As of Friday, May 16, 2025, a supplement to Chapter 9 to the City’s Infrastructure Design Manual (IDM) was issued and went into effect immediately. The update revised and clarified Sections 9.1 – Stormwater Design Overview and Section 9.2 – Design Requirements, which includes stormwater detention requirements.
Key changes include:
-
Establish that the jurisdiction that directly receives the storm water determines the drainage design criteria.
-
Make the detention calculation user friendly by eliminating the curve detention table for non-single-family residential developments and establishes a flat detention rate.
-
Provide partial detention credit for removal of existing impervious cover when redeveloping a tract.
-
Recognize “Legacy Projects” that have approved master drainage plans where the detention facilities have been constructed and will allow the remainder of the project to be built out.
-
Establish criteria for allowable impervious cover that results in de minimis impact to the City’s drainage system.
-
Clarify when detention requirements are not invoked.
A Frequently Asked Questions (FAQ) document regarding these changes is available online.
To better assist you, please direct all questions to the Stormwater Section at [email protected] or 832.394.9402.