36 



• Pressure transducer gages. These instruments are usually mounted on 

 the seafloor or attached to structures. They record hydrostatic pressure, 

 which is converted to water level during data processing. A major 

 advantage of these gages is that they are underwater and somewhat 

 inaccessable to vandals. In addition, those like the Sea Data 

 Temperature Depth Recorder are compact and easy to deploy. 



• Stilling-well, float gages. These instruments, which have been in use 

 since the 1930's, consist of a float that is attached to a stylus assembly. 

 A clockwork or electric motor advances chart paper past the stylus, 

 producing a continuous water level record. The float is within a stilling 

 well, which dampens waves and boat wakes. The main disadvantage of 

 these gages is that they must be protected from vandals. They are 

 usually used in estuaries and inland waterways where piles or bridges 

 are available for mounting the well and recording box. Figure 17 is an 

 example of tide data from Choctawhatchee Bay, Florida. 



• Staff gages. Water levels are either recorded manually by an observer 

 or calculated from electric resistance measurements. The resistance 

 staff gages require frequent maintenance because of corrosion and 

 biological fouling. The manual ones are difficult to use at night and 

 during storms, when it is hazardous for the observer to be at the site. 



Typically, water level measurements recorded by gages are related to an 

 established datum, such as mean sea level. This requires that the gage eleva- 

 tions be accurately measured using surveying methods. The maximum water 

 level elevations during extreme events can also be determined by examining 

 water marks on structures or other elevated features. 



Water level information over paleoenvironmental time scales has been 

 investigated by researchers using stratigraphic coring, seismic techniques, and 

 radiometric dating. The reconstruction of ancient sea levels is one of the 

 powerful tools used in seismic stratigraphy (Payton 1977; Sheriff 1980). 



Current Measurements and Observations 



Need for coastal current data 



Currents, both shore-normal and shore-parallel, play a significant role in 

 shaping the geology of coasts. Knowledge of the magnitude and direction of 

 currents at the coast allows the prediction of sediment movements and thus is 

 basic to an understanding of landform development. Information concerning 

 cross-shore (shore-normal) currents and sediment transport can assist in pre- 

 dicting beach profile change, while knowledge of longshore (shore-parallel) 

 currents and associated transport can be used in predicting beach planview 



Chapter 3 Field Data Collection and Observation 



