by Lisa Cutshaw, PLA, ASLA
Stream restoration has become a necessary and timely tool in the effort to combat environmental issues like flooding and erosion, especially as they are accelerated by more frequent storm events associated with climate change. The author, Lisa Cutshaw, is the Principal Landscape Architect for Summit Design and Engineering and collaborates with colleagues to understand and implement emerging best practices to promote a more resilient approach to the built environment.
Is it ever a good idea to pour concrete in a stream bed? What about riprap and other common erosion control measures? To dig into the specifics, we spoke with Paxton Ramsdell of Ecosystem Planning and Restoration (EPR) in Raleigh, NC. Paxton has many years of experience with stream restoration, recently with Environmental Defense Fund and now with EPR.
Engineered solutions have fallen out of favor in recent years among sustainability advocates, but back in the day, it was common to create concrete channels to try to control streams. The idea was this would stop erosion and direct the water where people wanted it to go. The design professions learned the hard way that channelization actually compounded erosion and flooding problems, but riprap, etc., are still commonly used.
What are the biggest pros to using vegetated solutions rather than engineered solutions?
To be clear, a vegetated solution essentially means restoring the stream with a functional flood plain, allowing the plant root systems to stabilize the soil while also allowing the stream to overflow onto the flood plain when the water rises after rainfall. Research has found that in addition to soil stabilization, vegetated solutions have other benefits, such as slowing down runoff, reducing particulates and excess nutrients in the water, moderating stream temperature, and promoting groundwater recharge.
Paxton Ramsdell: “Vegetated stream restoration projects can reduce erosion and flooding problems, and they tend to last longer than engineered solutions. When streams are able to flood naturally onto the flood plain along the length of the stream, the severity of flooding downstream is reduced, and the stream bed itself has less scour to contend with. When they are properly designed and protected from encroachment, vegetated stream restoration projects should last for generations.”
When are engineered solutions the best alternative?
Paxton Ramsdell: “Engineered solutions still offer value in that they can address erosion and other challenges. I’d recommend exploring engineered solutions in situations where there isn’t space to create a stream restoration project with a functional flood plain. For instance, in towns or cities where homes or businesses are located close to the edge of a stream, engineered solutions are often the only viable option to protect infrastructure that cannot be moved.”
How does budget play into it?
Paxton Ramsdell: “Stream restoration can cost more up front, but it is cost effective in the long term. Importantly, there are programs to help fund stream restoration projects; for instance Hendersonville, North Carolina secured a zero-interest loan from North Carolina’s Division of Water Infrastructure to design and build a stream restoration project that had the additional benefit of protecting sewer infrastructure from failure caused by stream bank erosion. With financing tools like those offered by the Division of Water Infrastructure and other funding agencies, many localities are able to pursue stream restoration as a multi-benefit solution.
Engineered solutions benefit from being perceived as having a known cost, but the downside is there are under-accounted, or even unaccounted, costs long term, particularly when it comes to staff time and ongoing maintenance related to repairing riprap or floodwalls. Engineered solutions may seem less expensive on the front end, but that’s not always the case during a project’s lifetime.”
When are most stream restoration projects required?
Paxton Ramsdell: “Stream restoration is most often undertaken when someone builds a road across a stream bed or otherwise undertakes development that impacts a stream. The Clean Water Act regulates impacts to streams and wetlands, and the intent of the Clean Water Act’s mitigation hierarchy—some refer to this as no net loss—is that developers must first avoid impacts to streams and wetlands, then they must minimize impacts to the greatest degree possible, and only once you’ve reached that threshold and need to impact a stream or wetland, a developer is required to mitigate or offset those impacts via stream restoration.
Resources
Stream Quantification Tool: Ecosystem Planning and Restoration and its sister-company Stream Mechanics co-developed this tool to quantify the outcome of stream restoration projects. According to Paxton, “Practitioners can quantify the uplift, or improvement, possible from a stream restoration project using this tool. This data can be used to inform credit generation for mitigation purposes, or to justify funding requests. Further, the SQT can help a practitioner better understand whether a proposed stream restoration project would result in sufficient improvement or if another site would be better suited to restoration.” The stream corridor geometry and the stream bed/bank composition can also inform which type of solution would work best, with some projects utilizing both approaches in different reaches of the same corridor.
Iowa Flood Center: This is an example of a very effective research program that monitors streams and rivers and partners with upstream farmers to mitigate flooding and its impacts using nature-based practices such as cover crops and vegetated waterways.
Charlotte Stormwater Services: Charlotte, North Carolina is a great example of a major metropolitan area using stream restoration and vegetated solutions to improve water quality and reduce flood risk.
Lisa Cutshaw, PLA, ASLA, is Principal Landscape Architect for Summit Design and Engineering. She also serves as an officer for ASLA’s Sustainable Design and Development Professional Practice Network (PPN).