First change to Harris Co. flood rules in nearly 50 years takes effect

by Scott Klocksin

New development within flood plains in unincorporated areas of Harris County will now require developers to build five times as much water detention as they’ve had to in the past.

That’s because Harris County Commissioners has approved a new set of rules governing building in flood zones, to take effect immediately. The Commissioners’ unanimous vote will now require developers to build enough detention to prevent flooding in the 500-year floodplain that snakes through the area, flanking many bayous and rivers. These areas are thought to have a 0.2 percent chance of flooding in a given year.

Previously, the county’s requirement covered the 100-year floodplain—areas thought to have a one percent chance of flooding in the span of a year.

The vote comes as Barry, the first tropical storm of the year to hit the Western Hemisphere, churns in the Gulf of Mexico, kicking off this year’s hurricane season unusually early.

“We’re analyzing how much a new development would increase flooding by and asking the developers to detain that much water so that the net effect is zero,” Harris County Judge Lina Hidalgo told KHOU.

New construction development can contribute to flooding by paved roads giving water a clear path to flow toward lower ground, and the uprooting of natural vegetation can also create greater flooding risk.

Judge Hidalgo told the TV station that the building standard in the county hasn’t seen an update since 1971.

Bill Baldwin, a board member of the Houston Association of Realtors and an agent with Boulevard Realty, noted that many of the areas that would be required to be used for detention would likely have been park space even without the heightened requirements. “Overall, it’s a very positive step for the city and county to become more resilient,” he said. “If it makes them more resilient, that’s certainly better than flooding houses.”

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  • Diane Martin says:

    Detention- custody, imprisonment, confinement, etc.

    Retention – continued possession, use, or control of something

  • Randall Hebert says:

    I believe all homeowners in texas should be required to purchase flood coverage so flood coverage would be better funded and everyone is protected when flooding occurrs in a Harvey
    Randall hebert

  • Fran Marino says:

    thank you Bill Baldwin for your ‘Flood’ class regarding this change.

  • Jeremiah D. Kamerer, P.E. says:

    There appear to be several inaccuracies or not vetted statements in this post.

    Just to name a few:
    1. Floodplain regulations have been update several times in the last 50 years, in fact the latest change was just 6 months ago and was effective on 1/1/2019. The reference to 1971 is in regards to historic rainfall data, not floodplain regulations.
    2. Floodplain and flood insurance maps are updated regularly and are normally development driven.
    3. The new HCFCD regulations (Interim guidelines) are applicable to fill in floodplain, not storm water detention. Where did you get your information that detention facilities MAY grow 5x’s larger? The quote, which is not correct either, stated criteria may increase 20%.
    4. Changes to Harris County’s Infrastructure Regulations Stormwater Detention Rates – Storm sewer outfall rate increased from 0.65 to 0.75 ac-ft./acre.

    Bottom line in Harris County, Stormwater Detention Rates and Floodplain Mitigation are not necessarily linked. If you have any questions please feel free to reach out to your engineering community.

  • Lilly Hughes says:


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