Design Methods and Guidelines for New Technology, Low Cost Bank Stabilization Features Also Used for River Restoration
* What are the engineering and hydraulic performance properties of new methods of bank stabilization in both a fixed bed bend model and a mobile bed flume?
Need and Benefit
New methods of bank stabilization such as bendway weirs, root wads, J-Hooks, engineered log jams, stone toe protection, and deformable bank lines are being used in lieu of traditional riprap revetments for their cost saving and habitat benefits. In addition to bank protection, numerous applications for these structures exist. For instance, bendway weirs and spur dikes are also used for reducing sediment deposits in front of fish screens, intake structures, and bypass structures. These types of structures are also used in river restoration actions because they create variable velocity and depth flow conditions. Rootwads and engineered log jams also create fish cover. Existing design methods rely upon anecdotal information, individual professional experience, or incomplete methods that do not account for the near bank flow processes. Thus, many of these structures have been constructed without knowledge of engineering performance properties and as a result fail to perform their intended purpose and/or require frequent expensive repairs.
Reclamation engineers designing or maintaining in-stream water delivery structures, protecting river side facilities, or performing river restoration with these structures lack design guidelines based upon predictable engineering and hydraulic performance criteria. Reclamation personnel are tasked with implementing these type of structures on many rivers throughout the Western United States, including, but not limited to, rivers found in the Rio Grande Basin, the Columbia and Snake River Basins, the Sacramento River Basin and the Lower Colorado.
To address the lack of reliable methods and standards the Albuquerque Area Office began a physical hydraulic model study in fiscal year (FY) 2001 at Colorado State University (CSU), to measure the engineering and hydraulic performance properties of these structures in both a fixed bed bend model and a mobile bed flume. From FY 2001 to the present, the physical model has been used to measure performance of these structures relative to channel hydraulic properties, structure geometry, and spacing. The laboratory work uniquely represents near bank flow processes for bendway weirs, spur dikes, and native material features. Native material features include rootwads and engineered log jams placed sequentially along the outside bankline of bends. After CSU began model testing, the U.S. Army Corps of Engineers (Corps) Engineering Research and Development Center approached Reclamation about teaming up to combine physical modeling, field investigations, documented experience throughout the U.S., and literature review to develop design guidelines based upon predictable engineering performance criteria. The Corps has an excellent set of design criteria and methods for traditional flood control riprap revetments, yet they recognized that current design methods have the same limitations given above and that design methods and criteria need to be developed for these new methods applicable to smaller, lower cost flood control and restoration projects (Meg Jonas, and David Biedenharn Research Hydraulic Engineers, Corps, Personal Communication, Engineering Research and Development Center, 2005, 2007).
The National Engineering and Design Center of the Natural Resources Conservation Service (NRCS) also recognizes the need and is also conducting field performance surveys. The NRCS also recognizes that current design methods are incomplete and inadequate, leading to failure of these structures and/or high maintenance costs (Jon Fripp, Personal Communication, NRCS, 2006, 2007). The design guidelines will utilize hydraulics from a one -dimensional (1D) model such as HEC-RAS, and be easy to use with low design costs. Additionally, a benefit of this research is that Reclamation engineers and managers will have design guidelines based upon documented and predictable engineering performance to provide bank stabilization and river restoration.
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This information was last updated on April 20, 2014
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