Abstract: Session A  8:50 am (BACK)

A Decade of Changes – Monitoring Long Term Stability of Stream Restoration

Bradley Mowbray
Ben Blocher
Gannett Fleming Inc.
Baltimore, MD

Long-term post-construction monitoring is necessary for both verifying the overall success of a restoration and determining the effectiveness of individual structures used. A recognized issue with stream restoration is that it is a constantly evolving process and designs that were considered innovative ten years ago may have been abandoned for more aesthetic or cost effective methods. Usually stream restoration projects, especially in small urban streams, do not require post-construction monitoring further than five years. A decade later, two stream restorations adjacent to one another and within the same watershed, which used the most current Rosgen in channel structures as of 2004 and 2006; were re-evaluated with the same methods used at the time of construction and compared to all previous existing data to determine long-term trends in geomorphological stability and functional uplift.

This submission focused on reviewing post-construction monitoring data for these projects spanning a decade focusing on stream channel degradation, long-term in stream structure stability, and functional uplift. The first stream restoration project was constructed in wooded riparian buffer area with a focus on stabilizing the stream in place due to the close proximity of condominium complexes and townhomes. Imbricated boulders and rip-rap were used to armor banks and areas of high shear stress. During five-year post-construction monitoring, movement of rocks was evident in some of the step pool systems and scour was evident behind rock structures. The second project was located directly downstream in a much wider riparian area which allowed for realignment of the channel and regrading of the stream valley. Brush mattresses, live stakes, and structures using wood were more widely used in this project. The original monitoring cross section benchmarks were revisited, evaluated, and photographed to generate a comprehensive evaluation of changes that have occurred within these two projects after a decade. This evaluation provides valuable lessons learned and implications for future designs.