Sediment diversions may not be enough to save us

The outflow canal behind the Caernarvon diversion in Plaquemines Parish, LA (Photo/Chris Johnston)

The outflow canal behind the Caernarvon diversion in Plaquemines Parish, LA (Photo/Chris Johnston)


It has been reported by the NY Times that a the soon-to-released United Nations climate change report predicts that global sea-levels could rise more than three feet by the end of the century. This comes on the heels of an NOAA report that says Louisiana faces the highest rate of sea-level rise worldwide.

Situation dire for New Orleans

Anyone who has witnessed the devastation of Hurricane Katrina realizes the New Orleans and the surrounding areas exist in that sliver of land that rides just barely above current sea level. In the city itself, we live below sea level. This situation is only going to get worse as time goes on.

Dr. Denise Reed, Chief Scientist at the Water Institute of the Gulf, explains it like this, ” The relative elevation of your house, relative to water level surrounding the city is gradually getting lower year after year after year. When you add that to sea level on the outside rising gradually year after year after year, that kind of differential between the water on the outside and the elevation of the land on the inside of the levees gets greater all the time.”

Are diversions the answer

The state has released it’s Master Plan as the solution to Louisiana’s coastal land loss problem. As they explain it, the plan will guide the state’s coastal investments for the next 50 years. One of the key features of the plan is a series of large-scale sediment diversion structures along the Mississippi River. These structures will divert sediment-rich water from the river, to sediment-deprived wetlands that are behind the river levees.

Dr. Mark Kulp, a professor of geology at the University of New Orleans, questions whether they will work, “The big question is, does the river carry enough sediment these days to build land effectively. A lot of studies have shown that the sediment load in the river has been substantially reduced because of changes in upstream practices: dams, and agricultural changes, and things of that nature.”

Dr. Kulp explained that there are two schools of thought on diversions, “that diversions really, truly will build enough land that it will create some net positive benefit. Such as insulation from storm surge and so forth. Then the other school of thought is that the rate of relative sea level rise here, induced by subsidence and the global oceans rising, is so high, and there is so relatively little sediment that you can introduce through a diversion, that the diversion will never actually build land in the midst of that high rate of relative sea level rise.”

The clock is ticking for New Orleans and all of South Louisiana. One wonders if we can all come to an agreement before the time runs out.


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