Born on the Bayou

March 18, 2021, Feature, by Ted Vuong

2021 April Feature Born on the Bayou 410

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How a golf course was repurposed into the world-class Houston Botanic Garden 

Houston has long been a hub for visionary ideas in medicine, energy, manufacturing and aeronautics.

That same forward-thinking spirit inspired a group of Houstonians to work for more than 30 years to bring to their city a botanic garden like those they had witnessed firsthand having a positive impact in other communities around the globe.

By January 2015, that long-held vision became a reality when the Houston City Council unanimously approved a long-term lease agreement and partnership with the Houston Botanic Garden to transform the former Glenbrook Golf Course into a world-class garden.

“They had a desire that Houston join in the growing interest in botanic gardens and add to the city’s ecosystem of cultural institutions by creating a world-class garden in Houston,” says Claudia Gee Vassar, president and general counsel at the Houston Botanic Garden.

Located near Hobby Airport, the site for the Houston Botanic Garden offered easy accessibility to the greater Houston region and the opportunity to develop the garden around the Sims Bayou in an area with little investment in green spaces or cultural amenities.

“The influence and integration of the bayou in the garden allows visitors to understand these beautiful waterways that are integral to the resiliency of the ‘Bayou City,’” Vassar says.

The 132-acre Houston Botanic Garden is also a long-term investment in Houston tourism and another jewel in the city’s revitalization of its green spaces.

“It is a fantastic addition to the Houston area and one that will bring joy and serenity to future generations,” says Houston Mayor Sylvester Turner.

The Houston Botanic Garden includes eight different facets, each of which serves an educational component: Global Collection Garden, Susan Garver Family Discovery Garden, Culinary Garden, Pine Grove, Community Garden, Woodland Glade, Stormwater Wetlands and Coastal Prairie.

The garden also features two-and-a-half miles of walking and hiking trails, a lagoon and a nature play area for children.

Addressing Design Challenges

The Sims Bayou channel runs through the middle of the Houston Botanic Garden, dividing it into two separate areas — the Island and the South Gardens. Because the site was a former golf course on an island off Sims Bayou, many of the project’s challenges involved balancing the desire to maintain the existing tree canopy while constructing the landscape and structures of a botanic garden.

“We strategically designed the layout and systems to avoid as many existing obstacles as possible,” says Donna Bridgeman, senior landscape architect at West 8.

Engineering firm Walter P Moore was involved in the initial site review and served on the building team that created the more than $100 million master plan for the Houston Botanic Garden. Construction on Phase I of that master plan — which incorporated existing natural features and elements to mitigate potential flooding — commenced in spring 2019 and was substantially completed in fall 2020.

“Walter P Moore was instrumental in spearheading the challenges of permitting a multiphase project while leading the design of challenging structural, grading and drainage systems,” Bridgeman says.

Detention and Drainage

To develop the property, which encompasses an area of Sims Bayou and includes the floodway as well as 100- and 500-year floodplains, permitting required coordination with the U.S. Army Corps of Engineers, the Harris County Flood Control District and the City of Houston. During the design phase, in response to Hurricane Harvey, the city changed the detention and floodplain mitigation criteria for any development within city limits, which required additional coordination with the Houston Public Works Department on the project.

The Houston region is susceptible to flooding, and the city and Harris County reviewed the development criteria within the floodplain to address the flooding issues in this region.

“The permitting process of this project was at the time when Houston was about to update [its] detention and floodplain requirement,” says Chong Ooi, senior associate at Walter P Moore.

As a result, the new detention and floodplain volume mitigation were incorporated into the project’s master plan. The floodplain mitigation on the site was designed as the Coastal Prairie, which is a major ecosystem of the Houston region, to handle the inundation of stormwater during major rain events. Additionally, a detention pond serves as a Stormwater Wetlands exhibit, using the permanent body of water to allow planting of aquatic plants.

Typically, addressing floodplain mitigation requirements is done by offsetting the fill volume within the floodplain by removing the same amount through excavation. In most other developments, the areas excavated for floodplain mitigation are seeded and left unattended after completion.

“However, the Houston Botanic Garden incorporated this area as a part of the garden to demonstrate a unique natural land feature, usually located alongside a waterway, that can become inundated during high-water events,” Ooi explains. “After the water is recessed, naturally formed depressed areas in the Coastal Prairie temporarily hold water, and, over time, a unique ecosystem is developed in this area for flora and fauna.”

Furthermore, the garden’s innovative drainage structure in the Stormwater Wetlands was designed so it could be partially hidden within the bank of the pond’s slope. During a rain event, the amount of water that fills the area depends on the size of the storm event. Water above the Stormwater Wetlands area becomes detention volume. The structure’s weir wall controls stormwater release, draining within 24 to 48 hours.

Included in the weir wall are small orifices designed to control the water level and regulate release. These are water-flow control to imitate the pre-development storm runoff. During a rain event, the pond water level will rise beyond the Stormwater Wetlands, and the detained stormwater will be released slowly into a nearby stream through an orifice. A valve system allows additional control of the water level for maintenance purposes. One valve drains the entire Stormwater Wetlands, and a second valve controls the water level in the area.

Valuing Conservation 

Knowing the importance of water as a valuable natural resource for the garden, an additional riser structure was designed for the children’s lagoon. A small aquatic garden surrounds the lagoon, which is separated into two sections. The riser structure is hidden underneath a decomposed granite pathway — the only portions visible are the screen and the concrete top of the structure.

Conservation goals also had an impact on how the floodplain was constructed. The garden required excess soil material to be reused elsewhere for the project. To accomplish this, Walter P Moore used Civil 3D to do multiple design iterations of the entire project. As a result, excess material was limited to approximately 2,000 cubic yards of earthwork, which was recycled in the Global Collection Garden.

“The team designed with the existing soil, employing an extensive rehabilitation process of harvesting layers of existing soil, stockpiling and restructuring soils with cover crops and amendments,” Bridgeman adds.

In another example of the garden’s commitment to conservation, designs accommodated existing trees on-site and developed strict criteria for working around them.

“We had to work equipment strategically around the tree protection fence to ensure we did not damage the existing trees on the site,” says Carolina Hernandez, project manager at Harvey Builders.

The trees are a significant and stunning part of the entry drive and provide shade in Picnic Grove. The landscaping designs highlighted the proper spacing from these trees so they could continue to thrive and flourish in a new setting. The designs contained no grading around the trees, creating a design problem because of all the landscaping additions and a preference for adjacent areas with higher elevations. The result is a blend of new and existing flora and fauna.

Bridge Design and Maintenance

Because the site included the original Sims Bayou meander and newer channelized bayou cutting through it, connectivity across the bayou provided a unique challenge to the building team in creating access to and throughout the garden.

As part of the site review, five pedestrian bridges were evaluated for structural integrity. Improvements were recommended to extend the lifespan of the existing bridges. Some of the issues included deterioration from deferred maintenance, incomplete existing bridge drawings and documentation, and bridge scour.

Ultimately, a new entry bridge was designed and constructed to cross the Sims Bayou meander and allow vehicle, bicycle and pedestrian access from Park Place Boulevard to the Island.

To accommodate the bridge, areas at both ends were filled to raise the approach elevation, achieving the required floodplain clearance from the city and Harris County Flood Control District.

“The low-chord elevation is 25.65 feet above sea level and approximately two feet above the 100-year flood event,” says Muna Mitchell, managing director, bridge engineering at Walter P Moore. “The City of Houston provides minimum freeboard requirements, so new bridges do not block stream flow during flood stages or flood events.”

The raised approaches to the new bridge resulted in an additional prairie area just beyond the entry garden, featuring native coastal grasses and plants that can tolerate occasional inundation.

Positive Reaction

At the onset of this project, the goal was to give Houstonians another serene setting where they could enjoy nature and experience the physical and emotional health benefits of spending time outdoors.

“The garden is an enhancement to the city’s infrastructure and will serve as a place for inspiration and education for all Houstonians and its visitors,” Mayor Turner says.

Since opening its doors on September 18, 2020, the Houston Botanic Garden has admitted more than 24,000 ticketed visitors and continues to welcome first-time and returning guests every day.

“For being the first botanic garden in Houston, the reaction from the public has been overwhelmingly positive, especially during a global pandemic,” Mayor Turner says.

Ted Vuong, P.E., LEED A.P., ENV SP, is a Principal and Managing Director of Civil Engineering Services at Walter P Moore.