| OTIA III Bridge Delivery Program |
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| Web Brief (Apr 07) |
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Bioswales use layers of dirt to clean runoff from bridges.
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The upside of dirt: How ODOT is using soil to improve Oregon's water quality
What’s the tool ODOT uses most often to keep Oregon’s rivers and streams clean? Dirt. Lots and lots of dirt.
In the past, storm water mitigation was more about keeping drivers’ tires on the road during inclement weather and less about keeping waterways clean. Holes called scuppers were strategically placed on bridge decks to prevent water from pooling and causing drivers to hydroplane. However, scuppers do nothing to remove the pollutants gathered by water as it drains off a bridge surface into the water below.
Without treatment, water flowing off a bridge surface contains oils and other contaminants from motor vehicles. These contaminants then pollute Oregon’s waterways, and poison fish and other wildlife.
“We used to treat very little of the runoff, and now we treat all of it,” said William Fletcher, ODOT water resource program coordinator. “In urban areas our goal is to reduce the damage as much as possible, while in the more rural areas we want to make sure the waterways remain clean or become even cleaner.”
On the OTIA III State Bridge Delivery Program, ODOT has found that one of the most effective tools in maintaining and improving the water quality in the lakes, rivers and streams flowing under bridges is bioswales.
Bioswales are layers of dirt, plants and other natural vegetation that trap and even remove silt and pollution from surface runoff water. One of the earliest examples of a successful bioswale in the United States was the installation at the Willamette River Park in Portland, Ore., in 1996. More than 2,300 feet of bioswale was installed to capture pollutant runoff before it entered the Willamette River. Six years later, studies showed that solid pollutant levels in the river had been reduced by 50 percent.
On the bridge program, ODOT is using bioswales on two major projects: between Eugene and Roseburg on Interstate 5—Sutherlin to Roseburg, Bundle 353, and on Clarks Branch to Tunnel Mill Race, Bundle A02. CH2M HILL, the contractor on both bundles, is replacing inefficient scuppers that merely drain water off the bridge surface with specialized inlets on the bridge deck and unique bioswales underneath the bridge. The bioswales being applied on these projects include native grasses and, of course, lots of dirt.
The result of these improvements is runoff that often exceeds stringent Oregon water quality standards, as well as meeting or exceeding ODOT’s standards for public safety.
“Mimicking nature’s own filtration system by filtering runoff through dirt and plants represents one of the strongest innovations in storm water management today,” said Mark Anderson, CH2M HILL task leader for storm water management and hydraulic engineering on these bundles.
ODOT is developing a list of approved options for storm water engineers—known as batch performance standards—to streamline the bridge design process. By identifying the most effective and cost-efficient ways to treat storm water on bridge program projects, the agency is making clean water a priority.
“You’ve got bridges all over the state that are dealing with the same type of concerns,” Fletcher said. “The batch performance standards will give engineers proven alternatives and allow them to select the best method.”
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