This article was co-authored by Kyle Blank, PE, CFM

Houston Public Works has announced supplemental changes to the City’s 2020 Infrastructure Design Manual that take effect March 31st, 2021, impacting detention rate requirements for all new developments.

Depending on the tract size and impervious cover, commercial developments in the City of Houston will now be required to provide a minimum volume at a rate of 0.75 acre-feet per acre of disturbed area that results in impervious surface.

Public and private sector projects that submit plans for initial review after March 31st will be required to comply with these new standards.

You can read the supplemental changes HERE and the cover letter from the Director of Houston Public Works HERE.

Notable Changes to Houston’s Detention Requirements 

Tracts Less Than 1-Acre

Tracts less than 1-acre that are not considered a single-family residential lot will have a required detention volume at a rate of 0.75 acre-feet per acre, which is more than triple the previous rate of 0.20 acre-feet per acre.

Tracts Between 1 and 20 Acres

Like tracts less than 1-acre, those between 1 and 20 acres will be required to have a minimum detention volume at a rate of 0.75 acre-feet per acre. However, the required rate goes up based on the percentage of impervious cover, with some developments requiring up to 1 acre-foot per acre.

The complete detention rate requirements based on percent impervious surface are depicted in the chart below:

Tracts Greater than 20 Acres

Tracts greater than 20 acres will be subject to criteria in the Harris County Flood Control District’s (HCFCD) Policy Criteria and Procedure Manual (PCPM). HCFCD requires a minimum storage rate of 0.65 acre-feet per acre and will require an Impact Analysis (Drainage Study) with supporting calculations. The analysis may determine a higher minimum storage rate.

Our team remains up to date on regulatory changes affecting Houston developers. You can reach out to our Site Civil and Hydrology & Hydraulics experts for more information about how Houston’s updated detention requirements will impact your next project.