re: Planned freshwater diversions will doom LA salt fishing

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The maps on the master plan show most areas of Plaquimine and St Bernard with brown dots, meaning they are scheduled to be improved with sediment diversion which is supposed to build marsh.

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This is how it works. Historically the missisippi river was a huge bird foot delta. The distributaries meanreded, which means changed course over time. The bends in the river would grow away from the inside curve (point bar) until the river would eat through itself cutting off the bend resulting in an oxbow. Also natural annual floods would bring more depositions in the form of silt and clays to the adjacent lands on the other side of the natural levees.

We have done two things to disrupt this natural replenishment and growth.

First we have built levees to contain the floods. This stops the anual deposition of fertile silts and clays that runn off the greater portion of the continental US, on the adjacent lands. This sediment remains suspended in the water collum between the levees, until some is deposites in the venice area marshes. The majority o fthese sediments are carried out to sea.

Second we dredge the river to maintain shipping lanes. This reduces friction from the stream (river)bed causing more of the sediments to remain suspended due to the higher downstream velocities of the river current. This results in even more sediments being carried out to sea, and further.

Opening diversions will result in the deposition of sediment. Thre more sediment deposited by these diversions, the less effective the diversions will be. This means the job is partially done. With a lower velocity of fresh water moving in due to the deposition of these sediments, the saltier brackish waters, driven by tides will kill off fresh water species of vegetaton giving way to species more sutible to estuarian (brackish) enviroments.

The opening of these diversions will mimic a natural process no longer in process due to intervention of humans. This is a cyclical process and more diversions are needed and should be open and closed periodically to allow sediment loads to be distributed as needed. This is an expensive and long term project, but the models (wax, davis, carnarvon(sp.)) show this works.