ADCP INSTALLATION AND CURRENT STUDY, PELICAN ISLAND,


An engineering firm is investigating a potential liquefied 
natural gas berth location in the Galveston Bay area. Field 
data measurements on currents and total suspended solids 
are required for use in numerical models investigating ship 
maneuverability, hydrodynamics, and sedimentation at the 
site. Evans-Hamilton, Inc. (EHI), was contracted to 
conduct two intensive current surveys at spring tidal 
conditions and to install two bottom-mounted ADCPs at the 
site to measure currents for a year. EHI also will conduct 
water sampling, as required to determine total suspended 
solids concentrations at the site. 

Bottom mounted ADCP in trawler- 
resistant pod. 
SCOPE AND APPROACH 

A vessel-mounted, 600-kHz ADCP was used to conduct 
the intensive current surveys in November 2004 and 
February 2005. Differential Global Positioning System was 
integrated into the ADCP and was used to provide 
navigational information for the vessel. Current 
measurements were made along a series of transect lines 
over a complete tidal cycle. 

To collect the long-term current measurements, two 
bottom-mounted ADCPs have been installed in trawler 

GALVESTON, TX 

resistant pods. A diverless retrieval method is used for 
recovering the pods. In this method, acoustic releases on 
the pods are activated, allowing a buoy attached to the 
recovery line to float to the surface. The instruments 
collect a vertical profile of the water velocity magnitude and 
direction every 15 minutes. One of the ADCPs has been 
programmed to collect wave data at the site. 

The data from the vessel -mounted current surveys and the 
bottom-mounted instruments are being processed using 
custom software to provide both visual representations of 
the data as well as digital data that could be fed directly 
into the numerical models. Data output formats have been 
customized to be consistent with the client’s requirements. 

RESULTS 

The study is ongoing, but preliminary data have been used 
to develop tentative berth locations and configurations. 
The data also have confirmed the presence of a current 
shear at the site, which must be taken into consideration in 
positioning the berth.