Event Title

Stream Restoration - From Analogy to Prediction

Presenter Information

Peter Wilcock

Location

Eccles Conference Center

Event Website

http://water.usu.edu/

Start Date

3-28-2006 8:20 AM

End Date

3-28-2006 8:40 AM

Description

Current stream restoration practice is based on analogy – a template is sought in a nearby channel, stream type, or hydraulic geometry relation that the designer judges to be suitable. An analogy approach has some use in cases for which the channel disturbance is driven not by essential changes in forcing, but by internal, reversible changes, such as bank trampling by livestock or artificially straightening for flood conveyance. What is the alternative to an analogy approach to stream restoration design? It begins with specification of the materials and configuration of the stream valley and the water and sediment supply, including the variability and uncertainty in these quantities. In the essential next step, the specified conditions are connected via predictive relations sufficient to link cause and effect. The predictive relations must satisfy general physical principles of mass, momentum, and energy conservation and will include empirical relations of demonstrated generality. There is good reason that an analogy approach dominates stream restoration practice: sediment transport estimates of sufficient accuracy are difficult and time consuming. A predictive approach requires that the future supply of sediment is adequately forecast. With current technology, this is possible only for threshold channels, for which a precise estimate of sediment supply is not needed. The primary challenges facing development of a predictive stream restoration science are 1. Forecasting water and sediment supply. Stream channel change is driven by changes in water and sediment supply. Catastrophic failure of restoration projects can usually be attributed to a poor (or missing) estimate of the water and sediment supply. A reliable estimate of sediment supply is the essential threshold between analog and predictive design. 2. Variability and uncertainty. There is enormous uncertainty in virtually every aspect of channel design: historical trends, future forcing, and calculated water and sediment fluxes. Estimates of uncertainty are rarely made and incorporation of uncertainty in channel design is virtually absent. Ignoring uncertainty does not make its consequences disappear. 3. Watershed context. An adequate forecast of future water and sediment supply can only be done in a watershed context. The National Center for Earthsurface Dynamics (NCED), a Science and Technology Center funded by the National Science Foundation, has formed a Stream Restoration Group to organize and focus research relevant to stream restoration, to collaborate with agencies and practitioners in identifying knowledge gaps and developing improved tools for restoration practice, and to disseminate this knowledge to practitioners. Our goal is to move restoration practice to an analytical, process-based approach that will lead to better prediction and hence better design.

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Mar 28th, 8:20 AM Mar 28th, 8:40 AM

Stream Restoration - From Analogy to Prediction

Eccles Conference Center

Current stream restoration practice is based on analogy – a template is sought in a nearby channel, stream type, or hydraulic geometry relation that the designer judges to be suitable. An analogy approach has some use in cases for which the channel disturbance is driven not by essential changes in forcing, but by internal, reversible changes, such as bank trampling by livestock or artificially straightening for flood conveyance. What is the alternative to an analogy approach to stream restoration design? It begins with specification of the materials and configuration of the stream valley and the water and sediment supply, including the variability and uncertainty in these quantities. In the essential next step, the specified conditions are connected via predictive relations sufficient to link cause and effect. The predictive relations must satisfy general physical principles of mass, momentum, and energy conservation and will include empirical relations of demonstrated generality. There is good reason that an analogy approach dominates stream restoration practice: sediment transport estimates of sufficient accuracy are difficult and time consuming. A predictive approach requires that the future supply of sediment is adequately forecast. With current technology, this is possible only for threshold channels, for which a precise estimate of sediment supply is not needed. The primary challenges facing development of a predictive stream restoration science are 1. Forecasting water and sediment supply. Stream channel change is driven by changes in water and sediment supply. Catastrophic failure of restoration projects can usually be attributed to a poor (or missing) estimate of the water and sediment supply. A reliable estimate of sediment supply is the essential threshold between analog and predictive design. 2. Variability and uncertainty. There is enormous uncertainty in virtually every aspect of channel design: historical trends, future forcing, and calculated water and sediment fluxes. Estimates of uncertainty are rarely made and incorporation of uncertainty in channel design is virtually absent. Ignoring uncertainty does not make its consequences disappear. 3. Watershed context. An adequate forecast of future water and sediment supply can only be done in a watershed context. The National Center for Earthsurface Dynamics (NCED), a Science and Technology Center funded by the National Science Foundation, has formed a Stream Restoration Group to organize and focus research relevant to stream restoration, to collaborate with agencies and practitioners in identifying knowledge gaps and developing improved tools for restoration practice, and to disseminate this knowledge to practitioners. Our goal is to move restoration practice to an analytical, process-based approach that will lead to better prediction and hence better design.

https://digitalcommons.usu.edu/runoff/2006/AllAbstracts/36