08-05-13 | Newsadding="15" cellspacing="0" align="center">
Deaderick Green:
Creating Tennessee's First Green Street

By Kim Hartley Hawkins, Hawkins Partners, Inc., Nashville

The Deaderick Street sidewalks, here looking west toward Legislative Plaza, have a continuous flow of street trees: Pistacia chinensis, 'Highbeam' overcup oak and 'Princeton' American elm. Eleven-ft. tall pedestrian LED columns (Forms+Surfaces) are used to highlight special events throughout the year by changing the color of the shields. At right by the bike racks is a solar-powered computerized parking-space station. A parker just enters the space number (indicated at the center of each curb space) and pays, with no need to display the receipt in one's vehicle.

Bioswales of liriope, sedge, juncus (rushes), iris and itea bulb out on both sides of the intersection. A modified curb grate and concrete pavers dissipate the velocity of stormwater as it enters the planter, easing erosion of mulch and soil.

Deaderick Street has been a part of Nashville's history since its pioneer days.

The three-block street in the middle of downtown provides a strong civic axis between Nashville's Legislative Plaza and the city's public square. In the 1970s, Deaderick Street was reconfigured from a two-lane 65-ft. right-of-way with 3-4 story buildings, to a 112-ft. right-of-way with 4 lanes and 11-26 story buildings.

Until October 2009, Deaderick Street served as an outdoor transit mall. When the transit mall moved, Nashville Metro Public Works took that opportunity to reimagine Deaderick Street. This transformation marked a first project of Mayor Karl Dean, who had committed himself and the city to becoming a leader in sustainable initiatives.

The infrastructure improvements included many sustainable elements: a 700 percent increase in permeable surfaces through the use of LID (low impact development); use of recycled materials (fly ash, steel, crushed concrete aggregate) throughout; incorporating LEDs; solar parking meters; water-efficient irrigation; and over 50 percent native planting. The implementation also included environmental education by developing posters on public kiosks, demonstrating the sustainability benefits of rain gardens and urban trees for the project.

The proposed plan incorporated three primary LID design elements that helped to achieve the sustainability goals: continuous street trees and landscaped bioswales on both sides of the street; bioswale bulb outs at intersections; and pervious concrete pavement over structural soils. These elements combine to divert 1.2 million gallons of stormwater from the combined sewer system. When evaluating the engineering aspects, Metro Public Works was quite interested in exploring the potential of LID to provide a balanced solution. Eight way-finding kiosks were designed to include environmental graphic panels to educate the community about the $3.1 million dollar improvements.

The street trees are planted within either rain gardens or large tree grates with adjacent structural soils providing ample root zones, averaging 125 sq. ft. per tree.

This sidewalk planter includes liriope, boxwoods, hostas, oakleaf hydrangeas, hellebores, Coral Bells, overcup oaks.

The bioswales, medians, sidewalk planters and pervious concrete pavement over structural soils on Deaderick Street combine to divert 1.2 million gallons of stormwater from going into the Cumberland River.

Planted in the rain gardens or large tree grates are small stretches of street trees in double rows to create a pedestrian canopy. Structural soils capped with pervious concrete provide ample root zones, averaging 125 sq. ft. per tree. The sidewalks have a two percent cross-slope to drain stormwater into the planters.

Sidewalk zones with a two percent cross-slope drain into linear rain gardens. Extensive 8-ft. wide root trenches for the trees are provided through a combination of the engineered soils in the rain gardens. Structural soils are capped with pervious concrete, allowing for trees and plantings to have long term viability, while also accommodating pedestrian traffic. The engineered soil goes to a depth of 4 feet in the bioswales. Infiltration rates far exceeded the required 1/2-inch per hour rate, negating the necessity for under drains for the bioswales.

Pedestrian bulb outs at the intersections provide numerous functions: safer crossings for pedestrians; space for future retail kiosks; and infiltration bioswales. Within the bioswale bulb outs, existing storm drains were retrofitted with an overflow for major storm events. The north end of Deaderick Street had an existing slope of 7-8 percent. The velocity of stormwater flow presented a challenge. The dissipation for the water flow was accommodated by using a modified curb grate and concrete pavers insets at each curb cut.

The incorporation of sustainability measures at every level truly makes Deaderick Street one of the Southeast's first green streets. Deaderick quickly has become a model for other new planned streets within the city.

Project Team
Metro Nashville Public Works
Project Managers - Jim Snyder/Rick Kirkpatrick
Design Team
Hawkins Partners, Inc. - Landscape Architects
Civic Engineering - Civil Engineer
General Contractor
Roy Goodwin Contractors
Product/Manufacturer Information
Signage Kiosk
? Custom Kiosk, Forms + Surfaces
Pedestrian Lighting
? Light Column, Forms+Surfaces
Street Lighting
? Luminaire: Holophane Tear Drop
? Pole: Valmont
Median/Stormwater Baffle
? Hanover Appian Prest Brick, Tumbled Finish

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