Section I. INTRODUCTION 



1. Wave Program at CERC 



The Coastal Engineering Research Center (CERC) , formerly the 

 Beach Erosion Board, has been collecting data from wave gages for more 

 than 20 years. The program started in April 1948, when the first gages 

 were installed in New Jersey. Since then, many gages have been installed. 

 In addition to gages on the Atlantic, Gulf of Mexico, and Pacific shores, 

 gages have been installed in the Great Lakes, at Hawaii, and in smaller 

 inland lakes and reservoirs. 



Signals from 7 locations and 10 gages are now instantaneously re- 

 corded on a central panel in the CERC Laboratory. These signals are 

 carried by leased telephone lines. 



CERC uses two basic types of wave gages - the step-resistance staff 

 gage and the pressure-sensitive gage. The more accurate is the step- 

 resistance gage and it is favored for use in locations where a structure 

 is available for its installation or where the construction of a suitable 

 support is feasible. The pressure-sensitive underwater gage is selected 

 for those sites where a less accurate gage is acceptable for a measure- 

 ment program, and where the measurement of waves with periods of less 

 than 4 seconds is not required. 



2. Recording and Analysis 



Recordings from both types of gages are normally produced on a 

 pen and ink paper strip-chart recorder. The length of time that the 

 waves are recorded is selected in accordance with the mission of the 

 individual gage or within the overall program of wave study. Automatic 

 programming of the gage recording time is normally provided along with 

 a control for manual selection of special recording periods. 



Tide changes are not normally removed from the strip-chart record- 

 ings taken with the staff type step-resistance wave gage. However, tide 

 removal can be provided for this gage should the requirement for this 

 type operation arise. Tide changes are removed from the pressure- 

 sensitive wave gage. If such removal was not incorporated in the gage 

 operation, barometric changes would also be present in the recording, 

 thus a record that would be difficult to analyze would be produced. 



Data from both types of wave gages may be recorded on magnetic tape. 

 Records made on magnetic tape are analyzed on a spectrum analyzer in the 

 CERC Laboratory. The analyzer performs the following analyses from a 

 20-minute recording: 



a) Linear average wave height. 



b) Squared average wave height. 



c) Linear peak wave height. 



