The next consideration is the water table, which varies with the topog - raphy across the site and fluctuates up and down with the tides. When designing the hydrology on site, we needed to take all facets of water movement into consideration: the surface flow, surface infiltration, as well as the groundwater flow and how to control that. Our leading challenge was how do we design and engineer stormwater solutions to best serve the property with these considerations in mind. What stormwater solutions did you implement? The final Riverfront Park design has a suite of stormwater control mea - sures to detain and treat the water-quality on-site and provide protec - tion for the Cape Fear River. The site features seven state-regulated stormwater control measures: two infiltration systems and five permeable pavement systems. The infiltration system in the loading dock includes a subterranean sand trench under the stage building that hydrologically connects directly to the river. We worked closely with Eagle Resources to make sure the water was able to infiltrate between storm events. For both infiltration systems, an open-bottom vault stores the water on site allowing it to infiltrate through the native soils, with consideration for how that’s related to the river and the fluctuating nature of the hydrology on site. From the beginning, the project’s goal was to respect the hydrology on site and go above and beyond the minimum requirements. The infiltra - tion gallery in the main lawn is a good example of how we were able to both infiltrate the water as much as possible for the site’s ecology and maximize the functionality of the site, helping to ensure it drains well from a venue perspective. I understand there are a lot of passive solutions in play. Can you elaborate on those? The site’s natural ability to infiltrate water was prioritized during the design. Planned programmatic elements were married with the storm - water design approach to maximize the public’s use of the site, and go beyond minimum regulatory requirements, to incorporate many pas - sive stormwater treatment elements that support the overall narrative of the park serving the broader community. There is a significant amount of passive runoff where the soil itself was designed to infiltrate and detain that water quality volume of water. There are also five permeable pavement systems, three along Front Street and two on Nutt Street promenade. These soil systems designed by Landis, LLC will serve the project per - petually by being paired with native plants that will maintain surface infiltration rates as the park ages and matures. It sounds like having a strong understanding of local topologies and native plants can play a large role in these projects. Can you tell me more about that? Landscape architects at Hargreaves Jones counseled with our land - scape architecture team at Stewart to understand the ecoregions of the Carolinas in the selection of plantings. The team identified what would work well in an urban evolving riverfront condition for the topologies
and ecosystems of the riparian riverfront all the way up into the up- lands gardens, ultimately including more than 200 trees of 20 different species and understory plants. Using native species is an approach indelible to the Stewart design process, as well as meeting WEDG standards, that creates sustainable projects that are easily maintained but also display the beauty of the natural environment that is occasionally overlooked. You mentioned one of the infiltration systems included elements that go under a building, and I understand you worked closely with your firm’s structural engineers. Can you share how the below-grade water systems impacted the structures on site? Riverfront Park features three buildings and a performance stage, as well as monolithic stairs and walls, all designed by our structural engi- neering team at Stewart led by Tom McLane, PE, project manager, in collaboration with Sage and Coombe Architects. Based on information gathered by Stewart’s geotechnical engineers through a comprehen - sive exploration program consisting of cone penetration testing (CPT) and test pits, the amount of debris and variations in the existing soil was discovered to vary greatly, even over short distances. Using this information, our structural team designed the buildings, and several of the cast-in-place concrete retaining walls to be supported by 8-inch diameter timber piles that were driven an average of 45 feet into the ground to develop the required capacity. The interior floor and stage slabs were also designed as reinforced structural slabs due to the potential of settlement to reduce the potential for cracking. The buildings are also elevated at least two feet above the base flood elevation, meaning the park and its facilities will be a valuable community resource for years to come. Beyond the stormwater solutions, another piece of the complexity is there are two public sanitary force mains that were installed under the Cape Fear River and through the property during the park design pro - cess. The utility provider shared the intended location of these under- construction force mains and the structural team developed creative structural solutions spanning the stage structure over the force main. Helical piles were used near and battered away from the force main to allow for 12 feet of clearance on each side at the same elevation. The helical piles made the battering of the piles easier and removed the impact and vibrations that the driving of the timber piles would have caused, which could have damaged the force main. A similar ap- proach was used at the Cowen Street retaining wall. This 9-foot-tall cantilevered and tapered board-formed face retaining wall is a feature at the entrance to the park that also spans 40 feet over the force main. This allowed for the park to seamlessly function on the surface while the structural design solutions respected below-grade utilities through a horizontally spanning foundation system. Throughout our conversation, the features of the existing soil as identified by Stewart’s geotechnical team continue to arise. Can you touch on the importance? Without the experience and perspective that our geotechnical engi -
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