and DA is equal to H + h . while DG equals H « h - The hjrclrostatic press\ire 

 (tiTd) at the base C of the wall is scaled out froin 8 and plotted as Ed The 

 triangle CDE is the hydrostatic pressxxre distribution against the wall due to 

 water at still x^rater levels As the surface of the clapotis moves above or 

 below still water it will increase or decrease the hydrostatic pressure at 

 the base of tte wall by the amount P. » This change in pressure is 



Cosh -Y~- 



205« Plotting P, in both plus and minus directions from point E gives 

 points B and F as the maximum and minimum pressures, respectively, at the 

 base caused by the clapotis against the sea face of the wall* The solid 

 curved lines labelled maximum wave pressure and minimum wave pressure denote 

 the pressure distributions conputed by theoretically exact formulas «. These 

 curved lines are so close to a straight line that it is permissible, and 

 conservative, to approximate this distribution by use of straight dashed 

 lines connecting A to B and G to F as shown in Figure 7h^ Plgure 75 shows 

 the equation for h reduced to graphical form, indicating values for Lh for 

 different ratios of 2d/L and for wave heights at 5-foot intervals up to°UO 

 feeto Figure 76 shows the equation for P_ reduced to graphical form, indi~ 

 eating values of P_ for different ratios of 2d/L for the ssaiB wave heights^ 



206« Assuming the same still water level on each side of the wall, an 

 outward or seaward pressure exists which is equal to the hydrostatic pressure 

 shown by the triangle CDE in Figure "Jk^ As the two pressures at still water 

 level balance each other, the resultant pressure on the xirall when the crest 

 of the clapotis is against it is toxirard the land and is shoxoi by the area 

 ABED or AD'B'C« V/hen the trough of the clapotis is at the wall the resultant 

 pressure is toward the sea and is represented by the area DEFG or DG'F'C* A 

 diagram of the resultant pressures on a vertical wall is also shotm in Figure 

 7U« Should there be no water on the landxjard side of the wall, then the 

 total resultant pressure would be represented by the triangle ACB when the 

 clapotis crest is at A© If there were wave action on the landward side, 

 then the condition of crest of clapotis on the sea side and trough of the wave 

 on the harbor side would produce maximum pressure from the sea sides The 

 maximum pressxare from the harbor side xrould be produced x-rhen the trough of 

 the clapotis on the sea side and the crest of the clapotis on the land side 

 are at the structure* 



207» For a unit length of x-xall, xd.th h as the mean level of the clapotis 

 above the still water level and P- the common length of the segments EB and 

 EF_ the resultant IL and the moment about the base, 1-L are given respectively, 

 for the maximxim crest level (subscript e) and the mihimura trough leveK^bsc'pti) of 

 the clapotis by the formulas: 



103 



