Abstract: Session D  11:30 am (Back to Session D)
Semi-Dynamic Cross Section Design - Creating Stable Fish Passage while Encouraging Riparian Encroachment

Michael Thompson
Biohabitats, Inc.
Baltimore, MD

Biohabitats teamed with the Delaware Department of Natural Resources and Environmental Control (DNREC) to design and oversee the restoration of 3,500 linear feet of Pike Creek in northern Delaware. Pike Creek is one of six stocked trout streams in the state of Delaware and as such it requires additional attention to detail. This reach of stream was successfully designed and constructed utilizing a natural channel design approach. Based upon the success of the first phase of the project, Biohabitats was again contracted to design and oversee construction of a second phase of an additional 3,000 linear feet of the stream on private property. Due to the higher degree of slope within the second phase of design, significant focus was placed on designing a cross section that would maintain fish passage as well as improve the adjacent riparian buffer.

Biohabitats set out to design a stable cross section within an incised channel that would maintain a sufficient depth at base flow to allow trout passage yet would have low enough stresses outside of the baseflow channel that would encourage sediment deposition and channel-ward encroachment of riparian vegetation. The baseflow channel would need to be comprised of large enough material to remain stable but would also have to provide sufficient habitat and resting areas for fish. Out of bank flows would have to be spread over a large cross section in order to reduce out of bank velocities and shears and encourage deposition that would provide suitable and stable media for vegetative establishment. Additionally, the project is located within potential bog turtle habitat. While no bog turtles were found during site investigations, adjacent riparian wetlands were designed to provide potential habitat, including emergent wetland vegetation and microtopography to create hummocky habitat. The restoration was completed in January of 2008 and has shown signs of successful stability and evolution both.