a refraction diagram for the graphical development „ 



In addition to the evaluation of the relative degree of exposure of 

 coastal points to wave action , refraction diagrams also can be used to 

 determine prevailing directions of littoral currents and other factors 

 which are of great importance in the transportation of beach materials. 

 Thus j from a refraction diagram the angle between the wave front at the 

 point of breaking and the shore and the breaker height can be determined „ 

 The strength of the littoral current is a function of this breaker angle, 

 the beach slope , and the breaker height „ The interruption of the normal 

 movement of littoral drift by the installation of coastal structures may 

 and has had serious effects in the vicinity of the works For example, 

 at Santa Monica and Santa Barbara, California, the construction of break- 

 waters so interferred with the wave action ( and consequently the littoral 

 drift) that heavy deposits of sand occurred upcoast from the structures 

 and serious erosion resulted to the beaches on the downcoast side. Both 

 the Santa Monica breakwater and the original breakwater at Santa Barbara 

 were constructed approximately parallel to the shore with the expectation 

 that the sand transported by littoral currents would continue to move un- 

 interrupted down the coast . Wave refraction around the breakwater, how- 

 ever, was such that the littoral current carrying the sand was greatly 

 reduced in strength with the result that serious shoaling occurred to 

 the lee of the structure. Similar difficulty of upcoast deposits and 

 downcoast scour has occurred at Oceanside, Alamitos Bay, and Port 

 Hueneme, California, where jetties more or less perpendicular to the coast- 

 line has been constructed in an attempt to stabilize the harbor entrances . 

 Periodic pumping of the sand from the upcoast deposits to the opposite 

 side of these entrances appears to be the only solution in keeping the 

 harbors open and in supplying sand to the downcoast beaches . 



In addition to the refraction of waves due to bottom effects, 

 refraction can result in some instances from tidal currents » A current 

 which opposes waves entering an inlet may have the effect of increasing 

 the steepness of the waves and cause them to break. Such conditions 

 very often occur on the ebb tide at many harbor entrances and may prove 

 extremely hazardous to shipping operations., A consideration of the wave 

 and current characteristic permits a designer to orient a harbor entrance 

 so that the undesirable effects of wave refraction by currents can be 

 greatly minimized 



Wave Diffraction 



Wave diffraction is considered to be the phenomenon in which water 

 waves are propagated into a sheltered region formed by a breakwater or 

 similar barrier which interrupts a portion of an otherwise regular wave 

 train. A knowledge of diffraction behavior has important application in 

 the design and location of breakwaters in connection with harbor develop- 

 ment. It also appears to have an application to the distribution of wave 

 energy along beaches located in the lee of headlands and offshore islands, 



