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Types of wave gages 



Wave gages can be separated into two general groups: directional and 

 non-directional. In general, directional gages and gage arrays are more 

 expensive to build, deploy, and maintain than non-directional gages. 

 Nevertheless, for some applications, directional instruments are vital because 

 the directional distribution of wave energy is an important parameter in many 

 applications, such as sediment transport analysis and calculation of wave 

 transformation. Wave gages can be installed in buoys, placed directly on the 

 sea or lake bottom, or mounted on existing structures, such as piers, jetties, or 

 offshore platforms. 



Of the non-directional wave gages, buoy-mounted systems such as the 

 Datawell Waverider are the most expensive to purchase initially but are 

 accurate and relatively easy to deploy and maintain. Data are usually 

 transmitted by radio between the buoy and an onshore receiver and recorder. 

 Bottom-mounted pressure gages measure water level changes by sensing 

 pressure variations with the passage of each wave. The gages are either self- 

 recording or are connected to onshore recording devices with cables. Bottom- 

 mounted gages must be maintained by divers, unless the mount can be 

 retrieved by hoisting from a workboat. Internal-recording gages usually need 

 more frequent maintenance because the data tapes must be changed or the 

 internal memory downloaded. Advantages and disadvantages of self-contained 

 and cable-telemetered gages are listed in Table 3. Structure-mounted wave 

 gages are the most economical and most accessible of the non-directional 

 gages, although their placement is confined to locations where structures exist. 

 The recording devices and transmitters can be safely mounted above water 

 level on the structure. 



Directional wave gages are also mounted in buoys or on the sea floor 

 (Figure 16). Arrays of non-directional gages can be used for directional wave 

 analyses. Directional buoy-type wave gages are often designed to collect 

 other parameters such as meteorology. The buoys are relatively easy to 

 deploy, but they cost more initially and continuing maintenance is required. 



Placement of wave gages 



The siting of wave gages along the coast depends on the goals of the 

 monitoring project, funds and time available, environmental hazards, and 

 availability of previously collected data. The user must usually compromise 

 between collecting large amounts of data for a short, intensive experiment, 

 and maintaining the gages at sea for a longer period in order to try to observe 

 seasonal changes. There are no firm guidelines for placing gages at a site, 

 and each project is unique. A priori knowledge of the site or practical 

 considerations may dictate gage placement. Table 4 summarizes some sug- 

 gested practices based on budget and study goals. Suggestions on data 

 sampling intervals are discussed in Chapter 5. 



Chapter 3 Field Data Collection and Observation 



