BEsT MANAGEMENT PRACTICEs HANDbooK - Tahoe BMP

8.16 APPENDICES8.16.1 DESIGN CALCULATIONSThe following section contains calculations to be used for design of shorezoneBMP’s and delineation of the backshore boundary. These are intended to assista professional engineer.8.16.1.1 WIND-WAVE GENERATIONThe following points are assumptions and recommendations as to how toprovide guidance and instruction regarding wind-wave generation modeling:• The selection of the design wind speed is critical to projecting adequateprotections based on statistical modeling. The present guidance uses the 80mile an hour - 1-hour duration design storm wind event. The CEM providesalternative design storm standards that may be more accurate andappropriate in achieving the region’s policy objectives.• The mathematical descriptions provided below are simplifications; theyassume the 80 mile an hour – 1-hour wind speed generates a fetch-limitedwave; this is true of all but the longest fetches over the lake. While thedescriptions reflect shoaling, the effects of refraction are not included.• The use of more sophisticated approaches to wind-wave generationmodeling is acceptable and encouraged. Particularly, the use of commercialor publicly available wind-wave generation hindcast programs includingACES, STWAVE, and MIKE-21 or SWAN provided that they are appliedby engineering firms that regularly provide this service. Analysis ofhistorical wind conditions in the area is encouraged.The simplest direct calculation method is as follows (CEM II-2-36 to II-2-38).These equations give the significant deepwater wave height and period to beused for design. Note the calculations below must be performed in SI units.The acceleration due to gravity, g, is 9.81 meters per second in SI units.Determine the maximum fetch X (Refer to Figure 8-q). This is the longeststraight-line distance from the project site to the opposite shoreline, measuredin meters. The procedure is as follows:• The design wind speed U10,mph is an 80 miles per hour wind sustained forone-hour, measured at an elevation 10 meters above the water surface, basedon winds blowing from the quadrant corresponding to the maximum fetch.This corresponds to a design wind speed U10 of 35.76 m/s in SI units.TRPA BMP HandbookCHAPTER 8: Shorezone Protective Structures and BMPs2012 Page 8-99