New MoCo Drainage Criteria Manual Still Not Finalized

11/27/24 – Montgomery County is operating off a 1989 Drainage Criteria Manual that received minor updates in 2019. MoCo still has not finalized its new drainage criteria manual, a process it began in August 2022.

In February 2024, Montgomery County published a draft of a comprehensive new update to its drainage criteria manual. The draft brought the County’s standards up to date and made them more in line with surrounding areas’ standards.

In April, I discussed the major changes. They included, but were not limited to:

• Use of industry-standard modeling software by engineering companies submitting plans
• A requirement that new developments produce “no adverse impact” on downstream areas
• Mandates to use certain “roughness coefficient standards” for different situations. These determine how models calculate flood peaks.
• Stipulations that all projects shall mitigate and attenuate runoff for 5-, 10-, and 100-year storm events
• Stormwater detention for all developments regardless of size
• A discussion of flood mitigation measures
• Identification of entities responsible for maintenance of stormwater detention facilities, channels, etc.
• Adoption of Atlas-14 rainfall rates
• A minimum detention rate of .55 acre-feet per acre (almost up to Harris County’s rate)
• Prohibition of hydrologic-timing surveys (also known as flood-routing or beat-the-peak studies).

For a more complete discussion, see my April post which contains links to the relevant documents. Also see below. After publication of the draft, MoCo sought public comment.

Public Comment Period Remained Open for 10 Months

Since April, I have checked back periodically to see whether MoCo had finalized the new Drainage Criteria Manual after the public comment period.

Until earlier this week, the invitation to make public comments remained up on the county’s website. Most public-comment periods last a month or two. So this was highly unusual.

The MoCo engineering department has had some serious turnover recently. It was caused in part by retirements and the sudden, unexpected death of a County Engineer.

So, I emailed the County Engineer’s office to ask why the public comment period was remaining open so long.

Thomas E. Woolley Jr., Director of Engineering Services, wrote, “Thanks for pointing this out. With all the reshufflings in the department, this was overlooked. We will remove the Drainage Criteria Manual Draft from our website until we are ready to move forward.”

I next asked when they would move forward. Woolley replied that he hoped to get it passed by May 2025. He says that he’s currently focused on a related project – updating development regulations.

Developers Reportedly Recommending Which Changes to Adopt

Reportedly, MoCo is having or will soon have a committee incorporate public comments into the draft Drainage Criteria Manual. Before it could be adopted, the revised document would likely have to go back out for another round of public comment. However, it could also depend on the extent and nature of public comments made on the first draft, which still have not been published to my knowledge.

Most Important Recommendations Likely At Risk

I am told (not by Woolley) that developers comprise the committee. While they are certainly important constituents and their opinions should count as much as anyone else’s, reportedly they are pushing back on the most important recommendations in the first draft.

Those include:

• The stormwater detention requirement for all new developments
• Elimination of hydrologic-timing surveys.

New developments without sufficient mitigation typically increase the amount and speed of runoff during storms. One hundred percent of the water hitting concrete runs off quickly, rather than soaking into forest floors and wetlands.

To compensate, stormwater detention basins hold back water during a flood. But they cost money to build and they reduce the number of lots developers can sell. They increase developer’s expenses and reduce their income.

Hydrologic-timing surveys are a way some engineers use to exempt their clients from requirements to build detention basins.

In theory, if they show a developer can get runoff to a stream or river faster than the peak of a flood arrives, then the development won’t add to the flood peak…so no detention is required. Hence their nickname, “beat the peak” surveys.

However, in reality, such surveys have faults. According to the previous Montgomery County Engineer, they:

• Don’t consider the cumulative effects of other developments.
• Almost always rely on outdated hydrologic models
• Assume “ideal” storm conditions.

Such surveys encourage developers to get their floodwater to rivers as quickly as possible. That’s exactly the opposite of what you need to reduce flooding.

Only good things come from more detention. But when developers don’t build detention, people downstream can pay the price.

Which Way Will Political Currents Flow?

MoCo commissioners already rejected the elimination of hydrologic timing surveys and mandatory detention requirements in 2019 when they did a minor update to drainage regs developed in the 1980s.

Will they do so again now that more and more of their own residents are flooding? We won’t know for certain until May at the earliest. But it’s pretty easy to see which way the political currents are flowing.

Posted by Bob Rehak on 11/27/2024

2647 Days since Hurricane Harvey

The thoughts expressed in this post represent opinions on matters of public concern and safety. They are protected by the First Amendment of the US Constitution and the Anti-SLAPP Statute of the Great State of Texas.