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<br />,~,.,~-- <br /> <br />~. <br />I. <br /> <br />, <br /> <br />~ <br /> <br />! <br /> <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br /> <br />Design Guideline 1 <br /> <br />Bendway WeirslStream Barbs <br /> <br />Introduction <br /> <br />Bendway weirs, also referred to as stream barbs, bank barbs, and reverse sills, are low <br />elevation stone sills used to improve lateral stream stability and flow alignment problems at <br />river bends and highway crossings. Bendway weirs are used for improving inadequate <br />navigation channel width at bends on large navigable rivers. They are used more often for <br />bankline protection on streams and smaller rivers. The stream barb concept was first <br />introduced in the Soil Conservation Service (now the Natural Resource Conservation <br />Service, NRCS) by Donald Reichmuth (1993) who has applied these rock structures in many <br />streams in the western United States. <br /> <br />The U.S. Army Corps of Engineers Waterways Experiment Station (WES) developed a <br />physical model to investigate the bendway weir concept in 1988 (Prokrefke 1995). Since <br />then WES has conducted 11 physical model studies on the use of bendway weirs to improve <br />deep and shallow-draft navigation, align currents through highway bridges, divert sediment, <br />and protect docking facilities. WES has installed bendway weirs to protect eroding <br />banklines on bends of Harland Creek near Tchula, Mississippi. The U.S. Army Corps of <br />Engineers, Omaha District, has used bendway weirs on the Missouri River in eastern <br />Montana. The Missouri River Division (MRD) Mead Hydraulic Laboratory has also <br />conducted significant research and testing of underwater sills. Bendway weirs are a <br />relatively new river training structure and research is providing useful information on their <br />use and effectiveness. <br /> <br />Design Concept <br /> <br /> <br />Bendway weirs are similar in appearance to stone spurs, but have significant functional <br />differences. Spurs are typically visible above the flow line and are designed so that flow is <br />either diverted around the structure, or flow along the bank line is reduced as it passes <br />through the structure. Bendway weirs are normally not visible, especially at stages above <br />low water, and are intended to redirect flow by utilizing weir hydraulics overthe structure. <br />Flow passing over the bendway weir is redirected such that it flows perpendicular to the axis <br />of the weir and is directed towards the channel centerline. Similar to stone spurs, bendway <br />weirs reduce near bank velocities, reduce the concentration of currents on the outer bank, <br />and can produce a belter alignment of flow through the bend and downstream crossing. <br />Experience with bendway weirs has indicated that the structures do not perform well in <br />degrading or sediment deficient reaches. <br /> <br />Bendway weirs have been constructed from stone, tree trunks, and grout filled bags and <br />tubes. Design guidance for bendway weirs has been provided by the U.S. Army Corps of <br />Engineers, Omaha District, WES, and the NRCS. The following geometric design guidelines <br />for stone bendway weirs reflect guidance provided by LaGrone (1996), Saele (1994) and <br />Derrick (1994 and 1996). The formulas provided by laGrone were developed to consolidate <br />many of the "rules of thumb" that currently exist in the field. The formulas are not based on <br />exhaustive research, but appear to match well to current practices. Installation examples <br />were provided by Colorado Department of Transportation (CDOT) and Washington State <br />Department of Transportation (WSDOT). <br /> <br />I <br /> <br />,;,,'\. <br /> <br />1.3 <br />