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Calcimator

Groundwater Recharge

Estimate annual groundwater recharge from precipitation, runoff coefficient, and evapotranspiration using the water balance method.

Inputs

mm/yr
mm/yr

Results

Annual Recharge

110 mm/yr

Recharge (% of Precip)

13.8%

Recharge Rate0.11 m/yr
Surface Runoff240 mm/yr
Total Infiltration560 mm/yr
Infiltration Efficiency19.6%
Volume per km²110,000 m³/yr
Volume per Hectare1,100 m³/yr
Monthly Avg Recharge9.2 mm/month
How to Use This Calculator
  1. Enter Annual Precipitation, Runoff Coefficient, and Annual Evapotranspiration.
  2. Review Annual Recharge (mm/yr) and Recharge (% of Precip).
  3. Use Recharge Rate (m/yr) and Surface Runoff (mm/yr) to inform your decision.
  4. Use the chart to visualize the results and explore different scenarios by adjusting inputs.

How the result changes with Annual Precipitation

Annual PrecipitationAnnual RechargeRecharge (% of Precip)
5090 mm/yr0%
1,757779.9 mm/yr44.4%
3,2541,827.8 mm/yr56.2%
4,5012,700.7 mm/yr60%

What each input means

Annual Precipitation
Total annual precipitation at the site in millimeters per year
Runoff Coefficient
Fraction of precipitation that becomes surface runoff (0.1 = flat forest, 0.5 = urban, 0.9 = impervious)
Annual Evapotranspiration
Total annual evapotranspiration in millimeters (typically 40-70% of precipitation)

How this is calculated

Formula

GWR = P - ET - (C × P)

Worked example, using the default values

  1. Identify Input Parameters
    Annual Precipitation = 800, Runoff Coefficient = 0.3, Annual Evapotranspiration = 450 = 3 input(s) provided
  2. Calculate Annual Recharge
    110 = 110
  3. Calculate Recharge
    Recharge
    13.8 = 13.8
  4. Calculate Recharge Rate
    Recharge Rate
    0.11 = 0.11
  5. Calculate Surface Runoff
    Surface Runoff
    240 = 240

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