The Sims Bayou Federal Flood Damage Reduction Project, with one of its detention basins shown here, started in 1990 and is scheduled for completion in 2009. Total project cost is estimated at $345 million; the federal government will pay $220 million and the Harris County Flood Control District will cover the remainder. Photo: Harris County Flood Control District.
Chapel Hill, N.C., is in its final stages of building a large public works operations facility, which includes geothermal systems; rainwater collection systems; active and passive solar, bioretention, and pervious asphalt; with the latter two shown here. Photo: Town of Chapel Hill
The O&M Issue
Routine maintenance on bioretention cells can be relatively simple. “Our department of public works is responsible for planting, mowing, and removing invasive species,” says Levin. Her team is trying to establish a community agreement in which residents water and weed the sites after the city has put the cell in place.
But the cost and general nature of operations and maintenance of bioretention sites is relatively unknown. Chapel Hill, N.C., is about to open a new public works and transportation facility sited on 90 acres, and there are five bioretention areas onsite.
The town of Chapel Hill has brand new stormwater regulations that require the volume, rate, and quality of stormwater runoff to be controlled. Flooding in low-lying areas of Chapel Hill has historically been a problem, so bioretention cells have been put into place on this new project to help control runoff that might otherwise cause offsite problems. The city also wants to set a good example for private citizens and local businesses by using low-impact development on its own building sites, so it added environmentally friendly options into the overall engineering budget.
The facility also boasts porous asphalt in its parking spots and turf stone in which turf is grown between pervious pavements. These turf stone roads are not major access roads; they're used mostly for fire access. Though the entire site could have achieved Leadership in Energy and Environmental Design certification, they chose not to pursue it.
The bioretention sites are excavated areas filled with sandy loam, with native plants on top to take in some of the stormwater. The trench below has plastic pipes that remove the water not absorbed and filtered by the plants. “We don't know what the future maintenance will hold,” says Curtis Brooks, landscape architect with the city's public works department.
In general, bioretention is new, so its long-term requirements and costs haven't been determined. Brooks estimates that in 10 to 20 years he'll have to replace the plants and loam as they become less permeable due to silt buildup. Data are not available to support his estimates, however, and long-term issues have yet to be seen in field trials.
Consultant Hadsell emphasizes that proper initial design and construction can lead to proper operations and maintenance. Many cities that he works with request a yearly check-up of retention, detention, or bioretention sites—smart since problems can be caught early and fixed before they become costly (and a public relations nightmare).Easier shopping
A university team will develop a method for you to select the best BMP for the job.
The Water Environment Research Foundation recently awarded an $800,000 contract to Colorado State University's Urban Water Center to develop and study planning tools for municipalities. The tools will determine the best way to protect urban waterways from pollution due to stormwater runoff.
Stormwater management agencies in Denver, Los Angeles, Seattle, and Philadelphia have volunteered to participate in the study, which is intended to provide municipalities with effective tools for improving stormwater drainage. The study will examine whether best management practices (BMP) for stormwater pollutant control are directly linked to improved water quality in streams, says Larry Roesner, PhD, PE, professor in the Department of Civil and Environmental Engineering and director of the Urban Water Center.
His team will develop a computer model, available in 12 to 18 months, to help users compute whole life cost of several BMPs.
“We'll look at stormwater control scenarios, what to apply where, how much pollution is in stormwater,” says Roesner. It will help stormwater managers make more rational decisions on BMPs, and help them calculate how to finance them over their whole life, including construction, maintenance, and eventual salvage, says Roesner.
For more info, visit http://newsinfo.colostate.edu.