*L while Equation 1 tends to underestimate inshore PL , and Equation 2 

 provides a logical limiting value on H^ . Based on the success of the 

 hybrid model in predicting known data, the model was applied to the NCE study 

 to estimate H^ at the toe of the structure. Subsequent analysis of pre- 

 dicted and observed maximum runup elevations suggests that the hybrid method 

 makes good estimates of U mo in shallow water. 



14. The wide range of water depths tested in the NCE study had been 

 included partly to investigate the influence of water depth on wave runup. 

 This concern is strongly reflected in the discussion of wave runup in the 

 Shore Protection Manual (1984). From previous studies it was known that runup 

 would be strongly influenced by the surf condition on the structures (Ahrens 

 and McCartney 1975), but it also seemed logical that the maximum runup would 

 be dependent on the shape of the wave-height distribution and nonlinear 

 effects. The last two influences would be very dependent on the water depth 

 at the toe of the structure and the wave periods. To investigate the influ- 

 ence of surf characteristics on runup, the surf parameter for irregular waves 

 £ is defined as 



tan 8 



H \ U2 

 mo 



L 



o 



(3) 



where 



tan 6 = tangent of the angle 6 between the structure slope and 

 the horizontal 



2 



L Q = gTp/2ir = the deep-water wave length 



g = the acceleration of gravity 



When a runup model was formulated using the surf parameter, it was found to 

 contain some systematic errors which could be related to the relative wave 

 height H^/dg . However, when a surf parameter was defined by using the 

 local wave length, a model could be formulated which did not include 

 systematic errors related to the relative wave height. The modified surf 

 parameter 5. is defined 



tan 9 

 " , H J/2 

 mo 



L 



P 



11 



(4) 



