Thursday, October 8, 2009

Brown Water Operations—ensuring that the Western Rivers remain open

Excerpt from U.S. Coast Guard “Proceedings of the Marine Safety & Security Council” magazine. By LCDR Wayne R. Arguin Jr., LCDR Phillip Ison, and LTJG Ellen M. Motoi, U.S. Coast Guard.

A call to Sector Lower Mississippi River’s command center indicates that a 36-barge tow has intentionally grounded along the river bank north of Memphis, Tenn.

If this had been a similar call to a coastal command center, it may have spooled up investigators and inspectors, alerted aids to navigation (AtoN) teams, and elicited a flurry of calls to notify the command. But the intentional grounding of a tow is commonplace throughout the Western Rivers.

Towing vessel operations regularly “push in” to the bank to allow larger tows to pass in tight bends or to rearrange barges within a tow at a barge fleeting area. Since typical towing vessels are not equipped with anchors, they use the thrust of their power plants to hold position.

This is No Sea Cruise
However, the unintentional grounding, collision, or allision of even a single tow can have a significant economic impact on the entire Western Rivers system. Where coastal channels are charted and regularly maintained through periodic dredging, river channels are always shifting, largely influenced by the rate of change in the river’s elevation, sedimentation, and man-made structures. Shoals and strong currents can appear just hours after a tender has verified the sailing line.

The system of locks, dams, and bridges adds to the operational challenges faced by today’s towboat operator. Additionally, the result of even a minor incident in this system can have major consequences. For instance, if a multi-barge tow hits a bridge, this can lead to the complete failure of the tow’s integrity, turning a composite unit into 30 to 40 individual hazards to navigation.

Groundings within the navigable channel are particularly disruptive because they often result in extended river closures, especially when lower river conditions require narrower-than-normal channel widths.

A Case in Point
Casualties occur more often during high water conditions. Strong currents require downriver-bound tows to maneuver with precise coordination between rudder commands and engine orders to safely pass between bridge spans.

In one case in January 2007, a 42-barge tow allided with the Natchez I-20 Bridge, sending all 42 barges careening downriver. Other towing vessels pushed their tows into the bank and assisted with the capture of barges that had drifted nearly 20 miles from the initial impact site. Three of the barges sank within 300 yards of the bridge—very close to the marked navigable channel.

U.S. Army Corps of Engineers (USACE) survey vessels confirmed the location of each submerged barge so that commercial traffic could resume with minimal delay, but salvage and removal of the damaged barges could not be immediately completed due to the extreme currents.

Incident Recovery
After any grounding or similar incident, recovery and restoration is time sensitive and often requires multi-agency coordination to ensure the safe and efficient movement of commerce on the nation’s largest marine transportation system.

Officers in charge of Coast Guard river tenders rely heavily on the U.S. Army Corps of Engineers and National Weather Service river stage forecasts to determine the most effective way to mark the river so that tows can proceed without incident.

A rapid change in river levels (greater than two feet per day) can wreak havoc on a channel’s integrity, leading to more frequent AtoN verification patrols and channel surveys by USACE resources to identify trouble spots that may lead to casualties.

Salvage and Lightering, Western-Style
Salvage activities on the Western Rivers are sometimes complicated by the lack of available resources and the unique challenges posed by high currents and ever-changing river levels. In most cases, a typical dry cargo hopper barge must be lightered using clam shell cranes, one scoop at a time.

Liquid cargo barges may require “over the top” or manifold-to-manifold transfers. Temporary repairs, including using wooden shingles to plug fractures in the hull plating, are the most common repairs used to restore watertight integrity to a damaged barge so that it can be delivered to a repair facility.

Coast Guard-certificated tank barges must be issued “permits to proceed” prior to continuing voyages so that damage can be permanently repaired at an approved facility.

Even when salvage resources are available, water conditions may delay recovery. Strong currents may prevent dive teams from patching holes in submerged barges. If the holes are too large, salvage pumps cannot remove enough water to allow the vessel to float free. In these cases, each day the submerged barge remains on the bottom decreases the likelihood of a successful recovery, due to sedimentation.

When low water conditions exist, barges may not be able to be floated free and may need to be completely emptied of cargo. If cargo removal is not an option, owners may simply wait for Mother Nature to provide a boost in the form of rain. In other instances, teams of towing vessels may attempt to pull the stranded barge into deeper water rather than attempting to lighter cargo from the barge. In all cases, broadcast notices to mariners are issued to advise waterways users of the hazards, so that appropriate passing arrangements can be coordinated.

About the authors:
LCDR Wayne Arguin has served in the Coast Guard for more than 15 years within the marine safety specialty. He has actively worked to improve towing vessel safety on the Western Rivers.

LCDR Phillip Ison has served for more than 20 years, with 18 years in the marine safety specialty.

When this article was originally published, LTJG Ellen Motoi was completing her first year in the marine safety field.

For more information:
Full article and “U.S. Coast Guard Western Rivers Sectors” edition of USCG Proceedings is available at Click on “archives” and then “2007-08 Vol. 64, Number 4” (Winter 2007-08).

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