Restoration in Dynamic Rivers: The Importance of Process-based and Multi-benefit Approaches Throughout Design and Construction
Julie Ash1*, Corey Engen2*
1 Stillwater Sciences, Boulder, Colorado; jash@stillwatersci.com
2 FlyWater, inc., Fort Collins, Colorado; corey@flywater.com
River restoration in Colorado has had a strong focus on resilient solutions in recent years, spurred by new approaches implemented during flood recovery efforts following Colorado’s 2013 Front Range flood event. The resiliency focus has brought increased awareness on what rivers do and what rivers need. Rivers move water, sediment, nutrients, and biota and they need room to do it. While every stream is a dynamic system continually altered by the changing character of its watershed, some systems are more dynamic than others and Colorado has its share of highly dynamic systems, which are characterized by easily eroded bed and bank materials, high sediment transport capacity, and/or large sediment supply. Protecting assets and maintaining desired ecosystem functions is most successful when resilient solutions are implemented because resilient solutions maintain natural riverine processes and “work with the river” to enable better performance long term through flood, fire, and drought cycles, as well as changes in water and sediment delivery, including those associated with hydromodification and climate change. Studies show that static restoration approaches that target one state of equilibrium require costly maintenance and/or replacement over time, especially in highly dynamic stream channels, because they cannot accommodate the large post-construction adjustments that are common in these systems. However, design and construction that accommodates adjustment is a challenge and tools are needed to help designers and contractors more fully understand the process dynamics that drive and shape complex fluvial systems and to help project proponents manage the expectations placed on river restoration investments. Process-based and multi-benefit approaches to design and construction are important in this regard, providing tools to understand geomorphic setting and trajectories, hydraulic and sediment transport implications, and methods to address the uncertainty and risk that is unavoidable in highly dynamic systems, as well as to broaden stakeholder and community understanding of what successful resilient solutions look like. As we continue implementing process-based and multi-benefit approaches, we will further a new vision of what healthy rivers and protected assets looks like.