Mississippi River shooting through Bonnet Carre Spillway faster than expected

A week after the opening of the Bonnet Carre Spillway, the height and pressure of the Mississippi River is shooting water through the spillway well above its rated capacity.

Even though only 330 of its 350 bays are open, an estimated 316,000 cubic feet of water per second is passing through the control structure, more than the structure’s rated capacity of 250,000 cfs, spillway manager Chris Brantley said Monday.
The spillway was designed to divert as much as 250,000 cubic feet of water per second away from New Orleans. It is opened whenever the volume in the river is expected to surpass 1.25 million cubic feet of water per second.

The extra flow is driven by the river’s height, he said.
Each cubic foot of water contains 7.48 gallons, which means that more than 8.5 billion gallons of water per hour is moving toward Lake Pontchartrain.

All that water seems to be filling up the 7,600-acre spillway, and parish work crews, along with the corps and state officials, have been shoring up low spots along the levee, particularly on the west side of the U.S. 61 bridge across the spillway.
“We’re monitoring the levee very closely, and we’re seeing freeboard of about 5 feet, with a couple of exceptions, where it’s about 3 feet,” Brantley said.

St. Charles Parish work crews, with the assistance of the state Department of Transportation and the corps, closed a small portion of the outer eastbound lane of Airline Drive to build a small dirt levee as an additional safety margin.

Another low spot is on the other side of the bridge in the westbound lane, which corps officials are closely monitoring, Brantley said.

Motorists who stop along the highway to watch the fast-moving water are being shooed away, and signs warning motorists not to park on the shoulder of the bridge have been posted.
Brantley said corps hydrologists will calculate river flows to determine whether more bays should be opened Tuesday.

The last time all Bonnet Carre bays were opened was in 1983.

Matt Scallan can be reached at mscallan@timespicayune.com

Flood will deal blow to struggling oystermen

By Nikki Buskey
Staff Writer

Published: Friday, May 6, 2011 at 11:00 p.m.
Last Modified: Friday, May 6, 2011 at 11:42 p.m.
HOUMA — Oystermen just beginning to recover from the BP oil spill are facing another blow as the state prepares for major floods that could kill the few productive oyster grounds that remain.

The Corps of Engineers plans to open at least one spillway on Monday to protect people, homes and businesses along the swollen Mississippi River.
Freshwater diverted from the river via the Bonnet Carre spillway will ease pressure on levees, but it will also go into the salty waters where the shellfish grow, potentially killing them. The Bonnet Carre Spillway, about 30 miles northwest New Orleans, diverts river water to Lake Pontchartrain and east into Lake Borgne and the Mississippi Sound.
The corps is also considering opening the Morganza Spillway, about 35 miles northwest of Baton Rouge. It diverts river water into the Atchafalaya Basin. It hasn't been opened since 1973.
Opening the Morganza Spillway could send torrents of freshwater into the Atchafalaya Basin and communities in Terrebonne and Lafourche.
If they open the Morganza spillway “from the Houma Navigation Canal going westward, we could see 100 percent oyster mortalities,” said Mike Voisin, owner of Motivatit Seafood in Houma and a member of the state's Oyster Task Force. “Two of the major areas propping up the oyster industry right now will be significantly impacted.”
Freshwater kills oysters because it wreaks havoc on their metabolism, preventing them from keeping a saltwater balance.


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