Perhaps of equal importance to predicting wave behavior is the need 

 to be careful that the effect of currents does not lead to significant 

 errors in interpreting and using wave measurements. As discussed in 

 Section II, 2, the correct dispersion equation for waves on a current 

 should be used in reducing wave data recorded by pressure sensors 

 submerged under significant currents. If that is not possible, an 

 engineer should be satisfied that currents are below some appropriate 

 threshold value (see Table). 



The effects of a vertical variation of mean current velocity are as 

 yet poorly understood. Such vertical variation is rarely measured so 

 it is difficult to give guidance on these effects, but they are briefly 

 mentioned in Section II, 3, and should be considered where field condi- 

 tions warrant. 



Application of wave-current knowledge to practical problems of 

 sediment transport and wave forces is in its infancy. The experimental 

 evidence indicating the accuracy of existing theories is discussed for 

 sediment transport in Section III, 3. Limits on the use of the Morison 

 equation (eq. 28) for wave force calculations are discussed in Section 

 III, 2. 



6. Development of Capability and Understanding . 



Mathematical books such as Phillips (1977), Lighthill (1978), and 

 Whitham (1974) and research papers are not the most effective means of 

 communicating with practicing engineers. Case histories and summaries 

 in technical handbooks are more likely to be effective. The significant 

 new knowledge gained over the last decade must be converted to a format 

 usable in engineering practice by appropriate applied research. 



Perhaps the easiest applied research to accomplish is the 

 computation of refraction across idealized models of selected realistic 

 current fields. For example, flow around a headland, with and without a 

 separation eddy behind it, should show the tide race effect and whether 

 there is any correspondingly sheltered shoreline. As another example, 

 the flood and ebb flows through a tidal inlet are quite different, and 

 the interaction of these different flows with incoming waves should be 

 examined . 



Field research to verify whether refraction theory does describe 

 ocean wave propagation onto coasts is desirable. There are so few 

 examples of field observations, even for ordinary depth refraction, that 

 its basis might be questioned. Comprehensive field observations require 

 much time and manpower but are valuable to a proper understanding. 

 Prominent examples of such field studies are Mallory (1974) on wind, 

 wave, and current interaction, and Short's (1978) long-term studies of 

 beach development. A number of remot e- sens ing techniques are now 

 available and could be used in an area with strong currents. 



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