slope part of the curve represents nonbreaking wave conditions. The 

 maximum value of R/H^ on the curve represents initiation of breaking, 

 followed by constant or decreasing relative runup for increasing wave 

 steepness. The above interpretation is consistent with Granthem (1953), 

 who observed conditions when waves were breaking or nonbreaking. Similar 

 observations were also made by Hunt (1959), Hosoi and Mitsui (1963), 

 Le Mehaute, Koh, and Hwang (1968), Raichlen and Hammack (1974), and the 

 Technical Advisory Committee on Protection against Inundation (1974) . 



(a) Sloping beach, 

 ds 



_R_ 

 Hb 1.0 



Constont 



QT< 



Nonbreaking , Breaking 



0. 

 0.0001 



0.001 



gT< 



0.01 



'_ (b) Flat bottom. 



_R_ 

 Hb 1.0 



Nonbreaking Breaking 



0.0001 



0.001 



gi 2 



0.01 



Figure 12. 



Sample lines of constant d g /gT z for runup on 

 structures on sloping and flat beaches (values 

 of d /gT 2 not necessarily the same). 



Another characteristic of the runup curve for a structure fronted by 

 a sloping beach is shown in Figure 12(a). Waves breaking seaward of the 

 structure toe will have relative runup equal to or less than that for 

 waves breaking at the structure toe. This breaking condition exists for 

 wave steepness values for which the negative slope of the dg/gT 2 curve 

 is equal to or steeper than the slope of a line of constant R/gT 2 

 (Fig. 13). The maximum dimensional runup will occur for the wave steep- 

 ness value where the d s /gT 2 curve becomes tangent to a line of con- 

 stant R/gT 2 . 



5. Maximum Runup . 



Maximum relative runup, R/H^, for a range of wave conditions is 

 readily determined from dimensionless plots. However, maximum dimen- 

 sional runup, R, for the given conditions, is not necessarily coinci- 

 dent with maximum relative runup, R/H^. 



36 



