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Coastal Wetland Restoration

The land that we were standing on in Venice this summer is only 500 years old! This was before Hurricane Katrina. The land south of Cape Girardeau, Missouri was a gift from the Mississippi River. It deposited a huge amount of sediment, and this land was created. Then came the levees. The levees were built to prevent periodic flooding, which in turn meant that the sediment no longer replenished south Louisiana. And the land began to sink, making it more vulnerable to hurricanes. The loss has been greatly worsened by pipelines and shipping channels that cut through the vast marsh and speed erosion. We are losing the equivalent of land the size of a football field every 35 minutes!!

Where rivers have been controlled so that their sediment bypasses wetlands, and the resulting problem is one of sediment deficit, it makes sense to consider projects which will divert sediment-laden river water into a shallow estuary, causing mudflats and new wetlands to be created much as in the natural cycle of delta building. Ultimately, such building of new land (which can also be done in other ways) is the primary solution to the problems of subsidence and relative sea level rise.

There are several steps that can be taken to reverse this loss. One is to divert the sediment that is plentiful in the Mississippi River. Sediment diversions restore fluvial processes in the wetland environment. Levees can have inserted into them pipes so that some portion of river flow can move into the wetlands on the opposite side of the levee. These sediment diversions capture flows which are laden with the inorganic sediments most effective in building new land. Consequently, they also divert large quantities of river water. While this fresh water can benefit wetlands by decreasing salinity in the area which receives the outflow, the primary purpose of a sediment diversion is to build new land by mimicking the natural delta-building and wetland maintenance processes.

We could all encourage our congressional representatives and senators to allow the Army Corps of Engineers to be able to spend some more money so that they could help increase the sedimentation build-up by using what they dredge out of the Mississippi, which must be done in order to keep the 9-foot navigational channel.

The Barataria Terrebonne National Estuary Program has useful suggestions for this issue.

 

 

 

One River Mississippi

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Plaquemines Parish : Environmental Issues

June 24
2006