A simple graphical method for the determination of the wavelength 

 is introduced. Graphs and tables are presented for direct determination 

 of wavelength and height for a given dimens ionless water depth and 

 current flux. Explicit wavelength expressions are given for deep and 

 shallow water. 



The velocity potential is produced for two-dimensional flow, and 

 this leads to an expression for the depression of the mean water surface 

 below the mean energy level, the so-called setdown. The necessity of 

 using a horizontal datum when calculating the energy flux is shown in 

 this connection. 



It is further demonstrated that the energy flux equation with the 

 mean energy level as a datum is a special case of Garrett's (1967) 

 adiabatic invariant expression (i.e., introducing the new concepts, wave 

 action and flux). 



The findings are generalized to three-dimensional flow in JONSSON 

 (1978a) and JONSSON and WANG (1980). 



Coastal Engineering Significance. Significant to coastal engineering is 

 the convenient calculation of the wavelength in a three-dimensional 

 current wave situation, and in the formula given for solving the 

 conservation equations for two-dimensional flow. A numerical example 

 illustrates this, and a final example demonstrates the importance of 

 taking the effect of a possible current into consideration when calcu- 

 lating wave heights from bottom pressure cells. 



30. KATO, H., and TSURUYA, H., "Experimental Study of Wind Waves 

 Generated on Currents," Proceedings of the 16th Coastal Engineering 

 Conference, American Society of Civil Engineers, Vol. I, 1978, pp. 

 742-755. 



Keywords. Currents, Unidirectional; Currents, Vertical Shear; Currents, 

 Wind-Drift; Experiment; Fetch; Spectra; Waves, Wind; Wind Shear; Wind 

 Velocity Profile. 



Discussion. Experimental results are presented of wind waves generated 

 on currents in a wind-wave tunnel with a water circulating pump system. 



The uniform test section was 1.5 meters wide, 1.3 meters high, and 

 28.5 meters long. Water depth was 0.50 meter. Average windspeeds 

 were nearly 5.6, 8.2, and 11.0 meters per second. The average cross- 

 sectional current velocity ranged from about +30 to -20 centimeters per 

 second. 



The waves were measured with a resistance-type wave gage, and wind 

 velocity profiles by a pitot static tube and a differential pressure 

 transducer. Current velocities were measured with a small propeller- 



37 



