[StBernard] Chef, Rigolets passes would get floodgates in Louisiana's coastal plan

[Westley Annis]

Chef, Rigolets passes would get floodgates in Louisiana's coastal plan

Print Email Mark Schleifstein, NOLA.com | The Times-Picayune By Mark
Schleifstein, NOLA.com | The Times-Picayune 
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on January 03, 2017 at 12:00 AM, updated January 03, 2017 at 6:52 AM

Gates to block hurricane storm surge from entering Lake Pontchartrain -- an
idea first by the Army Corps of Engineers a half century ago -- are included
in a major 2017 update of Louisiana's coastal master plan released Tuesday
(Jan. 3). The gates and accompanying structures, a huge undertaking that
would cost $2.4 billion to build, could save as much as $1.2 billion a year
in surge damage in St. Tammany and other lakeshore parishes. 

Combined with proposed levees for Slidell, the gates would represent the
largest effort to date to reduce storm surge flooding on the North Shore.
The gate and weir structures would be built in the Chef Menteur and Rigolets
passes where they flow under U.S. 90. The passes are 35 feet to 50 feet deep
beneath the highway bridges at those locations, funneling large amounts of
water into the lake during storms.

The project would include about 5,200 feet of earthen levee and 630 feet of
floodwall built on sheet piling. Also part of the proposal are a 150-foot
closure gate and multiple vertical lift gates at each pass, to maintain
tidal exchanges. 

The gates are the biggest of a number of projects in the 2017 plan update to
benefit St. Tammany Parish. Others include completion of levees in a U shape
around Slidell to protect the highly populated area from the effects of
surges caused by a hurricane with a 1 percent chance of occurring in any
year, a so-called 100-year storm.

The 2017 master plan update has major implications for other parts of the
New Orleans area, including:

* Raising levees along St. Bernard and other parishes on the east bank of
the Mississippi River
* Abandoning plans for a higher levee around the Jean Lafitte area on the
West Bank of Jefferson Parish in favor of measures to elevate structures
there.
* Building a new levee east of Lake Salvador to protect the west bank of St.
Charles Parish. 
* The updated plan also includes much of St. Tammany Parish in a regional
"nonstructural" risk reduction program. That's designed to protect low-lying
business buildings and either to raise homes as much as 14 feet above the
ground or to buy homes in flood-prone areas.

At the same time, the plan includes wetland restoration projects along St.
Tammany's lakefront or along the land bridge separating New Orleans and St.
Tammany Parish, aimed at reducing surge heights.

Gates to be built within 30 years 

The 50-year master plan guides the state's spending on coastal restoration
and projects to reduce flood risk. This year's plan is a major update from
the 2012 version, which has gotten minor revisions every year.

The new plan lists the Chef Menteur and Rigolets gates among projects to be
built during the first 30 years of the plan, rather than among a number of
fast-track projects to be built in the first 10 years. The fast-track
projects will be largely paid for by money from various settlements with BP
and its drilling partners resulting from the Deepwater Horizon oil spill in
2010.

The gates are to be built to a height of two feet above sea level. State
officials rejected proposals to raise the gates -- and U.S. 90 -- to 10 feet
or more above sea level, which would have turned the highway itself into a
higher surge barrier. That option was rejected after scientists concluded
the added height would increase flooding -- and flood damage -- along the
Mississippi Gulf Coast and the eastern shores of St. Bernard and Plaquemines
parishes.

Bren Haase, who oversees the master plan development process for the state
Coastal Protection and Restoration Authority, said Louisiana will ask the
Corps of Engineers to begin the process of having the gates authorized by
Congress as a hurricane risk reduction project, which would make it eligible
for federal funding. That process that could take several years, which is
one of the reasons why the project is in the master plan's 30-year list.

Gates first proposed in 1970s

For the corps, the Chef Menteur and Rigolets gates proposal is the latest
iteration of a recommendation that the agency's engineers made as part of
the comprehensive plan before Hurricane Betsy in 1965 to protect New Orleans
from hurricanes. By the mid-1970s, the corps had completed the official
project report and an environmental impact statement that included the two
pass gates and a third gate at the lakefront entrance to the Industrial
Canal.

The environmental group Save Our Wetlands Inc. filed suit against the corps
in 1976, charging that corps violated the federal National Environmental
Policy Act because the environmental report inadequately considered
alternatives. U.S. District Judge Charles Schwartz Jr. halted construction
of the gate system in December 1977 because of the failure to consider
alternatives. But Schwartz also said he was not ruling against the corps'
plan, and he urged the agency to complete its required review.

It took the corps until the mid-1980s to re-evaluate the project revise the
environmental statement. By then, it recommended abandoning the lake pass
gates and the gates at the lake ends of drainage canals -- what it called
the "barrier plan" -- as too expensive. Instead, the corps adopted a plan
that called only for higher levees in the New Orleans, St. Bernard and East
Jefferson.

Some of those earthen levees in New Orleans and St. Bernard failed during
Hurricane Katrina. And without barriers to stop surge from entering the
lake, many North Shore areas flooded and some canal walls in New Orleans
failed, flooding most of the city.

Post-Katrina measures not aimed at North Shore 

In the aftermath of the catastrophic Katrina failures, Congress ordered the
corps first to rebuild the New Orleans area levees on both the east and west
banks of the Mississippi to new engineering standards, developed as a result
of lessons learned from the 2005 storm. The result was a series of higher
levees designed to withstand surges caused by a 1 percent, or 100-year,
storm. Those plans include combination pumping stations and gates at the
three major drainage canals on the east bank of New Orleans, a surge barrier
floodwall and navigation gates along the northwest corner of Lake Borgne and
a surge gate at Seabrook on the Industrial Canal.

But the post-Katrina plan was limited to protection for the south shore of
Lake Pontchartrain. It did not include the Chef Menteur and Rigolets pass
gates.

However, Congress also ordered the corps to complete a separate study of
ways to protect all of Louisiana's coast, including New Orleans and St.
Tammany Parish, from surges caused by the equivalent of a Category 5
hurricane, one much stronger than the Category 3 Katrina. As part of that
study, finally submitted to Congress in March 2009, the corps again laid out
two alternatives for Lake Pontchartrain: higher levees and a combination
gate-weir barrier plan. The report, however, recommended that further study.

Meanwhile, Louisiana officials adopted the state's first master plan in
2007, before the corps study was completed, in part to assure that Congress
saw the state's approach to such levee issues before it decided whether to
adopt the corps proposals. The 2007 master plan, and the 2012 revision, both
included the lake gates as proposals.

The 2007 plan recommended reviewing various combinations of floodwalls,
levees and gates along the New Orleans East land bridge and the passes as a
barrier to surge entering the lake. The 2012 plan recommended starting
engineering and design work aimed at selecting a viable alternative. Now the
2017 version recommends moving from planning to construction, once money for
the project is found.

The decision against building a levee -- or elevating U.S. 90 -- is based in
part on the results of three studies.

A 2012 study of potential levee costs conducted for the Coastal Protection
and Restoration Authority suggested building a 17-mile levee along the path
of the CSX Railroad tracks, a bit farther east than U.S. 90, but without the
gates, at a cost of $1.1 billion.

Two studies for the state in 2016 by Arcadis and the Rand Corp. focused more
on the surge effects that various combinations of levee and gates would have
on damages around Lake Pontchartrain and in Mississippi and along the shores
of St. Bernard and Plaquemines parishes. Those two studies concluded that
building just the gates, and not the levees, would cause a much smaller
increase in surge heights along the Mississippi coast, less than six inches.

The Rand study determined that not including the levee and limiting the gate
height to two feet above sea level would reduce damages to properties around
the lake almost as much as if the gates were built to 10 feet and the U.S.
90 roadway was built to 10 feet above sea level. But the gates-only approach
also produced the least damage, both in Mississippi and in St. Bernard and
Plaquemines parish, where the road and levee height would have also
increased damage.

According to those reports, storm surges accompanying a 100-year hurricane
would cause an average $3.2 billion in damage a year without either gates or
levees, including $2.1 billion in damages in St. Tammany, $500 million in
New Orleans and Jefferson Parish, $500 million in other lakefront parishes
and $100 million in Plaquemines and St. Bernard.

The gates could slice $1.2 billion in annual damages from that total, to $2
billion. St. Tammany's damage would be reduced by $600 million, New Orleans
and Jefferson by $300 million, other lakefront parishes by $300 million,
while the damage levels in St. Bernard and Plaquemines would remain the
same.

Slidell to get U-shape levee

The U-shaped levee improvements proposed for Slidell have also been included
in previous versions of the master plan. This year, the proposal is for
building almost six miles of earthen levees and about 2 and 3/4 miles of
concrete and sheet pile T-walls, all to an elevation of 16 feet above sea
level, enough to protect the area inside from a 100-year storm surge.

The project would cost $181.3 million. The state and St. Tammany Parish are
likely to request that the corps be involved, to assure that the federal
government pays the majority of the cost.

The master plan also includes parts of St. Tammany Parish subject to
flooding in a nonstructural risk reduction project. The state would set
aside as much as $7.8 million during the plan's first 30 years for three
types of risk reduction projects:

* Floodproofing non-residential properties where flood depths are expected
to be one to three feet.
* Elevating residential properties where 100-year flood depths are expected
to be three to 14 feet.
* Acquiring residential properties in areas subject to 100-year flood depths
greater than 14 feet.
* Participation in the program would be voluntary. St. Tammany has included
a version of this proposal in its own coastal master plan, which was
recently authorized by Congress, and this might be eligible for some federal
financial support.

The master plan also includes a number of coastal restoration projects that,
while designed largely as environmental improvements, will also help reduce
storm surge levels in St. Tammany Parish. Three are considered fast-track
projects, to be built within the plan's first 10 years. They are:

* New Orleans East land bridge restoration, including 11,700 acres of new
and restored marsh, at a cost of $421.1 million.
* Guste Island marsh creation in about 700 acres along the northwest Lake
Pontchartrain in St. Tammany, at a cost of $64.3 million. This project is
included in a parish coastal restoration plan recently authorized by
Congress, so it could be eligible for federal funding.
* Unknown Pass to Rigolets shoreline protection, including rock breakwaters
installed to an elevation of 3 1/2 feet more than a mile of the Lake
Pontchartrain shoreline, at a cost of $11.6 million.
* Two similar projects are proposed to be funded later in the master plan,
between years 11 and 30:

-- New Orleans East land bridge restoration, including 21,400 acres of
marsh, at a cost of $1 billion.

-- St. Tammany marsh creation, involving 5,900 acres along the northern
shore of Lake Pontchartrain, for $194.9 million.