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I I I I I I I I I I I I I I I I I I I 5.2.4 Bank Stability Measures Artificial bank protection may be used to control meandering, protect against high velocities or shear stresses along the bank, prevent toe scour and removal of sediment deposits that would encourage progressive bank failure due to lateral movement of the channel. A variety of measures are available, from conventional structural options (stone armor to flexible mattresses) to bioengineering and vegetative methods. Understanding the nature and severity of the bank erosion at each location is necessary for evaluation and selection of appropriate protection measures. For the types of soils observed in the lower portion of the river, the angle of repose for the granular sediments would be between 30 to 45 degrees. Simons and Senturk suggest using a side slope of 1.5H: I V for stable channel design with soils made up of clay, silt and sand mixtures. Based on these factors, the maximum side slope recommended is 2H: I V for bank stabilization measures. Recommendations where bioengineering treatments may be used as bank protection are for areas where velocities are not to exceed the range of 6 to 8 ips (Biedenham, et.al., 1997). Because of the high velocities within the reach being considered, more traditional structural measures have been considered. It is anticipated that these measures could be softened by some vegetative enhancement. The concept of spur dikes or jetties to protect the sharp bend area upstream of U.S. 40 was eliminated due to the amount of protection that would be required to offset scour at the nose of these structures under the high velocities. Riprap armor was considered for protection of the channel banks. Design procedures are consistent with those followed by the USACE (EM 1110-2-1601) and presented in Biedenham, et.al., 1997. The concept is shown in Figure 5.3. A sample ofrock from Maybell Enterprises, a local quarry, had been submitted and tested by Ground Engineering Consultants, Inc. to meet specifications in the USACE procedure. The sample met requirements, and the design and quantities have been based on the resulting information. Gradation from the sample is given in Table 5.1. Copies of the rock test results are included with the calculations in Appendix 1. The armor is based on a thickness of3 ft with a side slope of2H:IV. The height of protection was estimated to be an average of 7 to 8 ft (accounting for superelevation in the bend). The riprap armor was to be keyed into the bank at both the upstream and downstream ends of the revetment. Scour calculations were performed for the toe protection requirements. An estimate of 8.5 ft for scour was accounted for in the design. Since placement conditions were somewhat uncertain, a launched toe protection method was included in the estimate. This method assumes that the excess riprap is placed along the bank at the toe, and will provide protection as scour occurs. Copies of all pertinent calculations have been provided in Appendix J. 33