[Rhodes22-list] Re: KY style Katrina - TN

[Bill Effros]

Rik,

The last time I was in New Orleans (which was about 4 months ago) there 
were huge berms on the Mississippi River side of NO.  We are talking 
about 10-20 feet high.  You climb up them, and peer down to the water 
below, which is kept in the channel by a concrete lining on the berm.  
When I was there, the water was far below.  It was not possible to dip 
your feet in the Mississippi mud.  I don't believe the Mississippi 
breached the walls.

Much of the land bordering the Mississippi in New Orleans is above sea 
level.

On the other side, the Lake Ponchartrain side, it's more like beaches, 
and homes at the water's edge.  Then there are canals and concrete lined 
bayous that come into the city from the Lake side.  It is my 
understanding that the levees broke on the canals, and that the lake 
water rose over the edge of it's boundaries.  However, on the lake side, 
most of the land is below sea level.

Apparently, on the lake side, the water on land reached a depth of 20-30 
feet.  But the lake was still higher than that, so water continued to 
flow onto the land.  As I understand it, the water was still flowing 
into the city from the lake this afternoon.  The lake side water got 
higher than the Mississippi side land, so the water overflowed into the 
French Quarter, and the Mississippi side of town.  But it could not exit 
over the berms, into the Mississippi without pumping, even though the 
Mississippi is lower at that point than the land.

Now, I suppose some of the water can flow back into the lake, 
naturally.  But the very canals that protect the land from the water 
most of the time are built with edges above lake water level to protect 
the land behind, which is below lake water level.  But at some point, 
when the water gets down to around 7 feet above sea level in the low 
lying sections, all the remaining water has got to be pumped out. 

An acre foot of water is 325,851 gallons.  There are 115,616 acres of 
land in New Orleans.  If an average of only 1 acre foot of water 
remained on land after all was said and done, NO would still have to 
pump out more than 37 billion gallons of water.  All the hurricane 
simulations that I have seen assumed that the hurricanes would not 
overtop the levees.  The pumps seem to lose the ability to keep ahead of 
the water when the elevation of the water reaches roughly 7 feet above 
normal sea level.  At that point the pumps are pumping roughly 4 1/2 
million gallons of water (I'm not sure over what time period, but it 
doesn't matter because the point is that the water is replacing itself 
with water flowing from higher places as fast as the pumps can pump--the 
water level does not go down below the 7 foot level in the low-lying 
regions where the pumps are located.)

How long does it take before the pumps start lowering the water level 
below the 7 foot mark?  Got me.  But at that point, the excess water is 
spilling into the rest of New Orleans, not back into the lake--and most 
of the city is less than 7 feet above sea level.  The water will not go 
back out over the tops of the berms and levees--it's going to have to be 
pumped out.  And the pumps on hand won't do the job.

That's what I think.  We'll see.

NPR!?

Bill Effros



Rik Sandberg wrote:

>Sorry Bill,
>
>But yep, That water ran in there because of the storm surge. The water in the city
>now is higher than the normal level of the lake now that the storm surge outside
>the floodwalls is running back out to the sea.  I agree that, since much of the 
>city is below sea level, ALL of the water will not run out. BUT, as I said before,
>much of it will, if they let it. The rest will have to be pumped. They cannot run
>their pumps though, until the dikes are fixed.
>
>I was listening to a gentleman from the Army Corp of Engineer on NPR just this morning
>describing this very scenario.
>
>Rik
>
>-----Original Message-----
>From: Bill Effros <bill at effros.com>
>Sent: Aug 31, 2005 9:26 AM
>To: sanderico at earthlink.net, 
>	The Rhodes 22 mail list <rhodes22-list at rhodes22.org>
>Subject: Re: [Rhodes22-list] KY style Katrina - TN
>
>Nope.
>
>The land behind the dikes is lower than the water in the lake and the 
>Mississippi.  All the water that gets into the "bowl" must be pumped 
>back out.  A lot of water got in.
>
>Bill Effros
>
>
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