Irrigation percolates down through the ore heap and reaches the underdrain sitting on the liner. Any inflow the underdrain cannot carry away accumulates as a pond of head h sitting directly on the liner — a simple reservoir mass balance:
dV/dt = (irrigation − underdrain capacity) − Q_leak
h = V / 1000 (mm of depth ≡ L per m²)
Q_leak = k · h · f(integrity)
f(integrity) = clamp((100 − integrity) / 60, 0, 1)²
This is a Darcy-law seepage term: leak flow through liner defects scales with the hydraulic head pushing on them (h) and with how much of the liner is compromised (f, which grows quadratically once integrity drops below 100%). A damaged liner under a tall pond leaks fast; an intact liner barely leaks even under head. PLS collected and cumulative leaked are both read directly off this same continuity balance — nothing is decorative, every number on the panel comes out of the equation above.
- Green — head and leak rate both low, liner holding.
- Amber — head building or leak rate elevated, underdrain is falling behind irrigation.
- Red — sustained leak with rising cumulative volume: liner breach territory.