updated to modern time. This second capability will require some effort, 

 but could be accomplished within a calendar year. 



Project-Specific Operational Gauges 



The backbone network, described in Recommendation 1 and in 

 Table 6, is the system of long-term gauges and selected short-term gauges 

 that serve as primary references and furnish continuous records. The 

 backbone network serves the common need of all TCOON Steering 

 Committee member agencies. 



The CESWG has its own specific needs for short-term water-level 

 measurement and reporting at the project level. Such a project might have 

 duration on the order of 1 to 6 months. Voice-reporting project-specific 

 gauges would greatly reduce cost and improve reliability in performing 

 reconnaissance surveys, project-condition surveys, contract-payment 

 surveys, and surveys made during the course of dredging in navigable 

 channels and waterways. The minimum number of operational gauges 

 necessary can be determined through the process of reconnaissance and 

 tidal zoning as described in this report. Typically, one to three short-term 

 project gauges might be necessary if gauges from the backbone network 

 augment their capability. 



As part of a long-term plan, permanent or semi-permanent platforms or 

 mounting areas must be constructed and maintained. The platforms 

 should be designed such that a permanent vertical elevation can be 

 identified, allowing the water level measured at the project-specific gauges 

 to be tied to the NOS datum applicable to those waters. 



Project-specific water-level gauges need not be to the same high 

 accuracy as backbone gauges that have the function of making 

 measurements to determine traditional tidal datums. Backbone gauges 

 employ equipment and procedures to assure overall accuracy on the order 

 of a few millimeters. The function of project-specific gauges is to control 

 soundings taken in maintenance of navigation channels. In project-related 

 hydrographic surveys made in water depths of 10 to 25 ft, for example, 

 sounding equipment and procedures are expected to have total-system 

 accuracy of ± 0.2 to ±0.5 ft (USACE 1991), depending on sea state and 



Chapter 6 Conclusions and Recommendations 49 



