Stream Functions Pyramid - A Tool for Assessing Success of Stream Restoration Projects
The U.S. Fish and Wildlife Service, Chesapeake Bay Field Office, Coastal Program - Stream Assessment and Restoration team developed the document "A Function-Based Framework for Stream Assessments, Restoration Goals Performance Standards, and Standard Operating Procedures.” The document describes the Stream Functions Pyramid, a five-level hierarchical framework that categorizes stream functions and the parameters that describe those functions. There is also a 3.5 day training course available at National Conservation Training Center or upon request.
Stream functions pyramid overview. Click for a larger view.
Stream restoration practitioners have long been struggling with how to determine the success of restoration projects. Part of the problem lies in failure to link stream restoration with the restoration of stream function. For example, many restoration project goals fail to recognize the full range of stream functions and how they support each other. Federal mitigation guidelines already require stream restoration practitioners to determine the functional improvement of their project.
The difference in the pre-restoration functional condition and the post restoration functional condition is known as functional lift. The functional lift can then be used to develop stream mitigation credits or to quantify the overall benefit of any stream restoration.
Stream funtions parameters. Click on image to enlarge.
The stream functions pyramid provides a framework for assessing stream functions, setting design goals, and evaluating performance. The pyramid shows that restoration of functions must occur in a certain order for maximum functional lift to occur.
Hydrology functions create the base of the pyramid. These functions determine how much water is produced by the watershed and include measures such as the rainfall-runoff relationship and bankfull discharge determination. Hydraulic functions are shown above hydrology functions and describe the flow dynamics in the channel and floodplain where floodplain connectivity and flow dynamics are critical measures. Geomorphic functions are next and integrate the hydrology and hydraulic functions to transport sediment and create diverse bed forms.
Once this structure is in place, physiochemical functions can improve, including increased dissolved oxygen, lower stream temperature, denitrification, and organic processing. At the top of the pyramid are the biological functions because they rely on all of the below functions. These functions include the life cycles of fish and macroinvertebrates, riparian condition, and more.
The stream functions pyramid helps practitioners set goals to ensure that the design addresses the appropriate functions. This may sound obvious, but research has shown that many assessment protocols and project designs ignore the base level functions of hydrology, hydraulics, and geomorphology.
In addition, the pyramid can be used to design monitoring plans that quantify functional lift by assessing the baseline functional capacity of the stream corridor. The design should then focus on improving impaired functions, rather than just focusing on channel form (i.e. improving channel dimension, pattern and profile). Monitoring can then quantify the improvement or lift in each of those functions.
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