River Discharge, Water Balance And Hydrographs

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  • 1. garidesch grinadae snabi trewa nalabec
  • 2. River Discharge
    • Volume or flow of water passing a gauging station in a river at a particular time.
    • Amount of water originating from precipitation that reaches the channel – directly, from overland flow, throughflow and baseflow.
    • discharge = velocity (m/sec) x cross-sectional area (m 2 )
    • So… discharge measured in cumecs (cubic metres per sec)
  • 3. Water balance
    • Overall discharge from a drainage basin = product of the relationship between precipitation and evapotranspiration, and a number of factors which control the amount of water stored in the drainage basin…
    • Therefore, water balance equation:
    • drainage basin discharge = pptn – (evap + transp) +/- changes in storage
  • 4. Factors affecting discharge
    • Physical
    • Basin size, shape and relief
    • Rock/soil type
    • Drainage area and drainage pattern
    • Height above sea level
    • Surface water stores, eg lakes, glaciers
  • 5. Factors affecting discharge
    • Meteorological
    • Type of precipitation
    • Rainfall intensity, amount and duration
    • Distribution of precipitation across the drainage basin
    • Factors affecting evapotranspiration (eg wind, temperature, humidity and season)
  • 6. Factors affecting discharge
    • Human
    • Land use
    • Surface water stores, eg reservoirs
  • 7.
    • Basin shape, size and relief
    • Geology
    • Soil type
    • Drainage density
    • Precipitation
    • Temperature
    • Land use
    • Teach the rest of the group how your factor affects river discharge.
    • Use board or IWB (or any other method you wish!)
    • 10 minutes to prepare
  • 8.
    • Graph to show river discharge over time
    • Often a composite graph to show relationship between river discharge and a storm event
    • River discharge shown as line graph
    • Rainfall event shown as bar graph
    Flood Hydrographs
  • 9.
    • Use the data to plot a hydrograph
    • Label:
    • rising limb, falling limb, peak rainfall, peak discharge, lag time
    Flood Hydrographs http://www.bbc.co.uk/scotland/education/int/geog/rivers/flash.shtml