Tag Archive for: EHRA

Enclave Construction Stopped While Engineers Review Drainage

6/4/25 Update: Construction has not yet stopped and it may not. It continues as City and County Authorities try to set up a meeting to review drainage plans with engineers.

6/2/25 – Construction has stopped, at least temporarily, at the Enclave, a new 11-acre residential development adjacent to the Northpark expansion project in Montgomery County.

Both Montgomery County and the City of Houston have asked engineers to review the drainage plans, which showed the development’s detention basin overflowing into the only evacuation route for 78,000 people during extreme weather events.

Enclave Detention Basin

HNTB, the engineer for the Northpark Expansion project, is going to conduct a peer review of EHRA plans for the Enclave’s drainage. They need to hurry.

Detention Basin Already Dug Out

Photographs taken between 5/31 and 6/2/25 show that construction crews have already excavated the proposed detention basin. And they are starting to install pipes and junction boxes for drainage.

Looking E. Northpark on left. Detention Basin, partially filled with water from last week’s rains, is already excavated.

However, I have received word that both the City and Montgomery County have asked for construction to be paused for a new independent peer review of the development’s drainage plans.

Partial Update to Outdated Drainage Plans

The new development is technically part of Kings Mill, which had its drainage plans approved in 2012. But after Harvey in 2018, Montgomery County and the City of Houston both adopted Atlas 14 rainfall probability statistics, which are 33% higher than those used to design virtually all of Kings Mill’s infrastructure.

That means Kings Mill – which is 20 times larger than the Northpark Enclave – funnels much more stormwater toward the Kingwood Diversion Ditch than it was designed to handle.

Yet Enclave engineers designed its detention basin to hold only the difference between the old and new rainfall statistics. And only for 11 acres, not all 240.

Concerns about Capacity, Its Impact and Inconsistencies

Several other things have happened since approval of the 2012 drainage study.

  • The Northpark Expansion project started. A major goal: to create an all-weather evacuation route when Hamblen Road, Kingwood Drive and Mills Branch Road are cut off by high water.
  • The developer’s plans raised concerns about where Enclave overflow will go during an extreme event. (See construction diagram above.)
  • Hurricane Harvey flooded hundreds of homes adjacent to the Kingwood Diversion Ditch, raising as-yet-unaddressed concerns about the capacity of the receiving ditch.
  • Construction plans showed inconsistencies between the initial drainage impact analysis and today, including the size of the Enclave.
  • The developer claims it can build ten homes to the acre with only 55% impervious cover, an extremely ambitious goal.

Photos Show Drainage Route to Kingwood Diversion Ditch

Photos below show the new Northpark Enclave development and the path that stormwater will take on its way to the Kingwood Diversion Ditch, which already has capacity problems of its own.

Hundreds of homes have flooded because of the ditch’s diminishing capacity as insufficiently mitigated new subdivisions began draining into it.

Harris County Flood Control District (HCFCD) has completed its preliminary engineering review of the Diversion Ditch. HCFCD is now in the process of selecting an engineering company to make final recommendations for improving the ditch. But it could take years to find the money to construct any recommendations that come out of the study.

So, MoCo and the City want to make sure they get this right. The photos below show how all the drainage will connect.

Looking SE over the intersection of Loop 494 and Northpark Drive at construction of the Northpark Enclave.
Still looking SE. From the new development, stormwater will move to the giant detention basin in the upper center of frame.
Contractors are already starting to install culverts that will carry runoff to the main Kings Mill Detention Basin.
From the Kings Mill Detention Basin, stormwater will flow into the ditch that angles toward top and then makes a left turn toward Russell-Palmer Road in the upper left corner of the frame.
Stormwater runoff goes a half mile east toward Russell-Palmer Road. Kings Mill’s drainage on left. Kings Manor’s on right.
Looking S along Kingwood Diversion Ditch and Russell-Palmer Road. Kings Mill Ditch on lower right. Kings Manor Ditch above it. Both outfall under the road into the Diversion Ditch. Bridge at top of frame by water tower is Kingwood Drive.

Once contractors have drain pipes and culverts in the ground and start pouring concrete, it will be very difficult to make any changes. So, it’s good that construction has been paused now for peer review.

Posted by Bob Rehak on 6/2/2025

2834 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.

Enclave Detention Basin Will Overflow into Kingwood Evacuation Route

5/30/25 – The Northpark Enclave detention basin may be undersized and the developer plans to dump overflow stormwater during extreme events into the only all-weather evacuation route for 78,000 people. That’s according to construction documents and drainage plans obtained from Montgomery County under the Freedom of Information Act.

From Page 9 of Construction Plans, Part II Red highlight added.

The last thing you need during a mass evacuation is street flooding.

EHRA, the developer’s engineering company, told Ralph De Leon, project manager for the Northpark expansion project, that all drainage for the new subdivision would be routed south to the Kings Mill Stormwater Detention Basin and then via an outfall channel to the Kingwood Diversion Ditch near the County Line. But the construction drawing above indicates otherwise.

Technically a part of Kings Mill, this 11-acre strip bordering Northpark is just now being developed for single-family residential. Most of Kings Mill was built in phases between 2004 and 2018. And therein lies a huge problem.

Old Plans Use Antiquated Rainfall Statistics

Some of the drainage analyses/plans for the Enclave detention basin date back to 2002 – almost 25 years ago.

Back then, assumptions about “probable maximum rainfall” were very different from today’s. Montgomery County defined a 100-year rainfall then as 12.1 inches in 24 hours.

However, today, MoCo defines a 100-year/24-hour rainfall as 16.1 inches – a 33% increase. But for this development’s location, NOAA defines one as 17.1 inches – a 41% increase. Why the difference?

MoCo adopted Atlas 14 rainfall statistics in 2019. But NOAA fine-tunes its statistics for individual locations. And MoCo regulations use Conroe’s statistics for the entire county. Rainfall decreases as you go farther inland and Conroe is 40 miles north of this location. But that’s not all.

Confusing Documents Don’t Match

It’s not clear how engineers have updated the old drainage analyses in the new plans. MoCo did not provide an updated drainage analysis in response to my FOIA request.

Yet within the construction plans, it appears that EHRA may have tried to mitigate for higher rainfall standards in the development of this tract within Kings Mill.

Calculations on page 9 of Construction Plans Part 2 reference 2023 City of Houston Regulations for detention volume. They show the size (line 3 below) as 11 acres.

Plans do not provide a narrative explaining how all the pieces of this jigsaw puzzle fit together. And trying to track the pieces back through documents dating back almost 20 years is confusing.

For instance, the same plot that’s 11 acres in 2025 was listed as 15.6 acres in the October 2012 drainage analysis.

15.6 acres in 2012 magically became 11 acres in 2025.

At the very least, it’s safe to say that unexplained differences like these make one question the quality and consistency of calculations in the plans.

55% Impervious Cover?

And they never do explain how they can put 100 homes on 10 acres (minus one acre for the detention basin) and get only 55% impervious cover. Experience suggests that more realistic estimates for that much density would range from 65% to 85% depending on the size of homes and garages.

For More Information

Montgomery County Engineering provided:

There Should Be A Law

Only two things became clear after struggling to understand these documents:

  • There should be a statute of limitations on “grandfathering” permits based on when someone first applied for them.
  • Someone should have required a new drainage analysis for this project.

More news to follow.

Posted by Bob Rehak on 5/30/25

2831 Days since 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.