Few of us think about where the water goes once we flush a toilet or turn off a faucet. Likewise, we give little thought to the fate of stormwater unless we’re in a flood—and it turns out that flooding is the most significant hazard affecting Knox County, Knoxville, and Farragut. A local group, the Beaver Creek Task Force (BCTF), is trying to change that by using community education and demonstration projects to bring about a fundamental shift in the way we think about and manage stormwater.
Between 1993 and 2010 there were 27 flood events in Knox County causing an estimated $26 million in property damage. Urban development increases flood risk, because buildings and paved surfaces prevent rain water from soaking into the ground. In fact, runoff from an urban area can be six times greater than runoff from an equal-size area that still has natural vegetation. Water quality is also affected by pollutants washed off paved surfaces, buildings, and construction sites.
BCTF was created in 1998 to “stop the creep of watershed degradation in Knox County,” according to Roy Arthur, watershed coordinator for Knox County Stormwater Management. By this time, flooding and water pollution were understood to be consequences of land-use activities throughout a watershed, which is the entire land area that drains to a particular water body. Little could be done to reverse the effects of urbanization in the watersheds of the county’s core, but there was still a chance to protect Beaver Creek in the northern part of the county. More than 50 percent of the watershed was still open space, but land use in the watershed was rapidly changing from low-density suburban and agricultural use to higher-density urban development.
BCTF was originally a partnership of the University of Tennessee Water Resources Research Center, Knox County, and TVA. Hallsdale-Powell Utility District joined soon after. The traditional way of dealing with stormwater has been to get water off the land as quickly as possible, but BCTF is promoting a new approach that enhances on-site infiltration and reuse, treating stormwater as a resource rather than a nuisance.
The watershed-based approach used by BCTF emphasizes managing stormwater as close as possible to where the rain falls. Rather than focusing primarily on Beaver Creek itself, BCTF employs many decentralized measures throughout the watershed that each handles a relatively small amount of water. Flooding and water pollution are reduced, and groundwater is replenished to supply wells and sustain stream flows during dry weather.
BCTF was one of the first groups to use EPA’s watershed planning criteria, and they received a grant of almost $1 million for water-quality improvement projects. Many of these projects demonstrate “green infrastructure” that promotes stormwater infiltration or reuse. For example, Halls High School now has a cistern that collects runoff from their greenhouse roof and filters it for reuse to irrigate plants in the greenhouse and raised-bed garden. BCTF and Knox County have also installed at least 25 rain gardens, which are essentially flower beds that are slightly sunken instead of raised. Rain gardens collect and hold the first inch of rainfall from a drainage area so the water can soak into the soil where it is used by plants in the rain garden or may eventually become groundwater. Halls High School’s outdoor classroom and the Powell Station Park include rain gardens installed by BCTF.
Harrell Road Stormwater Park is scheduled to open this June as a passive nature park with demonstrations of stormwater management practices, including a pervious concrete parking lot and pervious pavers to demonstrate new technologies for creating a hard, durable surface that can withstand vehicular traffic while allowing stormwater infiltration through the pavement.
Some of BCTF’s projects have involved direct rehabilitation of damaged portions of Beaver Creek. With the cooperation of 10 Mill Run subdivision homeowners, BCTF stabilized 1,400 feet of stream where flooding had eroded backyards and increased the creek’s width from 8 feet to over 20 feet. BCTF collaborated with UT engineering professor John Schwartz and doctoral student Keil Neff to improve a 300-foot channelized section of Beaver Creek behind the Food City in Halls. Channelizing a stream removes the pool-riffle-run configuration that supports a healthy community of fish and other aquatic life. The stream corridor between the Food City parking lot and a county greenway was too narrow to allow reconstruction of the meanders that would allow pools and riffles to develop, so Schwartz and Neff designed a unique system of alternating wide and narrow segments to function similar to meanders. Early monitoring indicates more fish living in that section of Beaver Creek.
Engaging and educating the local community is a major part of BCTF’s mission. Adopt-a-Watershed is a program that combines classroom training with hands-on service projects, and about one-third of the 15 or so schools that participate each year are in the Beaver Creek watershed. Community workshops hosted by BCTF include construction site education for contractors, making rain barrels for collecting roof runoff for reuse, and installing rain gardens.
BCTF is among the nation’s best models of multi-agency collaboration to improve water quality and reduce flooding. A recent federal grant of about $167,000 will allow BCTF to continue its work in this 86-square-mile watershed that is home to 80,000 people, including drainage improvements in the Cedar Crossing subdivision and cost-sharing projects on agricultural lands in the upper portion of the watershed.
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