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diversions. The flatter and smaller vane angle arm will extend farther upstream to intercept <br /> proportionately more water and increase the length of bank protected. <br /> Vane slope. The slope of the vane extending from the bankfull stage bank should vary between <br /> 2-7 percent. Vane slope is defined by the ratio of bank height/vane length. For installation in <br /> meander bends,ratios of J-Hook Vane length/bankfull width is calculated as a function of the <br /> ratio of radius of curvature/bankfull width and departure angle (Table 1). Equations for <br /> predicting ratios of J-Hook Vane spacing/bankfull width on meander bends based on ratio of <br /> radius of curvature/bankfull width and departure angle is shown in Table 2. Vane length is the <br /> distance measured from the bankfull bank to the intercept with the invert elevation of the <br /> streambed at 1/3 of the bankfull channel width for either Cross-Vanes or J-Hook Vanes. For <br /> very large rivers,where it is impractical to extend the vane length to 1/3 of the bankfull width, <br /> vane slope is calculated based on the specified angle of departure and the ratio of bank <br /> height/vane length where the vane arm intercepts the proposed invert of the structure. <br /> Table 1. Equations for predicting ratio of vane length/bankfull width (VI) as a function of ratio <br /> of radius of curvature/width and departure angle, where W=bankfull width. (SI units) <br /> Rc/W Departure Angle (degrees) Equation <br /> 3 20 VL=0.0057 W+0.9462 <br /> 3 30 VL=0.0089 W+0.5933 <br /> 5 20 VL =0.0057 W+ 1.0462 <br /> 5 30 VL=0.0057 W+0.8462 <br /> Table 2. Equations for predicting ratio of vane spacing/width (Vs) as a function of ratio of <br /> radius of curvature/width and departure angle, where W= bankfull width (SI units) <br /> Rc/W Departure angle (degrees) Equation <br /> 3 20 Vs= -0.006 W+2.4781 <br /> 3 30 Vs=-0.0114 W+ 1.9077 <br /> 5 20 Vs=-0.0057 W+2.5538 <br /> 5 30 Vs=-0.0089 W+2.2067 <br /> The spacing of.T-Hook Vanes can be increased by 0.40W if there exists a low bank erosion <br /> hazard rating(BEHI)of less than 30(Rosgen, 1996, 2001). <br /> Bank height. The structure should only extend to the bankfull stage elevation. If the bank is <br /> higher, a bankfull bench is constructed adjacent to the higher bank and the structure is integrated <br /> into the bench. The use of a Cross-Vane is shown in Figure 8 where a bankfull bench is created <br /> adjacent to a terrace bank. <br /> Footers. The minimum footer depth at the invert for cobble and gravel bed streams is associated <br /> with a ratio of 3 times the protrusion height of the invert rock. This is applicable to all three <br /> structures and is shown in Figure 9 for a J-Hook Vane. For sand bed streams,the minimum <br /> depth is doubled due to the deeper scour depths that occur. All rocks for all three structures <br /> require footers. If spaces are left between the invert rocks for Cross-Vane and W Weirs, then the <br /> top of the footer rocks becomes the invert elevation for grade control. If no gaps are left,then <br /> the top of the surface rock becomes the base level of the stream. <br /> 12 <br />