Submarine Transmission Cable Installation Cook Inlet, Alaska

Our staff produced a desk-top study using maps, published regulations, and public information to compile a concise report. The final report summarized the conditions of the cable corridor and influenced the design and the installation of the cable.

Our hydrographers conducted a survey of the proposed route from the Point MacKenzie station to the Point Woronzof station. The survey included a topographic survey of the uplands at both ends of the route, and a hydrographic and geophysical survey of the sea floor between the inter-tidal zones.

The topographic surveys provided profile information for the cable routes and located the existing adjacent cables. The hydrographic survey of the area was accomplished using the M/V Sea Ducer, our 31' vessel. Both bathymetric and geophysical data were collected.

After the hydrographic survey, the data collected was reduced and analyzed. TerraSond produced maps and plan and profile sheets showing the sea floor conditions and suggested routes. Final route selection was made by working in conjunction with the design engineers and client representative. The installation drawings included the final determined cable lengths.

The navigation support for the cable lay operations included DGPS navigation systems for a barge and two tug boats. During the cable lay, a navigator was present on the barge to provide navigation redundancy. Following the cable lay, the four cables were surveyed with a single beam echo sounder and sidescan sonar system to determine whether they were in continuous contact with the sea floor. The results were reviewed immediately to expedite remedial action.

Tide data for the reduction of soundings were obtained from the National Oceanic and Atmospheric Administration's (NOAA) tide gauge at the Port of Anchorage. The location of the cable in the tide flats to the sub-station was surveyed for inclusion in the as-built drawings. The data collected during the post-lay survey was incorporated into the as-built drawings. Final drawings depicted the cable route as laid in both plan and profile. Drawings were produced that conformed to Alaska's Department of Natural Resources (DNR) standards for recording the land-use easements and were certified by an Alaska Registered Professional Land Surveyor (RPLS).

The following equipment was used for the surveys:

• Odom 3200DF Mk2 dual frequency echo sounder
• EG&G 260 side scan sonar
• Datasonics CAP-6000 chirp acoustic sub-bottom profiler and side scan sonar
• Trimble Ag120 Differential GPS (DGPS) system
• Trimble 4000 SSi on-the-fly Real-Time Kinematic (RTK) system
• Coastal Oceanographics HYPACK hydrographic software
• Triton ISIS data collection system

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