2 Water Level Definition, 

 Measurement, and 

 Properties 



This chapter introduces basic nomenclature related to tidal datums and 

 water-level measurement. Some typical characteristics of the water level 

 observed on the Texas coast are compared to those from tide records on 

 the Atlantic Ocean and Pacific Ocean coasts of the United States. The 

 material is intended to provide a background for further technical 

 discussion and to serve as motivation for establishing an appropriate 

 navigation datum for the inland coastal waterways of Texas. 



Historical Setting 



Tidal datums and their application have been an issue in the United 

 States since the founding of the nation. Both the need to establish a line of 

 delineation between the land and sea interface and the appropriate method 

 for determining the proper elevation were addressed early by the nation. 



In 1807, the U.S. Congress assigned to the Coast and Geodetic Survey 

 the tasks of delineating the sea-land interface and displaying it on charts 

 (Shalowitz 1964). That agency, apparently having most experience on the 

 U.S. east coast (where the astronomical tide is very regular), concluded 

 that the most appropriate way of determining that interface or line would 

 be by measurements of the rise and fall of the tide. This procedure 

 entailed setting of a tide gauge, which was connected by differential 

 leveling to fixed points on the land that could be used by engineers to 

 survey the sea-land interface for charting. These procedures have 



Chapter 2 Water Level Definition, Measurement, and Properties 



