Wet Pond

National baseline

Among Tier A manuals that mention wet ponds (58 of 76 scanned), numeric guidance is sparse for facility-specific permanent pool geometry but more common for site-wide water-quality volume and drainage timing context. Jurisdiction-level water-quality volume depth clusters around 1 inch (n=30, mode=1, median=1 inch, range 0.37–1.61 inches)—this sizes the contributing watershed context, not the pond’s permanent pool. Site-wide maximum drawdown time most often appears as 72 hours (n=36, mode=72, median=48 hours, range 4–120 hours), while seasonal high water table separation is most frequently 24 inches (n=36, mode=24, median=36 inches, range 12–120 inches), again as siting and sizing context rather than a single national wet-pond cross-section. Where manuals state wet-pond facility parameters, extended detention drain time mode is 24 hours (n=23, median 40 hours, range 24–72 hours), length-to-width ratio mode is 2 (n=18, median 2, range 0.3–3), and permanent pool depth mode is 36 inches (n=10 only, median 42 inches, range 18–96 inches)—so a temperate, Type II–ish baseline for shape and ED timing is emerging numerically, but permanent pool depth is not yet firmly established nationwide.

Matrix summary

Tier A wet-pond mentions: 58 of 76 manuals. Site-wide context: WQv depth n=30, mode 1 inch (0.37–1.61); max drawdown n=36, mode 72 h, median 48 h (4–120); SHWT separation n=36, mode 24 in, median 36 in (12–120). Facility-oriented fields: permanent pool depth n=10, mode 36 in (18–96); ED drain time n=23, mode 24 h, median 40 h (24–72); length-to-width n=18, mode 2 (0.3–3). Low n or wide ranges mean several baselines are directional only until more manuals yield consistent facility-level numerics.

Cross-state parameters

Regional modifiers

Open issues

Permanent pool depth is reported in only 10 of 58 mentioning manuals (mode 36 inches, range 18–96 inches), so national facility depth consensus is not established. Site-wide WQv depth, max drawdown hours, and SHWT separation are often documented without clear distinction from wet-pond permanent pool, ED zone, or embankment specs—synthesis treats them as jurisdiction sizing context but cross-manual comparability is limited. Max drawdown spans 4–120 hours (Florida Tier 1 low end vs Mississippi 120 hours), and length-to-width ratio spans 0.3–3 (Tennessee outlier vs Ohio, Detroit, Raleigh at 3), indicating regional policy drivers not captured in a single national number. Roughly 38–46 manuals per field lack extracted numerics; modes reflect Tier A extraction consensus, not an adopted standard. Extended detention drain time (n=23) and L:W (n=18) have modest sample sizes relative to 58 practice mentions.