Bioswale “Greens” A Library Branch

Allan Appel PhotoSoon, not only will books return to Westville’s Mitchell Branch Library. Water will return to the earth in greater volumes (pun intended) on the library grounds.

That’s because an 18-by-44, six-foot-deep pool-sized “green” pit for rain and stormwater is nearing completion adjacent to the library’s parking lot on Harrison Street.

The project, one of the city’s largest “bioswales”—dug-up dirt with plantings designed to keep water out of the sanitary lines by directing it back into the earth—is slated to be completed in about three weeks, said Dave Lawlor, a Department of Public Works staffers on the job this week.

The bioswale at the Mitchell branch is one of 16 bioswale projects completed, with 50 more on the drawing board, out of a total of more than 200 ultimately planned as part of a citywide “green infrastructure” drive, said City Engineer Giovanni Zinn who is helming the project.

Click here for a previous story on other recent bioswale installations on West Park Avenue, near the Edgewood School, and elsewhere. The lion’s share of the costs are being funded by a $2.5 million federal community block development grant.

“We’re trying to make New Haven the leader regionally in green infrastructure,” said Zinn.

“Green” infrastructure, contrasted with the “grey” of traditional drains and sewer systems, means simply the creation of areas of layered dirt and gravel, with grass and plantings above, through which water can be filtered and returned to the earth the old-fashioned way from before we had so many buildings, parking lots, paved streets, and impermeable surfaces.

Many bioswales, like this one on Emerson Street, are small, almost like curbside gardens to receive and filter down runoff water from the street. The rebuilding of the Mitchell Branch Library’s parking lot—along with putting on a new roof—afforded the opportunity to make a big splash of a bioswale.

Lawlor said Mitchell’s bioswale, which he estimated to be about 40 by 60 feet, like an Olympic pool, is the largest he’s worked on in his five and a half years with the department.

When he and his crew arrived three weeks ago, they got to work taking out the old decaying concrete of the parking lot, installing serious new granite sections, and two storm drains on the north and south corners of the lot.

A repaving and reslanting of the lot to expedite water flow down to the bioswale remain to be done in the days ahead. The drains are already working, taking water into the bioswale-in-the-making immediately adjacent in Beecher Park.

Lawlor and his crew at first dug a hole six feet deep adjacent to the parking lot. Then they added three feet worth of gravel. Over that large plastic pipes were—and are—being laid to receive the water both from the parking area, but also from the three downspouts that remain to be constructed down from the new roof of the library.

All three downspouts will enter the ground behind the library, beside the bioswale, and drain into it without being seen. “You’ll never know it’s there,” said Lawlor.

The downspouts remain to be finished, along with the repaving and shaping the slant of the driveway.

Beside the bioswale-in-the-making stood sections of granite curbing yet to be installed in the parking lot, along with remaining pipe and a fabric that is to be laid over the pipes.

The fabric (pictured in a roll) is to keep dirt from clogging the pipes receiving the rain water and filtering it back to earth through the gravel layer, Lawlor added.

The project has gone well, he said. That was after some delays when the work crews discovered gas and electrical lines that had to be dealt with.

When it’s complete, the bioswale infiltration system will have another three feet of dirt laid over the fabric or membrane, bringing the level up to the grass level in the park.

The new ground infiltration bioswale will take care of all the stormwater needs of the parking lot and about two thirds of the runoff from the roof, said Zinn.

The other third of the roof runoff will go directly into Beecher Park next to library.

During the construction, Lawlor and his crew have received “I love it!” comments from about two dozen patrons on their way into the library.

“We’re doing all the design in house, developing a lot of expertise, and keeping costs down,” Zinn said.

In general green infrastructure is a lot cheaper than grey.

Zinn said that in sewer separation projects a rule of them is it costs you $15,000 for each new storm drain.

“We keep finding ways to keep costs down [for the bioswales]. Our goal is to get into the $5,000 to $7,000 [range] each,” he said.

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posted by: Brian Tang on October 16, 2015  3:04pm

Last I checked, a “bioswale” is defined as a surface conveyance intended to filter water through vegetation and other media while transporting that water from one location to another down a gentle slope. This installation sounds more like a subsurface infiltration bed, similar to a dry well, but spread over a large area. This sounds like a great project, but it is neither biological nor a surface conveyance and therefore is not a bioswale.

posted by: Brian Tang on October 16, 2015  3:12pm

Just looked up “swale” in the dictionary. Apparently it may refer to a linear surface depression of any kind, so a rain garden or bioretention that takes a linear shape may arguably be a “bioswale” even if it is not intended to convey water down a gentle slope. However, I maintain that a subsurface infiltration bed is not a swale if the surface is level.

posted by: theNEWnewhaven on October 16, 2015  3:32pm

I love it. Great work!

posted by: oldswede on October 17, 2015  11:01pm

But Brian, all swale that end swale.