Originally posted on Engineering News-Record
After 20 years, the end of the $550-million Brays Bayou Flood Damage Reduction Project in Houston is finally in sight.
Known as Project Brays, the work includes 21 miles of channel modifications, including widening and deepening; modifications to about 30 bridges; and construction of four stormwater detention basins that will hold roughly 3.5 billion gallons and span 900 acres.
The project was started long before 2017’s Hurricane Harvey, but was expedited after the storm. A 1988 Army Corps of Engineers study on Buffalo Bayou and its tributaries indicated that the benefits of a flood damage reduction project along Brays Bayou would outweigh associated costs. The latest economic impact, done in 2015, shows a benefit-cost ratio of 7% on a 2.97% investment.
The Corps and Harris County Flood Control District (HCFCD) began work on the project soon after, and in 1998, HCFCD took over the planning and implementation of Project Brays.
“We’ve got about 75 individual projects that make up Project Brays, and we’ve only got two more that we’ve got to go out to bid. So we see the light at the end of the tunnel,” says Gary Zika, federal projects manager at HCFCD. “With it, we’re reducing the risk of flooding in the Brays Watershed, which has about 700,000 people in it.”
Nathan Hayden, director of construction of HCFCD, says the work will not eliminate Harvey-like flooding, but it may reduce the amount of floodwater from the bayou as the changes will allow the bayou to accommodate more water.
The Brays Bayou watershed encompasses approximately 128 miles in Harris County, and the Brays Bayou channel itself is approximately 31 miles long and flows into Buffalo Bayou and the Houston Ship Channel below the Turning Basin, says Franchelle Craft, project manager, USACE Galveston District
“This project will reduce the risk of flooding along major traffic commuter routes such as SH 288, which is below ground level for much of its length crossing the Brays Bayou watershed,” Craft says.
Project Brays will also reduce the risk of high water causing life safety concerns on feeder roads and adjacent roadways along Interstate 45, a hurricane evacuation route through Houston and Harris County, Craft adds.
“This project is different from other projects because Brays Bayou protects the Texas Medical Center during flood events,” Craft says. There are 40 buildings at the TMC located in a 100-year floodplain, and daily economic loss during a flood is more than $30 million, she says.
Lead Switch
On a project such as this, the Corps typically takes the lead with design and construction, and HCFCD would support the work by acquiring rights-of-way and relocating utilities. However, federal legislation allowed HCFCD to take over the project because the district could execute the project faster and cheaper than the Corps, Zika explains.
“This one’s a little different in that we’ll go ahead and not only purchase rights-of-way and do utility relocations, we do the design work and then subcontract or contract out the construction work,” Zika says. “And then what we’ve got to do is get segments done or like individual projects done and then submit those invoices to the Corps, and then the Corps pays us.”
Craft says at its own financial risk the HCFCD had the option to design and build the project in advance of plan approval by the Corps before agreements were in place.
“Being able to begin implementation as soon as possible was critical in a rapidly developing urban area like Harris County, so benefits could be realized much sooner and at lower costs,” Craft says.
“When you have a one-sided wall, it’s very difficult to brace it— especially when some of those walls are 12 to 14 ft tall.”
– Gary Conaway, Senior Vice President, Serco Construction Group Ltd.
All 75 projects are being delivered as design-bid-build, and each one is competitively bid, so the same contractors aren’t working on every channel section or detention basin.
The last of the 75 projects will cover modifications to seven bridges, Zika says.
Without the bridge modifications, when high water hit the bridges, it would fan out into neighborhoods, Hayden says.
“Once we get that last segment excavated, the only obstruction will be the bridges,” he says. HCFCD is being careful in planning to avoid work being done on two adjacent bridges to allow residents to come and go without a lengthy detour, he says.
The project has taken over 20 years because construction could only progress when money was available from the Corps, Zika says.
“We’d have to do our design work—it usually took about a year for a particular project—get the project bill and then turn an invoice in. It’s about a three-year process to do all that,” he says. Additionally, “We would never know how much money we would get from the Corps from every year. Basically, Congress had to allocate money to the Corps and then they would either give it to this project or give it to other projects.”
That dynamic changed in February 2018 with the passage of the Bipartisan Budget Act, which made the rest of the required funding available for Project Brays at the end of 2018.
“So that’s why these last seven bridges, we’re putting them in one package. Otherwise we would’ve been doing each individual bridge as a package and working out the funding from the Corps,” Zika says. “Now that we know we’ve got the money, we were able to put them into a bigger package, and we’ve got the funding available from the Corps after we get the work done.”
Budget-wise, “the project started out at about $540 million. We’re estimating it’s going to be $480 million when we complete. So we’re under the original budget,” Zika says.
Though the district worked with more than two dozen contractors throughout the more than 70 projects let or completed to date, it was able to keep them all on the same page through the use of technology. Based on lidar surveys, HCFCD created 3D models of the channel sections and detention basin. Contractors were able to download the model “right to their equipment. They could then dig and excavate to our design surface,” Zika says.
Supporting Bridges, Digging Detention
Work currently underway includes reconstruction of three bridges—Ardmore Bridge, which will be complete in early August; Greenbriar Bridge, construction of which started in January and will last a year; and the Buffalo Speedway Bridge, construction of which will begin in early 2020. An extension to Stella Link Bridge also began in mid-July and is expected to last six months.
The last remaining channel section is also under construction and will be complete in late August.
Serco Construction Group Ltd. is the contractor on the last channel section, construction of which began in July 2018. This $11.7-million package covers a span of Brays Bayou from upstream of South Rice Avenue to upstream of Fondren Road, along with a section on the northern bank from South Post Oak Road/Loop 610 to South Rice Avenue.
Serco’s scope of work included expanding the lower channels to enhance the bayou’s flood capacity, explains Gary Conaway, senior vice president at Serco.
“It goes through a residential area—most of Brays does in this area,” Conaway says. “So the challenges included dealing with the residents’ concerns with traffic control and moving almost 300,000 yards of excavated soil off the project and disposing of it to create the bigger channels.”
During the channel widening, the Project Brays teams have modified 32 bridges that cross Brays Bayou, many of which are quite old, resulting in a variety of unknowns that weren’t identifiable until crews began digging, Zika explains. This included 16 replacements, four extensions and one raising.
Serco’s segment included three bridge modifications, at Fondren, Braeswood and Hillcroft roads.
Under Hillcroft, “there was one monolithic structure that wasn’t supposed to be there, probably there from maybe 30, 40 years ago and we couldn’t put soil nails through it,” Conaway recalls. “So we basically just worked with the engineer, did an analysis on the thickness of the concrete and were able to actually drill in and epoxy and tie in anchors into the existing concrete instead of trying to demolish it or move it back to some unknown depth.”
The team also saved HCFCD costs for checking for contaminated soil before mass excavation, as called for in the contract. The potholing found the soils were not actually contaminated, Conaway says.
HCFCD also used retaining walls beneath 11 of the bridges instead of widening and replacing each one to ensure the bridges could stay in service as the bayou expansion progressed.
“We’ve been using some of the TxDOT standard, what they call soil nail walls,” Zika says, which are earth-retaining structures typically used in roadway projects.
“That hasn’t been really used that often on our channel work—we either have gravity walls or drill shaft walls,” Zika says. “But the soil nail walls are kind of a unique item in that we could put these retaining walls underneath the bridge and the bridge stays in service the whole time.”
The process kept construction progressing without impact to the public or utilities on the bridges “and has resulted in a savings of about a factor of 10,” Zika says.
Contractors on some of the earlier segments ran into difficulties with keeping the walls vertically aligned, and rework was necessary “because when you have a one-sided wall, it’s very difficult to brace it—especially when some of these walls are 12 to 14 ft tall,” Conaway adds.
Serco’s team used a proprietary interior wall system. The retained earth is held back by soil nails and shotcrete, but Serco designed “both the connection methodology and the wall-tie strength to match the forms and the maximum concrete hydraulic pressures,” Conaway says. “The process greatly slowed the installation but prevented rework and improved the wall integrity and architectural appearance.”
After excavation, installation of the soil nails and placement of the shotcrete, the team installed interior wall ties, the exterior forms, walers and braces.
The retaining walls also have a special form liner pattern on them, which is a fractured fin form on a picture frame pattern with smooth finish columns and sandblasted coping, Conaway says. “The footer was stepped with most of the walls under bridges and adjoining abutments. All wing walls sloped to match grade with the same pattern requirements,” he adds.
Serco custom-built the wall ties and utilized a thickened, water-based form release agent specifically designed for use on expanded polystyrene (EPS) foam forms and form liners that the firm has previously used in similar situations, but not in Texas, Conaway says.
Serco installed 16,567 sq ft of retaining walls on the firm’s section of Project Brays. The contractor also performed detailed estimating for HCFCD for the possible elevation of Hillcroft bridge in the future to allow for greater flow capacity.
In addition to the channel work, a complex system of channels and detention ponds were added so that during periods of high water, water will spill over into a channel that will travel to a series of four detention ponds. The detention basin area is “pretty elaborate,” Hayden says, and is based on elevations and gravity flow.
The wet bottom basins attract birds and fish. A portion, called Willow Waterhole, is a roughly 300-acre multi-use recreational area managed by a conservancy, and can hold approximately 600 million gallons of stormwater.
Lecon Construction excavated a portion of Willow Waterhole, totaling approximately 1.25 million cu yd of soil during a $10 million, 15-month contract that began in May 2014.
The detention ponds were “broken out into pieces as well. You may have one pond that may have actually entailed five phases just due to the economics of it more than anything—they would dig it in phases,” says Dan Lloyd, president of Lecon, which also performed some excavation work on each the detention ponds at some point over the course of about six years.
“The last time we worked on Brays was probably 14 months ago,” he says. “The biggest portion of the projects we did was mass excavation of earth. There was also some pipe or drainage, some concrete slope paving as well as some rip-rap, which is a broken-up concrete for erosion protection as well.”
Craft notes that one of the innovative elements on Project Brays is the use of recycled concrete in lieu of other erosion protection materials, resulting in cost savings.
End in Sight
The overall Project Brays work, which was sped up after Hurricane Harvey, did have to take a pause when the storm hit.
“Of course, anytime you’re working in a bayou, flood control is always an issue. [With] any significant storm upstream, you’re going to have your equipment or the pumps under water within 15 to 30 minutes,” Conaway says. “So pulling out and revolving back in, cleaning up and keep going—but that’s sort of the nature of what we do.”
The final project under the scope of Project Brays will be let for bid in late 2019, so the 20-plus year design and construction process will finally wrap up in 2021.
Over the course of that journey, the team has learned a great deal, such as “engagement with the public, engagement with elected officials, design standards that have changed because of the project, using websites and social media,” says R. Russell P. Lannin, project manager with HCFCD. “When Project Brays started, email and websites were basic and not used by the broad public.”
HCFCD, the Corps and the many contractors involved with Project Brays have dealt with a variety of other challenges, from coordination with utility companies and utility relocations to dealing with the public when they were not happy with the project, Lannin explains.
“Having long-term agreements with different agencies was very helpful [on this job, as was] having a project theme and staying with it for the entire project,” Lannin says.
Although the channel segments and bridges were completed separately on this project, Lannin observes that had the bridges been put down with the channel segments, the work would have been smoother.
The process also would have been helped along if more funds were available so that “bigger and more projects would have been able to go on at one time,” he adds.
