south; therefore, ty = tg = 0.5 tz. The conservation of transport equation is 
then used to calculate the average wave heights Hy and Hs. The results of 
these calculations are given in Table 5. 
Table 5. SSMO averages for Holland Harbor. ? 
Month 
ANDMNNMUNNKHUNNUNAAD 
er Oa 6 noe Oitenieiie °° ° 
° ° 
68) 
-0 
.5 
6 
oS) 
ol 
8 
-8 
-0 
-6 
-0 
of 
3 
NILWNWWDNODNDDNPNON BG 
0. Wea oOo Of Gasol 0 Oa GS-6 
OLD DADUNFPWAHEHLODANW 
CMIWVUOUADWWHEUWOFH 
Annual 
+ 
ho 
“I 
° 
tEor Da 885 Ohne 
The computer program described in the Appendix was used to calculate the 
evolution of the shoreline from September 1967 to May 1968. The historical 
1967 and 1968 shorelines, as well as the computed 1968 shoreline, are shown 
in Figure 29. The calculation assumes that Ax = 100 feet with > = 1 which 
gives a value for At which varies from 8 to 20 hours depending on the monthly 
wave characteristics. The principal discrepancy between the predicted and 
actual 1968 shoreline occurs near the breakwater. Although the shapes agree, 
there is an erosion in the calculated shoreline which is probably due to the 
approximations used in the calculation of the diffraction coefficients, and 
incoming wave angles which are functions of x in the shadow region of the 
diffraction zone. The unaltered theory of Penny and Price (1944) was incor- 
porated into the numerical scheme since most breakwaters can be represented 
as line barriers, and hence is almost always useful. However, for the case 
of Holland Harbor a universally valid prediction of the shoreline would re- 
quire the detailed calculation of the diffraction effects due to the geometry 
of the breakwaters. Also, the convenient choice of incoming wave direction 
obscures the fundamental problem of how to properly use the statistical wave 
summaries. 
IV. CONCLUSIONS AND RECOMMENDATIONS 
The basic idea of Pelnard-Considere (1956), i.e., to investigate shoreline 
evolution by concentrating on conservation of mass as a special one-dimensional 
problem, has been generalized to essentially its limits of applicability. These 
physical processes of refraction and diffraction (where applicable) have been 
incorporated, including deterministic variations in lake level, bluff height, 
and beach slope. The inclusion of refraction makes possible the proper use of 
the known physical relationships between wave energy and littoral drift on a 
priori basis without necessarily determining these as results from the past 
recorded shorelines at a given location. Accurate determination of shore be- 
havior in the lee of a breakwater requires inclusion of diffraction in some 
39 
