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| Shared Street Concept in Broad Channel |
January 23, 2015
Superstorm Sandy's direct hit in 2012 on Broad Channel in Queens made the coastal community a poster child of the storm's devastation, with nearly every house on the tiny island in Jamaica Bay swamped by several feet of water. But when New York City's Department of Design and Construction started a $28-million roadway reconstruction and bulkhead project there last spring, it was targeting a more chronic and crippling problem—regular flooding of community streets at high tide.
"The water went up 8 feet in the street and halfway up the first floor of the houses in Sandy," says Joseph Branco, president at EIC Associates, the project's Springfield, N.J.-based general contractor. "But this is going to fix the everyday tidal situation. At high tide, half of those streets can get flooded."
The project is elevating three streets that stand below the mean high tide level and flood with up to 2 ft of water when wind, barometric, and tidal conditions all align unfavorably, says Ahmed Bashjawish, DDC deputy director. That occurs all too often on West 11th, 12th, and 13th roads, he notes.
"The federal government is granting people money to raise the foundations of their homes," Bashjawish points out. "The city wants to solve the street flooding problems for the long term."
But the flooding problem has resulted in a complex project that goes beyond just adding a few feet of pavement. It involves an array of tasks that require careful orchestration—including building large bulkheads, outfall structures and erosion barriers; installing underground retaining walls and a new storm sewer; replacing utilities above and below ground; and incorporating a unique "shared street" design. DDC is handling the work on behalf of the city's transportation and environmental protection departments.
The project is set to run through June 2017, with the battery of excavation, pile-driving, utilities placement, outfall construction and road paving taking about a year on each street. DDC and the project team have been studying ways to accelerate the schedule by completing some tasks simultaneously, Bashjawish says.
"We're looking at various methods and means to see if there's a way that we could finish quicker," he says, noting that a second project that will conduct similar improvements on other Broad Channel streets is now in design.
Raising the Road
The current project's end result will be quite different from a standard city street reconstruction, says Joseph Menzer, senior associate at RBA Group, the project's design architect. The crowded, 700-ft-long streets in the waterfront neighborhood already are atypical.
Residents "use their streets in a very suburban sort of way, where kids are out in the streets playing," he says. "These are dead end streets [with] local only traffic … that are almost like an extension of the front yards of the homes."
The flooding problems, parking needs, narrow streets half the width of normal New York City roadways and quaint usage have all fed into a design solution that will have no local precedent. Starting with the core need to raise the road elevation by 2 ft, RBA decided to tap the "shared street" concept from Europe, which blends street and sidewalk into a single, flush surface, Menzer says.
"It's going to be the first installation of such a type of system in New York City," he says. "It's almost like a pilot program."
The idea centers on creating a communal "driveway" for residents and will allow parking on both sides of these roads for the first time. But the design achieves the right road height by shedding standard curbs and sidewalks, which tend to be 6 in. higher than the pavement and would have been misaligned with driveways, stoops and entrances to houses. However, not having a curb line, which typically serves as the catch basin for rainwater that drains off the center of a slightly arched roadway called for another odd facet on the project—inverting the streets to instead dip inward.
"The center of the street becomes a drainage swale, with the water collecting in the middle and flowing into the storm sewer," Menzer says.
The simple-sounding street design is a significant departure, Branco adds. "I've been doing this work in the city for a long time," he says. "This is the first time I've seen anything like this."
Beneath that flush, inverted surface will be busy infrastructure, with the design calling for new water and sanitary sewer mains and the new storm sewer system. At the ends of each street, the plan is for large bulkhead and stormwater outfall structures. The design also calls for detailed modifications to nearly every private property on all three roads in order to smooth their transitions to the raised roadways.
Construction Puzzle
The project team's first major construction task entailed using a barge to erect three cofferdams (pictured above) in the bay at the end of each street, sandbagging between the houses and installing water pumps—all in an effort to keep the site dry for excavation and drilling work, Branco says.
However, with tidal water still seeping through the crawl spaces of houses into the construction zone, the team was studying this winter whether to try additional containment measures or simply limit work to hours when tides are lower.
The team also has removed utility poles and replaced them with temporary structures in order to allow equipment, including a 90-ft pile-drilling rig, to access the site, Bashjawish says.
The next big task on each street will be installing piles at the mouth of the storm sewer to support the outfall structure. The team will also drill piles 50 ft to 65 ft below grade to support the new storm sewer, sanitary sewer and water pipes. It will install up to 300 10-in.-dia minipiles on each street for that task because of the poor soils.
Another challenge involves the use of a lightweight slag material instead of conventional fill in order to prevent the soil from eventually settling, which would drop the street's elevation and potentially reintroduce tidal flooding problems, Branco says. But the lightweight slag has a very loose consistency and even floats in water, so the team is installing permanent retaining walls under the street to keep the unruly material in place for the long haul.
"It is not an easy material to work with," he says.
Capping the effort will be erection of the bulkheads and outfalls at the end of each block. The reinforced concrete outfall structures will encase 38-in.-dia storm drains and feature a 500-lb riprap stone apron at their headwalls.
The structures also will have a hard composite sheet pile structure that stands roughly 40 ft wide and 20 ft deep in the ground at the bay's edge to prevent erosion. "We want to sustain the design life of what we are doing now," Bashjawish says.
Community Coordination
Another signature aspect of the project is an intensive level of community outreach from DDC and its team— "like no other project I've ever worked on," Menzer says.
"We met with every single homeowner one-on-one within the entire project area to understand specifically their concerns and explain to them exactly what we're doing in front of their homes ... and how we could mitigate that effect in our design," he says.
The team also has a liaison with Broad Channel's civic association and community board, who is fielding questions and complaints, Bashjawish says. "She is our eyes and ears in the community," he says. "The solution is going to be different for each homeowner."
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