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Dredging a Shallow River

 
 
gollum
 
Reply Wed 22 Aug, 2012 07:43 pm
I read that the drought is causing some parts of the Mississippi River to be too shallow for certain ships. Accordingly, the river is being dredged in those areas.

I think dredging the bottom would lower the whole river not make the river deeper.

Please explain.
 
Rockhead
 
  1  
Reply Wed 22 Aug, 2012 07:53 pm
@gollum,
they just cut the channel out deep enough to clear the barges and ships.

the river might get narrower, but the shipping will have a clear path...
0 Replies
 
sozobe
 
  2  
Reply Wed 22 Aug, 2012 07:56 pm
@gollum,
I'd imagine it would be in a specific channel -- diverting the existing water to that spot and making it deep enough for the barge.

Yeah, just found this:

Quote:
A spray of sand laced water shoots out from the Dredge Jadwin, a U.S. Army Corps of Engineers vessel that is clearing out some of the silt and left over mud and debris from last year's record flood on the Mississippi River and cutting a deeper channel for barges and their towboats to navigate north of Greenville, Miss., Wednesday, Aug. 22, 2012. Coast Guard Capt. William Drelling said Wednesday that authorities would inspect the channel near Greenville, Mississippi, then reset navigation buoys allowing barge traffic to resume on a limited basis as both federal agencies deal with the continued drought that has lowered the Mississippi River.


http://www.fresnobee.com/2012/08/22/2961143/coast-guard-reopens-mississippi.html#storylink=cpy

-signed, grew up blocks from the Mississippi
0 Replies
 
Miss L Toad
 
  0  
Reply Thu 23 Aug, 2012 02:28 am
@gollum,
Quote:
I think dredging the bottom would lower the whole river not make the river deeper.


Love your thinking gollum, the whole river would be lower but the effect would be spread out so the dredging would only make the river deeper ( more navigable) in the area of concern.

0 Replies
 
raprap
 
  3  
Reply Thu 23 Aug, 2012 05:46 am
@gollum,
First the bottom of the Mississippi river below Memphis is below sea level. Dedging only lowers the bottom which is somewhat backfilled from the gulf--this is already being demonstrated as increased salinity in municipality potable water suppies is being encountered along the lower Mississippi.

Second--Eads Wiers (those dikes built perpendicular to the river banks) work by increasing channel flow to scour the channel bottom. If the river surface flow isn't there because of lower river surface elevation, channel scouring won't happen. IOW the mechanical scouring of the channel is necessary because the engineered scouring isn't happening.

Additional--keeping the Mississippi open is transportation mission critical. One barge is equivalent to 100 semi truckloads or 40 train carloads. Along the Ohio, Misissippi, Missouri, Tennessee an Kentucky Rivers barges is the cheapest method of bulk freight--bar none. Losing this transportation venue, even temporarily, can be economically significant.

Rap
0 Replies
 
 

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