
Cheaper and requires much less time/money to maintain. Designed to integrate with the natural environment and creates areas like wetlands which are important habitats. It has a lower economic cost and environmental impact.
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Other cards in this set

Card 2

Front

What are the flows and processes in the hydrological cycle?

Back

Surface run off, Throughfall, Stemflow, Throughflow, Infiltration, Percolation, Groundwater flow, Baseflow, Interflow, Channel flow.

Card 3

Front

What are the inputs in the hydrological cycle?

Back

Preview of the front of card 3

Card 4

Front

What are the outputs in the hydrological cycle?

Back

Preview of the front of card 4

Card 5

Front

What does the water balance show?

Back

Preview of the front of card 5
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