Where can I get more or future information?
To get project updates as they become available, please sign up for notifications on the Tunnels project webpage at www.hcfcd.org/Z-08.
What is the cost of a tunnel system? What is the average cost per mile, per foot?
The preliminary total project cost for a potential tunnel system is estimated at about $30 billion. This would include anticipated engineering, environmental permitting, right-of-way (ROW) acquisition and construction costs. The cost to design and build a single representative 10-mile tunnel section is estimated to be in the range of $3-$4 billion. This is equivalent to $300 million to $400 million per mile, or $57,000 to $76,000 per linear foot. We will continue to refine cost estimates as part of Phase 3.
Which costs less to achieve the same benefits – tunnels or traditional flood risk reduction methods?
Monetary costs are difficult to quantify at this early stage of the study process. However, work done to date suggests that the cost of tunnels can be comparable to traditional flood risk reduction projects that would achieve the same level of benefits.
The answer to which method costs less depends on the specific project site, what traditional method(s) would be most effective at that location, and how much undeveloped land is available. Monetary costs are not the only costs we will examine, however. For example, there is also the cost in community disruption, especially in areas that are already heavily developed with homes and businesses.
How long will it take to design, permit and build? When will the construction start? Wouldn’t a traditional project be quicker?
A tunnel system like the one outlined in the presentation is a multi-decade project. At this time, a detailed schedule cannot be provided, since we need to complete our study process.
Individual traditional projects might be quicker than a tunnel but would not offer the same flood risk reduction benefits. Large-scale federally funded projects such as Project Brays and the Sims Bayou Federal Project typically include multiple individually bid and constructed projects over many years or decades.
The Flood Control District continues to deliver traditional flood mitigation projects while progressing through the remaining phases of the tunnel study. For updates to current projects in your area please visit www.hcfcd.org.
Funding: Where will the money come from? Will FEMA pay for this? Can recovery money be used to build the tunnels? How much will my taxes go up?
In our Phase 3 work, we will be exploring funding across local, state and federal resources. At this time, it is too early to estimate what the impact might be on individual property owners’ tax bills.
Can’t the tunnels be larger (100’ in diameter?), smaller, or can we have two tunnels side by side?
We currently estimate that tunnels within a future system would be at most between 30 and 45 feet in diameter. The maximum diameter limit is based on the current construction technology for soft soils. However, as technology advances, larger diameter tunnels may become a potential option in the future.
Dual-diameter tunnels are also potentially being considered, especially where multiple alignments may converge. A dual diameter section may help bridge the gap where a much larger single diameter tunnel may not be a viable option.
Smaller tunnels are also possible. However, the potential tunnel boring machine would be limited to one size for the life of its use, so minimizing size changes along the alignment could potentially be beneficial in managing costs. This optimization of diameter sizes will be examined further during Phase 3 investigation.
Pumps: Can we use pumps to maximize capacity? Can all tunnels use pumps?
Phase 3 of the study will examine the use of active stormwater management and pumps to increase capacity, maintain the system and improve stormwater quality.
Galveston Bay: How will storm surge impact tunnel performance?
Storm surge is a rising of the sea as a result of atmospheric pressure changes and wind associated with a storm (for example, an incoming hurricane). Traditionally, this information is based on historical gage data along the receiving stream(s). In Phase 2, we evaluated this historical data to determine the preliminary tunnel outfall structure elevations. We also recommended the use of a potential gating system that works by closing the tunnel outlet or intakes when storm surge pushes up against the outward flow of stormwater from the tunnels. In Phase 3, tunnel performance under storm surge conditions will be evaluated.
There are other mega-projects occurring along the Gulf Coast, including the U.S. Army Corps of Engineer’s Coastal Barrier project. Are you coordinating with those teams to ensure there are no conflicts with a tunnels project?
The project team has already started communicating with different project teams across Harris County. This coordination (including for the Coastal Barrier project) will continue during the Phase 3 investigation and extend through the life of the project.
How will stormwater release impact water quality in Galveston Bay?
We know that stormwater quality impacts must be avoided, such as the potential for pushing low-quality water into the receiving body of water (including the Houston Ship Channel and Galveston Bay). We have and will continue to engage the Port of Houston and will be exploring the use of pumps and other stormwater quality mitigation in our Phase 3 study.
Why can’t the water be stored and treated for drinking water, or released broadly across the region in a way that could potentially combat drought conditions?
The mission of the Flood Control District is flood risk reduction, which is driven by the immediate need to move excess stormwater through flood infrastructure, including the proposed tunnels, to reduce the loss of life and structural damage. Water supply has not been identified as a benefit of flood risk reduction projects. Goals and methods for water supply-focused projects could conflict with our primary flood risk reduction goals for tunnels.
Why not make new reservoir(s) to hold stormwater?
The Flood Control District has and will continue to build stormwater detention basins to temporarily hold excess stormwater during rain events. These are not “reservoirs” built to hold water for longer periods, or as a community water supply. They are designed to temporarily store excess stormwater and allow stormwater to quickly drain back out into the bayous and creeks after a storm.
The U.S. Army Corps of Engineers has jurisdiction over the two federal reservoirs in Harris County, Addicks and Barker. www.swg.usace.army.mil/
Won’t the silt pile up and block the tunnel? How will you manage silt?
Maintenance is a factor for all stormwater management systems. This includes Flood Control District channels which are subject to erosion repair and desilting, as needed. For tunnels, maintenance would likely include routine inspections, dewatering between storms, and periodic desilting and debris removal. This will be explored more during Phase 3. Historically, other tunnel systems have not had significant problems with silt build-up.
Isn’t Harris County very flat and not very far above sea level? How can gravity alone push the stormwater uphill to sea level from deep underground?
Studies show the change in elevation (244 feet from the highest point in the county to sea level) is enough to convey a substantial amount of stormwater. This means that the force of gravity has the ability to move stormwater into and along a tunnel system, and out into the Ship Channel and Galveston Bay – although not from every area of the county. As part of our next phase, we will weigh the benefits of optimizing the performance of the system by including pump conveyance.
What is the Phase 3 study timeline?
Phase 3 work is expected to begin in 2023 and is estimated to take a minimum of three (3) years to complete. Prior to Phase 3 work beginning, the Flood Control District would need to develop a detailed scope of work (i.e., what work efforts will be included for study during Phase 3) and hire an engineering firm with appropriate qualifications to conduct the work. Part of the process of developing the scope is taking into account the feedback from the public during the open commenting period.
Will there be a tunnel near me?
No decision has been made as to the location of any particular tunnel alignment. Preliminary study has identified areas where tunnels would be most feasible. Based on preliminary evaluation, the eight (8) recommended alignments were in watersheds with characteristics that included but were not limited to:
- A significant number of identified damage centers, which are concentrated areas that have and will continue to flood repeatedly, with water in homes and businesses
- Sufficient slope to allow for gravity flow
- Areas where it is difficult to find sufficient undeveloped land for current project approach
- Areas with greater population density and less open land
- Location outside the high-risk zone for storm surge
One of the most difficult challenges the Flood Control District faces is constructing effective projects that are sensitive to community and natural values in a highly urbanized area. Location and population density are key considerations. This information can also pinpoint areas that are less likely to recover quickly or be resilient after major storm events.