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Rock size. The relationship of bankfull shear stress to minimum rock size used for all three <br /> structures is shown in Figure 10. The application of this empirical relation is limited to size of <br /> rivers whose bankfull discharge varies from 0.56 ems(20 cfs)to 113.3 ems(4,000 cfs). For <br /> example, appropriate minimum rock sizes for values of bankfull shear stress less than 1.7 kg/m2 <br /> (0.351bs/ft )are associated only with stream channel bankfull depths from 0.26- 1.5m(2-5 ft). <br /> This relation would not be appropriate for applications outside the limits of the data for a river <br /> slope of 0.0003 and a mean depth of 6.1m, even though a similar shear stress results as in the <br /> example presented. <br /> 1.4 <br /> y = 0.1724Ln(x) + 0.6349 <br /> 1.2 • <br /> • • • • <br /> 1 <br /> • • <br /> Li 0.8 • N • <br /> U <br /> c° 0.6 <br /> • <br /> E 0.4 <br /> • Cautionary note: Use of this relation is limited to rivers with a bankfull discharge <br /> 0.2 between 0.5 and 114 ems and corresponding bankfull mean depths between 0.3 <br /> and 1.5 meters. <br /> 0 <br /> 0 5 10 15 20 25 <br /> Bankfull Shear Stress (kg/m2) <br /> Figure 10. Minimum rock size as a function of bankfull shear stress <br /> Materials. The Cross-Vane can be constructed with boulders, logs and a combination of both. A <br /> geotextile fabric is required to prevent scour under the structure when logs are used or when <br /> rocks are used in sand or silt/clay bed channels. The design using logs only and a duckbill <br /> anchor system is shown in Figure 11. Large flat rocks can be substituted for the duckbill anchor <br /> and cable to keep the logs in place. <br /> Hydraulics. The center cell of Cross-Vane and J-Hook Vane structures generally contain 0.80 of <br /> the bankfull discharge. The left and right 1/3 cells of the structure each generally contain 0.3 of <br /> the mean velocity, 0.02 of the shear stress and 0.01 of the stream power of the entire bankfull <br /> channel. A velocity isovel showing the distribution of velocity over a J-Hook Vane on Turkey <br /> Creek, Colorado is shown in Figure 12. The Cross-Vane isovels are similar to those of the J- <br /> Hook Vane, as they distribute the velocity from the near-bank region to the center of the channel. <br /> 15 <br />