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to arrive at a stable riprap size. chart 2 in Appendix C provides a solution <br />to Equation 8 and Equation 9 using correction factor C. <br />The stability factor, SF, used in equation 6 and Equation 9 requires <br />additional explanation. The stability factor is defined as the ratio of the <br />riprap material's critical shear stress and the average tractive force <br />exerted by the flow field. As long as the stability factor is greater than 1, <br />the critical shear stress of the material is greater than the flow induced <br />tractive stress, the riprap is considered to be stable. As mentioned <br />above, a stability factor of 1.2 was used in the development of <br />The stability factor is used to reflect the level of uncertainty in the <br />hydraulic conditions at a particular site. Equation 6 is based on the <br />assumption of uniform or gradually varying flow. In many instances, this <br />assumption is violated or other uncertainties come to bear. For example, <br />debris and /or ice impacts, or the cumulative effect of high shear stresses <br />and forces from wind and /or boat generated waves. The stability factor is <br />used to increase the design rock size when these conditions must be <br />considered. fable 1 presents guidelines for the selection of an <br />appropriate value for the stability factor. <br />Table 1. Guidelines for the Selection of Stability Factors <br />Uniform flow; Straight or mildly curving reach (curve radius /channel width > 30); Impact 1.0 -1.2 <br />from wave action and floating debris is minimal-, Little or no uncertainty in design <br />parameters. <br />IGradually varying flow; Moderate bend curvature (30 > curve radius /channel width > 10); 1.3 -1.6 <br />mpact from waves or floating debris moderate. <br />Approaching rapidly varying flow; Sharp bend curvature(10 > curve radius /channel width); 1.6 -2.0 <br />Significant impact potential from floating debris and /or ice- Significant wind and /or boat <br />generated waves (.30 -.61 m)); High flow turbulence; Turbulently mixing flow at bridge <br />abutments; Significant uncertainty in design parameters. <br />4.1.1.2 Application <br />Application of the relationship in Equation C. is limited to uniform or <br />gradually varying flow conditions. That is in straight or mildly curving <br />channel reaches of relatively uniform cross section. However, design <br />needs dictate that the relationship also be applicable in nonuniform, <br />rapidly varying flow conditions often exhibited in natural channels with <br />sharp bends and steep slopes, and in the vicinity of bridge piers and <br />abutments. <br />