USA, Mississippi: High river season - risk of grounding


Published: 5 April 2016

We have seen a recent increase of groundings and other incidents in Mississippi River and two of these groundings involved Skuld entered vessels. All members whose vessels are or soon will be operating in the US Gulf / Mississippi River Range need to be mindful that the Mississippi River High River Season has started. High River is measured at the New Orleans Carrollton Gauge, and High River deep draft vessel restrictions implemented by the US Coast Guard and the Mississippi River Pilots usually begin when the rising river measures 12 feet. In comparison, a normal river is in the 5 - 8 foot range, and a low river in the 2 - 5 foot range.

The High River Season

Mississippi River High River Season happens every year, usually from mid-March to mid-May, rarely into June – depending upon the snowpack in the Rocky Mountains and the Appalachians, and upon the springtime precipitation across the US Midwest and South. The high river stage results in strong, turbulent river currents in the 4 - 6 knot range (sometimes 7 knots in the bends), as well as heavy shoaling requiring constant dredging. The shoaling is worse this year because US Government budget restrictions have reduced the number of dredges working from Baton Rouge down to Southwest Pass.

Restricted visibility due to fog

Fog is another complication of the high river season. The spring runoff river water is ice cold, and the ambient atmospheric conditions from Baton Rouge to the river mouth are sub-tropical – resulting in frequent dense fog usually about 30 feet (10 meters) thick above the river surface. The fog prevents vessel navigators from seeing visual reference points and smaller towboat flotilla river traffic. During high river season – the time vessel navigators need visual observation most to gauge slide in bends and during close in maneuvers like docking – they are blinded by fog.

Strong currents and shoaling

As the river rises above 12 feet, to 14 feet and above, additional restrictions are put in place. The river rarely measures above 17 feet at the New Orleans Carrollton Gauge because the US Army Corps of Engineers will open spillways upriver and maintain 17 feet to protect New Orleans levees from breaching. These high river conditions create strong river currents in the 4 - 6 knot range compared to the normal 1 - 2 knot range the rest of the year. The strong river currents erode the edges of the dredged deep draft channels and create shoals as the dredged channel collapses. The shoaling is especially bad in the straight reaches between New Orleans and Baton Rouge, and down in the Pilottown / Cubit's Gap area (Mile 0 - 6 Above Head of Passes "AHP") and at the very mouth of the Southwest Pass.

Mud eruptions

In addition to the shoaling is a condition called "mud lumps" which are sudden eruptions of mud up about 20 feet (6.5 meters) from the 47 foot (14.4 meter) dredged channel river bottom – like mud volcanos – that often happen during high river and almost never during normal river. There is also a condition that develops from Cubit's Gap down to Southwest Pass called "flocculation" which is a colloidal suspension of mud, sand, fresh water and salt water the consistency of pudding extending from the river bottom up to about 10 - 20 feet (3 - 6.5 meters) above the river bottom which oozes downriver. Thus, even though the fathometer may show 47 foot (14.4 meter) depth, the actual good water is only about 27 - 37 feet (8.2 - 11.3 meter) in depth, and deeper draft vessels despite being at full ahead will simply slow to a crawl and may even come to a stop.

Overheating of engines

Not only do the strong currents and shoaling create a hull, rudder and wheel damage risk from grounding, with consequent substantial refloating expense and damage repair costs, but deep draft vessel main engine and generators frequently will overheat when trying to refloat. Engine overheating damage risk also happens when the vessel is trying to force her way through flocculation, mud lumps and shoals. This is because the sea chest is sucking in mud, not water.

The draft can be less in the High River Season

Counterintuitively there is actually less depth available for deep draft vessels and more risk of grounding during high river season than there is during normal or low river season when the full 47 foot draft dredged channel is available. For example, presently due to high river shoaling and flocculation the recommended draft is only 43 feet, with one way traffic in some areas for vessels with more than 40 foot draft, and with vessels more than 38 feet in draft required to wait outside Southwest Pass for high tide before entering, and to wait up at Boothville Anchorage for high tide before departing. This can lead to significant delays if the vessel unthinkingly was loaded to more than 43 foot draft as in normal or low river season. We know of at least one vessel that is lightering off now at considerable expenses to reduce her draft from 47 feet to 43 feet.

Vessels' ground tackle and hawsers may not be strong enough

Despite the precautions and restrictions recommended by the Mississippi River Pilots and enforced by the US Coast Guard, as soon as the rising river is above 12 feet we see anchor loss, anchor dragging, grounding, collision and vessel and barge breakaway incidents begin to increase. This is because most deep draft vessel ground tackle is not designed to handle currents above 4 knots – especially when the vessel is loaded. Likewise vessel mooring hawsers alone are inadequate when the vessel is secured to a wharf, hold in tugs are a necessity during high river. When the river is above 14 feet, incidents increase even more – as on the recent day at 14.9 feet when two of our member's vessels grounded near the Cubit's Gap area (Mile 3) , one of them grounded again at Boothville Anchorage (Mile 16), and then a vessel entered with another Club dragged anchor at Grandview Anchorage (Mile 148) and struck a downriver wharf and the Gramercy Bridge.

Thereafter the safety restrictions for deep draft vessels were increased as described above, and the upriver vessel at Grandview Anchorage was required to have a Mississippi River Pilot aboard and two standby tugs made fast 24/7. This last restriction underscores the reality that foreign vessel masters cannot and do not have the skill or the training to manage a high river anchor dragging or wharf breakaway situation for 2-3 hours until a pilot and tugs arrive after an emergency call.

Please note the Mississippi River Pilots generally are very good, and every year during high river season hundreds of deep draft vessels make it up and down the river without actual incident (never mind the near misses), but dozens of deep draft vessels do not. In comparison, there are very few anchor loss, anchor dragging, grounding, collision, vessel or barge breakaway cases here during normal and low river season – unless there is a hurricane.

General advice

Owners and charterers need to carefully consider and to contract for the reality of high river season strong river currents, fog and shoaling – and the extra tug/pilot expenses and risks of damage and delay associated with same – when conducting charter party fixture negotiations and also later when loading the vessel.

They also should consider using the links below when planning a voyage to the Mississippi River, especially during high river season, and monitor the daily NOBOT/MCR and the pilot association websites thereafter during the voyage, as shoaling conditions and applicable restrictions change rapidly during high river season.

    If not allowed to subscribe to the New Orleans Board of Trade Marine River Currents (NOBOT/MCR), ask the local agent to send you copies of the past two weeks NOBOT/MCR's so you can get a sense of the high river and recent developments
    Associated Branch Pilots website – they pilot from the sea buoy to Pilottown
    Crescent River Port Pilots Association – they pilot from Pilottown to New Orleans
    NOBRA Pilots – they pilot from New Orleans to Baton Rouge
    Louisiana River Port Pilots Association – an association of Louisiana Pilotage Groups

This is not an all-inclusive list, prudent owners, charterers, operators, managers and mariners should exercise their own judgment and do their own research concerning Mississippi River High River conditions.

The Association is grateful to Michael Butterworth of Phelps Dunbar, New Orleans for contributing to this update.