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Started By
Message
re: Planned freshwater diversions will doom LA salt fishing
Posted on 3/27/13 at 10:16 am to Deege
Posted on 3/27/13 at 10:16 am to Deege
quote:
The more informed I have become on the subject the more I think the diversions will accelerate coastal erosion.
LINK
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.
I see CFS figures, but that measures water flow, not sediment load. Does anyone have reliable information on whether the proposed diversions will carry more sediment than Davis Pond or Caernarvon.
2
Posted on 3/27/13 at 10:24 am to jimbeam
That shite didnt do anything in manchac besides make it smell.
Not trying to be punny
Not trying to be punny
Posted on 3/27/13 at 10:25 am to ToulatownTiger
It's cheap though and has been shown to work. Just read a nice article on that kind of work
Posted on 3/27/13 at 10:30 am to jimbeam
Blow the levees and be done with it. The river is eventually going to change course as it want to, it is only a matter of time.
Posted on 3/27/13 at 10:36 am to GREENHEAD22
That is the obvious answer but its not so simple, socially speaking
Posted on 3/27/13 at 10:42 am to Deege
quote:
I am leaning toward the "Dredge don't Divert" if anything is to be done. Spoil from dredging can build strategic land ridges to buffer storm surge and contain salt marshland.
You obviously don't know how much dredging cost.
Posted on 3/27/13 at 10:45 am to dat yat
quote:
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.
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.
Posted on 3/27/13 at 10:46 am to 34venture
quote:
You obviously don't know how much dredging cost.
Couple that with the fact that it washes away almost as quick as it is dredged since there isn't any new material coming down to reinforce it.
Posted on 3/27/13 at 10:47 am to mylsuhat
quote:
Your kind is stupid as hell!
Short sighted and next you'll bitch when there is no more South Louisiana
LSUHat. My thinking used to more in line with yours. I am more informed now.
Come back with facts, links, studies. Dont come at me with ad hominem.
Posted on 3/27/13 at 10:48 am to Deege
I won't matter...builds marsh....puts rich silt in other places....which will create more shallow marsh pools for shrimp...which will make the speckle trout and redfish pop jump....do some research.
Posted on 3/27/13 at 10:48 am to bayoudude
Exactly. We need to stop trying to change a whole coastline. Let nature do what we undid
Posted on 3/27/13 at 10:51 am to dat yat
Call me crazy, but would it work any better to stir up a bunch of sediment via turbulence and then allowing it to go through a diversion? That way the top, skimmed stuff would have much more suspended sediment that just straight skimming off of the top?
Maybe pumping air into the thicker bottom(I know there is basically no serious bottom, but the sediment load would be more down there. You could even pump high pressure water.
Maybe pumping air into the thicker bottom(I know there is basically no serious bottom, but the sediment load would be more down there. You could even pump high pressure water.
Posted on 3/27/13 at 10:52 am to Hammertime
There's still a crazy amount of silt in the Mississippi
Posted on 3/27/13 at 10:54 am to jimbeam
quote:
Exactly. We need to stop trying to change a whole coastline. Let nature do what we undid
we need the river for navigation and trade.
How else would we give away all that grain to the third world.
Posted on 3/27/13 at 10:57 am to bayoudude
Also there are huge differences between a sediment diversion and a freshwater diversion in the design.
Everything that has been designed previously is a water diversion first and the design did not really incorporate sediment transport into it.
The new ones will be designed as sediment diversions so expect to see something that looks like Morganza flood way or bonnet carre spillway. Something wider and flatter instead of a large box culvert.
They also don't need to be operating at full capacity (in theory) all the time. The sediment load of the river peaks prior to the flood water peak. If designed and operated properly the sediment can be captured while the peak flood flow can be sent down the river to wash out the mouth of the river (SW pass).
That concept would hopefully allow the state to get a permit from the corps which previously required the state pay for increased dredging of shipping channels due to water flow changes from diversions. The increased dredging cost requirements has killed many water/channel re-alignment and proposed diversion projects in the past.
Everything that has been designed previously is a water diversion first and the design did not really incorporate sediment transport into it.
The new ones will be designed as sediment diversions so expect to see something that looks like Morganza flood way or bonnet carre spillway. Something wider and flatter instead of a large box culvert.
They also don't need to be operating at full capacity (in theory) all the time. The sediment load of the river peaks prior to the flood water peak. If designed and operated properly the sediment can be captured while the peak flood flow can be sent down the river to wash out the mouth of the river (SW pass).
That concept would hopefully allow the state to get a permit from the corps which previously required the state pay for increased dredging of shipping channels due to water flow changes from diversions. The increased dredging cost requirements has killed many water/channel re-alignment and proposed diversion projects in the past.
Posted on 3/27/13 at 11:00 am to eng08
Exactly. Has to have sediment. Will also slow down tr Mississippi and can form a birds foot in Venice againe
Posted on 3/27/13 at 11:03 am to hardhead
It is a little more complicated than that Hardhead
LINK
"Operating the diversion consistently in
response to saltwater intrusion events
may help to
maintain marsh species composition
along the estuarine gradient while
increasing species
survival and rates of production.
Whatever benefits result from increases
in the inorganic
sediment supply should be weighed
against the impact of adding nutrients
that may weaken the
soils."
and
LINK
Per RnR poster Steve: "This report is a study of how much the roadbed of highway 23 in Plaquemines Parish has sunk in the last 25 years.
Go to the bottom of the report, and click on the link that says HTML slide show, then click on slide 13.
What you will see is that highway 23 in Belle Chasse has sunk 15 centimeters (6 inches) in the last 25 years. 6 inches doesn't sound like a lot, but it is when you are near sea level.
Down by Myrtle Grove to Empire, highway 23 has sunk 26 centimeters, or just over 10 inches in the last 25 years! That means the entire land and roadbed between the 2 levees has sunk that much.
Want the reason? It sure ain't the oilfield canals, is the LEVEES. And thats just in 25 years, what about the 50 years before that? How much did it sink then?
Hate to say this, but the only solution is to either get a couple dozens dredges in the river and start filling the marsh, or wait until the entire marsh ecosystem is destroyed and open up the levees WIDE OPEN, and not these little piss ant diversions. Suggesting anything else is like talking about fishing conditions when the boat is sinking..."
LINK
"Operating the diversion consistently in
response to saltwater intrusion events
may help to
maintain marsh species composition
along the estuarine gradient while
increasing species
survival and rates of production.
Whatever benefits result from increases
in the inorganic
sediment supply should be weighed
against the impact of adding nutrients
that may weaken the
soils."
and
LINK
Per RnR poster Steve: "This report is a study of how much the roadbed of highway 23 in Plaquemines Parish has sunk in the last 25 years.
Go to the bottom of the report, and click on the link that says HTML slide show, then click on slide 13.
What you will see is that highway 23 in Belle Chasse has sunk 15 centimeters (6 inches) in the last 25 years. 6 inches doesn't sound like a lot, but it is when you are near sea level.
Down by Myrtle Grove to Empire, highway 23 has sunk 26 centimeters, or just over 10 inches in the last 25 years! That means the entire land and roadbed between the 2 levees has sunk that much.
Want the reason? It sure ain't the oilfield canals, is the LEVEES. And thats just in 25 years, what about the 50 years before that? How much did it sink then?
Hate to say this, but the only solution is to either get a couple dozens dredges in the river and start filling the marsh, or wait until the entire marsh ecosystem is destroyed and open up the levees WIDE OPEN, and not these little piss ant diversions. Suggesting anything else is like talking about fishing conditions when the boat is sinking..."
This post was edited on 3/27/13 at 11:06 am
Posted on 3/27/13 at 11:05 am to Deege
Also drilling for oil is not helping. Not saying we shouldn't, or bein a hippie., just saying
Posted on 3/27/13 at 11:05 am to Deege
quote:
It is a little more complicated than that Hardhead
no shite?
If you want a more in-depth article then send me a grant and you will get one.
Posted on 3/27/13 at 11:07 am to jimbeam
My thinking behind that is different strata layers in the river with different amounts of silt, with different sized particles. Stir up the bottom heavy stuff a mile of half mile before the diversion and properly place the diversion according to the bends in the river.
It is obvious that the diversions are only pulling the very top, less sediment dense portions of water. Get the sediment to the top and less CFM of water is required, less deep diversions, and costs exponentially less than dredging
It is obvious that the diversions are only pulling the very top, less sediment dense portions of water. Get the sediment to the top and less CFM of water is required, less deep diversions, and costs exponentially less than dredging
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