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• Also, these results and Manning's Equation were used to estimate a roughness coefficient for each <br />section. The calculated roughness coefficients were relatively consistent among sections with a mean <br />value of Manning's n of 0.041 and a standard deviation of 0.00694. Using the estimated roughness <br />coefficient and the slope of the water surface from April 16, 1999, a bank full flow and corresponding <br />channel velocity were determined for Sections 4 through 8 as shown on the cross sections in Appendix <br />A. Bank full flows in these sections range from 2320 cfs to 5560 cfs as compared to the estimated <br />100-year flood flow of 3930 cfs. Average velocities th these sections at bank full conditions range <br />from 3 to 6.4 feet per second. <br />2.3 Design Evaluations <br />The required spacing for the rock vein design was determined using the guidelines from LaGrone <br />(1993) as adapted for rock barbs by Wittier et al (1997). From the channel survey, the radius of <br />curvature of the meander bend, R, is determined to be 113 feet (see Drawing 1). The channel widths <br />in the meander bend at Sections 6 and 7 are approximately 60 and 40 feet, respectively. A rock vein <br />• length (distance the rock vein extends into the channel), L, of 13 feet was used since this distance was <br />slightly less than 33% of the minimum channel width. !n this design, rock vein lengths shorter than 13 <br />feet have been used upstream and downstream of the meander bends because longer bends at these <br />locations would have the potential to cause significant channel adjustment. <br />Using the specified 13 foot vein length, the maximum spacing between rock veins, 5,,,,<, is determined <br />from Equation 1 as: <br />Sm~< = R(1-(l-L/R)z]o.s <br />= 113[1-(1-13/115)2]05 = 33 feet <br />Using Equation 2, an ideal spacing , S~, of 32 feet is determined fora 40 foot channel width and rock <br />vein length of 13 feet. A 26 foot spacing is estimated fora 50 foot channel with a rock vein length of <br />13 feet. For this design, an average spacing of 30 feet and maximum length, L, of 13 feet is used, <br />although the actual spacing between each rock vein will be established by the field engineer based on <br />observations during construction. <br />• <br />Al IA Filename HmpircDcsip~ doc 9 07/30/-9 <br />