WASILLA — The Wasilla City Council heard a positive report from Catherine Cheadle of the Sustainable Design Group and Mat-Su Conservation Services on a stormwater drainage rehabilitation project of Cottonwood Creek along Fern Street off of Knik-Goose Bay Road.
Cheadle’s research indicated that the developing Cottonwood Creek watershed along KGB could double the influx of the volume of roadside runoff. Cottonwood Creek has been monitored by the Alaska Department of Environmental Conservation after community water quality concerns. The DEC awarded $45,00 to the Mat-Su Borough to investigate stormwater impacts to Cottonwood Creek, which is Federally funded through the Environmental Protection Agency. The DEC awarded an Alaska Clean Water Action (ACWA) grant and Cheadle has been working over the last two years to update the stormwater remediation plans and provide an improvement to riprap drainage into Cottonwood Creek near Fern Street. Among the concerns for pollution of Cottonwood Creek were bacteria and rising temperatures as well as sediment, which can be harmful to juvenile salmon in the creek.
“This is a hot topic as our community expands is, how do we manage things like runoff, how do we make sure that we can develop responsibly yet also keep quality of life. We want to have fish and development,” said Cheadle. “You can see how this culvert is just shooting a plume of sediment laden water, just everything muddy that happens in breakup on a road system is dropping straight into Cottonwood Creek which is a salmon stream.”
Cheadle detailed the process for excavating and refilling the storm drainage to include compacted soil under larger seat rocks and boulders and plants distributed above the stormwater drainage to assist in filtration of roadside runoff sediments.
“The basic intent is to slow it down, spread it out, and soak it in,” said Cheadle. “I’m a drainage nerd. I get excited about seeing these things correctly excavated and correctly back filled with the right mix of sand and soil.”
Cheadle showed images of the spring breakup runoff and overflow of roadside water into Cottonwood Creek and the previous riprap of large rocks that sat adjacent to the culvert. The project at Fern Street was singled out to be an example of how using plants as a natural filtration system can be accomplished relatively inexpensively.
“We’re going to continue these kinds of demonstrations on how this bioengineering or low impact development techniques can be used,” said Cheadle. “The function of this project is really to serve as a demonstration where we can bring people to educate them.”
Cheadle then showed images of volunteers who spent hours over the last two summers removing native plants that were replanted after excavation and proper backfill to the storm drainage. Cheadle said that willows, irises, ferns and dwarf fireweeds were all replanted along Cottonwood Creek to help filter road sediments and ensure the quality of the creek water.
“We’re doing just a beautiful job of slowing it down. You just don’t see that sediment plume going into Cottonwood Creek anymore. It’s been a really nice success,” said Cheadle. “There’s a lot more behind what the city is doing and what all our partners are doing to keep the creek and the salmon healthy than just a roadside ditch.”