Therefore, for assuring safe navigation, we recommend that the 

 CESWG develop project low-water datums based on water-level 

 observations. The project low- water datums, specific to certain locales 

 depending on the known properties of the water level variation, would be 

 referenced to an existing NOS chart datum, if available. A specialized 

 effort needs to be implemented to develop rational and defensible project 

 low-water datums. That is, project low-water datums should be based on 

 observation and sound procedures, and the determined values should not 

 be unreasonably conservative, thereby causing unnecessary dredging. 



Engineering Utility of Archived Data 



The existing WWW internet site (http://dco.cbi.tamucc.edu/data) for 

 accessing TCOON data is a sound basic system. Data loaded to the site 

 may be as recent as 3 hr old. Lists of data and plots can be generated by 

 command for arbitrary time intervals, and the queried information can be 

 downloaded. 



Presently, the data are reported to the (arbitrary) local staff zero, called 

 the "datum of tabulation." The datum of tabulation remains constant 

 through the life of a station (even if the physical gauge is removed, later to 

 be replaced) and is one of the key procedures in the process of relating 

 water level to fixed benchmarks on land. However, the datum of 

 tabulation is arbitrary and not, of itself, physically meaningful. Two 

 enhancements to the WWW site need to be made for applications of the 

 data by the CESWG and its contractors. These enhancements will also be 

 valuable for any engineering or scientific study or project. 



First, the WWW site should provide the relation between staff zero and 

 the mllw datum (or msl if mllw cannot be defined, as in nontidal waters) 

 and an option given to plot the data to mllw or msl. This capability can be 

 added with little effort. Second, all tidal datums available for the 

 individual stations should be accessible. Other datums, such as mhw and 

 msl, enter in regulatory functions and environmental modeling conducted 

 by the CESWG and its contractors. Extreme high- and low-water levels 

 contained in the record, as well as the tidal range, should be given. As 

 much as possible, and in coordination with NOS, the tidal datums should 

 be computed to the most recent 19-year interval if the NTDE is not 

 48 Chapter 6 Conclusions and Recommendations 



