Photo credit: Balmori Associates

Site Description

The stormwater management measures are intended to accomplish the following:

1. Decrease the stormwater volumes and velocities associated with development-induced changes in hydrology;
2. remove suspended solids and associated pollutants entrained in stormwater volumes; and
3. Retain hydrological conditions that closely resemble those of the pre-disturbance condition.

The system consists of a vegetated roof and stormwater retention and reuse.

The vegetated roof is designed to include approximately 57% of the site area (75% of the open roof area). Beneath the vegetation and soil the design includes a water retention layer that reduces the velocity of water flow, giving soil and vegetation an opportunity to utilize the stormwater before it reaches the building stormwater infrastructure. The planting materials include drought-tolerant self-sustaining shrubs, perennials, and bamboo, resistant to wind damage and adaptable to shallow soil depths between 6” and 18”.

The stormwater retention system is designed to retain 10,000 gallons of stormwater in a tank located in the basement. Within this tank is a sediment basin and treatment system. The retained water is reused for irrigation for the vegetated roof and adjacent park. The planted roofs and high-albedo roofing materials minimize the building's contribution to the urban heat island effect.

• Lot size: 16,700 ft2
• Building footprint: 16,700 sq ft (1,550 sq meters)
• Previously developed land

Water Conservation and Use

20 River Terrace has an on-site blackwater system that recycles 100% of the building’s wastewater. Water recaptured by the system is used to supply the cooling tower and the building’s toilets, and 5,000 gallons per day are provided to the adjacent public park. 50% less potable water is needed from the municipal water supply than would be used in a conventional apartment building, and no potable water is used outdoors. Low-flow appliances and fixtures are used, and the public restroom facilities use waterless urinals.

Stormwater runoff is collected in a storage tank in the building’s basement. The system will capture approximately 170,000 gallons of water per year, to be used for irrigation of the rooftop gardens. The system was designed to precisely accommodate the irrigation load for the site, allowing for reduction of the capacity of the retention tank by 60% and utilizing 100% of the stormwater captured on the site.

Rooftop plants were selected for visual interest, drought tolerance, resistance to wind damage, and adaptability to shallow soil depths. They consist of masses of self-sustaining shrubs, perennials, and bamboo. The roof system beneath the plants was designed to retain nearly 70% of rainwater for eventual use by the plants. The process of evapotranspiration contributes to a cooling effect in the garden’s microclimate.

Water Data

Water Use

• Indoor potable water use: 4,440,000 gal/yr (16,800,000 liters/yr)
• Outdoor potable water use: 0 gal/yr (0 liters/yr)
• Total potable water use: 4,440,000 gal/yr (16,800,000 liters/yr)
• Potable water use per occupant: 7,680 gal/person/yr (29,100 liters/person/yr)
• Potable water use per unit area: 12.4 gal/sq ft (507 liters/sq meter)

Green Strategies

• Runoff Reduction
  • Design a green roof system
• Water Conservation Education
  • Educate residents about water conservation
• Low-Water-Use Fixtures
  • Use low-flow toilets
• Managing Stormwater
  • Use subsurface infiltration basins
• Rainwater Collection
  • Collect and store rainwater for landscape irrigation
  • Collect and filter rainwater for use in cooling towers
• Wastewater and Graywater Recycling
  • Design buildings to use treated wastewater for non-potable uses
  • Plumb building to accommodate graywater separation
• Irrigation Systems
  • Retain water on site in pond for irrigation
  • Recycle graywater for landscape irrigation