Full document / COSOC-W-86-002 - the National Sea Grant Library

Estuarine and Coastal Management • Toots ofthe
Trade. Proceedings ofthe Tenth National Conference
of The Coastal Society. October 12-15.1986. New
Orleans. LA. Copyright by The Coastal Society
1987.
BENEFICIALUSES OF DREDGED MATERIAL
IN NEW ORLEANS DISTRICT
Suzanne R. Hawes
U.S. Army Corpsof Engineers
New Orleans District
P.O. Bo* 60267
New Orleans, LA 70160
Introduction. Louisiana Is losing wetlands at a rapid rate. Recent
figures (Wicker, 1980) Indicate a loss of 50 square olles per year - arvt
the rate aay well be Increasing. There are nuraerous reasons for this
loss. Natural forces such as subsidence, compaction, and sea level ris-:
ore part of the cause. Han's activities also play a part. In order to
make southeastern Louisiana habitable, it has been necessary to levee
the Hisslsslppi River to prevent destructive flooding. The presence of
the levees prevents the periodic nourishment of the marshes with
sediment and nutrients* Petroleum exploration has turned many areas of
coastal marsh Into a maze of canals. These canals can prevent sheet
flow and marsh nourishment, and Impound water on the marsh. Navigation
channels have allowed saltwater intrusion which has destroyed marsh.
Freshwater Diversion. The trend of land loss is real. It can probably
never be reversed, but some measures can be taken to slow it. One
method of reducing it would be to divert fresh water from the
Mississippi River Into the marshes. Some sediment would be carried by
this fresh water - enough to build a 2,500 acres In Davis Fond and 700
acres In Big Har (U.S. Army Corps of Engineers, 1984). But upstream
dams have halved the volume of sediment being carried by the river, so
less is available to create land. The river nutrients would nourish the
marsh and the fresh water would prevent future marsh loss: 83,000 acres
at Davis Pond, 16,000 acres at Caernarvon, and 4,000 acres at Bonnet
Carre.
Value of Harsh. Host measures we take to reverse the trend of marsh
loss will fill shallow open water. Thus, we need to compare the values
of shallow bays and marshes. Bays are Inhabited by various benthic
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