Knowledge of R H can also be used to estimate whether current effects are 

 great enough to warrant being taken into account when using an observed bottom 

 pressure fluctuation magnitude, P, to get a wave height, H. For the range 

 of current speeds, average depths, angles between the current vector and wave 

 orthogonal, and wave periods, the largest and smallest values of R [{ (denoted 

 by % l and ^H S> respectively) are estimated. If both are within the 

 acceptable range, then the current correction can be neglected and the wave 

 height estimated from 



H = H A (13) 



where H A is given by equation (10). If either R 



H,L 



R„ c or both are 

 Practical limits 



out of range, then equation (12) must be used to compute H. 

 on the acceptable range for both R H L and Rh,S are 1.15 and 0.85; i.e., if 

 the wave current interaction produces R H values which differ from 1.0 by 

 ±0.15 or less, the effect of the current can be neglected. Figure 3 shows 

 that % l is tne % va l ue corresponding to the smallest F and largest 



the R H value corresponding to 



$2 that is expected. Analogously, R H s 



the largest F and largest Q that is expected. 



fiL, is given approximately by 



I2L = 



2tt / otA 1 

 TS\ g / 



/2 



The largest expected il, 



(14) 



where TS is the smallest wave period of interest and dx L the largest 



time-averaged water depth expected (i.e., largest value of drr. expected). 



The largest F, FL, and the smallest F, FS, that can be expected are 

 given approximately by 



and 



FL 



(VL) cos(eS) 



if 0° < 9S < 90° (o rad < 8S < y rad) 



FL = - 



(* 5 T,s) 1/2 

 (,S) cos(eS) if 90° < OS < 180° (| < 9S < » rad) 



(e"V) 1/2 2 " " 



FS = 



_ -(VL) |cos(9L) 1 . 



(^T.s) 1 



/2 



if 90° < OL < 180° (j rad < 9L < rad) 



(15a) 



(15b) 



(16a) 



FS 



(VS) cos(OL) 



K,l) 



1/2 



if < 9L < 90 



(» 



rad < 6L < 



, d ) 



(16b) 



where (VL, VS) are the (largest, smallest) current speeds expected, (6L, 9S) 

 are the (largest, smallest) values of the angle 9 expected, dj g is the 

 smallest time-averaged water depth expected (i.e. , smallest value of 



expected), and d 



T »L 



has already been defined. If FS is 



FM value corresponding to 0, = UL, then FS is reset equal to 



less 



FM. 



than 



Unr, 



the 



In computing the wave height elevation, H, from the fluctuating bottom 

 pressure magnitude, P, there may be a range of wave periods over which a 

 current can be neglected (H is given approximately by H, where H. is 



16 



