GUIDE 08 - 2027 EDITION
Stormwater Detention Pond Quick-Reference in TX, NC, and FL
Texas, Florida & North Carolina (2027)
Rules of thumb for early planning of detention ponds by drainage area. Final sizing always requires a site- specific hydrology (H&H) analysis.
TX
4-8 ft
3:1
slopes
FL
4-8 ft
3:1
slopes
NC
3-6 ft
4:1
slopes
Typical depth and side slopes (or flatter), drainage area under 5 acres.
Important Note: The information in these guides is for general reference only. A licensed Professional Engineer should review any actual design or construction work. JRH Engineering assumes no responsibility for the application or use of these materials.
TX - 2027
Detention ponds in Texas
In Texas, a detention pond serving a drainage area of <5 acres typically needs 21,780–32,670 cubic feet of storage per acre, a surface area of about 1.5%–2.5% of the drainage area, depths of 4–8 ft, and side slopes of 3:1 or flatter. Larger drainage areas require a site-specific hydrology and hydraulics (H&H) study.
Drainage Area Acres | Required Volume cu ft per acre | Typical Surface Area % of drainage | Typical Length Width Ratio | Typical Depth ft | Typical Side Slopes H:V |
|---|---|---|---|---|---|
<5 | 21780 - 32670 | 1.5 - 2.5 | 3:1 to 5:1 | 4 - 8 | 3:1 or flatter |
5-20 | 32670 - 43560 | 2 - 3 | 3:1 to 5:1 | 5 - 10 | 3:1 or flatter |
20-50 | 43560 - 54450 | 2.5 - 3.5 | 4:1 to 5:1 | 6 - 12 | 3:1 or flatter |
>50 | Site-specific H&H study required | 2.5 - 4 | 4:1 minimum | 6 - 15 | 3:1 or flatter |
01
Volumes are approximate guidance. Always run site-specific hydrology per current local criteria. JRH performs full H&H studies.
Updated 2027 • Criteria based on TCEQ / iSWM / local manuals • Confirm with current county criteria
Top 5 Mistakes That Kill Approval
01
Wrong runoff coefficient → Use TCEQ / iSWM tables
02
Undersized orifice/outlet → Double-check hydraulic calculations
03
No water quality volume → Add 0.5–1.0 inch WQv
04
Poor maintenance access → Minimum 12 ft wide ramp
05
Missing emergency spillway → Required for all ponds >10 acre-ft
Notes & assumptions
FL - 2027
Detention ponds in Florida
In Florida, a detention pond serving a drainage area of <5 acres typically needs 21,780–32,670 cubic feet of storage per acre, a surface area of about 1.8%–3% of the drainage area, depths of 4–8 ft, and side slopes of 3:1 or flatter.
Drainage Area Acres | Required Volume cu ft per acre | Typical Surface Area % of drainage | Typical Length Width Ratio | Typical Depth ft | Typical Side Slopes H:V |
|---|---|---|---|---|---|
<5 | 21780 - 32670 | 1.8 - 3 | 3:1 to 5:1 | 4 - 8 | 3:1 or flatter |
5-20 | 32670 - 43560 | 2.2 - 3.5 | 3:1 to 5:1 | 5 - 10 | 3:1 or flatter |
20-50 | 43560 - 54450 | 2.5 - 4 | 4:1 to 5:1 | 6 - 12 | 3:1 or flatter |
>50 | Site-specific required | 3 - 4.5 | 4:1 minimum | 6 - 15 | 3:1 or flatter |
01
ERP process with Water Management Districts can take 90-120 days. JRH designs to current WMD criteria.
Updated 2027 • FDEP / Water Management District criteria • Confirm with SJRWMD, SFWMD, etc.
Top 5 Mistakes That Kill Approval
01
Wrong runoff coefficient → Use FDEP / WMD tables
02
Undersized orifice/outlet → Double-check hydraulic calculations
03
No water quality volume → Add required WQv
04
Poor maintenance access → Minimum 12 ft wide ramp
05
Missing emergency spillway → Required for larger ponds
Notes & assumptions
NC - 2027
Detention ponds in North Carolina
In North Carolina, a detention pond serving a drainage area of <5 acres typically needs 21,780–32,670 cubic feet of storage per acre, a surface area of about 1.5%–2.5% of the drainage area, depths of 3–6 ft, and side slopes of 4:1 or flatter.
Drainage Area Acres | Required Volume cu ft per acre | Typical Surface Area % of drainage | Typical Length Width Ratio | Typical Depth ft | Typical Side Slopes H:V |
|---|---|---|---|---|---|
<5 | 21780 - 32670 | 1.5 - 2.5 | 3:1 to 5:1 | 3 - 6 | 4:1 or flatter |
5-20 | 32670 - 43560 | 2 - 3 | 3:1 to 5:1 | 4 - 8 | 4:1 or flatter |
20-50 | 43560 - 54450 | 2.5 - 3.5 | 4:1 to 5:1 | 5 - 10 | 4:1 or flatter |
>50 | Site-specific required | 2.5 - 4 | 4:1 minimum | 6 - 12 | 4:1 or flatter |
Updated 2027 • NCDEQ criteria • Side slopes often 4:1 • Watershed nutrient rules may add requirements
Top 5 Mistakes That Kill Approval
01
Wrong runoff coefficient → Use NCDEQ tables
02
Undersized orifice/outlet → Double-check hydraulic calculations
03
No water quality volume / nutrient treatment → Address WQv and loading limits
04
Poor maintenance access → Minimum 12 ft wide ramp
05
Missing emergency spillway → Required for larger ponds
Notes & assumptions
01
Nutrient sensitive watersheds add loading limits. JRH designs full compliance packages including ESC.
Frequently Asked Questions
How big does a stormwater detention pond need to be in Texas?
In Texas, a detention pond serving a drainage area of <5 acres typically needs 21,780–32,670 cubic feet of storage per acre, a surface area of about 1.5%–2.5% of the drainage area, depths of 4–8 ft, and side slopes of 3:1 or flatter. Larger drainage areas require a site-specific hydrology and hydraulics (H&H) study.
How big does a stormwater detention pond need to be in Florida?
In Florida, a detention pond serving a drainage area of <5 acres typically needs 21,780–32,670 cubic feet of storage per acre, a surface area of about 1.8%–3% of the drainage area, depths of 4–8 ft, and side slopes of 3:1 or flatter.
How big does a stormwater detention pond need to be in North Carolina?
In North Carolina, a detention pond serving a drainage area of <5 acres typically needs 21,780–32,670 cubic feet of storage per acre, a surface area of about 1.5%–2.5% of the drainage area, depths of 3–6 ft, and side slopes of 4:1 or flatter.
How current is this guide?
This guide was updated in October 2026 for 2027. Construction costs are uplifted roughly 4% from the 2026 baseline, and references reflect ASCE 7-22 and, for Florida, the Florida Building Code 9th Edition (effective December 31, 2026).
Can I use this guide for my specific project?
No. These figures are general reference ranges, not engineering advice. Always verify current local codes, fee schedules, design criteria and site conditions with the Authority Having Jurisdiction, and contact JRH Engineering for project-specific sealed designs, estimates and permit packages.
Disclaimer: These guides are for general reference only and are not engineering advice for any specific project. Verify current local codes, fee schedules and site conditions with the Authority Having Jurisdiction.
Proprietary reference material of JRH Engineering. Free for personal and professional use with attribution. Commercial redistribution prohibited without written permission.