Since its opening in the mid-1950s, Nashville’s Hillsboro High School (HHS) has remained a fixture for residents of the Green Hills community, however the city’s population surge forced Metro Nashville Public Schools (MNPS) to reassess the school’s capacity for growth. The projected upward swing in student enrollment coupled with the age of the campus meant one thing for HHS—it was time to expand and renovate. Working as a subconsultant to ARTifice architecture, Gresham Smith developed a sustainable solution for managing the complex urban site’s stormwater while meeting MNPS’ budget for the school and Metro Nashville’s stormwater ordinances.
linear feet of pipe
Small Site, Big PlansThe project called for new classroom buildings, renovating existing buildings, increasing parking for students and faculty, redesigning sports fields, and adding a Goodwill drop-off center and a WeGo Public Transit neighborhood transfer station. Many new high schools with similar scope requirements would require a parcel of land in excess of 50 acres, however we were limited to the 29 acres the site originally sat on due to the landlocked nature of urban redevelopment. These constraints led to the design of a multi-story campus with a structured rooftop flex field over parking.
Surprises in StoreOver the course of HHS’ nearly 70-year lifespan, the school’s campus experienced at least five additions. While we always planned to demolish the existing storm infrastructure and replace it with a new design, the lack of historical drawings provided a challenge in understanding existing flows to the public storm infrastructure in the right-of-way as it relates to existing onsite drainage basins.
We also discovered a piped stream running through the school’s site, which required additional permitting from the Tennessee Department of Environmental Conservation and the Army Corps of Engineers. The large piped stream also conveyed stormwater from approximately 40 acres of developed area from the Green Hills community, further limiting the site footprint available for green infrastructure practices.
If stormwater surprises weren’t enough, our team also discovered unusual site conditions while excavating for a new parking lot. The fill was never compacted and contained blocks and stumps—what turned out to be basements from houses on the property that were demolished in the early 1950s and 1960s.
The Best Bet: Bioretention PondsIn 2016 Metro Nashville implemented mandatory development regulations that require all site designs to utilize green infrastructure to meet stormwater runoff water quality requirements. To keep the project within its $73 Million budget, the most efficient and cost effective design solution for managing the site’s enormous amount of stormwater was bioretention ponds. The campus’ seven bioretention ponds contain a combined treatment volume of approximately 40,000 cubic feet.
Due to the site’s space constraints, many of the ponds had to be placed close to buildings and structures. While we typically avoid such pond placement considering basins’ gravel, soil and other loose media doesn’t provide ample support for structural foundations, we involved the project’s structural engineer to balance the depth of the building footings and distance between the features, making sure everything was structurally sound.