By Tom Douglas
In October 2020, the U.S. Army Corps of Engineers issued an Interim Feasibility Report entitled “Buffalo Bayou and Tributaries Resiliency Study, Texas.” Two of the Interim Report’s recommendations immediately met with strong opposition: (1) enlarging and concrete-lining the channel of Buffalo Bayou; and (2) constructing a very large reservoir over valuable habitat on the Katy Prairie.
In response to the Feasibility Report, a coalition of community groups, business interests, and environmental/conservation organizations began work on a Buffalo Bayou Community Plan that would offer constructive alternatives to address Buffalo Bayou flooding. To garner input that can inform future planning, a relatively small Environmental Roundtable was convened. Its first session focused primarily on one of the Community Plan’s four components, namely, the creation of additional storage and enhancement of habitat features within the Addicks and Barker Reservoirs. The results of that discussion were reported in the February 2022 issue of the Bayou Banner.
Tunnels
On March 8, the second Environmental Roundtable session considered a different component of the Community Plan: flood tunnels. Scott Elmer, Assistant Director of Operations at Harris County Flood Control District, outlined studies being conducted by HCFCD. He pointed out that because flood tunnels are underground, they do not require anywhere near as much land as traditional approaches. But the envisioned 22+ miles of flood tunnels that are currently being studied at a conceptual level would not offer a quick solution – they would come at an estimated cost of around $30 billion and would require 10-15 years to construct.
The final report for Phase 1 of the HCFCD Deep Tunnel Study, which was released in September 2019, reached four principal conclusions: (1) tunneling in Harris County is feasible based on the geotechnical conditions and project experience in similar soils; (2) geological faults may require special design and construction considerations where crossed by the tunnel, but are not fatal flaws; (3) tunnels can move a significant rate of stormwater operating entirely by gravity as an inverted siphon; and (4) costs for a representative 10-mile-long, 25-foot or 40-foot diameter tunnel, including a 50% contingency, would be approximately $1 billion or $1.5 billion, respectively.
Phase 2 of the Deep Tunnel Study is almost complete, and release of its final report is anticipated within a month. Goals of the Phase 2 study are to: (1) consider how to measure tunnel success; (2) recommend tunnel alignments that reduce flooding risks along major bayous and creeks while not causing negative impacts at the discharge locations; (3) estimate cost – including the cost of community disruption – as compared to potential flood risk reduction benefits; (4) determine an estimated timeline for building tunnel projects; (5) identify environmental impacts and permit requirements; and (6) compare tunnel costs, benefits and implementation timelines to those of other flood risk reduction projects.
If Phase 2 identifies actionable recommendations, HCFCD will proceed with Phase 3, which will include a county-wide analysis of the benefits of tunnels, consider synergistic effects of a system of tunnels, and provide preliminary engineering studies. An anticipated Phase 4 study would then refine the recommended tunnel alignments, to prepare them for design and implementation.
As had been hoped, there was a lively interchange of ideas regarding flood tunnels. One participant asked whether adequate consideration had been given to potential problems that might occur where a tunnel crosses one of the Houston metropolitan area’s numerous geological “growth faults,” where the elevation of the land surface on one side is slowly and continuously rising relative to that on the other. Other questions involved the potential effects of sea level rise, tides, and rain events of increasing frequency and intensity. It was pointed out that tunnel inlets can be opened and closed, depending on where rainfall occurs. Tunnels will be pumped empty between storms to prevent the discharge of stagnant, poorly oxygenated water when the next storm arrives. The projected conveyance capacity of the tunnel system for Buffalo Bayou would be about 13,000 cubic feet per second (cfs), which compares with the 15,000 cfs that was released from Addicks and Barker Reservoirs during Hurricane Harvey. (Though, the total flow in Buffalo Bayou is estimated to have been somewhere between 40 and 50 thousand cfs when inputs from other bayous are taken into account.) Yet another question involved the possible advantage of having two smaller tunnels instead of a single large one.
Litigation
Some of the legal and financial issues related to flood tunnels were addressed by Larry Dunbar (SSPEED Center and P.B. Bedient & Associates, Inc.) and Stephen Robinson (Allen Boone Humphries Robinson, LLP). A suit seeking compensation for land owners downstream from the two reservoirs has been dismissed, but it is being appealed. In contrast, the U.S. Court of Federal Claims has ruled that the federal government is liable for damages that occurred to properties located upstream of the two dams, and within their respective flood pools. It was determined that, in effect, the government had taken a Permanent Flowage Easement on these properties, the monetary value of which has not yet been adjudicated. At present, it is unknown how the existence of such an easement would affect the value of these properties or their eligibility for flood insurance – a situation that could potentially be devastating for the affected communities.
Finance
A recurring theme in the discussion was whether funds arising from the court’s judgement would better be used for “fixing the problem,” as opposed to “giving the right to further destruction.” Should the Buffalo Bayou tunnel project be federalized, this would have a major effect on its financing. This unusual state of affairs has greatly complicated the benefit/cost analysis that would normally be conducted by the Corps of Engineers for a proposed project.
Next Steps
There are preliminary plans for two additional Environmental Roundtable sessions. One of them will address the remaining two components of the Buffalo Bayou Community Plan: (1) retention and storage of floodwater in the Addicks Watershed; and (2) land protection, restoration, and shallow storage of floodwater in the Upper Cypress Creek Watershed, with the goal of preventing overflows from it into the Addicks Watershed and thence into Buffalo Bayou. A fourth and final Roundtable session will be devoted to answering questions that were raised during the preceding three sessions.
When the work of the Environmental Roundtable has been completed, a series of larger meetings is being planned for the broader community. These will discuss ways that flooding can be addressed, both in Buffalo Bayou and in other Harris County watersheds.
NOTE: Since the above article was originally posted in late March, discussions of the merits of flood tunnels have continued. On April 14, Congresswoman Lizzie Fletcher held a Virtual Community Conversation on Flood Mitigation and Recovery. In addition to Congresswoman Fletcher, the panelists included Col. Timothy Vail | Galveston District Commander, U.S. Army Corps of Engineers; Alan Black | Deputy Director of Engineering and Construction, Harris County Flood Control District; Steve Costello | Chief Recovery Officer, City of Houston; and Lt. Col. Rhett A. Blackmon | Incoming Galveston District Commander, U.S. Army Corps of Engineers. All expressed optimism that cooperation among local, state, and federal agencies on flooding issues will continue to improve. Thanks to Congresswoman Fletcher for her ongoing efforts to address flooding in the Houston region.
Photo credit: Houston Stronger
https://gbep.texas.gov/wp-content/uploads/2021/04/2021-04-21-HS-BBCP-HPB-Overview.pdf