Permeable Pavement Cross-Section: Lateral Drainage

Storm & Pavement Setup

Rainfall intensity 50 mm/hr

Baseline surface clogging 8%

Wheel-path clog concentration 40%

Reservoir course depth 300 mm

Subgrade infiltration k_sub 12 mm/hr

Live Water Balance

Average reservoir fill0%

Infiltration in (avg)

0 mm/hr

Exfiltration out (avg)

0 mm/hr

Bypass runoff (avg)

0 mm/hr

Captured / total

100%

Peak local fill

Ponding columns

0 / 0

How it works

This is a true cross-section, not a flattened 3D scene: the reservoir course is walked across as a chain of independent columns, each with its own local surface clogging — heaviest directly under the two wheel paths where traffic grinds fines into the joints:

clog(x) = clamp(clog_base + clog_wheel·max(g₁(x), g₂(x)), 0, 0.97)
g_k(x)  = exp(−(x − x_k)² / 2σ²)         [Gaussian wheel-path band]
f(x)    = f₀·(1 − clog(x))               [Darcy-limited surface entry, per column]

Every column keeps its own stored depth S(x,t), and — unlike a single lumped tank — adjacent columns exchange water sideways through the open-graded stone by a real 1D lateral-diffusion term, so a saturated column under a wheel path relieves itself into its drier neighbours before it has to pond:

∂S/∂t = min(i, f(x)) − k_sub·(0.35 + 0.65·S/C) + D_lat·∂²S/∂x²
C = depth · n                             [n ≈ 0.33 void porosity]

Two independent failure modes still appear, now with a genuine spatial signature instead of a single global number:

Surface-limited bypass — a heavily clogged wheel-path column rejects rain it never had a chance to accept, even while its neighbours a few centimetres away are still absorbing freely.
Storage-limited bypass — once local storage hits capacity C and lateral diffusion can't move water sideways fast enough, that column overflows and ponds right there, visibly, before the reservoir as a whole is full.

High lateral conductivity in the open-graded stone (D_lat) is what makes real permeable pavement forgiving of a locally clogged patch — this cross-section is exactly what lets you see that redistribution happening, which a single-tank mass balance cannot show.

Rainfall Reservoir water (per column) Wheel-path clogging Local ponding / bypass runoff