Montgomery County Development Regs Revised, New Drainage Criteria on Hold

3/14/15 – Montgomery County Development Regs have been revised and became effective on 3/4/25.

The MoCo Engineer has posted them online. For convenience, I have also posted them under the Regulations Tab on the ReduceFlooding Reports Page.

The primary audience for the regulations is developers. However, neighbors near new developments may wish to study the regs, too, to ensure developers follow the rules.

On a separate but related note, MoCo’s new Drainage Criteria Manual is still on hold.

Changes

Montgomery County Subdivision Regulations were adopted in 1984 with an update in 2021. This rewrite includes many significant updates, such as:

• Privacy fences at least 6-feet high between new commercial developments and existing single-family homes.
• An entire section related to Traffic Engineering Study requirements.
• Planting requirements along curbs
• A new minimum lot width standard of 40′ for concrete curb and gutter and 65′ for asphalt open ditch lots
• Commercial Drainage Plans will now be reviewed before acceptance of the entire permit submittal
• A modified “impervious cover” threshold
• New requirements for Stormwater Pollution Protection Plans.

What Developers Must Submit

Section Three outlines what developers must submit to Commissioners’ offices. This could come in handy if you ever need to submit a FOIA request. Requirements include:

• Timelines
• Maps
• Construction traffic routing/access points
• Drainage Reports and Studies
• Spreadsheets used in calculations contained in those reports
• Construction Plans including a Drainage Impact Analysis

Separate plans must be prepared for each subdivision.

Section 4 covers drainage plan requirements. Among other things, a drainage plan must provide for the disposition of runoff entering the development from adjacent property, runoff within the development and runoff leaving the development to an acceptable outfall.

Floodplain and Floodway Development

Section 5 specifies additional requirements for drainage studies when developers build in floodplains and floodways. For instance, they must obtain a Conditional Letter of Map Revision (CLOMR) from FEMA prior to the County’s approval of a drainage plan or study when:

• Proposing to construct a detention pond or alter the floodway landscape
• Relocating a stream

A CLOMR is a FEMA comment on a proposed project that could impact flood-hazard areas. And it indicates whether the project, if built as proposed, would meet National Flood Insurance Program (NFIP) standards and warrant a change to the Flood Insurance Rate Map (FIRM). 

Alteration of a stream or river also requires TCEQ approval and the approval of any governing entities within 1,000 feet.

Status of Updated Drainage Criteria Manual

On a separate note: MoCo will soon update its Drainage Criteria Manual (DCM). The county is still working off an old DCM from 2019 that was a minor revision of a 1989 document.

In February 2024, Montgomery County finally published a draft of a comprehensive new DCM. The draft brought the County’s standards up to date and in line with surrounding areas’. 

Major changes 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” when calculating 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).

I’ll let you know when/if MOCO adopts these new drainage standards.

By the way, people always ask me why I list “days since Harvey,” on all my posts. I want to dramatize how long political change takes. And this is a prime example.

Posted by Bob Rehak on 3/14/25

2754 Days since Hurricane Harvey

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