may be necessary to construct several diagrams for 

 different stages of the tide. On the Cahfornia 

 coast, where the range of tide is approximately 

 5 feet, diagrams prepared for an average stage 

 of tide usually will suffice. 



REFRACTION DIAGRAM, MONTEREY BAY, 

 CALIF. 



It is desired to prepare a refraction diagram for 

 Monterey Bay and obtain values of Ka for points 

 along the coast from Monterey to Santa Cruz. 

 The diagram is to be prepared for a mean tide 

 condition of 2 feet above M. L. L. W., direction of 

 advance in deep water from W. N. W., and T=14 

 sees. Thus, L„=5.12 T^=5.12 (14)2=1,000 feet 

 and the depth which is the dividing contour be- 

 tween deep and shallow water is L„/2 = 500 feet. 



U. S. C. and G. S. charts that are available to 

 show bottom topography are No. 5402, scale 

 1:214,000 and No. 5403, scale 1:50,000. 



The contours appearing on these charts are in 

 fathoms. The equivalent values in terms of 

 dILa are as follows: 



40 t„U,om,; f= "»W)+^ -0.242 



For accuracy in preparing the refraction dia- 

 gram, it is necessary to use the chart with the 

 largest scale (chart 5403); however, this chart 

 does not extend to deep water (that is, beyond a 

 depth of 500 feet) ; hence chart No. 5402 must be 

 used, necessitating carrying the waves part way 



on this smaller scale chart and then transferring 

 the front to the larger scale chart (No. 5403) near 

 to the shore line. (Usually it is desirable to 

 draw refraction diagrams on tracing paper placed 

 over the hydrographic chart; however, for illus- 

 trative purposes in this report, the diagrams are 

 drawn directly on the charts.) 



Figure 6 shows a portion of USC and GS Chart 

 5402 with 14 wave crests marked 1, 2, .... 14. 

 Crest 1 lies in deep water and is drawn as a 

 straight line. The southerly portion of crests 

 1-14 remain in deep water (that is, where the 

 contours of o?/L„ have values greater than 0.5), 

 and the distances between them are equal to a 

 constant multiple of Z„. The northerly portions 

 of the crests advance into shallow water with the 

 result that the distances between the crests 

 decrease. The position of each crest is deter- 

 mined from that of the crest behind it by locating 

 a few points on the new crest and drawing a 

 smooth curve through them. These points are 

 shown as small circles in figure 6. The points are 

 located by means of scale B in figure 5 which has 

 been cut out and placed on the refraction diagram 

 as illustrated in figure 6. For example, to locate 

 point c on crest 12: 



1 . Lay the scale on the chart so that the dashed 

 center line and the line of rf/io = 0.302 on the scale 

 intersect with the contour (^/i„ = 0.302 on the 

 chart (point a). 



2. Move the scale so that condition (1) remains 

 satisfied and the lower side of the scale is tangent 

 to crest 1 1 on the diagram at the end of the d/Lo = 

 0.302 line on the scale (point 6). 



3. Mark point c where the d/L„ = 0.302 line on 

 the scale reaches the upper side of the scale. 



4. Thus, other points as d, e, and/ are found by 

 making use of the d/Lo contours of 0.242, 0.182, 

 and 0.122, respectively. The process is repeated 

 until a sufficient number of points are found to 

 determine the position of crest 12. 



In a similar manner to that outlined in items 

 1-4, above, other crests are located until the 

 diagram is carried into a locality which is within 

 the limits of a larger scale chart. On figure 6 it is 

 noted that crest 14 is within the limits of the area 

 shown on chart 5403. This crest is then trans- 

 ferred from chart 5402 by taking offsets from a 

 convenient longitude (122°), correcting for scale 

 ratio, and replotting on chart 5403 (fig. 7). Thus, 

 the offsets in inches at each minute of latitude on 

 chart 5402 are multiplied by the ratio 214,000/- 

 50,000=4.28 and are shown plotted on chart 5403 



