Hydrographic Survey – LNG Plant, Sabine, Texas
Immediately after the construction of this LNG facility in 2007, the client asked CRA to conduct routine depth sounding surveys. As it became clear that the facility had an unusually high sedimentation rate, the frequency of surveys were increased to one every month. Lines were run over the entire berthing area at a 50 foot separation. Later, additional areas were added to the scope to extend the data along the western shoreline both to the north and south of the berthing area at a 100 foot line separation. A traditional single-beam depth sounding system was used (sometimes single Odom Hydrotrac), sometimes dual frequency (Odom Echotrac MKIII). Horizontal positioning was via real time differential GPS, using a Trimble AG132 and corrections from the Navbeacon system.
Data acquisition and processing software was “Hypack.” At the finish of each survey, drawings were made in Bentley Microstation showing the existing bottom elevation contours as well as contours showing the thickness of sediments that had accumulated during the prior month. Cross-sections were produced over the area (2) plus one more each north and south to show the accumulation in side view. Volume computations were also made to show the monthly and total accumulation in cubic yards. Other services performed under this contract include sidescan sonar data post-storm (Hurricane Ike), and an upcoming sediment sampling program using an electric vibracorer prior to dredging.