To the north and south of the tunnels, 50 acres of endangered, native Gulf Coast prairie and additional wetlands will add a new habitat that also helps absorb and clean stormwater in the park.
During construction, crews will move a half-million cubic yards of dirt, excavating 10 feet down for the prairie restoration and transporting the dirt to form the land bridge over the tunnels.
“When we looked at how to build the mounds for the land bridge, one of the fundamental questions was how we would source and manage dirt, and we very quickly realized that the best way to control it was to generate it onsite,” said Randy Odinet, Executive Vice President of the Memorial Park Conservancy, the nonprofit organization that operates and maintains most of the park.
Keeping all the dirt movement within the 100-acre site also avoids impacting over 4 million people who visit the park each year. To minimize inconvenience to drivers, the project team determined a new roadway alignment that allowed tunnel construction without closing Memorial Drive.
Construction Manager at Risk Tellepsen began construction in August 2020. In March 2022, the new eastbound alignment opened to traffic, followed by westbound in May 2022. Traffic now travels through two sets of 25-foot-tall, 54-foot-wide tunnels in each direction. A break between the tunnels allows for air flow and light infiltration.
When the project finishes late this year, the new land bridge above the tunnels will offer greenspace overlooking the park and the city. In the restored prairie, observation sites will allow visitors to watch for birds and other wildlife, while a new stream channel provides an animal crossing under the road.
Funded mostly through private philanthropy, the $70 million Land Bridge and Prairie project is part of Memorial Park’s 10-Year Plan. In 2018, a catalyst gift from the Kinder Foundation – which leveraged public funding through the Uptown Development Authority – and support from other donors enabled the Conservancy to accelerate this and other projects in the Memorial Park Master Plan.
“Part of what’s elegant about this is there’s virtually no import and no export,” said Jeff Aten, Associate Principal for Lead Designer Nelson Byrd Woltz Landscape Architects.
That eliminated the need for haul trucks to cross park trails or roadway. The bulk of the dirt for the land bridge comes from the excavation of four existing ball fields that will be relocated, as well as associated parking lots and roadway.
“The only material we hauled in was some rock for one of the drainage layers within the structural zone of the tunnels,” Odinet said. “Everything else we’ve been able to provide out of the excavation of the prairie or a little bit of mining of sand within the prairie footprint for a structural zone alongside the tunnels.”
About 90,000 yards of dirt was onsite before construction began. That material came from another Memorial Park project – the Clay Family Eastern Glades. When crews started digging the lake for that project in 2019, planning had started for reconstruction of the 18-hole Memorial Park Golf Course.
“We were able to dovetail into the beginning of that work and haul all of the spoil from the Eastern Glades Lake across the golf course to the land bridge site,” Odinet said. “That kept 20,000 to 30,000 truck crossings off Memorial Drive and our highest-use trail amenity.”
“Tellepsen was really instrumental in helping us define an alignment for Memorial Drive that let us build the new tunnels and keep two of the three lanes of traffic open in each direction, while minimizing impact outside of the land bridge work area,” Odinet said. “They did a really specific assessment of how to install the arches and how much work area they needed to backfill them to specifications. We were able to build all the tunnels and new roadway just south of the old alignment.”
The tunnels are made from approximately 300 6-foot, precast segments that came in halves. After crews pieced them together, they raised them as a single arch.
In the tunnels’ headwalls, as the sections emerge out of the mounds, they start to draw away from each other, leading to a unique design solution.
“Because that cantilever is significant, we would have needed very large buttresses off to the side of each of those sections in order to keep them upright and have earth laid against their backs,” Aten said. “Instead of doing that, we used a ring beam that connects the tops of all those arches and draws them together as one section.”
In the design, “We tried to be fairly artful,” he added. “The profile of the beam starts flat, basically perpendicular to the roadway, then as it climbs up the face of all the cast sections, it rotates so at the very top it sits vertical, or plumb with grade. As it turns and goes down the other side, it rotates again and drops so that it’s horizontal, or level with the ground.”
The beam is made from cast-in-place concrete. However, “There was pretty incredible steel formwork that had to be set in place to be able to pour that beam onsite and bind those all together,” Aten said.
For instance, in designing the new channel, the team mimicked a natural stream with faster-moving sections and pools. “Those pools will be created by root wads and logs harvested from the site during the early phases of construction,” Aten said.
As the channel flows under Memorial Drive, “We made some extra efforts to make that section usable by riparian creatures – turtles, salamanders, frogs, and others,” Aten said. “There’s an area that will silt up and collect debris, allowing them to shelter and stay in a moist environment.”
In addition, a series of manholes with open covers will allow light into the channel under the roadway. Above Memorial Drive, the land bridge will allow animals to move around without navigating the road. As the prairie reaches maturity in the next five to seven years, Aten said they expect more bird and pollinator species to make it their home.
In the southernmost part of the channel, “A concrete restrictor will hold water, allowing some of it to infiltrate in the prairie, then slowly run at predevelopment rates into an existing ravine and then on to Buffalo Bayou,” Aten said.
However, “The biggest thing relative to stormwater management is the difference that a prairie can make for rainfall absorption,” Odinet added.
According to the Conservancy, the prairie is designed to be two times as effective as developed land for processing and conveying stormwater and up to six times more cost-effective than engineered stormwater infrastructure. In addition, the prairie habitat will be able to sequester 14.2 metric tons of carbon each year and establish a more resilient ecology to aid with onsite detention during flooding.
- Architecture and Creative Infrastructure: METALAB
- Architecture: Kathleen English Associates
- Archaeology: Gray & Pape
- Channel Design: Freese and Nichols
- Civil Engineer and Prime Consultant: Gunda
- Client Representative: Texas Project Administration Services
- Construction Manager at Risk: Tellepsen
- Engineering Consultant: Arup
- Environmental Science: Berg Oliver
- Geotech: Paradigm
- Irrigation: James Pole
- Landscape Architecture and Lead Designer: Nelson Byrd Woltz Landscape Architects
- Lighting: G2LD
- MEP: Hunt & Hunt
- Metal Fabrication: Renfrow + Company, Iron Access
- Signage and Wayfinding: Minor Design, Graphtec
- Soils: Olsson
- Structural Engineering: Walter P. Moore, Henderson Rodgers
- Landscape Architect CM: White Oak Studio
- Prairie Consultants: Wildlife Habitat Federation, The Nature Conservancy
- Precast: Tricon Precast Limited
- Earthwork: W.T. Byler Co
- Landscaping: Shooter & Lindsey, Inc.
- Channel: RES Environmental Operating Company
- Waterproofing: Western Waterproofing
- Electrical: Pieper Houston Electric
- Demolition: Cherry Demolition
- Roadway: Reytec
- Utilities: JD Foster and Company
- Tree Transplant: Environmental Tree and Design
- Site Concrete: Building Concrete Solutions
- Paint: Milam & Co. Painting
- Soil Treatment: Construction EcoServices
- Boardwalks: York Bridge Concepts
- Engraving: Schlitzberger Stone Designs
- Fencing: Foster Fence