West Bay Diversion and Shoaling

One of the more well known projects of the Breaux Act was the West Bay Diversion (MR-03) and as evidenced by its name it was a freshwater diversion project. Lets recap what that means…

  • Freshwater Diversion

Uses gates or siphons to regulate the volume of water flow. Freshwater is channeled form a nearby river or water body into surrounding wetlands. This infusion of water, sediment, and nutrients helps slow saltwater intrusion and promotes the growth of a new marsh.

  • Sediment Diversion

This uncontrolled diversion promotes the creation of new marsh in place of open-water areas. A gap (called a crevasse) is cut into a river levee, allowing river water and sediment to flow into nearby wetlands and mimic natural land-building processes.

The West Bay Diversion was the first on the list of the Breaux Act’s list of projects. It was supposed to serve as a model example of how the Mississippi can quickly and effectively rebuild wetlands. In hind sight, let’s hope it is not. You may have noticed that I have been writing about the diversion in the past tense…this is because earlier this year, a decision was made by the Breaux Act Task Force to discontinue the diversion. When it was flowing at full capacity,  the diversion was supposed to allow 50,000 cubic ft/sec of river water to flow into West Bay, which is located just north of Pilottown and the Head of the Passes in Plaquemines Parish. However, in 2007-8 only about 27,000 cubic ft/sec were flowing into the bay.

So why was the poster-child of freshwater diversions canceled? Was it because it didn’t work? Not really. As the water flowing south in the Mississippi River came to the diversion it slowed the water speed and allowed sediment to drop out in the River. Why is this a bad thing? Well, because the West Bay Diversion was placed directly adjacent to a rarely-used shipping anchorage (parking spot). The slowing of the water was causing sediment to drop out in the anchorage, which cost the State millions of dollars every three years to dredge. This battle between restoration and navigation eventually lead to the demise of the West Bay Diversion.

Two years ago, the Army Corps alerted the Breaux Act task force that the diversion was silting in the anchorage and argued that because of the particular location of the anchorage they were not allowed to pay for that particular dredging. The Breaux Act originally worked out a compromise to pay for the dredging but they have now decided that the cost is no longer worth the reward. A recent study by the Corps found that they diversion was only responsible for the silting and the anchorage would be silting in either way, but nevertheless the project is done. Was this just a political battle between shipping and restoration? Sort of, but there is also a little line hidden in a recent Times-Picayune article that may have a bigger story.

While the corps study concluded the diversion wasn’t entirely to blame for silting in the anchorage, it also found it wasn’t doing much to build land in West Bay.” Wait What?! Why wasn’t it working? The study was unclear but the lack of progress could have been because of sediment moving beyond the bay or because of Hurricanes. (hurricane Katrina passed almost directly over West Bay) Lack of sediment? What about that which was clogging the anchorage? Either way, the State felt that the Corps should pay for the dredging and vice-versa. When asked about the project, CPRA chairman Garrett Graves (LA representative to Breaux Act task force) said that keeping the diversion open and paying for the dredging was essentially wasting money and dirt that could be used elsewhere.

The failure of the West Bay diversion could be seen as an engineering mishap, but is it a sign of more to come with respect to the other freshwater diversions? The Breaux Act Task Force stated that the failure “was not a threat” to the seven other major freshwater diversions upstream. Hopefully the authorities can learn from the mishaps at West Bay and properly site and manage the existing and future diversions. However, the failure of West Bay is a huge blow to the possibility of diversions being the main force of restoration.

 

References

WestBayrGeomorphicAssessment1DModeling

Charles D. Little, Mississippi River Geomorphology & West Bay Diversion

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WestBayDiversion ERDC Draft Report 25 Nov 2009
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west bay presentation_Introduction

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