BEsT MANAGEMENT PRACTICEs HANDbooK - Tahoe BMP

not always conservative enough and its use can lead to the under sizing ofmaterials. A depth-limited wave is used as the design wave height in Hudson’sequation, the designer should account for any long-term erosion that maychange the depths or slopes of the foreshore.Shorezone revetments are often located where the design setting is depthlimited,i.e., the depths are so shallow immediately offshore of the location ofthe revetment that the storm waves have broken and the largest waves are onflat offshore slopes. The maximum height of a broken wave can be calculatedwith Equation 3.1H b = 0.8d s (Equation 3.1)Where:Hb = maximum breaking wave heightds = design depth at the toe of the structureThe preceding equation does not account for the distance over which wavestravel as they break a depth some distance offshore of the toe (i.e., onewavelength) 27 ; higher design wave heights are appropriate in those cases inwhich offshore slopes are steep.It is important to note that Hudson’s equation has no factor-of-safety. Hudsonestablished the KD values such that there was some small level of damage to thestructure. The damage level was defined as the level where 5 percent of therocks on the revetment structure armor layer face were lost. Thus, it is entirelyappropriate for some conservatism or factor of safety to be added to the designprocess based on sound engineering judgment and regional experience. Thefactor of safety could be included through the selection of a conservative designwave height used (such as in Hudson’s equation) or it could be through anincrease in the specified design median rock weight. 28Applications of Hudson’s equation in situations with a design storm waveheight of H = 5 feet or less have performed well. Revetments with design waveheights much greater than H = 5 feet require more judgment and input from atrained, experienced coastal engineer. Other details about the design ofrubblemound revetments are discussed in the Coastal Engineering Manual. 2927USACE, 1984, USACE Waterways Experiment Station, Vicksburg MI, Shore Protection Manual, 4 thed. 2 Vol.28USACE, 1984, USACE Waterways Experiment Station, Vicksburg MI, Shore Protection Manual, 4 thed. 2 Vol.29USACE, 2008, Coastal Engineering Manual - Parts I-6CHAPTER 8: Shorezone Protective Structures and BMPsTRPA BMP Handbook8.3 Static Revetments 2012Page 8-34