City of Houston 2021 Stormwater Detention Regulation Changes
On January 4, 2021 the City of Houston replaced within Chapter 9 of the Infrastructure Design Manual (IDM) how stormwater detention is calculated within the City of Houston. This was announced on January 20th, 2021 and was to go into effect on February 4th, 2021, sending developers and engineers into a frenzy to get projects submitted to the county by the deadline. On January 26th, that deadline was pushed back to March 31st, 2021.
Here is what you need to know about the new regulations and how they impact you:
- Single Family Lots of 7500 SF or less that will disturb less than 65% of the area = 0.0 acre-ft/acre Detention Rate
- Single Family Lots of 7500 SF or less that will disturb more than 65% of the area = 0.75 acre-ft/acre Detention Rate (The old rate was .2 acre-ft/acre, so this is a 3.7X increase)
- Tract of 1 Acre or Less = 0.75 acre-ft/acre Detention Rate (The old rate was .2 acre-ft/acre, so this is a 3.7X increase)
- Tract of 1 to 20 acres = Detention requirement will be based on the percentage of impervious that is a result of the disturbed area on site determined by the following chart:
This is an increase of up to double the existing rate.
Tract size over 20 acres = Detention will be based on the most current version of the Harris County Flood Control District Policy and Procedure Criteria Manual. The typical increase in rate would be to .65 acre-ft/acre.
While these changes are significant in most cases, the City of Houston also released the first phase of it’s Houston Incentives for Green Development. The first phase that was approved in December, 2020 was a tax abatement program that allows dollars used to fund Green Infrastructure on private development to be reimbursed through a tax abatement program that pays back over a 10 year period. Visit http://www.houstontx.gov/igd/ for more details.
While there are plans to allow reduced detention rates for the use of Green Infrastructure, much like those that HCFCD and Harris County currently allow, that adjustment is not expected before until 2022.