MoCo Changing Drainage, Subdivision Rules

9/12/26 – On 9./18/26, Montgomery County (MoCo) Commissioners Court will consider changes to its Drainage Criteria and Development Regulations. See Item 12A on the agenda.

Just last year, Montgomery County adopted a new drainage criteria manual. It was the first major update in decades. The new manual was first proposed in early 2024. That followed a minor update in 2019 from the county’s old 1988 drainage criteria manual in effect at the time of Harvey.

It adopted many, but not all of the minimum drainage criteria proposed by Harris County for other counties draining into Harris. MoCo allows fill in the 500-year floodplain, but Harris doesn’t. And Harris requires homes to be built at the 500-year flood elevation, whereas MoCo requires only the 100-year.

Proposed Drainage Criteria Changes

Here are the MoCo drainage criteria adopted in 2025. And here are the changes proposed for 2026. The changes are summarized on the first two pages.

The changes seem predominantly focused on:

• Making the manual easier to understand and use. For instance, it clarifies the meaning of many terms
• Improving navigation in the document by adding hyperlinks to the table of contents in the PDF version
• Expanding the scope of approved modeling software
• Clarifying the County’s position on:
  • Nonproprietary (Primary) Modeline Software
  • Proprietary Modeling Software
  • Advanced Modeling
  • Spreadsheet Calculations
  • Secondary (Check) Analysis
• Adding a section on “TAILWATER.” Tailwater is the downstream water level that controls or influences how easily upstream water can get out. The following items are described in this new section: free outfall, normal depth, fixed elevation, rating curve, regulatory, dynamic, conservative maximum, and required documentation.
• Modifying content discussing “MINIMUM DETENTION RATE” for clarity and better alignment with FEMA and County floodplain requirements.
• Adding to “DETENTION STRUCTURE DESIGN” to better explain the concept of “Hydraulically Connected Detention Ponds”
• Creating a new section called “BASE LEVEL ENGINEERING,” explaining what BLE is and how to use BLE in proposed designs submitted to the County for permitting.
• Clarifying requirements for “Drainage Submittals” and deliverables.
• Adding new definitions for numerous concepts.

By and large, these changes seem focused on clarifying the County’s requirements so that developers and the County’s Engineering Department can minimize “back-and-forth” changes/requests.

Amendment to Development Regulations

MoCo will also discuss changing its development regulations by adding a fourteen (14) calendar day response period for written acknowledgment from Commissioner’s offices.

MoCo regulations require developers to submit plans to commissioners before submitting them to the engineering department for final approval.

On the plus side, the amendment will help ensure timely processing and improve government efficiency.

But this change also comes with a potential downside, in my opinion. Two weeks doesn’t allow much time for public input or protest. It usually takes that long to get copies of documents via FOIA or Public Information Requests, assuming the requests don’t get appealed to the attorney general. So the two week requirement effectively excludes the public from the process…at least with the commissioner who directly represents him/her.

Since these are infrastructure decisions that could affect communities for a hundred years or more, is it wise to rush them. The language in the proposed amendment reads like a sharp elbow to the gut of commissioners. It basically says, “If you can’t do your job, get out of the way. The Engineering Department will do it for you.”

Gee, what if the commissioner’s staff member is on vacation?

Posted by Bob Rehak on 9/12/2026

3201 Days since Hurricane Harvey