Note: Info about Mud Creek Storm Water Planning
Municipal Sewer & Water June 2007
http://www.mswmag.com/editorial/84/2007/06
Published June 2007
STORM: Finessing the Flow
By Dan Heim (page 26)
A Kansas community surpasses EPA stormwater standards using infrastructure replacement, pollution monitoring, and residential rain gardens to mitigate runoff
The City of Lawrence, Kan., lies between the metropolitan areas of Kansas City and Topeka. While retaining its small-town, Mid-western atmosphere, Lawrence is surging forward into the future of stormwater management.
A modest 1- to 2-percent growth rate allows the luxury of focusing more on infrastructure planning, upgrade, and replacement, and less on the complexities of managing expansion.
The city complies with EPA storm-water requirements, in part thanks to a progressive, integrated program comprised of infrastructure management and upgrades, pollution monitoring, and promotion of residential storm-water management practices, including rain gardens.
Measures like these enable the city to manage runoff from annual precipitation that averages about 40 inches per year and ranges from 27 to 54 inches. The stormwater program helps the city prevent flooding and protect water quality in the Kansas and Wakarusa rivers and several creeks.
Keeping floods in check
According to EPA data, impervious surfaces, as measured by equivalent residential units (ERUs), create nine times the runoff of natural surfaces. Increasing runoff catalyzed the creation of the city’s Stormwater Engineering division in 1996.
“Based on the ERUs at the time, it was decided that we needed stormwater engineering,” says division manager and stormwater engineer Matt Bond. “Previous to that, stormwater respon-sibilities fell to the general Public Works staff.”
Also in 1996, the city developed its Stormwater Master Plan, a major study of problem areas around the city. The plan was conducted in three phases, addressing stormwater runoff problems in order of priority.
One of the highest priorities, the 13th and Oregon project, was completed in 2005. It required removal of a subterranean tunnel system constructed in 1936. The 10-foot by 6-foot reinforced concrete tunnel drained 1,390 acres, operated entirely by gravity flow, and was increasingly overwhelmed by stormwater runoff.
The proliferation of impermeable surfaces, accumulating from development over the 70 years since the tunnel was built, dictated the need for greater conveyance. The solution was to remove the tunnel and “daylight” the flow.
Now, in place of the tunnel, and following its original contours, there is an attractive open channel. “We even put some meanders into it to make it look more natural,” recalls Bond, “And instead of the usual fescue or rye, we planted it with native vegetation that has deeper roots and holds up better in high-speed water.”
The channel has a trapezoidal cross-section, averaging 165 feet across at the top and 25 feet at the base, with an average depth of 6 feet. That represents a 950 percent increase in conveyance before flooding.
Like most jurisdictions, Lawrence tries to design conveyance systems for 10-year events. “Unfortunately,” Bond observes, “we were flooding every two to five years. This new channel has taken a lot of the properties in that area out of the flood plain.”
Both homeowners and insurers benefit. Bond has recently submitted a revised flood plain map to FEMA. The entire project cost $3.9 million, part of which was federally funded, and it took two construction seasons to complete. The average construction season runs from late March to early October. In Kansas, frozen ground precludes most work at other times.
Detention for inspection
While improving stormwater conveyance, the city also needs to accurately monitor pollution. In another major project, completed with help from an EPA grant, the city built a detention basin to monitor pollutant levels in streams that drain to the Haskell University and Baker Wetlands area. Bond wants to add a second monitoring basin north of that in an area of recent residential growth.
The basins do the usual work of improving infiltration, but they serve areas where pollution sources are suspected. With continuous inflow, pollutants concentrate in pooled water and topsoil, allowing better detection and precise measurement.
“We’re going to try and tell those residents, ‘Hey, why not fertilize your lawns with more natural substances, instead of those chemicals you get off the shelf in discount stores,’” Bond says.
Standard detention basins are used throughout the city. For any property half-an-acre or larger, Lawrence mandates a maximum 1.8 cfs per acre outflow, in addition to what enters from adjacent properties. Beyond that, onsite detention basins are required.
Rain gardens to the rescue
Lawrence tries to encourage individual homeowners to do their part in runoff prevention. To that end, the city has learned from Kansas City’s 10,000 Rain Gardens program. Using the Kansas City model, Lawrence initiated its own program.
In a residential rain garden, downspouts from a home are routed into a specially designed containment area that functions as a miniature detention basin. Rain gardens are lined with rock or brick, filled with a highly permeable mix of peat moss and sand, and planted with attractive flowers or small shrubs. They provide a visual accent to the property — and significantly reduce runoff.
Done improperly, rain gardens can create ponding that leads to mosquito problems. The West Nile virus has been detected in surrounding Douglas County, but there have been no reported human infections. Properly designed rain gardens don’t pond, as the peat moss and sand help keep the soil loose and permeable.
“If we could get every house in a neighborhood to take one or two downspouts into a rain garden,” Bond notes, “I think they’d be surprised at how much less runoff they’d get. It’s a water quality issue too, since you’re not flushing oil off your driveway and debris off the street, and eventually into the rivers.”
The city runs continuing workshops, coordinated through local civic groups, for residents who want to learn how to build rain gardens. The city’s web site also provides information, including downloadable plans and specifications.
Unfortunately, there is no easy way to assess the number of rain gardens in use. Some residents have built them on their own, and there is no central registry. Kansas City has such a registry, and residents there are invited to post photos of their rain gardens for others to see and learn from.
Bond has plans for a similar program on the Lawrence web site, and he is also considering utility rebates or other financial incentives. “I’d be thrilled if we could get, say, five percent participation on this program, but right now there’s just no way to know how many have been installed,” he says.
Over the levee
The city’s work also includes inspecting and maintaining existing stormwater infrastructure. The North Lawrence Watershed is bounded by the Kansas River and Mud Creek levees, standard earth dam structures built by the U.S. Army Corps of Engineers. Built in the 1950s in response to significant flooding early in that decade, they have stood the test of time.
“We had them inspected in June of last year, and everything came back just fine,” says Bond. “Flood levels in 1993 exceeded those of 1951, and we’ve had no problems.”
In fact, the only “problem” caused by the levees is the need for lift stations to move stormwater over them into the river. Two lift stations are used, one of which is an old, converted, sanitary lift station. “One of our next capital improvement projects will be to increase the capacity of that station, since it was designed to move only around 28 cfs, and we need something more like 240 cfs,” Bond observes.
“We’re also looking at diverting some of that flow to Mud Creek, since that would result in less required capacity, and a smaller, cheaper pump station.” Diversion to Mud Creek would require another open-channel system, similar to that used on the 13th and Oregon project.
Day-to-day details
Bond’s crew of seven handles routine system maintenance with a small fleet of equipment: a vacuum truck, a trackhoe, a Bobcat skid-steer loader, and several dump trucks. The Storm-water Division shares the fleet with the Streets Division as needed.
“I’ve got a good crew,” says Bond. “They’ve done a lot of other work around this town that saved the tax- payers money. Like this relief channel we did for a development. It probably would have cost the taxpayers $300,000 if we had hired a contractor, and we just did it for basically material and labor.”
The Stormwater Engineering division at present lacks funds for significant capital development, but small jobs keep the crew busy. Installation of new inlets, construction of new diversion channels, and clearing of debris from existing channels and detention basins comprise the bulk of day-to-day tasks.
Much of the stormwater infrastructure in Lawrence is relatively new — 25 percent of it was installed in 1985 or later. The city is not yet on a regular maintenance schedule, where a fixed number of inlets or miles of pipe need to be replaced each year, but Bond is moving in that direction. He recently completed a full infrastructure survey.
Lawrence already meets EPA standards for stormwater discharge quality, and Bond expects no future problems. “We’re already ahead of most communities,” he says. “My predecessor, Chad Voigt, our first stormwater engineer, did a great job acting on the results of our 1996 study. In fact, we get a lot of calls from other NPDES Phase Two communities wanting to know how we did it.
“EPA is finally coming through with some teeth on the 1972 Clean Water Act, and that has prompted many communities to consider creating a stormwater engineering division. It happened here, and for Lawrence, I think it’s worked extremely well.”
