209 o W aves Breaking on a Structure » - Ordinarily bulkheads and seawalls 

 are so located that storra wax'^es vxaj break directly on th8m„ Even those 

 structures which are located laiidward of the low water shore line may be ex- 

 posed to the action of breakj.ng waves at times of high waters 



210o There have been tlxree major attempts to correlate the high pressures 

 Imovni to exist with measurable wave parameterso In 193hf DeA<, Molitor pub- 

 lished a su.ggested solution of this problem, using a serni- theoretical approach 

 and making use of the observations of D. Do Gaillard taken on Lajce Superior 

 in I90I!. and spring djmamometer readings taken during a storm at Toronto in 

 191^0 Unfortunately since publication of the papery pressures have been 

 observed far in excess of those predicted by the Molitor equations, and 

 structures have failed wM-ch according to the Molitor equations were ade- 

 quately designed 8 



211» Essentially t'he Molitor wave pressure solution formed an envelope 

 of the dyTLamometer readings taken in 191^* The measurements were taken 

 throughout the storm and the maxima at various elevations recordedo Thus, 

 though his equations purport. to give a pressure curve for a single im- 

 pinging wave, they really give a cux-ve represf^nting the maxiimirn pressiare 

 recorded from many waves „ This would ordinarily lead to conservative 

 results but the range of wave parameter variables was too restr'icted for 

 the results of these measurements to be applied to general wave conditions c 



212o In 1939s R-» Ao Bagnold reported on measurements of shock pressures 

 due to breaking wavqs recorded under model conditionso Pressux-es so recorded - 

 were greatly in excess of any prior predicted oneso Bagnold found that for 

 these "shock pressures", a correlation could be established between the 

 magnitude of the pealc pressure and the thickness of a cushion of air en^ 

 trapped by xraves breaking on a structure o Unfortunately these ejjperiments 

 xrere interrupted and no further relationship has been established between 

 the thickness of the air cushion and various wave parameters o 



213 o The last approach to the determination of wave pressures was made 

 in 19h6 by R, Ro Mnikino Although this m.ethod has some inconsistencies^ it 

 probably represents the closest approach to the actual pressures caused by a 

 breaking waveo With the Miniki.n methods, failures of structures, otherx-d.se 

 unpredictable, may be explained o 



21Ilo Mnikin Method s Forces Due to Breaking W aves» " According to 

 Minildn, the total pressure caused by waves breaking on a structure is due 

 to a combination of dynamic and hydrostatic pressures o The dynaniie pressure 

 is concentrated at still water level, and is equal to 



p = l^iM X ^ (D + d) (25) 



m I^, D 



where H = the height of wave just breaking on the structure (in feet) 



w = the unit weight of the water (in pounds per cubic foot) 



d = the depth of water at the structui-e (in feet) 



D an.d L^ = deeper water depth and wave length re,spectively (in feet) 



107 



