Anastomosed Stream Channel Restoration: Design, Modeling, Implementation and Monitoring
Tanner Lambert
Water and Land Solutions
Morgantown, WV
Robert Stewart, PE
Water and Land Solutions
Johnson City, TN
Authors: Lambert, T., Stewart, R., PE
Anastomosing stream channels provide important geomorphic complexities to floodplains by creating areas of refuge during high flows, localized scour and deposition, and diverse microhabitats for biota (Ward et al., 2002). Anastomosing systems are of high geomorphic value and, because of industrialization, agriculture expansion, and urban development, many of these systems have been converted to single thread meandering channels (Walter & Merritts, 2008). In the Northeast and Mid-Atlantic regions, many of these lowland anastomosed systems have been impacted by mill dams, mining, channel straightening and tile drainage. In recent years, Water and Land Solutions has aimed to restore these systems, where appropriate, with the use of two-dimensional hydraulic modeling to identify areas that are well suited to an anastomosing system. Appropriate site selection is critical to the implementation and success of a restored anastomosed system. Research shows multiple channels are supported in low energy, net aggradation reaches and as a result, restoration project should target these areas (Makaske 2001).
Recent projects in West Virgina and Pennsylvania designed by Water and Land Solutions have used multiple active channels to achieve different project objectives. In West Virgina, an area that experienced robust coal mining, an anastomosed channel was used to increase water and vegetation interaction to facilitate processes that would filter heavy metals.
In other systems, two-dimensional hydraulic modeling is employed to predict localized areas of increased shear stress on the floodplain during storm flows. Rather than stabilize these areas in place, multiple alternate channel paths with vegetated islands are designed to create diversity and uniqueness on the floodplain while reducing mainstem shear stress. In addition, the use of these chute channels promotes the attenuation of storm flows on the floodplain and an increase in groundwater, surface water and vegetation interaction. Through monitoring and post construction hydraulic modeling, the use of anastomosed systems in stream restoration has proven to be an effective strategy for managing local hydraulics and increasing floodplain variability.
References
Ward, J. V., Tockner, K., Arscott, D. B., & Claret, C. (2002). Riverine Landscape diversity. Freshwater biology, 47(4), 517-539.
Bart Makaske,. Anastomosing rivers: a review of their classification, origin and sedimentary products, Earth-Science Reviews, Volume 53, Issues 3–4, 2001, Pages 149-196, ISSN 0012 8252
Walter, R., & Merritts, D. (2008). Natural streams and the legacy of water-powered mills. American Association for the Advancement of Science, 299-304.
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