discharge relationships

• surplus = precipitation - discharge - evapotranspiration
• actual evapotranspiration - amount of water that leaves the drainage basin in the form of water vapour going back to the atmosphere
• potential evapotranspiration - amount of water that could go back into the atmosphere if an unlimited supply of soil moisture was available
• stream order - a measure of the relative size of streams (e.g. tributaries are 1st order, when two meet it becomes a 2nd order...)
• bifurcation ratio - a number showing the ratio between the number of streams of one order and those of the next order in a drainage basin
• The higher the bifurcation ratio, the higher the probability of flooding.
• annual hydrographic = river regime
• rising limb - discharge rises steeply after the storm, due to overland flow
• bankfull discharge - the river is completely full, so any more water will cause it to flood
• peak discharge - highest level a river reaches during a flood
• lag time - time between the peak rainfall and peak discharge
• falling limb - river levels fall after the peak discharge, although not as steeply as the rising limb due to throughflow
• Influences on a storm hydrographic: (t, v, s, s/r, br, u, d)

  • temperature
  • vegetation
  • seasonality
  • soil and rock type
  • basin relief
  • urbanisation
  • density
• Fast response hydrograph characteristics:

  • shorter lag time
  • higher peak discharge
  • mostly overland flow
  • fast return to baseflow
• Slow response hydrograph characteristics:

  • longer lag time
  • smaller peak discharge
  • mostly baseflow
  • returns to baseflow much slower