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Attachment #7 <br />Riprap Sizing Calculations (2 pages) <br />Federal Highway Administration Method <br />Riprap was sized using the Federal Highway Administration HEC -11 methodology (Chapter 4: Design <br />Guidelines for Rock Riprap). Copies of the relevant portions of this document are included in this <br />Attachment #7 following these calculations. In general, this method provides a required D50 size for <br />riprap in a straight channel with known side - slopes, flow- depth, and discharge velocity. The equation is <br />metric and is as follows: D50 = 0.00594 (V)'/ d05 K' S where V = channel velocity (meters /sec), d = <br />normal depth (meters), and K is a variable dependent on the riprap side -slope and angle of repose. <br />K = (1 —sin 20 /sin2�)05, where e = riprap side -slope angle from horizontal (@ 3:1) , and = riprap angle of <br />repose (from horizontal, conservatively estimated at 1:1). <br />Therefore: K = 0.7746 (2:1 sides), K = 0.8944 (3:1 sides), K = 0.9900 (10:1 sides) <br />Pond Inlet Channel (Section D -D), 3:1 side slopes <br />V = 4.49 fps = 1.37 mps (meters per sec) (from worksheets in attachment #3) <br />d = 0.43ft = 0.13m (meter) <br />D50 = 0.00594 (V)3 / d0 s K' S <br />D50 = 0.00594 (1.37)3 / (0.13)05(0.8944)1.5 = 0.0501 meter =197 inches <br />Therefore: 6" D50 specified is adequate <br />Pond Inlet Bottom (Section E -E), 10:1 side slopes <br />V = 5.62 fps = 1.71 mps (meters per sec) (from worksheets in attachment #3) <br />d = 0.21 ft = 0.064m (meter) <br />D50 = 0.00594 (V)3 / dos K' s <br />D50 = 0.00594 (1.71)3 / (0.064)0.5(o.9900)15 = 0.1192 meter = 4.69 inches <br />Therefore: 12" D50 specified is adequate <br />