Stormwater Detention Calculator

We'll generate a FEMA flood map link for this address.

Used for reference and for the reduced-detention-rate check on HCFCD channel outfalls (see methodology below). Harris County's per-acre detention rate itself is based on gross site area, not impervious cover.

Houston applies different detention rules by development type. Single-family homes and small SFR/MUR tracts are often exempt below an impervious-cover threshold — see methodology below.

For a single-lot home site, Houston's actual reviewed outcome tends to follow the plat: lots on plats recorded 2000 or earlier are typically treated as individual lots under Criteria 1, while lots on plats recorded 2001 or later that don't already provide detention are typically routed to Criteria 3 instead — even though Table 9.6 itself doesn't state a plat-date test. This reflects Cunningham Civil's practical experience with City review, not IDM text.

Leave blank to use a typical assumption for your outfall type. If you already know your basin depth, enter the total depth from top of bank to bottom, including the required 1-ft freeboard.

HCFCD PCPM §6.4.3 caps grass-lined detention basin slopes at 3:1 or flatter. Anything steeper — including 2:1 — must be concrete-lined per §6.4.3 and §10.4.3, which also caps concrete slopes at 2:1 (the steepest allowed under any lining).