Several practical problems in coastal engineering which involve the 

 action of wind on water and which generate the need for considering the 

 construction of a wind tvinnel for coastal engineering research are 

 discussed in Section II. Hydrodynamic phenomena of geophysical scale 

 responsible for these practical problems are discussed in Section III. 

 The use of laboratory facilities in studying the interaction of wind 

 and waves, brings important new problems not present under prototype 

 conditions. These are reviewed in Section IV. Some earlier laboratory 

 studies are reviewed in Section V; a summary and conclusions are pre- 

 sented in Section VI. 



II. SOME COASTAL ENGINEERING PROBLEMS INVOLVING 

 THE EFFECT OF WIND ON WATER 



Several practical problems and solutions which might be facilitated by 

 the use of a wind-water research facility are discussed in this section. 

 The applicability of existing wind tunnel-wave channel technology is 

 discussed only to the extent necessary to clarify the problem, and is 

 designed to provide motivation for technical discussions later. 



1 . Wave Generation . 



The waves of the real sea are generated by wind. Nearly every wave 

 differs from its immediate predecessors in height, period, and shape. 

 Mechanically generated laboratory waves are usually nearly uniform in 

 height, period, and shape. Wind- generated laboratory waves share some of 

 the irregularities of natural waves. Thus, there is a reason to believe 

 that a better simulation of natural waves would be achieved if the lab- 

 oratory waves were generated by wind. 



The coastal engineer is often faced with the need for wave infor- 

 mation from locations where no wave records exist. The standard method 

 for dealing with this problem is to simulate wave records in the form 

 of significant wave heights and periods from the available meteorological 

 records by using wave hindcasting procedures. Verification of available 

 hindcasting procedures suitable for use in engineering offices shows that 

 they are not fully capable of satisfying coastal engineering needs for wave 

 data and that different procedures lead to conflicting results. Estimates 

 of the wave climate obtained by two hindcasting procedures are compared 

 with each other and with an estimate based on visual observations in 

 Figure 1 (U.S. Army, Corps of Engineers, Coastal Engineering Research 

 Center, 1975, p. 3-43). Locations for prediction points and verification 

 areas are shown in Figure 2. A wave-wind research facility could be use- 

 ful in evaluating some of the proposed theories for wave generation and 

 some of the assumptions employed in developing hindcast procedures. This 

 should help in developing more satisfactory hindcasting procedures. 



2. Wave Modification. 



The profile of mechanically generated waves in the laboratory is gen- 

 erally symmetric with respect to the wave crest. Wind- generated waves in 

 the laboratory and waves in the sea, with high winds, are generally steeper 



10 



