(Update: Since posting this story, HCFCD has provided a link to the entire 1860-page flood tunnel study online.)
On June 16, 2022, Harris County Flood Control District (HCFCD) held a virtual meeting to present the results of Phase 2 of its flood-tunnels study. Phase 2 recommended eight tunnels estimated to cost $30 billion for further study. The purpose of Phase 3: to advance the design far enough to quantify the benefits and validate cost assumptions in order to apply for grants that would help offset costs.
The secondary purpose of the meeting: to gage public support for tunnels, none of which would benefit the Lake Houston Area.
Below, see a brief summary of the one hour and twenty minute meeting.
Watersheds Where Tunnels Being Considered
Phase 2 recommended additional study for tunnels in the following watersheds:
- Brays Bayou
- Buffalo Bayou
- Clear Creek, Berry and Vince Bayous
- Halls and Hunting Bayous
- Little Cypress and Cypress Creeks
- Sims Bayou
- White Oak Bayou
The conveyance of all eight projects would TOTAL approximately 75,000 cubic feet per second (CFS). To put that in perspective, that’s approximately 4,000 CFS less than the SJRA released from Lake Conroe during Harvey.
Potential Advantages of Tunnel System
Scott Elmer, P.E. CFM and Assistant Director of Operations for HCFCD, gave most of the presentation. A large part of it focused on the benefits of a flood tunnel system. The hour and twenty minute presentation contained more information than the presentation online. So, I will try to fill in some blanks for you.
Mr. Elmer talked extensively about “inherited flooding.” Much of Harris County, he says, developed before we fully understood flood risk and developed regulations to reduce it. For instance, he showed a series of three images around Halls Bayou and I-45.
- #1 showed rural farmland.
- #2 showed development starting near the bayou.
- #3 showed development so dense that it would require buyouts before mitigation by conventional means.
Mr. Elmer then discussed the time, cost, and disruption of buying out enough properties to construct basins and widen channels. I posted about this last year in regard to the detention basins that straddle Halls at US59. Entire subdivisions had to be bought out before construction could begin. Each of those two basins took approximately a decade to finish, with most of the time consumed by buyouts.
Example of Ideal Location
Here’s an example of another location, farther up Halls between I-45 and Airline Drive.
Many homes in this flat area are no more than a foot or two above the bayou banks. Some even sit below street level.
The entire area lies within some kind of flood hazard. And keep in mind, that this flood map was developed after Tropical Storm Allison in 2001. It does not even represent the risk under Atlas 14, the new flood probabilities developed after Harvey.
Harris County’s Flood Warning System shows Halls has come out of its banks at Airline Drive at least 12 times since 1984. Yet there is very little room to widen the channel or build detention basins.
Best Locations for Tunnels
Tunnels represent an ideal complement to traditional solutions in such cases. They:
- Expand options for flood damage reduction
- Make the county’s stormwater network more robust
- Reduce community disruption and increase resiliency
They make the most sense in areas where:
- Land for traditional solutions is unavailable
- Residential property acquisition would disrupt neighborhoods
- Surface solutions would result in environmental impacts
Elmer presented a hypothetical situation to demonstrate equivalent risk reductions. Thirty-four acres required for tunnel construction could offset 3,145 acres of land needed for channel improvements and stormwater basins.
How Tunnel Locations Chosen
In describing how HCFCD chose the eight watersheds for further study, Elmer focused on:
- Population density
- Damage centers with high risk
- Safety of lives
- Strategic locations for intakes and outfalls
- Identifying opportunities to integrate tunnels with other flood damage reduction measures
- Avoiding geologic and man-made hazards, such as oil and water wells; or geologic faults.
As for the absence of tunnel recommendations on the eastern side of the county, Elmer simply said, other solutions would be more cost effective. He did not provide additional explanation.
To see a YouTube Video of this entire presentation including the Q&A that followed, click here. The meat of the presentation starts at about 8 minutes and 30 seconds into the video.
- Elmer’s presentation lasts a little more than half an hour.
- A moderator describes the need for public comment before September 30 at 41:26.
- Q&A begins 42:30.
- The video ends at 1:18:00.
Items Not Covered
HCFCD gave no specific rationales for:
- Locations of each of the eight tunnels.
- Excluding large areas of the county.
I, for one, want to read the entire report before submitting my comments. But HCFCD has not made the report available online.
Since 2000, the watersheds benefitting from the eight tunnels have already received 64 percent of all flood mitigation investments in Harris County. That includes partner spending. For instance:
- Brays Bayou has received $575.3 million.
- White Oak has received $526.3 million.
- Sims Bayou has received $460 million.
- Cypress and Little Cypress have received $442.5 million.
- Greens has received $440 million.
- Hunting and Halls have received $293.7 million.
Full Study Not Released
Before I vote on flood tunnels for these areas, I want to know how much flood risk remains compared to other areas that received less investment.
However, HCFCD has not yet released a study on the level of service (flood frequency likelihood) for every channel in the county.
The Phase 2 study just completed indicates we could spend $30 billion more on 132 miles of tunnels. That works out to almost a quarter billion dollars per mile.
Before I invest that much, I want to know how engineers arrived at these recommendations. Specifically, how much did politics enter into these decisions? The write up on HCFCD’s tunnel page makes it clear that “equity considerations” including the social vulnerability index weighed heavily.
I also want to know how the Cypress tunnel emptying into the San Jacinto West Fork between US59 and West Lake Houston Parkway would affect flooding in the heavily populated Humble/Kingwood Area.
Public Comment Period Lasts Through September 30
If you wish to submit public comments on the flood tunnels, you have until September 30, 2022. Submit comments at Public Input.com/tunnels. I intend to request the entire engineering study and will post more when I learn how HCFCD made the recommendations.
Posted by Bob Rehak
1755 Days since Hurricane Harvey