(7) 



III. 



CURRENT-INDUCED CORRECTIONS WHEN BOTTOM PRESSURE 

 MEASUREMENTS ARE USED TO DETERMINE SURFACE WAVE HEIGHTS 



Peregrine (1976) 4 and Jonsson, Skovgaard, and Wang (1970) 5 indicate the 

 errors involved in not correcting for the current when using bottom pressure 

 measurements to determine wave heights. They give numerical results which 

 cover some of the conditions encountered in practice. A more extensive set of 

 correction curves is presented in this section. These curves allow an esti- 

 mate of curreut corrections to be made for the range of circumstances which 

 usually occur in the field. 



Peregrine (1976)° indicates that if a monochromatic surface wave height, 

 H, has a bottom pressure fluctuation magnitude, P, then H can be esti- 

 mated from P by 



(8) 



H = H 



where 



cosh 



dud. 



V 



PS 



(9) 



with cosh the hyperbolic cosine, p the water density (2.00 slugs per cubic 

 foot or 1,031 kilograms per cubic meter); g, d T , and Ly are the same as 

 previously defined. Equation (9) takes the current into account since the 

 wavelength Ly for a nonzero current rather than L. for no current is 

 used. Usually the current is not taken into account when estimating H from 

 P. Rather, the equation analogous to (9) but with L. instead of L„ is 

 used to estimate H from P; i.e., H = H. is usually used where 



"V 



H A =2 



2-rrd, 



cosh 



P,S 



The wave height factor, R„ , where 



R H - H 



H y cosh(2TTd T/ /L v ) 



cosh(2ird /l ) 



(10) 



(11) 



Peregrine, d.h., op. cit. , p. 10. 



5 J0NSS0N, I.G., SKOVGAARD, C. , and WANG, J.D., "Interaction Between Waves 

 and Currents," Proceedings of the 12th Conference on Coastal Engineering, 

 American Society of Civil Engineers, Vol. 1, 1970, pp. 489-509. 



6 PEREGRINE, D.H. , op. cit. 



14 



