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• The design considerations for bendway weirs for stream bank protection are described in a report by <br />Smith and Wittler (1998) for an installation to protect the highway bank along the Blue River near <br />Silverthorn, Colorado . Adaptation of the USACE bendway weir design procedures for design of rock <br />barbs or rock veins for stream bank protection is described by Wittler et al (1997). <br />The rock vein is keyed into the outside bank. The rock vein generally extends into the channel more <br />than 10% but less than 33% of the channel width. The crest of the rock vein slopes from the top of the <br />bank to the base of the channel and is usually angled 40 to 45 degrees upstream into the flow (see <br />Figure 2-1). Although flow is directed away from the bank by the rock vein, secondary currents can <br />cause bank scour or scalloping downstream of the rock vein if the structures are too faz apart. <br />Wittler et al (1997) indicate that proper spacing is more important than keying or providing toe <br />protection. As a general guide, the maximum spacing, 5,,,,,, is determined from the intersection of the <br />bank line with the tangent flow line at the point of the rock vein: <br />• 5,,,,,~ = R[1-(1-L/R)z~os (Eq. 1) <br />Where R is the radius of curvature of the meander bend and <br />Lis the length that the rock vein extends into the channel <br />A spacing closer than the maximum is required to prevent scour or scalloping downstream of the rock <br />vein. A design spacing , S~, is specified in the US Army Corps of Engineers, Bendway Weir Design <br />Guidance (LaGrone , 199.1): <br />S,, = 1.5 L (R/W)oa (L~o3 (Eq. 2) <br />Where W is the channel width <br />2.2 Channel Survey and Hydraulic Analysis <br />A detailed survey of channel sections and channel and water surface profiles was conducted by Epp <br />and Associates on April 16, 1999. Eleven channel cross sections were surveyed starting from just <br />below the Eagle Mines service road bridge and downstream to just below the last meander bend before <br />• <br />AHA Flcnamc' EmpueDevym doc 5 07/30/99 <br />