On July 1, 2020, the City of Houston published a new Infrastructure Design Manual (IDM) acknowledging that Harris County and Harris County Flood Control adopted the new Atlas 14 data on June 4, 2019. The City stated that they would consider and edit the new Atlas 14 information for a future release date.
Fast forward to January 4, 2021, and the City of Houston has prepared and signed a supplement to chapter 9 of the IDM, bringing its detention requirements more in line with what both Harris County and Harris County Flood Control adopted in 2019.
Detention is storing a calculated volume of rainwater and releasing it at a controlled rate so as to not overwhelm the existing stormwater infrastructure. Detention ponds and other stormwater infrastructure play a major role in the way a site is designed, and the upcoming changes will result in detention pond designs becoming much larger in size. This will likely add to project costs and occupy additional valuable acreage that could otherwise be utilized for a larger development area.
These changes are scheduled to go into effect on March 31, 2021, and will greatly impact detention rates for sites of all sizes. Current projects will be grandfathered from the new requirements as long as plans are submitted to the City for review prior to the effective date.
Changes to section 9.2.01.H. of the IDM are summarized below:
Detention Waivers:
Calculation of Detention Volume:
If you still have questions about how these changes to the Infrastructure Design Manual (IDM) will affect your project in Houston, contact us today and our engineering team is happy to assist!
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