of wave height between two points is 



H l - b 2 



H 2 b! 



where b2 and bj_ are the distances between orthogonals at points 2 and l s 

 respectively.. The right-hand member of this equation is termed a "refrac- 

 tion coefficient",, A convergence of orthogonals indicates a concentration 

 of wave energy (large wave heights), and a divergence of orthogonals 

 indicates a spreading out of energy (low wave heights )„ 



A refraction diagram can be prepared for a selected locality by merely 

 tracing, from a vertical aerial photograph,, the wave crests onto a trans- 

 parent over la y| however , to cover the whole range of wave periods and 

 directions that a compilation of statistical data on wave characteristics 

 indicate as being possible s refraction diagrams are constructed graphically 

 by means of special scales „ The details of this graphical method are 

 described in the publication "Graphical Construction of Wave Refraction 

 Diagrams",, U S Navy Hydrographic Publication No 605 ° 



Once a series of refraction diagrams for various periods and directions 

 have been prepared for a given locality,, orthogonals to the wave crests 

 can be constructed and refraction coefficients then computed by the above 

 equation from measurements taken directly from the dia grams „ Such coeffic- 

 ients afford a convenient method of comparing wave heights at various 

 localities On Figure 5 S for example , refraction coefficients (that is, 

 ratios of wave height at given points to the deep-water wave height) are 

 given for various points along the shore for 10=second period waves from 

 WSW„ Examination of this figure indicates that wave heights near Moss 

 Landing would be approximately half of the deep-water height „ That such 

 a condition exists under actual wave conditions is indicated by Figure 6 

 which shows an aerial photograph of Moss Landing and vicinity., Note the 

 "flat" water at the end of the pier where the Monterey Canyon approaches 

 the shore Small boat operators have long recognized that the sea is 

 relatively calm at the head of a submarine canyon 



Wave refraction analyses are rapidly approaching the status of a 

 standard component of shore line investigations „ The primary value of re- 

 fraction diagrams is in evaluating the relative degrees of exposure of 

 coastal points to wave action; that is, their application permits the 

 determination of the critical direction and wave period from which damage 

 can be expected When used in connection with wave forecasts from 

 synoptic weather charts , refraction diagrams permit the forecaster to 

 predict, for at least a day in advance, the wave conditions that will ex- 

 ist at a given pointo Such forecasts are of great importance to the con- 

 struction engineer engaged in operations along the coasto The decision as 

 to the most desirable location for a permenent installation such as a 

 breakwater or docking facilities must be made by the design engineer using 

 statistical wave data and refraction diagrams „ Usually only a few periods 

 and directions need be drawn even for quantitative use, the remaining 

 conditions being supplied by inspection and interpolation „ After some 

 experience an engineer very often can substitute a mental construction of 



