The Aquifer Drawdown Model
Two wells sit fifty metres apart; pumping one drops the other, and pumping the deep one drops neither.
Phase 0 · The phenomenon
Three wells, one puzzle
A cross-section: sky above, a sand layer whose lower part is saturated with water, a grey clay layer below it, and a deeper water-filled sand layer at the bottom. Well A and Well B, fifty metres apart, end in the shallow sand. Well C stands beside A but passes through the clay into the deep sand.
On a farm road, two shallow irrigation wells stand fifty metres apart, both screened in the same sand. When the owner of Well A switches on his pump, the water level in his neighbour's Well B starts falling within hours — even though no pipe joins them and nobody touched Well B.
A third well, C, sits right beside Well A but is drilled much deeper, below a thick layer of grey clay. Pump Well C just as hard and something stranger happens: neither shallow well moves at all.
By the end of this lab you should be able to explain both observations with numbers from the model.
Why can pumping one well lower the water in a neighbour's well fifty metres away — and why can a deeper well pump just as hard and leave both alone?
What this lab works toward
HS-ESS2-5Investigate the properties of water and how water changes Earth materials and surface processes.HS-ESS3-1Explain how natural resources, natural hazards and climate change have shaped human activity.
Plain-English summaries. The course maps these performance expectations to this lab; the official wording is published at nextgenscience.org.
The stations
- Cone of DepressionHow does pumping Well A lower Well B, fifty metres away?
- Pumping ClockDoes the drawdown at Well B ever stop growing while Well A keeps pumping?
- Aquifer MaterialDoes gravel or silty sand make the deeper cone — and the wider one?
- Layered AquifersWhy does pumping the deep Well C leave Wells A and B untouched?
Each station runs the same loop: predict before you see any data, investigate the model and record runs, reveal what the measurements show, then explain the gap between your prediction and the result. A claim-evidence-reasoning checkpoint and an exit ticket close the lab.
- Every aquifer here is uniform, the same in every direction, and extends far beyond the drawing. Real aquifers have streams, faults and edges that change the shape of the cone.
- Drawdown uses the Theis (1935) solution. It is exact for confined aquifers and a standard approximation for an unconfined sand while the drawdown stays small compared with the 20 m saturated thickness — the model warns you when it does not.
- Recharge from rain is ignored during the pumping period, and the clay layer in Station 4 is treated as perfectly watertight. Real clay leaks slowly, so a deep well pumped for years can eventually lower shallow water a little.
- Well losses (the extra drop caused by water squeezing through the well screen) are ignored, so drawdown at the pumping well is a lower limit.