Stream restoration using sculpted concrete drop structures and soil lifts

Rock Creek in Boulder County, Colorado was historically an ephemeral stream. Upstream urbanization has lead to increased peak flows, and year round flows. The channel of Rock Creek is highly erosive, and channel incision has been observed in recent years in response to increased flows. In 2005, Boulder County Parks and Open Space initiated a stream restoration project on Rock Creek in collaboration with the Denver Urban Drainage and Flood Control District to prevent future channel incision, loss of riparian habitat, and degradation of water quality. Six drop structures constructed from colored concrete sculpted to look like natural rock were installed along a two-mile stretch of stream to raise the channel invert. Deeply incised streambanks were regarded, and bioengineering techniques with soil lifts were utilized to stabilize streambanks and reintroduce native plants. Before restoration, streambanks were infested with reed canarygrass (Phalaris arundinacea). In areas that were re-graded, soil with reed canarygrass was either buried or moved to the uplands. Native sedges were contract grown for streambank reintroduction, including the local Emory’s sedge (Carex emoryi). Native cottonwoods, willows, and shrubs were also planted to enhance riparian habitat. Volunteers and youth groups planted almost 10,000 native plants over two years. Establishment of native wetland plants along the streambanks has been successful while restoration of uplands continues.