Channel Evolution and Sediment Transport in a Restored Sand Bed Stream

Successful restoration projects return functionality to stream corridors through proper design practices. The desired result is a dynamically stable dimension, pattern, and profile that resemble typical regional stream types. The Coastal Plain of the Southeastern United States contains many low gradient, sand bed streams with bottomland hardwood forested floodplains. Detailed analysis of existing and constructed streams is necessary to predict the type of dynamic equilibrium that can be expected in this region. The North Carolina Clean Water Management Trust Fund supported construction and research of a stream restoration project in the Core Creek watershed in the Lower Coastal Plain region of Eastern North Carolina. Researchers investigated sediment transport on the newly constructed channel using sediment budget techniques. The sediment budget used a series of intermittently surveyed, permanent cross sections to monitor channel stability and evolution. The Rosgen Classification system was used to communicate stream evolution patterns. The design stream was a sinuous E5 channel with a width to depth ratio of 11.1, valley slope of 0.1%, and well developed flood plain. Following construction, the average top width of the channel widened while the average depth decreased, resulting in a higher than designed W/D ratio. The instability in the banks was mostly due to geotechnical forces. As vegetation stabilized banks, the cross sections deepened and tended more to an E5 classification. The final average channel width was 4.74 m and average depth 0.4 m, resulting in a width to depth ratio of 11.8. Data illustrate the establishment of beneficial scour pools and stable riffles. Sediment loss was restricted to pools. Recent large discharge events have resulted in deposition and channel narrowing. Results indicated the restored reach was able to self-adjust based on incoming sediment loads to a stable dimension, pattern, and profile with minimal anthropogenic maintenance. Vegetation establishment played a key role in channel stabilization. Future work includes evaluation of bank full flow return interval, establishment of a sediment rating curve, and calculation of the effective discharge.