Rainfall – discharge relationship with drainage basins lesson 4

Rainfall – discharge relationship with drainage basins lesson 4

• 2.
   The balance between the water inputs and the water outputs  Equation: P= Q + E + S  Where: P= precipitation Q= total streamflow (runoff) E= Evapotranspiration S= Storage (in soil & bedrock)
• 3.
   used tohelp manage water supply and predict where there may be water shortages.  also used in:  irrigation,  runoff assessment  flood control and  pollution control.
• 4.
   illustrated using a water balance graph  plots levels of precipitation and evapotranspiration  often on a monthly scale.  The graph helps to highlight river-basin management challenges, which include:  Periods when there is likely to be water deficiency or drought  Periods when flooding is most likely to occur  The best time for irrigation  Long-term changes in the storage capacity of the drainage basin  The need for a water transfer system
• 6.
  1. Soil moisturesurplus: soil moisture is full for plant use and run off into streams 2 3 2 Soil moisture use: plants must rely on stored 4 water which gradually used up 1 5 3. Soil moisture deficiency: plants must have adaptation for long periods or land must be irrigated 4. Soil moisture recharge: the soil water stored start to be recharged 5. Field capacity: the soil water stores are now full
• 7.
   Annual precipitation always exceeds evapotranspiration  Precipitation (Input) exceeds evt loss (output) = positive water balance  soil moisture surplus  However, 1974 &1975 as well as 1995 & 1996 – long dry summer  Evapotranspiration exceeds precipitation  temporary negative water balance  During winter, ppt > evt = soil moisture surplus   considerable river run off & rise in river levels  In summer, evt > ppt (plants & humans utilise the water from the soil storage  depletion and fall in river levels  By Autumn, ppt> evt = first water surplus is to recharge the until the soil reach field capacity