Unseating place-based reference systems for generalizing from natural analogs to improve stream restoration practices

Background/Question/Methods

Destabilized by early anthropogenic activities and ongoing landscape-level change, our streams are novel ecosystems.  The science of stream restoration has been based on decades of studying the processes of open channel flow without temporal context.  As a result, many restoration researchers and practitioners improperly rely upon disturbed and actively adjusting stream systems as templates for developing restoration projects.  Our current stream condition in developed watersheds can be characterized by increased runoff volume, reduced time of concentration, higher peak discharges, channel enlargement/erosion on a trajectory to optimize conveyance, incision of the stream below its floodplain , drained groundwater, reduced perenniality, and poor aquatic habitat.  Measurements from the ‘least worst’ of these streams are used as templates to ‘restore’ the worst of these streams.  Logically, this represents only a fraction of the potential functional uplift possible.  This presentation will focus on the values of using historic geomorphic condition as a natural analog for stream restoration.  An examination of the historic geomorphic stream condition attained through excavation across these same stream valleys gives us a much different understanding of stream resource condition and potential.

Results/Conclusions

The historic system was exceptionally well connected to its floodplain, included a thick peat substrate established and maintained by vigorous wetland growth, was characterized by shallow flows that became wider, not deeper with precipitation, and had a large surface area to water volume.  A comparison indicates we have lost many of the ‘material processing’ capabilities of these historic streams.  Sediment and nutrient loading further compromise water quality and result in the reduction of important aquatic habitat and associated species.  The use of the natural analog, applied with a focus towards enhancing/restoring ecosystem function, demonstrates we can make significant positive contributions to the quality and quantity of our stream resources and improve the quality of life in our local communities.  The presentation will include a presentation of monitoring results from multiple projects which have documented the positive effects on urban hydrology during multiple storm events (i.e., reduced peak discharge, increased time of concentration), water quality improvements (i.e., order of magnitude reductions in total suspended sediment and nitrogen and phosphorus loads), wildlife habitat, metrics of societal quality of life, as well as other metrics of ecosystem services (e.g., reduced temperature, increased groundwater and perenniality of stream flow).