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<br />.,......r,..-u, . <br /> <br />. <br />. <br />'. <br />. <br />. <br />t <br />. <br />, <br />. <br />. <br />. <br />, <br />I <br />I <br /> <br />available and where the bendway weir is longer than 9 m (30 ft), access will need to be <br />made from the bank and equipment may need to be driven out on the weir as it is being <br />constructed. <br /> <br />Supplemental information on the use of bendway weirs on tight bends (small radius of <br />curvature) and complex meanders can be found in LaGrone 1996. <br /> <br />Material Specifications <br /> <br />1. Stone should be angular, and not more than 30 percent of the stone should have a <br />length exceeding 2.5 its thickness. <br /> <br />2. No stone should be longer than 3.5 times its thickness. <br /> <br />3. Stone should be well graded but with only a limited amount of material less than half the <br />median stone size. Since the stone will most often be placed in moving water, the <br />smaller stone will be subject to displacement by the flow during installation. <br /> <br />4. Construction material should be quarry run stone or broken, clean concrete. High quality <br />material is recommended for long-term performance. <br /> <br />5. Material sizing should be based on standard riprap sizing formulas for turbulent flow. <br />Typically the size should be approximately 20% greater than that computed from <br />nonturbulent riprap sizing formulas. The rip rap Oso typically ranges between 300 mm <br />and 910 mm (1 and 3 ft) and should be in the 45 kg to 450 kg (100 to 1,000 Ib) range. <br />The 0'00 rock size should be at least 3 times the calculated Oso size. The minimum rock <br />size should not be less than the 0'00 of the streambed material. <br /> <br />6. Guidelines for the selection, design, and specification of filter materials can be found in <br />Brown and Clyde (HEC-11) (1989) and Holtz et al. (FHWA HI-95-Q38) (1995). <br /> <br />Installation Examples <br /> <br /> <br />Some illustrations of bendway weirs in use are shown in Figures 1.4 -1.7. Figures 1.4 and <br />1.5 show short bendway weirs shortly after installation by COOT on the Blue River near <br />Silverthome, Colorado in February 1997. These weirs were designed with weir lengths of <br />3.5 - 6 meters at e angles of 750 to the bankline tangent. The CDOT engineer indicated that <br />adjustments in the field are equally as important and necessary as original design plans. It <br />can be observed that the bendway weirs are'being constructed at low flow conditions as <br />discussed previously. <br /> <br />Figures 1.6 and 1.7 show bendway weirs installed by WSOOT on the Yakima River, <br />Washington in 1994. Figure 1.6 shows the weirs at low flow conditions and Figure 1.7 <br />shows the submerged weirs at normal to high flow conditions. Surface disturbances as flow <br />passes over the weirs can be observed in Figure 1.7. These weirs were designed at 9 <br />angles of 500 to the bankline tangent to direct flow away from a critical pier at a bridge just <br />downstream of this bend. <br /> <br />~ <br /> <br />1.8 <br />