Tag Archive for: no net fill

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).

Montgomery County Commissioners Court discusses new drainage and subdivision manuals in 8/23/22 meeting.

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.

Welcome News

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:

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)
  • Revisions
  • 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.

Immediate Impact

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.

Interim Guidelines for Atlas-14 Implementation Until New Flood Maps Released

While reviewing the MAAPnext website today, I came across this 1-page PDF that outlines major changes to Harris County’s Policy Criteria & Procedure Manual (PCPM). It describes changes – based on new Atlas-14 Rainfall Statistics – that engineers and developers must follow when designing and constructing flood-control features as part of any development within Harris County.

Atlas 14 Updates Rainfall Frequency Estimates Developed in 1960s

Developers must now design detention and storm sewers around rainfall rates that increase 16-32% compared to the old standards for Harris County.

Data included in Atlas 14:

  • Replaces rainfall-depth information used since the 1960s
  • Provides estimates of the depth of rainfall for average recurrence intervals of 1 year through 1,000 years, and durations from 5 minutes to 60 days.

NOAA collected this data in Texas through December 2017, which includes rainfall from Hurricane Harvey.

New Atlas-14 Rainfall Frequency Estimates for the Lake Houston Area

Floodplain, Detention & Fill Restrictions

The amended policy manual adopts the increased precipitation rates. It also specifies more rigorous criteria for detention basins and fill within the floodplain.

Amendments anticipate that the future Atlas-14 1% (100-year) floodplain will equal the current 0.2% (500-year) floodplain.

Harris County Flood Control District

Therefore, these amendments are considered to be interim and will be reevaluated once new floodplains have been produced as part of HCFCD’s Modeling Assessment and Awareness Project (MAAPnext) in late 2021. You can find more information on MAAPnext at www.maapnext.org.

Zero Net Fill

The old guidelines prohibited developers from adding fill only within the 100-year floodplain. Now they’re prohibited from adding fill within the 500-year floodplain, too. The policy is called “zero net fill.” It means developers cannot bring fill into the floodplains. They can, however, excavate fill from one part of their property and use it to build up another part of their property.

Under new guidelines, developers cannot bring fill into either the 100-year or 500-year floodplains.

For a 20-acre development, the average volume of stormwater within detention basins will increase by about 20%, or about 32,500 additional gallons per acre.

Effort to Harmonize Floodplain Regs with Neighbors’

Harris County works with surrounding counties and municipalities to upgrade and harmonize their floodplain regs. However, the effort has not yet yielded much fruit.

Surrounding counties, such as Liberty and Montgomery, have not yet mirrored these restrictions. In fact, those counties still use their comparative lack of regulation as a competitive tool to attract new development. That, of course, makes it doubly difficult for residents of Harris County. They must not only contend with their own runoff, they must contend with their neighbors’.

Posted by Bob Rehak on 11/30/2020

1189 Days since Hurricane Harvey