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Stormwater Management

Introduction

Consistent with the University Campus Plan, the Sustainability Plan proposes an ambitious program of integrated landscape and stormwater management that reduces demand for purchased water by capturing and using rainwater, and helps to preserve the regional watershed by reducing erosion and minimizing stormwater-related pollution.

Figure 15: Stormwater Management Sites on Campus
Stormwater_map
The campus features a number of stormwater management sites including green roofs for absorbing stormwater and reducing runoff, stormwater recharge/detention systems under athletic fields, and rain gardens for filtering stormwater runoff. Click to enlarge (.pdf).

Goal, Strategy & Progress

Goal: Manage stormwater events with an integrated campuswide ecosystem approach.

Strategy: As part of the University's Campus Plan, implement stormwater management practices, including rain gardens, rainwater harvesting tanks, porous paving, green roofs, and others to promote on-site stormwater retention and improvement of stormwater quality prior to entering streams and the lake.

Progress:

  • The following stormwater management practices were integrated into the Frick Chemistry Laboratory and its surrounding landscape:

    • A former 124-space parking lot and adjacent area along the Washington Road stream corridor was restored to a green space by expanding and enhancing a woodland buffer along the stream, and removing a source of pollution discharging into the stream.
    • Three bioretention basins, or rain gardens, were constructed that treat about half of the stormwater that runs off of the building’s rooftop and the project’s impervious site areas.
    • The remaining rooftop runoff is directed to an underground 12,000-gallon rainwater harvesting tank, which supplements the building’s toilet flushing demand.
    • On an annual basis, the Frick stormwater management project is estimated to reduce the volume of stormwater discharge by 583,270 gallons through the greening of the site, with an additional 582,860 gallons of stormwater estimated to be reused annually for toilet flushing, equating to more than 1.1 million gallons of stormwater retained on-site annually.
       
  • Real-time performance data from the Butler College green roofs are continuing to be monitored by faculty and students (see graph below). Mathematical modeling of total stormwater mitigation of the green roof across various storm type events is under way. In most cases, the green roof is delaying, lowering the rate and reducing the volume of stormwater runoff, compared to the conventional roof.
Figure 16: Stormwater Mitigation
Stormwater runoff

Stormwater Mitigation: These graphs show stormwater drainage from conventional (red line) and green (green line) roofs on the University's Butler College dormitories during a light rain event (360mm) in Graph A, medium rain events (600-650mm) in Graphs B and C, and a heavy rain event (1,900mm) in Graph D. In most cases, the green roof delayed, lowered the rate and reduced the volume of stormwater runoff, compared to the conventional roof. As demonstrated by Graph D, which shows three sequential rain events and varied levels of stormwater retention by the green roof, the success of the green roof in stormwater mitigation is directly related to soil moisture content before the rain event. "We continue to collect data for rain and stormwater runoff as well as soil moisture and thermal parameters, and are currently working on mathematical modeling of total stormwater mitigation of the green roof across various storm type events in collaboration with Nitsch Engineering Associates," said Eileen Zerba, senior lecturer in ecology and evolutionary biology, who provided the data for these graphs. [Click to enlarge]

What's Next

Short Term

  • Develop a monitoring program in partnership with academic programs to test the Frick Chemistry Laboratory bioretention basins for actual performance in filtering and retaining stormwater.
  • Enhance the campus stormwater plan with guidelines for managing stormwater on small and infill sites.
  • Complete the Washington Road stream restoration.
  • Study impact of Washington Road stream restoration on local water quality, and during peak runoff events.
  • Install real-time green roof performance data at the electronic building performance dashboard in Butler College.
  • Assemble and analyze data on Frick Chemistry Laboratory rainwater and condensate collection.

Long Term

  • The Neuroscience and Psychology complex will feature reduction of impervious surface by more than 10 percent, a stormwater reclamation system for nonpotable use, as well as permeable pavement and rain gardens.
  • Consider implementing the following proposed stormwater strategies:
    • Hibben-Magie: reduction in impervious area; use of amended planting soil that will increase porosity of the topsoil and reduce surface runoff; rain gardens and bioswales.
    • Andlinger Laboatory: green roofs; use of amended planting soils that will increase porosity of the topsoil and reduce surface runoff; biofiltration; rainwater harvesting; and permeable paving materials.

Frick rain garden

Rain gardens, such as this one, and biofiltration areas have been positioned to retain and filter building and site stormwater at the Frick Chemistry Laboratory.

 

"Princeton University is demonstrating that it is a leader in the movement to manage stormwater using a green infrastructure approach. By implementing strategies such as green roofs, porous pavements, landscape-integrated management practices, and rainwater harvesting and reuse, Princeton is acknowledging the importance of restoring the natural water balance by constructing buildings and landscapes that celebrate and integrate water.”
—Nicole Holmes, project manager, Nitsch Engineering