City of Houston & Harris County Stormwater Regulation Changes

City of Houston 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.

Retention Requirement Changes in the Addicks, Barker and Upper Cypress Watersheds

In March, new regulations were put on retention requirements in the Addicks, Barker and Upper Cypress Watersheds. You can find those new regulations HERE. Among other things, one requirement is providing infrastructure that allows the restrictor on detention ponds to be closed in the event there is a threat of a large storm event, to hold as much water as possible from entering the watershed until the downstream infrastructure has cleared. The result is relief to a system we have seen pushed to its limits over the last few years.

Outfalls into a County Roadway Must Meet County Criteria

Another change you may begin to see isn’t necessarily new regulation, its just enforcement of an existing regulation. In the last few weeks, several developers and engineers have come to us asking about “new” retention facility that has the capacity to support the surrounding real estate, that detention is not needed. The reality is that if you outfall into a County roadway (as opposed to a HCFCD ditch/ basin), you need to meet County criteria. They will not allow you to flood your immediate neighbors trying to get flows to the regional detention basin; a conveyance path must be included in the design, which becomes a challenge when the infrastructure put in place in the MUD doesn’t typically carry the 100-yr. This is becoming a significant challenge for smaller commercial lots within a MUD that are trying to tie into a MUD pond within proximity of the property.

Changes that are Coming

I put this in the changes that are coming category because although they have been passed, they are not yet being enforced. The City of Houston has changed it’s requirements for a stormwater quality permit from 5 acres or part of a larger common plan of development to 1 acre or part of a larger common plan of development. This change is going to significantly increase the number of stormwater quality permits and should have a dramatic impact on the amount of trash, sediment and other common pollutants that come off of impervious surfaces throughout the City of Houston. You can find the SWQ ordinance HERE. It’s coming, and on average will increase your development costs by about approximately $5,000 per acre.

The last big item related to detention & drainage is that Harris County is working with ACEC to develop criteria to force construction projects to not flood their neighbors. Designers go to great efforts to make sure that after the development is complete, there is no adverse impact to their neighbors or the downstream infrastructure, but what is being required during the construction phase activity? Together, they are working to create a local regulation or policy to force contractors to adhere to a current state law that has at times been ignored, Texas Water Code §11.086: Overflow Caused by Diversion of Water.

There will be more to come on all of these topics later this spring as there will soon be an educational forum announced that will further clarify the City of Houston, Harris County and Harris County Flood Control’s stance on these topics and more. Stay posted.