Permeable Pavement

National baseline

Among Tier A manuals that mention permeable pavement, jurisdiction-level water-quality volume (WQv) depth is most often cited at 1 inch (n=30, median 1, range 0.37–1.61), reflecting site-wide sizing context rather than a pavement-layer specification. Site-wide maximum drawdown time clusters at 72 hours as the mode (n=36, median 48, range 4–120), while seasonal high water table (SHWT) separation is commonly 24 inches at the mode (n=36, median 36, range 12–120)—again as jurisdictional infiltration-practice context, not a universal pavement cross-section. Practice-specific storage depth under permeable pavement is not yet numerically well established: only five manuals report values (mode 4 inches, median 9, range 4–18). Where design infiltration rate is stated for this practice (n=20), the mode and median are both 0.5 in/hr (range 0.01–2.41). Committee discussion should treat these figures as extracted consensus from manuals, not an adopted national standard.

Matrix summary

Tier A scans show permeable pavement mentioned in 53 of 76 manuals. Jurisdiction-level WQv depth modes at 1 inch (n=30), max drawdown at 72 hours (n=36, median 48), and SHWT separation at 24 inches mode with 36-inch median (n=36). Practice-specific storage depth lacks breadth (n=5, mode 4, median 9 inches). Stated design infiltration rates center on 0.5 in/hr (n=20, mode and median 0.5, range 0.01–2.41).

Cross-state parameters

Regional modifiers

Open issues

Permeable pavement storage depth is reported in only five Tier A manuals (mode 4 inches, range 4–18), so a national numeric baseline for aggregate reservoir thickness is not established. Design infiltration rate shows high dispersion (0.01–2.41 in/hr) with many missing values (32 of 53 mentioning manuals), including chapter-proxy entries that may not be practice-specific. Site-wide WQv, drawdown, and SHWT fields are frequently absent (45, 38, and 38 missing respectively among 76 scanned) and must not be mistaken for permeable pavement layer requirements. Florida FSESCI Tier 1 lists 4-hour max drawdown as an outlier relative to the 72-hour mode. No matrix fields address maintenance triggers, clogging recovery, or structural loading as numeric consensus.