Salt water moves up Miss. River, Army Corps reacts

[bluedigger]

[div class="excerpt" style="border-left: 1px solid #bfbfbf; border-top: 1px solid #bfbfbf; border-right: 1px solid #bfbfbf; border-radius: 0.3077em 0.3077em 0em 0em; box-shadow: 2px 2px 6px #bfbfbf;"]Salt water moves up Miss. River, Army Corps reacts[div class="excerpt" style="border-left: 1px solid #bfbfbf; border-bottom: 1px solid #bfbfbf; border-right: 1px solid #bfbfbf; border-radius: 0em 0em 0.3077em 0.3077em; background-color: #f4f4f4; box-shadow: 2px 2px 6px #bfbfbf;"]NEW ORLEANS (AP) - The Army Corps of Engineers says it will construct an underwater sill in the Mississippi River to stop salt water from threatening drinking water supplies in the New Orleans area.

The move is needed because water levels in the drought-stricken Mississippi have gotten so low that the river is nearly at sea level and this is allowing salt water from the Gulf of Mexico to move far inland.

At the latest check on Monday, salt water was on the outskirts of New Orleans.

The Army Corps is expected to issue bids on Tuesday to get work started on building a sill designed to stop the salt water from moving upriver and affecting freshwater intakes for Belle Chasse, a town in Plaquemines Parish south of New Orleans.
http://www.ksla.com/story/19209989/salt-water-moves-up-miss-river-army-corps-reacts

[Lint Head]

1. Climate changes slowly and it is here.

[Junkdrawer]

2. Climate changes slowly, until a tipping point is reached.....

activate the methane clathrate bomb and you're facing down a Permian–Triassic extinction event.

[kickysnana]

3. Cayce says to expect the rising sea levels to send the great lakes down the Mississippi eventually

That would be something to see. Downtown St Paul is down in a depression and the river down lower so at some time a lot of water was gong through where downtown St Paul is.

[intheflow]

4. Army Corps of Engineers is working on this?

Expect the "fix" to be completely FUBAR.

[bluedigger]

5. I'm interested in the "underwater sill" concept, myself.

It seems like it would have to impede the river traffic to be effective, particularly given the already low water level...

[intheflow]

6. I don't understand using an underwater sill to slow salinity in the water.

Underwater sills are used to slow beach erosion. Basically, they're an underwater dam to keep sand from washing into the larger body of water. It might work if the salt was separated from the water, since salt is heavier than water. But since saltwater is, by definition, salt dissolved/merged with the water, I just can't see how this is going to be much help.

[Lochloosa]

7. Salt water is heavier than fresh...it is creeping in at the bottom of the river

[intheflow]

8. But how high would the sill have to be?

This seems like a sort-sighted stop-gap expensive measure.

[FarCenter]

9. SALTWATER BEHAVIOR

The thalweg, or bottom profile, of the Mississippi River is deeper than the Gulf of Mexico water surface level up to River Mile 350 Above Head of Passes (AHP). This location is about 15 miles downstream of Natchez, Mississippi. Salt water in the Gulf of Mexico is denser than the fresh water flowing in the Mississippi. Therefore, at low river flows, the Gulf’s salt water moves upstream along the bottom of the River underneath less dense river fresh water.

A number of factors impact on the upstream movement of salt water from the Gulf. The dominant factor is the volume of flow in the River. However, flow duration, channel slope, wind velocity and direction, tides, and water temperature all influence the movement of the salt water.

http://www.mvn.usace.army.mil/eng/saltwater/wedge_overview.htm

[lunatica]

10. This means they're forced to start paying attention to climate change

Maybe they'll build dikes around New York City before long. They don't want the oceans to start flooding the subway system.

[intheflow]

11. Are you kidding?

These are the fools whose levies gave New Orleans the Katrina devastation. They'd been warned about those levies breaching for decades and did nothing.