(1) In most harbors, the depth is relatively constant so the diffraction analyses discussed above are

adequate to define the resulting wave conditions. However, if the depth changes significantly, then wave

amplitudes will change because of shoaling effects. If the harbor bottom contours are not essentially parallel

to the diffracting wave crests, then wave amplitudes and crest orientations will be affected by refraction.

(2) Where depth changes in a harbor are sufficient for combined refraction and diffraction effects to be

significant, the resulting wave height and direction changes can be investigated by either a numerical or a

physical model study. For examples of numerical model studies of combined refraction-diffraction in the lee

of a structure, see Liu and Lozano (1979), Lozano and Liu (1980), and Liu (1982). Physical models that

investigate the combined effects of refraction and diffraction are routinely conducted (see Hudson et al.

1979). The one major limitation on these models for wind wave conditions is that the model cannot have a

distorted scale (i.e., horizontal and vertical scale ratios must be the same). Sometimes, lateral space

limitations or the need to maintain an adequate model depth to avoid viscous and surface tension scale effects

make a distorted scale model desirable. But such a model cannot effectively investigate combined refraction-

diffraction problems.

(3) In many cases, the depth near the entrance to a harbor is relatively constant with the significant

depth changes occurring further from the entrance (in the vicinity of the shoreline). Then an approximate (but

often adequate) analysis can be carried out using the techniques discussed herein. The diffraction analysis

would be carried out from near the harbor entrance to the point inside the harbor where significant

II-7-12

Harbor Hydrodynamics

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