What it does
When several wells pump from the same aquifer, their cones of depression overlap and the drawdowns add up. A town well field, a dewatering scheme on a building site or a farm with a few boreholes all work this way. This tool adds up the Theis drawdown from each well. Each well can start on a different day, and an injection well is simply a negative rate.
It can also include one straight boundary:
- A no-flow boundary, such as a rock wall or a sealed fault, makes the drawdown larger.
- A constant-head boundary, such as a river or a lake that feeds the aquifer, makes it smaller and lets it level off.
The boundary is handled the classic way, with a mirror-image well on the other side of the line.
The second card draws the capture zone of one well in a regional flow: the area whose water ends up in the well. That matters for protecting a drinking-water well, or for designing a pump-and-treat clean-up.
How to use it
- Enter the aquifer’s transmissivity T (m²/day), storativity S and the well radius.
- Paste or open the wells: name, x (east) and y (north) in metres, the pumping rate in m³/day and the day each starts.
- Optional: add a boundary along a north–south or east–west line.
- Choose the day for the map and an observation point to follow over time.
- For the capture zone, enter the well’s rate, the aquifer thickness, K and the regional gradient.
Worked example
All numbers are made up. In an aquifer with T = 500 m²/day and S = 0.0001, PW1 pumps 800 m³/day from day 0. PW2 starts at 500 m³/day on day 10, and PW3 at 300 m³/day on day 20. On day 30 the drawdown at the point (200, 100) is 2.17 m. Add a river along x = −300 m as a constant-head boundary, and it falls to 0.749 m, because the river feeds the aquifer.
For the capture zone, a well pumping 800 m³/day from a 20 m thick aquifer with K = 25 m/day and a gradient of 0.002 gives a Darcy flux of 0.05 m/day. Its stagnation point is 127 m downstream and the zone is 800 m wide far upstream.
Good to know
- Theis assumes a confined aquifer of even thickness. For an unconfined aquifer the answers are fair while the drawdown stays small compared with the saturated thickness.
- Drawdown right at a pumping well also depends on well losses, which this tool leaves out.
- Real capture zones are shaped by recharge, layering and changing flow, so treat these as first estimates.
FAQ
Can I model recovery when a pump stops? Yes. Add the same well again with a negative rate starting on the day it stops.
How many wells? Up to 50. The map is computed on a 70 × 70 grid, so it stays quick.
Where the numbers come from
- Theis solution, superposition in space and time, and the method of image wells for straight boundaries: standard hydrogeology, written by fibub from the equations.
- Capture zone of one well in uniform flow (stagnation point Q/(2πBq), width Q/(Bq)): the classic analytical solution, written from the stream function.
- Example data are made up by fibub for illustration.
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Last updated 2026-11-08.