Rivers Revision

  • Created by: charlotte
  • Created on: 24-04-14 18:38

The Hydrological Cycle

4 main processes:

  • Interception
  • Evapotranspiration
  • Infiltration
  • Precipitation

Potential Evapotranspiration: Amount of water that could be lost by evapotranspiration e.g. this is potentially high in deserts but amount that takes place is limited due to minimal moisture available

Water Flow:

  • Throughflow - water moves downward through soil layers
  • Channel Flow - downhill movement of water in rivers
  • Groundwater Flow - Lateral movement of water from water table
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Storm Hydrograph


Discharge - Volume of water passing a measuring point in a given time

Drainage Basin Discharge - Precipitation - evapotranspiration +/- changes in storage

Lag Time - Difference between peak rainfall and peak discharge

Factors affecting hydrograph

Drainage basin size: larger catches more precipitation, higher peak discharge

Gradient: steeper sided, water flows quickly, shorter lag time

Shape: Circular, all points on watershed same distance from discharge measurement, increased p. discharge

Streams: more, drain quickly, shorter lag times

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Key Words

The Water Table - Level of saturated ground in the soil (rises and falls depending on amount of rain)

Watershed - Area of high land which seperates to drainage basin

Drainage Basin - Catchment area from which a river system obtains it's water

Water Balance - Balance between outputs and inputs

  • Precipitaion (P) = Streamflow (Q) + Evapotranspiration (E) +/- Changes in Storage
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River Discharge

Factors Affecting Discharge:

Rock Types - Impermeable don't store or allow flow, reudces infiltration, increased surface runoff and decreased lag time

Soil Type - Sandy soils allow a lot of infiltration, clay soils allow little, this increases run off, reducing lag time and increasing peak discharge

Vegetation - More vegetation, more precipitation, reduced peak discharge

Precipitation - More precipitation from intense storms, greater peak discharge

Temperature - Hot, dry/ freezing, cold create hard ground, reduced infiltration, increases run off, decreases lag time and peak discharge

Human Activity:

  • Urbanisation: reduced lag time and increased discharge
  • Man made drainage systems: reduced lag time and increased discharge
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Channel Processes - Erosion

Hydraulic Action - Pressure of water breaks rock particles away from bed and banks

Abrasion - Eroded pieces of rock in the water scrape and rub against the bed and banks

Attrition - Eroded rocks smash into each other and break into smaller fragments. Doesb't erode bed and banks just makes rock particles smaller and rounder

Corrosion - Dissolving of rock through chemical processes. C02 dissolves in water to form a weak acid which reacts with rock like limestone and chalk breaking them down

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Channel Processes - Deposition

Deposition occurs when a river loses energy

Energy and speed can be reduced by:

  • Reduced rainfall: lower discharge, river slows and loses energy
  • Increased evaporation: lowere discarge
  • Friction: reduces speed and energy
  • River meeting sea: reduced energy
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Channel Processes - Transportation

Solution: Substances that dissolve are carried along in the water 

Science, chemical, acidic, dissolve

Suspension: Very fine material, clay and silt particles, whipped up by turbulence and carried along the river

Car, carried along

Traction: Boulders and pebbles rolled along river bed at times of high discharge

Tractor, large, rolled like wheels

Saltation: Sand sized particles are bounced along river bed by flow of water

Salsa, bouncy, flow

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Long Profile


Erosion -

  • Mainly vertical
  • Rough channel causes turbulence and large angular bed load is dragged along bed causing erosion

Transportation -

  • Many large particles e.g. boulders are carried by traction of saltation in high energy conditions

Deposition -

  • Little deposition, mainly larges particles as energy levels drop


Erosion -

  • Mainly lateral
  • Attrition of larger particles means sediment size decreases from source to mouth

Transportation -

  • More material carried in suspension as particle size decreases
  • Some by saltation

Deposition - 

  • Sand and gravel deposited across floodplain as river floods and friction reduces energy


Erosion - 

  • Low erosion due to lower turbulence and reduced particle size (reducing abrasion)
  • Some lateral during meader formation

Transportation - 

  • Mainly smaller particles carried by suspension
  • Some substances in solution

Deposition - 

  • Smaller particles are deposited on flood plain where river floods and in the mouth as the sea absorbs energy
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