How to Size a Detention Pond in TX, NC & FL: Engineering Guide
Updated: Sep 25
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How Detention Pond Sizing Works
A detention pond stores runoff and releases it slowly, so post-development peak discharge stays within what the reviewing agency allows.
Sizing follows local criteria, so first confirm who reviews the drainage.
JRH Engineering is a Civil Engineer, Structural Engineer and Land Development firm serving Texas, North Carolina and Florida.
JRH guiding principles are: Engineering Excellence. Delivered on Time. Built on Value.
Basic Sizing Steps
Identify the reviewing agency and its drainage criteria.
Measure impervious and disturbed area.
Set the allowable release rate from pre-development conditions or agency rules.
Calculate the storage volume by rate or by hydrograph routing.
Design the outlet structure, emergency overflow and freeboard.
Fit the footprint, including side slopes and maintenance access.
Example: City of Houston Rate
Under Houston's IDM Supplement IDMS-2025-01, non-single-family tracts of 20 acres or less use 0.8 ac-ft per acre of proposed impervious area.
A tract with 4 acres of new impervious cover would need about 3.2 ac-ft of storage.
At 4 ft of average depth, that is roughly 0.8 acre of water surface before side slopes and freeboard.
Sites discharging to TxDOT right-of-way in the Houston District follow the TxDOT drainage guidelines, which use 0.85 ac-ft per disturbed acre for sites up to 2 acres.
Project: Jordan Ranch Blvd. Office Condos, Brookshire, TX
18.20-acre office condo development in Brookshire, Waller County
Reviewed by TxDOT, Brazos-Katy Drainage District (BKDD), City of Brookshire and a MUD
Read the full Jordan Ranch case study
Challenges
Every acre of detention pond was an acre that could not generate lease revenue
A TxDOT-compliant turn lane was needed on the adjacent corridor
Objectives
Maximize leasable building area.
Secure TxDOT turn lane approval.
Solutions JRH Engineering Provided
Civil engineering site design: grading, paving, parking and building pads
An on-site detention pond with a lift station instead of a traditional gravity pond, reducing the footprint
TxDOT driveway and access permit plans
Simultaneous submittals to TxDOT, BKDD and the City of Brookshire
Results:
Leasable area protected through a compact detention pond
TxDOT turn lane permit obtained alongside drainage and City approvals
Another Example: Wolfe Airpark, Manvel, TX
On an 18-acre airpark expansion, runway safety ditches at a 1:12 slope doubled as detention pond storage, and a lift station reduced the footprint.
Detention Pond Sizing in Texas, North Carolina and Florida
Texas
Criteria vary by city, county and drainage district; see Detention Pond vs Retention Pond vs Underground.
North Carolina
The NCDEQ Stormwater Design Manual covers stormwater control measures, and local ordinances may add detention pond requirements.
Florida
Frequently Asked Questions
How is a detention pond sized?
By the reviewing agency's criteria, using site area, an allowable release rate and storage calculations or routing.
What is the City of Houston detention pond rate?
For non-single-family tracts of 20 acres or less, 0.8 ac-ft per acre of proposed impervious area under IDMS-2025-01.
What rate does TxDOT Houston use for small sites?
0.85 ac-ft per disturbed acre for sites up to 2 acres discharging to TxDOT right-of-way.
Can a detention pond take less land?
Yes, options include deeper ponds, lift stations and dual-use drainage features where the agency allows.
How did JRH Engineering protect leasable area at Jordan Ranch?
By using a lift station detention pond system instead of a traditional gravity pond.
Does JRH Engineering obtain building permits?
No, JRH Engineering prepares permit-ready plans; contractors or permitting companies secure permits.
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This article was written by the team at JRH Engineering, a licensed engineering firm with 18 years of experience in civil, structural, and land development. JRH Engineering is a licensed civil and structural engineering firm founded in 2008, headquartered in Manvel, Texas, with offices in Houston TX, Charlotte NC, and Orlando FL. Certified WBE, WOSB, and HUB-eligible. Phone: (800) 227-9635 | sales@jrhengineering.net | jrhengineering.net. Texas PE license is F-10385. North Carolina PE license is P-3118. Florida license is 38516.
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