Applying Work and Energy Methods to Predict the Magnitude of Geomorphic Imbalances
Changing the timing and magnitude of flows in a river or altering channel hydraulics can result in geomorphic change impacting the fish habitat, in-stream structures, and near stream infrastructure. The existing Sediment Impact Analysis Model (SIAM) techniques can compare the magnitude of change between different alternatives, but the methods cannot predict an absolute sense of how far a change might progress. In some cases, management plans may create different impacts in a relative sense, but the absolute changes are negligible.
The research into the magnitude of geomorphic imbalances addresses how much geomorphic change a stream might experience due to flow, sediment loads, and channel modifications. The results will assist in determining if the predicted changes will adversely, beneficially, or negligibly impact river infrastructure, endangered species habitat, or other morphology-related criteria.
Need and Benefit
Reclamation constructs and maintains in-stream and near stream structures for delivering water. Channel changes can undercut, break apart, bury, bypass, or otherwise impair functioning of the structures. Endangered species and other biological criteria can restrict water operations. Evaluating the impact of channel changes can improve efforts to increase the biologic utility of water operations. Channel change can also destroy or impair structures designed to liberate water through improved utility of lower flows. Evaluating channel change improves the sustainability of river engineering structures.
Reclamation analysis tools for geomorphic change consist of professional experience, empirical relationships, analytic tools, and numerical modeling. All methods provide tools for understanding and designing river engineering systems, but have limitations. Professional experience can be highly subjective, difficult to defend, limited in range of applicability, and cannot always be incorporated into institutional knowledge. Empirical relationships depend upon understanding how differences and variability of site-specific conditions impact the results. Analytic solutions typically require simplified cases. Modeling efforts can provide more detailed results for site specific conditions and estimate future conditions. Modeling efforts can provide more generalized and repeatable techniques can require high level of expertise and significant efforts to setup, operate, and interpret.
The SIAM provides a quantitative screening tool for simplifying modeling efforts. The results can reduce the number of options considered for more detailed mobile boundary numerical modeling though relative comparisons between management options. Reduced modeling costs allow Reclamation to evaluate more options in more detail for less cost. Analysis can reduce costs, improve reliability, and potentially optimize the use of limited water resources. Improving the ability to use the SIAM model for absolute changes may allows for more thorough screening of alternatives. In some cases, SIAM may identify a large relative difference between alternatives when the real-world change is negligible under both alternatives.
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