Environmental Protection

River Spillway Flooding Caused New Land Formation in Louisiana

A team of geologists, civil engineers and one representative from the US Army Corp of engineers has found that when a spillway was opened last year to prevent flooding of the Mississippi river from drowning New Orleans, new land was created. The team, which has had their paper on the topic printed in the journal Nature Geoscience, says that this is the first time new land formation has been documented this way and now the technique might be used in the future to build up eroded lands.

In the spring of 2011, the Mississippi river became engorged as record amounts of snow melted along its northern route. The result was record flooding over a period of a month as news media marked its ominous march south. But because it took awhile for the extra water to reach areas in the south, planners had time to take action to best protect the most populated areas. They opened levees allowing water to spill over farmlands, enraging farmers, but saving many villages, towns, and even cities such as New Orleans, which of course was flooded in the aftermath of hurricane Katrina just seven years ago.

To save New Orleans, engineers opened levees (using dynamite) allowing water to enter the Bonnet Carré Spillway, which was dug for just that purpose after a massive flood back in 1927. The tactic worked, sparing New Orleans from what might have been a fatal blow. But another unexpected positive outcome appears to have been the formation of new land in some of the areas that had been flooded. It was a surprise because just ten to fifteen percent of the water volume from the river was diverted, which was mostly surface water, yet some thirty to forty percent of the silt load it was carrying managed to make its way into the spillway. The result was new land development adjoining the river and massive silt deposits left behind on the farmlands that had been covered. The research team says that until now, such land development has only been theorized, never documented.

Now, because it’s been seen in action, engineers and conservation groups can study areas that might benefit from temporary flooding, and perhaps dig spillways to make it happen. One idea is to use such spillways to restore delta lands that have eroded due to farming over many years. Another is to build up lands around areas that tend to flood regularly to build up natural barriers.

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