BEsT MANAGEMENT PRACTICEs HANDbooK - Tahoe BMP

• Use Equation 16.10 to calculate the wave run-up above the toe of the slope(CEM VI-5-3, VI-5-6). The surface roughness factor depends on the surfacetype and is given in Table 8-23 (CEM Table VI-5-3)1.50for 0.5 s0 2R u 2% rHtoe (Equation 16.10)3.0for 2 0s 3 4Table 8-23: Surface Roughness Reduction Factor (USACE)Surface Roughness Reduction Factor y r in Equation VI-5-3, Valid for 1 < E op < 3-4Type of Slope SurfaceSmooth, Concrete, Asphalt 1.0Smooth block revetment 1.0Grass (3 cm length) 0.90 – 1.01 layer of rock, diameter D 1 (H s /D = 1.5 – 3.0) 0.55 – 0.62 or more layers of rock, (H s /D = 1.5 – 6.0) 0.50 - 0.55Roughness elements on smooth surface(length parallel to waterline = l, width = b, height = h)Quadratic blocks, l = bh/b b/H area coverages0.88 0.12 – 0.19 1/9 0.70 – 0.750.88 0.12 – 0.24 1/25 0.75 – 0.850.44 0.12 – 0.24 1/25 0.85 – 0.950.88 0.12 – 0.18 1/25 (above SWL) 0.85 – 0.950.18 0.55 – 1.10 ¼ 0.75 – 0.85Ribs1.00 0.12 – 0.19 1/7.5 0.60 – 0.70This calculation gives the 2% wave run-up: that is, the height above the toe ofthe slope (including scour) exceeded by 2 percent of waves during a designstorm. The design crest elevation should provide some additional freeboard,which should normally be a minimum of one armor unit diameter, or one footabove the 2% run-up elevation, whichever is greater.The project proponent may select a lower crest elevation if desired, howeverthey must define how erosion upland of the structure will be managed. Theproject proponent may also select a higher crest elevation if desired, if a higherlevel of protection is desired.However, if the run-up value selected by the project proponent is more than 6feet or twice the run-up height given here, then the project proponent mustprovide justification for the need.yrTRPA BMP HandbookCHAPTER 8: Shorezone Protective Structures and BMPs2012 Page 8-105