Wetlands restoration will produce an unstable Mississippi River?

Wetlandsmiss · September 5, 2007

LA Speaks Draft Master Plan will not work because a river environmental disaster will occur with the plan as proposed

A shipping terminal has fallen in the river in the past (1974-75? near Plaquemine, La.) from high velocity water but I am sure the terminal was designed to meet government regulations with respect to piling depth...etc. After this event several diversions were added to the river and this has added piling undercutting capability to the river due to added velocity. Adding more diversions in the future may be the straw that breaks the back and, I believe, more shipping terminals will fall into the river. There should not be any added diversions that increases river velocities except for diversions close to the mouth of the river. Diversions close to the mouth of the river essentially do not increase river velocities and do not decrease the resistance of the river. But any diversions above the mouth of the river decrease the resistance of the river by creating a parallel run with the river. This parallel run starts at the point of the river diversion and continues downstream to the Gulf. These added diversions will decrease the downstream resistance and river velocity north of the diversion will be higher than before the diversions are added.

"A combination for shipping terminals to fall into the river"

I believe there is nothing that can be done to stop the added erosion power of the river from undermining shipping pilings. Also I believe, grading, armoring the river bank with stone, and installing concrete matt on the river bank will not stop the erosive power of the river, from higher velocities, undermining the levee at peak meander points. And this undermining of the levee will send a destructive tidal wave into Southeast Louisiana.

The Mississippi River Master Plan diversions will only work if:

• All future diversions are close to the mouth of the Mississippi River.

• Or the total flow of the bird foot delta area is decreased by the added upstream diversion flows.

A magnitude example of possible diversions

The Third Delta Conveyance Channel may well destroy Southeast Louisiana because the levee above Donaldsonville, Louisiana will be undermined. Higher river velocities above Donaldsonville will be generated by the Conveyance Channel flow because the flow will decrease the river resistance below Donaldsonville. These higher velocities will undermine peak meander points of the river above Donaldsonville and in turn the levee will be undermined and collapse sending a tidal wave south.

Please see below article that shows stream channelization increase flow velocity.

I believe one can safely conclude:

• Stream channelization reduces the resistance of a stream and this is why the stream has faster velocities.

• For the Mississippi River, approximate 1/3 of the river diverted by the Third Delta Conveyance channel will reduce the resistance of the river and as a result the velocity and the erosive power of the river upstream of the diversion will increase.

***********************************

…Because overall stream behavior is maintained in dynamic equilibrium, changes in one of several variables such as flow, velocity, or streambed substrate will result in compensating changes in the other variables. Channelization and armoring (rip-rapping) of a stream section will cause permanent changes, removing the dynamic nature of not only the altered section, but also affecting the adjoining stream sections further downstream than might initially be anticipated. Stream channelization often increases stream velocity, thereby increasing the erosive power of the stream. Durable protection or armoring is then required to ensure the stability of the engineered modification through all flow events….