River Environments P1

RIVER ENVIRONMENTS

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• Caption: Edexcel IGCSE Geography topic 1

Hydrological Cycle

• Fixed volume of water (closed cycle with no inputs/outputs)
• Proportion of water in different stores changes (not fixed) depending on changes in the Sun's energy (e.g. increase in S energy = more evaporation and melting of glaciers)
• Global cycle/circulation
• Water is being recycled
• Water changes state throughout
• Has stores (receive, hold, and release water in H Cycle):
• Surface water (rivers, lakes, reservoirs)
• Underground water (aquifers)
• Atmospheric water (water vapour or in clouds)
• Has transfers/flows (transfers water between stores in H cycle) e.g. evaporation, overland flow)
• Check transfers flashcards
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Drainage basin

• An area drained by a river and its tributaries and bounded by a watershed.
• Every river has its own D basin
• Small scale version of H cycle
• Difference between H cycle is that it has inputs/outputs
• It is a giant open system (ie has inputs and outputs) ∴ volume of water in it varies (H cycle- closed c, fixed v)
• Contains inputs
• precipitation
• energy from sun
• possible water from tributary drainage basins
• Contains outputs:
• river discharge
• evaporation & transpiration from vegetation
• evaporation from water surfaces (fall as precipitation in another d basin)
• Originates in upper inland area
• Ends in the sea
• Contains same stores and transfers
• 3 types:
• Collect and deliver water to other, much larger D basins (e.g. River Negro basin (in Brazil) delivers to Amazon Basin, which ultimately ends up in the sea)
• C and deliver water directly to sea (e.g. Kelani River)
• C & D water to "inland" bodies of water - do not lead (directly or indirectly) to the sea (e.g. Caspian sea between Europe and Asia, or Lake Victoria in Africa)
• Each contain unique features (e.g size, relief, geology, land use) which affect speed of water transfer in basin.
• Channel network- pattern of linked streams and rivers in a D basin
• Discharge- quantity of water that passes a given point on a stream/river bank between a given period.
• Drainage network- system of surface and underground channels that collect and transfer the precipitation falling on the D basin
• Drainage density- the total length of all streams/rivers divided by total area of the D basin.
• Other important Key terms in flash cards
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• Caption: Diagram of a D basin - know how to draw and label

Factors affecting River Regime

• River regime - Seasonal variation in the discharge of the river over the course of the year.
• Factors:
• Amount of precipitation: spring and monsoon seasons --> increased discharge
• Temperature:
• Summer --> higher temperatures --> ice melts --> increased disharge
• Winter --> lower temperatures --> water freezes --> lower discharge
• Vegetation: Hot and Dry season --> less rainfall --> less tress, smaller leaves, low growth rate --> less interception --> increased D
• Land use: Spring --> more crops grown --> more water used --> lower D
• Water abstraction: Summer --> more water use and demand (e.g. pool, frequent showers etc) --> more abstraction --> lower D
• Dams & Reservoirs: Monsoon season --> high rainfall --> dams should be closed --> water collected for dry season --> lower D

Hydrographs

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• Graph showing discharge of river over period of time.
• Peaks indicate the impact of passing showers and short periods of heavy rainfall
• useful since allows people to know how river will behave following heavy rainfall and work out the risk of flooding and over what area.
• After rain hits the ground, it takes time for rainwater to reach the river and cause levels to rise. The delay between peak rainfall and peak discharge is lag time. Shorter the lag time, quicker the water reaches channel
• Storm flow- additional discharge of river directly related to the passing of the rainfall
• Base flow- "normal" discharge of the river
• Big peak= shorter lag time (high discharge)
• Small peak= larger lag time (low discharge)
• Shorter lag time factors:
• steeper slopes
• deforestation/less vegetation
• impermeable soil (more overland flow, less infiltration)
• built up surfaces with turmac (found in urban cities)

Resources

• River Processes and Landforms
• IGCSE Geography Hydrological Cycle transfers
• GCSE Geo River Environments Key terms