factors, as are wind speed and direction with respect to the structure 

 axis. The volume rate of wave overtopping depends on structure height, 

 water depth at the structure toe, structure slope, and whether the slope 

 face is smooth, stepped, or riprapped. Saville and Caldwell (1953) and 

 Saville (1955) investigated overtopping rates and runup heights on small- 

 scale laboratory models of structures. Larger scale model tests have also 

 been conducted for Lake Okeechobee levee sections (Saville, 1958b.) A 

 reanalysis of Saville's data indicates that the overtopping rate per unit 

 length of structure can be expressed by. 



Q-(gQo*H:,t e 



in which 



or equivalently by. 



in which 



0.217 , /h-d 



tanh"' ^ 



a \ R 



h-d, 

 < < 1.0 



Q-(gQ:H;T^ e 



h-d. 



0.1085 /R+h-d, 



R-h+d / , 



< < 1.0 , 



- R 



(7-6) 



(7-7) 



where Q is the overtopping rate (volume/unit time) per unit structure 

 length, g is the gravitational acceleration, H'^ is the equivalent 

 deepwater wave height, h is the height of the structure crest above the 

 bottom, dg is the depth at the structure toe, R is the runup on the 

 structure that would occur if the structure were high enough to prevent 

 overtopping corrected for scale effects (Section 7.21, WAVE RUNUP), and 

 a and Q^ are empirically determined coefficients that depend on inci- 

 dent wave characteristics and structure geometry. Approximate values of 

 a and Q^ as functions of wave steepness H^/gT^ and relative height 

 dg/H^ for various slopes and structure types are given in Figures 7-23 

 through 7-31. The nimbers beside the indicated points are values of a 

 and Q^ (Q^ in parentheses on the figures) that, when used with Equation 

 7-6 or 7-7, predict measured overtopping rates. Equations 7-6 and 7-7 

 are valid only for <_ (h-dg) < R. When (h-dg) >_ R the overtopping 

 rate is taken as zero. 



It is known that onshore winds increase the overtopping rate at a 

 barrier. The increase depends on wind velocity and direction with respect 

 to the axis of the structure and structure slope and height. As a guide, 

 calculated overtopping rates may be multiplied by a wind correction factor 

 given by 



'h-d. 



k' = 1.0 + W 



R 



f 0.1 sinfl. 



(7-8) 



7-39 



