the early 1880s, sea level along the Texas and Louisiana coasts has been 

 rising, relative to the land, in great part due to subsidence (Swanson and 

 Thurlow 1973). The rate of relative sea-level rise varies along the Texas 

 coast, but has been measured to be on the order of several millimeters per 

 year (Swanson and Thurlow 1973; Lyles, Hickman, and Debaugh 1988), 

 depending upon location. Relative changes in land-water elevation will 

 directly alter water-level datums at the site of inland-water and coastal 

 operational activities of CESWG, and these changes must be tracked 

 through water-level gauging to fixed benchmarks on land. The National 

 Research Council (1987) has published a monograph discussing the 

 engineering implications of sea-level rise. 



Determination of the relation of mlt or of another navigation datum to 

 extreme annual low water level, as well as to mllw as required, will enable 

 CESWG to assure the proper navigable depth, while satisfying Federal- 

 wide and USACE policy. The complex water-level variations present on 

 the Texas coast and along its inland coastal waters necessitate measure- 

 ment of local water level and collection of long-term time series of 

 measurements. Operational requirements in support of dredging activities 

 call for real-time reporting of the data in many situations. 



Cost-Sharing Partners and the Needs Assessment 



The State of Texas, through sponsorship by the Texas General Land 

 Office (TGLO) and the Texas Water Development Board (TWDB), has 

 deployed and operates a system of tide gauges called the Texas Coastal 

 Ocean Observation Network (TCOON) (Michaud, Thurlow, and Jeffress 

 1995). TCOON is maintained to national standards and procedures 

 established and promulgated by the NOS. TCOON complements eight 

 NOS gauges presently operating on the Texas coast. As of September 

 1996, the TCOON consisted of some 40 gauges, most of which were 

 located in inland coastal waters, with three gauges located offshore near 

 the fairway of the Galveston Ship Channel and sponsored by CESWG. 

 The main purpose of the TCOON has been to provide water-level 

 information to the TGLO for marine boundary determination (boundary 

 between state-owned land and private land) and to the TWDB for its 

 estuary and bay circulation and salinity studies. 



Chapter 1 Introduction 



