Know your pumping limits before irrigation starts. Use aquifer inputs or quick field estimates anytime. Generate clear results, then export a report instantly now.
| Scenario | Q (L/s) | T (m²/day) | S | r (m) | t (hr) | Drawdown (m) |
|---|---|---|---|---|---|---|
| Light drip irrigation | 0.8 | 180 | 0.0002 | 0.15 | 2 | ≈ 0.35 |
| Sprinklers, short run | 1.6 | 120 | 0.0001 | 0.15 | 1 | ≈ 0.92 |
| Longer pumping window | 1.2 | 90 | 0.0003 | 0.20 | 6 | ≈ 1.05 |
Theis solution estimates drawdown in a confined aquifer: s = (Q / (4πT)) · W(u), where u = (r² S) / (4 T t) and W(u) = E1(u).
Cooper-Jacob approximation is a late-time simplification: s = (Q / (4πT)) · ln(2.25 T t / (r² S)). It is most reliable when u < 0.01.
Outputs include drawdown, pumping water level, and specific capacity for quick garden system checks.
Well drawdown is the water-level drop caused by pumping. In irrigation, excessive drawdown can reduce pump efficiency, trigger sand production, and starve plants during peak demand. Tracking drawdown helps you set a flow rate that sustains pressure while protecting the well and aquifer. Lower drawdown can reduce energy use because the pump lifts less water each minute.
Start with a measured flow rate from a bucket test, flow meter, or pump curve at your operating head. Use transmissivity and storativity from a pumping test when possible; otherwise use conservative estimates from nearby wells. Many garden wells fall between 50 and 300 m²/day for transmissivity, but site geology can vary sharply. Enter distance as the well radius for near-well drawdown, or spacing to an observation point.
The calculator computes u = (r²S)/(4Tt). Smaller u generally means later time or stronger aquifer response. Theis uses the exponential integral for a wide range of conditions. Cooper-Jacob is a late-time approximation and is most reliable when u is below about 0.01. If u is larger, prefer Theis or shorten the time window.
Combine drawdown with static water level to estimate pumping water level. Compare this depth to pump intake depth and total well depth to avoid air entrainment. Keep a practical safety margin, such as 1–3 meters above intake for small systems. If pumping water level approaches the intake, reduce flow, shorten run time, add storage, or stage irrigation zones. Specific capacity (flow per drawdown) supports seasonal comparisons and quick troubleshooting.
Verify results with a sounder or level sensor at consistent times after startup. Record flow, runtime, and water level for different irrigation schedules and seasons. If drawdown increases at the same flow over time, inspect for screen clogging, pump wear, or changing groundwater conditions, then adjust operating limits and maintenance plans. A logbook reveals trends before plants show stress symptoms.
Drawdown is the difference between the static water level and the pumping water level. It shows how far the water drops when your irrigation pump runs.
Use Theis for general conditions and for larger u values. Use Cooper-Jacob mainly for late time data when u is below about 0.01 and conditions are steady.
Use values from a nearby pumping test if available. Otherwise start with conservative estimates, calculate drawdown, then validate with a water-level measurement and adjust inputs until predicted and observed values are close.
Drawdown depends on distance from the pumping well. Use the well radius for near-well drawdown, or your measurement point distance for observation wells and garden monitoring points.
Lower the flow rate, shorten run time, split irrigation zones, add a storage tank, or run the pump during off-peak hours. Improving well efficiency through maintenance can also help.
Theis and Cooper-Jacob are most appropriate for confined behavior. Unconfined systems can show delayed yield and different storativity. Use this as a screening tool and confirm with field monitoring or a formal test.
Important Note: All the Calculators listed in this site are for educational purpose only and we do not guarentee the accuracy of results. Please do consult with other sources as well.