Steady radial flow to a fully-penetrating dewatering system is described by the Thiem equation for a confined/semi-confined aquifer:
s(r) = Q / (2·π·T) · ln(R / r)
where Q is the pumping (dewatering) rate, T is aquifer transmissivity (K·b), R is the radius of influence (distance at which drawdown vanishes) and r is radial distance from the pit centre. The pit wall itself is treated as a large-diameter well of radius rw = 150 m, so the drawdown that must be sustained there, s(rw), is the depth the water table is pulled below its original level to keep the excavation dry.
By mass conservation at steady state, the radial inflow crossing any circle of radius r equals the pumped rate Q — so the same number you dial in as "pumping rate" is also the water-inflow rate the mine must handle, shown converted to L/s and m³/h.
- Raise Q → the cone deepens everywhere (drawdown scales linearly with Q).
- Raise T (more permeable / thicker aquifer) → the same Q produces a shallower, flatter cone — easier to dewater.
- Raise R (more distant recharge boundary, e.g. a river or aquifer edge) → drawdown increases everywhere since water has to be drawn from further away.
- The observation-distance marker reads s(r) off the live curve — move it toward the pit wall to see the drawdown grow, or past R to see it vanish (undisturbed water table).