MoCo Updating Drainage Criteria Manual, Subdivision Rules
Montgomery County (MoCo) Commissioners voted on 8/23/22 to update the County’s Drainage Criteria Manual and its Subdivision Rules and Regulations. Precinct 2 Commissioner Charlie Riley made the motion (item 16.C on the 8/23/22 Commissioners Court agenda).
See the discussion in the MoCo Commissioner’s Court video. Select Item 16. The discussion starts at 3:12.
The previous Drainage Criteria Manual posted on the MoCo Engineer’s site is dated 1989, but appears to have some minor updates from 2019. The Subdivision Rules and Regulations for new developments date even further back, to 1984, although they too had new amendments and addenda incorporated in July, 2021.
MoCo hired Halff Associates to do the updating. Their fee: $302,000.
This is welcome news for people in northern Harris County. Drainage and engineering standards in MoCo have lagged those in Harris. That has created adverse downstream impacts even though developers may technically meet MoCo requirements. But the lower standards enable them to claim “no adverse impacts” when, in fact, there may sometimes be some.
Changes Could Reduce Flooding in MoCo and Harris Counties
Since Harvey, the Harris County Engineering Department and Flood Control District have worked to get surrounding counties to adopt five minimum drainage standards. They include:
- Prohibiting the use of hydrograph timing as a substitute for detention on any project
- Adopting minimum detention rates of 0.55 acre-feet per acre for any new development on tracts one acre or larger.
- Using Atlas 14 rainfall rates for sizing storm water conveyance and detention systems.
- Requiring “no net fill” in the current mapped 500-year floodplain
- Require the minimum Finished Flood Elevation of new habitable structures be established at or waterproofed to the 500-year flood.
Scope of Content Updates
The Scope of Work approved by MoCo Commissions last week shows that Halff will examine most, if not all, of these issues and more. The effort will evaluate and potentially update, at a minimum:
- Hydrologic methodology (this includes hydrographic timing but is broader)
- Detention sizing and outfall design
- Open channel design frequency and requirements
- Floodplain analysis.
Process for Updates
The scope of work also defines the process that Halff will follow. It includes:
- Coordination with County engineering staff
- Evaluation of existing manuals
- Identifying dated criteria/information
- Comparisons with neighboring counties‘ practices (see below)
- Development of the new documentation
- Stakeholder review and reporting
- Presentation to Commissioners Court
- Reporting approved changes to adjacent counties.
Work should take about a year.
Comparison with Regs in Other Entities
For the drainage Criteria Manual, Halff will compare criteria from TxDOT, Harris County, HCFCD, Waller County, Fort Bend County, and Brazoria County.
Halff will compare MoCo’s Subdivision Rules and Regulations to those in Harris, Waller, Fort Bend, and Walker Counties.
This is more good news for those in northern Harris County.
About Halff Associates
A source in the engineering community characterized Halff as a good company. He said, “The Montgomery County manual is in good hands….as long as they let Halff do the right things.”
Halff will work with the MoCo Engineer Jeff Johnson on the updates.
Subdivision Rules and Regulations
Neither the Scope of Work, nor Commissioners discussed specific recommendations for updates to Subdivision Rules and Regulations. But Commissioners did request an opportunity to discuss and review updates on both manuals before they came back to Commissioners Court for final approval.
One former MoCo employee said, “There is still the hurdle of the court adopting the updated standards. Expect a rush of drainage studies to be submitted in the next year so they can be grandfathered in.”
We saw this in the City of Houston (CoH), for instance, with the Laurel Springs RV Resort. The detention pond in that development is half the size required by new standards. CoH permitted it one day before the new standards went into effect.
Related News: MoCo Floodplain Administrator Office
At about 40 seconds into the video for Items 17 and 18 on the agenda, the Commissioners approved a motion to have Precinct 2 Commissioner Charlie Riley oversee MoCo’s Office of the Floodplain Administrator. Reasons for the change were not clear. Discussion happened in Executive Session.
All we have to go by is the outcome. And the outcome shows that MoCo is bringing the Office of the Floodplain Administrator – for the whole county – under the direct, political control of one precinct commissioner. Interesting.
Posted by Bob Rehak on 8/28/2022
1825 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.