By David Gambrel

The Mississippi River divides into three main branches 22 miles before it enters the U.S. Gulf: Southwest Pass, South Pass and Pass a l’Outre. Only Southwest Pass is maintained to accommodate deep draft vessels; the other two are far too shallow. When the Mississippi River reaches 10 feet and rising at Carrollton (New Orleans), the Corps of Engineers initiates more intensive dredging activities. Under rapidly-rising river conditions the main focus of the Corps’ activities centers around the Mississippi River outlet known as Southwest Pass, which is a superhighway for ships. It provides deep-draft access to more than 200 miles of refineries, grain terminals, break-bulk terminals, coal terminals and midstream operations lining the river all the way to Baton Rouge. The Pass is the throbbing heartbeat of the nation, the artery ever in peril of plugging.

The yardstick for the Corps’ dredging efforts, particularly when the river is rising, is the Carrolton Gage, which is visible out the front window of its office in New Orleans. At a gage of 10 ft and rising sedimentation and shoaling begin to increase rapidly in Southwest Pass. The river rose very swiftly this year. At New Orleans the rise from its normal 2-ft gage level began March 2 and raced past 10 ft in just 12 days. By May 11 it had risen to the flood stage of 17 ft and stayed there for nine days before it began falling.

When the gage reaches 10 ft or less at Carrollton, the Corps begins preparing for action. Hydrographic surveys are done on a daily basis with bottom-scanning sonar. Survey data are processed and CAD-color-printed on large sheets of paper. Initially, these charts are used to determine if it is appropriate to set a bid opening for a dredging contract. During the height of dredging activities a thick stack of these charts are prepared and delivered to the operations manager every morning for daily determination of dredging locations.

Southwest Pass is 22 miles long, and is maintained to a depth of 45 ft. The Corps maintains the width of the channel to 750 ft to Mile 18 BHP (below Head of Passes), and to a width of 600 ft thereafter.

Why should a coal shipper care about what happens in Southwest Pass? Same reason a grain shipper or oil tanker should care. Grounding any big ship in Southwest Pass can be as serious as a massive train derailment on the Joint line in the PRB, except in most cases it amounts to blocking export shipments rather than domestic shipments.

Holes & Shoals
Turbulent water does two things: it gouges holes and it deposits shoals. The shoals are actually collections of sediment. Daily hydrographic surveys (See Figure 1) are one of the essential tools available to the Corps’ Operations Manager to direct daily dredging activities. While the channel (light blue) is running deeper than normal at 46-47 ft, there are two shoals (green) that may be reached at a depth of only 41-42 ft. As of June 13, the shoals had risen 5-6 ft off the channel bottom and could have been hit by a vessel loaded to normal channel draft (45 ft). The dredge had to quickly cut through 1,000 ft of long narrow shoal to get to the two big shoals growing together 3,200 ft downstream. Meanwhile, deep draft vessels had to be light-loaded.

Siltation, Sedimentation and Dredging
Picture the Superdome in New Orleans filling with silt once every four weeks. That’s how fast sedimentation has been happening in the Lower Mississippi in 2011—basically 5 million cubic yards per month. For awhile five dredges in Southwest Pass could not keep up, including the Corps’ own large hopper dredge, the Wheeler.

In 2003, the Corps estimated that it spent $12.5 million to maintain the Wheeler in ready reserve, defined as 55 workdays plus emergencies, of which about $8.4 million is needed to cover costs when the vessel is idle. The total dredging budget in 2011 was reduced to $74 million compared to last year’s $117 million.

Bear in mind there are only 10 hopper dredges worldwide that are suitable for bidding on Southwest Pass dredging jobs. Since Southwest pass can shoal up so quickly during high water, bids are opened and awarded the day they are opened. Winners are usually capable of having a dredge on site in five to seven days, which is very quick considering it is not profitable for dredging companies to keep manpower and equipment on site unless working under contract. The coal mining equivalent would be keeping a dragline on stand-by.

Funds must be budgeted and available to issue a dredging contract. The Corps is required to determine a fair and reasonable cost estimate for a well-equipped contractor to perform the work. By law the Corps may not award a dredging contract if the price exceeds 25% of the Corps’ estimate. If the lowest bid does not meet this requirement, the Corps has several options: (1) It can cancel the solicitation (not really an option in this case); It can re-advertise the solicitation (not an option if timing is important); (3) It can consider challenges to its own estimates; (4) It can convert the solicitation to a negotiated procurement; or (5) It can use one of its own dredges to do the work. Again, Figure 1 should help show the urgency of action.

Tell Me Again, Why Should I Care?
A vessel containing 70,000 mt of met coal is headed for an Asian country for a price of $300/mt, or $21 million. Would you prefer to have it sail without incident, or do you care if it goes to anchorage after loading? Do you care if the demurrage clock is running? (Remember, in the maritime world “Once on demurrage, always on demurrage.”) If you are the charterer, demurrage is probably the least of your problems. You just paid the ship owner about 95% of the ocean freight, or will be required to do so within a day or two. If your freight rate is $50 per metric ton, you might have paid over $3 million in freight before your ship ever left the river. It can get very expensive, and there is no one who can make it better.

Short notice problems are best handled on a long term basis, making preparations for floods and dredging far in advance. Advanced planning for such events is best done when users of the river—particularly large users such as the coal companies—take the opportunity to get involved with the Corps, the Waterways Council, and with others whose job it is to keep Congress informed or to spend the money on urgently-needed river projects.

Dave Gambrel is president of Logisticon, a consultancy in coal transportation. He is available for private consultation at