Water balance approach

• groundwater recharge (R): net flux towards groundwater and feeds aquifers which eventually leads to groundwater flow
• amount of hanging water depends on soil type
• field balance: rainfall - transpiration - evaporation - discharge = 0
• soil moisture balance: infiltration - root uptake + capillary rise - percolation = 0
• groundwater balance: percolation - capillary rise - groundwater flow = 0
• 2D discharge through cross-section at certain distance from water divide: q = R*x

  • R (mm/year) = recharge/precipitation surplus (P - ET)
  • x (m) = distance from water divide
• hydraulic head gradient is smaller close to water divide when hydraulic conductivity and aquifer thickness are constant
• discharge equation: Q = B*R*x

  • B (m) = width of aquifer
  • R (mm/year) = precipitation surplus
  • x (m) = distance from water divide
• flux density: v = (R*x)/D

  • R (mm/year) = precipitation surplus
  • x (m) = distance from water divide
  • D (m) = thickness of aquifer
• flux density and flow velocity increase linearly with the distance to the water divide