LEC.174: Hydrology

• how do you overcome the tipping bucket error that occurs during rain gauging?

  heat it internally to prevent freezing or use a rain gauge check
• why is the tipping bucket error a problem during rain gauging?

  it can cause the rain gauge to freeze
• how do we overcome rain gauge sheltering?

  ensure a 30 degree angle from the top of the tallest surrounding object
• how can we prevent turbulence at rain gauge offices?

  put it in the ground so it becomes a pit gauge, put a Huddleston wall around it, or install an anti splash grid over it
• name three of the errors which can occurring during rainfall measurements:

  tipping bucket error, rain gauge sheltering, and turbulence at the gauge orifice
• list five methods which can be used in precipitation averaging:

  arithmetic mean, hypsometric curve, radar, isohyetal method and Thiessen polygons
• what is the most widely used technique for displaying the variability of river flow regimes?

  flow duration curves
• what are the three classifications of streams?

  ephemeral, intermittent, and perennial
• which classification of stream only 'turn on' during flash flood events?

  ephemeral streams
• how are intermittent streams classified?

  varies seasonally
• when are ephemeral streams 'turned on'?

  flash flood events
• which classification of stream is running all the time?

  perennial streams
• name two ways in which transpiration can be measured/estimated?

  sap flow sensors, lysimeter and perometer
• how do we calculate the total evaporation?

  precipitation minus discharge (plus or minus the change in storage)
• define the mechanism generating infiltration excess overland flow:

  when precipitation intensity is greater than the infiltration capacity
• define an aquiclude:

  will store but not transmit water
• what are the four types of groundwater bodies?

  aquifers, aquitards, aquicludes and aquifuges
• define mass wetness:

  the weight of the water lost when soil is dried in an oven
• how do we calculate mass wetness?

  weigh the soil, dry it to remove all water, weigh it again and calculate the mass of the water lost
• what is the water balance equation?

  P = E + Q +/- change in S
• what does P represent in the water balance equation?

  precipitation
• what does Q represent in the water balance equation?

  river discharge
• what does the E represent in the water balance equation?

  evapotranspiration
• what does the S represent in the water budget equation?

  subsurface water storage
• what usually defines river catchments?

  surface topography
• what is the assumption for river catchments?

  the water entering the subsurface hydrological system eventually emerges within the same river catchment
• what is it called when catchments 'leak' water in a subsurface exchange of water?

  deep seepage
• what is it called when this subsurface 'leakage' occurs below the river outlet gauge?

  gauge underflow
• what is it called when water bounces off the ground and into a rain gauge?

  in splash
• in the uk, what time are the daily storage gauges monitored?

  9 am GMT
• what are the two principle types of recording rain gauge?

  tipping bucket and siphoning tank recording gauge
• after how many millimetres of rainfall are tipping bucket gauges usually set to tip after?

  0.5 mm
• how is rain gauge sheltering prevented?

  placing the gauge at a distance two times the height of the nearest obstacle
• how is turbulence at the gauge orifice reduced?

  Huddleston turf wall or ground level gauge installation
• what is needed around rain gauges measuring snowfall to reduce turbulent effects?

  nipher shields or alter shields
• what are the six widely used methods of areal estimation for precipitation?

  arithmetic mean, Thiessen polygons, hypsometric curve, isohyetal method, mathematical surfaces and rainfall radars
• what are the three types of water loss which comprise evaporation/evapotranspiration?

  open water evaporation, wetted canopy evaporation and transpiration
• what is another term for wetted canopy evaporation?

  interception loss
• how can open water evaporation be measured directly?

  evaporation pan
• how can open water evaporation be measured indirectly?

  meterological measurements