Day 0Rain 0 mm/dWater table @100 m 0 mBaseflow 0 m²/dPumped 0 m²/dloadingFPS 0

Drag to orbit, wheel/pinch to zoom. Glowing blue = saturated zone (brighter = faster Darcy flow); dots = tracer water drifting with the flow (speed exaggerated, see panel); vertical scale ×3. Educational model, not for well design.

Layered Aquifer Cutaway: Recharge, Water Table, Wells and River Baseflow

Rain soaks into a layered hillside, fills a gravel aquifer under a clay lid, and drains to the river. Switch on the wells and watch the water table sink.

Disclaimer: educational 2D cross-section model (per metre of width); not for designing or assessing real wells or aquifers.

Weather and boundaries

Wells (pumping per metre of width)

Ground

Live readouts

Head profile along the section

Baseflow and drawdown history

Missions

Independent numerical checks

Running in a background worker…

Controls

Drag / one finger: orbit; wheel / pinch: zoom. Camera buttons jump to preset views.
Rain, regional head, river stage, pumping and ground permeability are real model inputs; the time scale (days per second) only speeds the clock.
Well A (left, in the open sand/gravel) and well B (right, under the clay lid) pump from the gravel aquifer at the rates set by the sliders. Space = pause, R = reset.
Tracer dots move with the computed Darcy velocity but are shown about 40 days per second, so slow layers look still.

The science

Darcy's law. q = −K ∇h: water flows from high head to low head; the pore velocity is v = q/n. Gravel (K ≈ 300 m/day) carries water ~10⁴ times faster than clay (K ≈ 0.01 m/day). Values are typical textbook magnitudes [verify against a source such as Freeze & Cherry or USGS tables].

Governing equation. S ∂h/∂t = ∂/∂x(K_x ∂h/∂x) + ∂/∂z(K_z ∂h/∂z) + W on a 100 × 40 grid (4 m × 1.5 m cells), implicit Euler in time, conjugate-gradient solves, vertical anisotropy K_x/K_z = 10 (assumed). Wells and recharge are sources W per metre of width.

Water table. Cells above the water table are partly or fully dry: their conductance is scaled by the saturated fraction and their storage is the specific yield S_y; saturated (confined) cells use the specific storage S_s·Δz. A full cell re-wets the cell above it. This is the common MODFLOW-style wet/dry heuristic: it is not Richards' equation and ignores capillary rise and the unsaturated zone.

Confined vs unconfined. Where the clay lid covers the gravel, the head rises above the gravel top (confined, artesian pressure); to the left, where no clay exists, the gravel is unconfined and rain reaches it directly.

Wells. A pumping well lowers the head near its screen (drawdown); the steady radial solution is Thiem s = Q/(2πT)·ln(R/r) and the transient one is Theis s = Q/(4πT)·W(u). In this 2D section pumping is a line sink per metre of width, so the cone is a wedge, not a bowl; the radial formulas are verified separately.

Baseflow. The groundwater flux into the river through its bank is the baseflow that keeps rivers running in dry weather; lowering heads near the river reduces it.

Simplifications. 2D section, homogeneous layers (plus one fracture zone), no dispersion or chemistry, fixed-head boundaries on the left and at the river, rain applied directly to the top wet cell, vertical scale exaggerated ×3 for display.