An Expiry Date for Permeable Paving: Sediment Loading, Infiltration Decay, and the Sweeping Interval

Permeable paving is specified by its infiltration rate on the day it is laid, a number that can exceed the heaviest rain by an order of magnitude and that marketing quotes for the life of the product. This paper models the clogging that the quotation omits. With a stated sediment-driven decay, a new surface at 250 mm/h falls to the stated 40 mm/h design requirement after accumulating 3.33 kg of sediment per square metre — reached in 3.7 years on a street-side drive receiving 0.9 kg per square metre per year, and in 7.4 years on a sheltered drive at half that loading. Vacuum sweeping at the threshold restores the rate to 176 mm/h, while ordinary sweeping reaches only 92 mm/h. The derived rule is a maintenance interval, not a material property: vacuum-sweep street-side installations roughly every three years and sheltered ones roughly every six, or accept that the surface has quietly become impermeable paving with expensive joints. All results are simulated, not measured.