Stream Mitigation Performance Standards Should be Based on the Restoration of Ecological Processes, not on Principles of Engineering Success
Bob Siegfried
RES
Richmond, VA
The performance standards and monitoring protocols for most stream mitigation programs are focused on maintaining the original design or as-built conditions (i.e., static stability). This is the traditional measure of success for most engineering projects. An as-built survey is compared to the design to determine the success of the construction of the project. Future monitoring is often compared to the as-built to identify deviations which are routinely considered negatively. This type of performance standard assumes that the original design or as-built provides the optimal solution to the restoration of the degraded stream. This answers the question – was the permitted design constructed and is it remaining static over time and space?
The science of stream restoration is not sufficiently advanced to know the optimal solution to a degraded stream. At best, the stream design corrects the most damaged features of the degraded stream (i.e., provides floodplain connection) and sets the stage for ecological processes to further improve the ecological uplift of the project. By relying on engineering success standards (i.e., minimizing change from design or as-built condition), the mitigation project is not allowed to achieve its full ecological uplift.
Performance standards have a significant influence on the design of a stream mitigation project. Performance standards that require minimal deviation from the original design will lead project engineers to harden projects against dynamic alluvial processes, leading to lower ecological uplift and reduced climate change resilience.
Design and construction of a stream typically creates a rather uniform channel based on typical sections. Yet, bed form and pool diversity are a desirable goal in a stream restoration project. Nearly all stream habitat assessments include measures of pool and riffle diversity. MBI performance standards should reward, not penalize the development of bedform diversity by using habitat assessments instead of profiles and cross-sections measurements.
Performance monitoring should compare the post-restoration conditions to the degraded, pre-restoration conditions to document the actual ecological uplift. The support of ecological success over engineering success will promote the acceptance of dynamic fluvial conditions which will adjust over time and space leading to maximum ecological outcomes.
About Bob Siegfried
Mr. Siegfried has over 35 years of environmental consulting experience with the last 25 years focused on wetland and stream restoration. In the 1990s, he took his first Rosgen courses at Dave’s Ski lodge in Pagosa Springs and since has enjoyed training from many experts. At RES, he leads the Innovation Leadership Program, and supports projects of national importance, including the USA’s largest Permittee Responsible Mitigation in northeast Texas, the Klamath Dam removal project, and the restoration of a large sandbed river in Florida. In addition to designing and managing restoration projects, he has co-authored state guidance and taught graduate level courses in stream restoration. Recently he has focused on modernizing how mitigation performance success is measured, including contributions to recent EPA guidance and workshops.