DIRECTIONAL CHARACTERISTICS 

 OF WAVES IN SHALLOW WATER 



PART I: INTRODUCTION 



Basic Problem 



1. Ocean waves in the so-called wind wave frequency band (roughly 0.04 

 to 0.3 Hz) are among the dominant forcing mechanisms in all coastal processes, 

 acting on both natural and man-made boundary surfaces. An engineer designing 

 a modification to the natural boundary needs to know the range and magnitude 

 of these forces to ensure that the modification can withstand these forces and 

 yet is economical to construct. Estimation of wave forces requires knowledge 

 of the sea state in the vicinity of the modification. Full description of a 

 sea state requires amplitude, frequency, and direction for each component of 

 the wave field. There are myriad observations of amplitude and frequency 

 from numerous field campaigns but very few detailed observations of wave 

 direction. The latter condition represents a distinct and very important void 

 in knowledge required for comprehensive engineering design. The intent of 

 this report is to provide guidance on the directional characteristics of 

 oceanic wind waves in shallow coastal waters based on a dedicated program of 

 field measurements. 



2 . This report is intended for a readership with somewhat diverse 

 backgrounds. As a result, some of the beginning material is basic and can be 

 skipped (or scanned briefly). In particular, the remainder of Part I 

 discusses importance of directional wave measurements, some past efforts in 

 this regard, and some fundamental differences between low- and high-resolution 

 directional wave gages. Part II is essentially a tutorial on frequency- 

 direction spectra and can be skipped by those familiar with this subject. It 

 also introduces basic notation and some conventional parameters. The reader 

 might wish to scan Part II for these or refer to Appendix B, which lists all 

 notation used in this report. Parameters introduced in Part II are also 

 summarized at the end of Part V. Part III is a description of the measurement 

 scheme, and the remaining parts are discussion and analysis of observations. 

 Starting with Part III, information is germane to the results and so should be 

 consulted. 



