Bottin, Chatham, and Carver, 1976). The tests indicated that special 

 placement of the bottom dolosse produces better toe stability than random 

 placement. The seaward dolosse in the bottom row should be placed with the 

 bottom of the vertical flukes one-half the length of the units (dimension C in 

 Fig. 7-112) back from the design surface of the primary armor layer to produce 

 the design layer thickness. Model tests to determine the bottom elevation of 

 the primary cover layer and the type of armor placement should be made 

 whenever economically feasible. 



(5) Toe Berm for Cover Layer Stability . As illustrated in Figure 

 7-117, structures exposed to breaking waves should have their primary cover 

 layers supported by a quarrystone toe berm. For preliminary design purposes 

 the quarrystone in the toe berm should weigh W/10 , where W is the weight 

 of quarrystone required for the primary cover layer as calculated by equation 

 (7-116) for site conditions. The toe berm stone can be sized in relation to 

 W even if concrete units are used as primary armor. The width of the top of 

 the berm is calculated using equation (7-120), with n = 3 . The minimum 

 height of the berm is calculated using equation (7-121), with n = 2 . 



Model tests can establish whether the stone size or berm dimensions should 

 be varied for the final design. Tests may show an advantage to adding a toe 

 berm to a structure exposed to nonbreaking waves. 



The toe berm may be placed before or after the adjacent cover layer. It 

 must be placed first, as a base, when used with special-placement quarrystone 

 or uniform-placement tribars. When placed after the cover layer, the toe berm 

 must be high enough to provide bracing up to at least half the height of the 

 toe armor units. The dimensions recommended above will exceed this 

 requirement. 



(6) Structure Head and Lee Side Cover Layer . Armoring of the head of 

 a breakwater or jetty should be the same on the lee side slope as on the 

 seaside slope for a distance of about 15 to 45 meters from the structure 

 end. This distance depends on such factors as structure length and crest 

 elevation at the seaward end. 



Design of the lee side cover layer is based on the extent of wave 

 overtopping, waves and surges acting directly on the lee slope, porosity of 

 the structure, and differential hydrostatic head resulting in uplift forces 

 which tend to dislodge the back slope armor units. 



If the crest elevation is established to prevent possible overtopping, the 

 weight of armor units and the bottom elevation of the back slope cover layer 

 should theoretically depend on the lesser wave action on the lee side and the 

 porosity of the structure. When minor overtopping is anticipated, the armor 

 weight calculated for the seaward side primary cover layer should be used on 

 the lee side, at least down to the SWL or -0.5 H for preliminary design; 

 however, model testing may be required to establish an armor weight stable 

 under overtopping wave impact. Primary armor on the lee side should be 

 carried to the bottom for breakwaters with heavy overtopping in shallow water 

 (breaking wave conditions), as shown in Figure 7-117. Equation 7-116 cannot 

 be used with values of K^ listed in Table 7-8 calculate leeside armor 

 weight under overtopping, since the K^ values were established for armor on 



7-238 



