River-Spanning Rock Structures Research and Design Guidelines
River-spanning rock structures are being used to enable fish passage at barriers and provide or improve the aquatic habitat for endangered fish species and water delivery. Current design methods are based upon anecdotal information applicable to a narrow range of channel conditions. As a result, scientifically supportable guidelines and methods for hydrologists and engineers are not available to estimate pool and scour-hole development, structure rock size, and scour countermeasures in order to design stable, cost effective, and sustainable river-spanning rock structures with predictable design lives (stability), consistent performance, and minimal maintenance requirements.
Need and Benefit
River-spanning rock structures are being used to enable fish passage at barriers and provide or improve the aquatic habitat for river restoration. Uses of river-spanning rock structures include replacing low head diversion dams, permitting fish passage, creating habitat diversity, and stabilizing stream profiles. In addition to new construction, existing structures require maintenance to preserve function. A scientific and mechanistic based understanding of structure behavior permits supportable planning and management decisions and adaptation to new circumstances.
Current design methods primarily rely on individualized professional experience and anecdotal information with mixed success. Design methods and standards based upon predictable engineering and hydraulic performance criteria do not exist. As a result, many installations lack long-term sustainability and fail to maintain performance of their intended functions throughout the design life. The river spanning rock structures research project seeks to take a multi-faceted approach towards developing a deeper understanding of river spanning rock structures by combining field work, physical modeling, and numerical computer simulations to develop engineering and hydraulic performance properties for these types of structures. A great deal of research has already been accomplished over the past 2 years and partial funding is available to continue this research in fiscal years (FY) 2008 and 2009. However, funds are presently lacking to complete the analysis of the three-dimensional (3D) numerical modeling and laboratory data to fully develop the design guidelines over the range of anticipated field conditions. Additionally, there has not been any work on modeling these types of structures using a 2-dimensional (2D) mobile boundary numerical model to predict the development of the scour holes and resulting performance of the structure. Understanding the processes governing success and failure allows designers to construct more robust river structures while minimizing the effort required to meet project constraints. An understanding of scour processes and quantities will provide design guidance for sustainable structures that meet habitat requirements for endangered species, ensure water delivery requirements, require fewer repairs, minimize disruption of service, and reduce maintenance costs.
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