EMCM's were aligned to form a six-element longshore array in the trough and a 

 five-element longshore array seaward of the bar. An additional current meter 

 placed on the bar between the longshore arrays formed a secondary cross-shore 

 array with three gauges. Data were collected continuously at an 8-Hz sampling 

 rate, pausing for about 10 min approximately every 8 hr to change data tapes. A 

 detailed description of the DELILAH experiment was provided by Birkemeier et 

 al.(1997). 



Infragravity shoreline variance 



As part of the effort of the Infragravity Waves in the Nearshore Zone Work 

 Unit 32430, infragravity variances measured at 8-m depth and at the shoreline 

 were compared with incident swell variance. This analysis examined data from 

 the SAMSON and DELILAH experiments, 4 through 20 Oct 1990, which 

 offered a wide variety of conditions (Figure 17). Incident waves were low to 

 moderate, ranging from 0.5 m to over 2 m FL^. Waves were typically out of the 

 southeast, generating a northward-directed longshore current (Table 2). Three 

 events of waves from the northeast occurred on 5, 16, and 19 October. The 

 second two were of sufficient 

 duration to reverse the 

 direction of the longshore 

 current. Also, on 12 October, 

 swell waves arrived from the 

 passage of Hurricane Lily far 

 offshore, that were 

 moderately high in energy 

 and narrow banded. 



The infragravity variance 

 in the 0.02- to 0.04-Hz band 

 was found to be significantly 

 correlated with incident swell 

 variance in the 0.05- to 

 0.15-Hz band. The frequency 

 limits for the infragravity 

 waves were set to isolate edge 

 wave variance from other 

 infragravity variance (bound 

 or leaky waves) and from 

 swell. The upper limit of 

 0.04 Hz avoids including low- 

 frequency swell variance. 

 The lower limit of 0.02 Hz is 

 the point at which edge and 

 leaky waves become 



unresolvable below this 



Figure 16. DELILAH surf-zone array 



Chapter 4 Field Observations 



35 



