In 1995, the expanding resources of the Internet allowed SAIC to access the 

 National Oceanographic and Atmospheric Administration (NOAA), Ocean and Lake 

 Levels Division's National Water Level Observation Network. This network is composed 

 of 181 water level stations located throughout the Great Lakes and coastal regions of 

 United States interest. These stations are equipped with the Next Generation Water Level 

 Measurement System tide gauges and satellite transmitters that have collected and 

 transmitted tide data to the central NOAA database every six minutes, since 1 January 

 1994. 



Observed tide data are available 1 to 6 hours from the time of collection in a station 

 datum or referenced to Mean Lower Low Water (MLLW) and based on Coordinated 

 Universal Time (UTC). Data from NOAA tide station 8467150 in Bridgeport Harbor, 

 Bridgeport, Connecticut, was used to re-correct both the July 1994 and March 1994 

 surveys at CLIS. The NOAA 6-minute tide data was downloaded in the MLLW datum, 

 corrected to local time, and modified to reflect tidal differences based on the entrance to 

 New Haven Harbor, New Haven, Connecticut. 



During the bathymetric survey a Seabird Instruments, Inc. SBE 26-03 Sea Gauge 

 wave and tide recorder was used to collect tidal data. The tide gauge, deployed in the 

 survey area, recorded pressure values every six minutes. After conversion, the pressure 

 readings provided a constant record of tidal variations in the survey area. These observed 

 tidal data were later used to compare and verify the corrected NOAA data generated by the 

 Bridgeport Harbor station (Figure 2-2). 



A Seabird Instruments, Inc. SEACAT SBE 19-01 Conductivity, Temperature, and 

 Depth (CTD) probe was used to obtain sound velocity measurements at the start, midpoint, 

 and end of each survey day. The data collected by the CTD probe were bin-averaged to 

 1 meter depth bins to account for any pycnoclines (rapid changes in density creating 

 distinct layers within the water column). A correction factor based on the mean sound 

 velocity was then calculated using the bin-averaged values and applied to the raw 

 bathymetric data. 



Analysis of the bathymetric data was performed with the use of SAIC's 

 Hydrographic Data Analysis System (HDAS), version 1.03. Raw position and depth 

 values were imported into HDAS, corrected for sound velocity, and standardized to 

 MLLW. The bathymetric data were then used to construct depth models of the surveyed 

 area (Murray and Selvitelli 1996). 



Monitoring Cruise at the Central Long Island Sound Disposal Site, July 1994 



