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<br />. <br /> <br />seems to be a viable and cost-effective alternative for this project. A sample drawing of the spur <br />dike concept is included in Appendix A. <br /> <br />Cable Concrete <br />Cable Concrete, which is manufactured by International Erosion Control Systems, is a form of <br />precast revetment than can be used to stabilize streambanks, hillslopes, lakeshores, spillways, <br />bridge abutments, and other features. Mats of pyramidal concrete blocks are bound together with <br />stainless steel cable and underlaid with durable geotextile fabric. Cable Concrete has been used <br />successfully for a number of diverse applications, and seems to be a viable alternative to riprap. <br />The block mats allow for vegetation to become established on the mitigate streambank, <br />providing for a more attractive appearance in the long run. Installation can be performed in a <br />fairly short time by just about any qualified contractor with the proper equipment. The mats <br />usually are manufactured in 4 foot by 16 foot sections and are delivered to the site by a flatbed <br />truck or boom truck. If Cable Concrete is used for this project, the concrete mats should be well <br />anchored due to the steep slopes and the high stream velocities. It appears that this alternative <br />may be very viable for the project. According to the company's engineer, the appropriate block <br />size for the this project is "CC 45" which means 45 pounds per square foot of mat area. <br /> <br />. <br /> <br />Other Alternatives <br />Other streambank stabilization techniques include vortex weirs, chevrons, kickers, vane dikes, <br />concrete paving, floodwalls, A-Jacks, sheet pilings, hard points, lunker structures, timber spurs, <br />willows, and other natural/bio-engineering methods. All of the techniques mentioned in this <br />document have been successfully implemented for various applications. The construction costs, <br />installation time, short and long-term effectiveness, and project life for each of these techniques <br />can be quite variable. <br /> <br />V. SELECTED AL TERNA TIVES <br />Based on the alternatives analysis, there are three bank stabilization methods that could work <br />well for this project. The three recommended methods are as follows: <br /> <br />· Selected Alternative 1: Traditional Riprap Revetment (3651.f.) <br />· Selected Alternative 2: Spur Dikes (three) <br />· Selected Alternative 3: Cable Concrete (365 I.f.) <br /> <br />. <br /> <br />For each alternative, earthwork and grading of the streambank would be required prior to <br />installation of the stabilization measure. The existing bank, which is now essentially vertical, <br />would need to modified in order to flatten the side slope. Ideally, the proposed side slope for the <br />project should be 2H to I V or flatter, however this is not entirely feasible due to existing width <br />constraints. Therefore, the proposed side slope for the project is 1.5H to IV. The steeper the <br />side slope, the more unstable the bank will be during future flood events. However, there is very <br />little choice in this case due to the placement and location of the existing driveway and garage. <br />Fill material will not be required for the earthwork. Existing bank material can be used as <br />necessary to push the toe of the slope toward the middle of the existing low flow channel. All <br />fill areas for the earthwork should receive 95% compaction using ASTM standards. <br /> <br />7 <br />