Can We Protect New Orleans?

Sources are cited by numbers. The numbers refer to categories in our References list.

Introduction

Team 4 greatly recognizes and emphasizes the need for the conservation and restoration of the wetlands. We could implement all our solutions and build all our structures, but they would be almost useless without the natural barriers, such as the wetlands and coastal islands. They serve as the first buffer from storm surges and as a major drainage outlet, not to mention their many other ecological benefits, such as water treatment. We encourage you to also look at Team 3’s website for more information on our class’s plan for the restoration and conservation of the wetlands. The wetlands are essential to the short and long-term survival of New Orleans.

We also face a two-fold problem with water encroaching on New Orleans from two sides. The Mississippi is rising in its banks on one side of the city, while the seasonal threat from powerful hurricanes makes us keep a worried eye on the ocean. Both have the potential to flood New Orleans. Our plan represented below deals mainly with the threat of a flood from a hurricane, but it also includes some features to protect against a flood on the Mississippi. For our class’s more comprehensive plan for dealing with the rising Mississippi River and subsidence in New Orleans look at Team 9’s website.

Many challenging factors had to be taken into account for our plan. As mentioned above, the loss of the wetlands over the years and the rising Mississippi River are two of the biggest threats, but subsidence and the fact that much of New Orleans is already below sea level also affected our solution. Our figures also had to be readjusted to account for global warming. In the future, global warming will cause sea levels to rise, which means more land loss and a rising water line, and it will also cause increasingly powerful hurricanes from the Atlantic, which means more powerful storm surges and flood waters. We also looked at the possible environmental effects of our plan because we didn’t want to greatly imbalance any ecosystem.

Many of the levee failures, which we looked at in detail in our Background section, were human error and bad engineering design, which can be fixed by careful design, construction, and maintenance. The New Orleans flood protection system was not built cohesively as one uniform system. It was built in phases and stages by many different groups. We emphasize the importance of standardizing the construction, monitoring, and maintenance of the system.

The above was just to give you a little insight into our thought process as we researched and formulated our solution. Our plan, presented below, is designed to preserve and protect New Orleans from future floods in the long-term.

 

Barrier Across Opening to Lake Pontchartrain

By the time Hurricane Katrina had reached New Orleans, it had shrunken to a category 3 hurricane. One main reason for why the damage was so catastrophic was because Lake Pontchartrain was rising rapidly due to surges that were caused by Katrina when it was still a category 5 hurricane.

In addition the Lower Ninth Ward was flooded in part due to surges coming down the Intracoastal Waterway connecting the Mississippi River to the entrance to Lake Pontchartrain.

We propose solving both of these problems by installing large sluice gates across the opening to Lake Pontchartrain just before the opening to the Intracoastal Waterway (see map for exact location). These gates will be modeled after a similar sluice gate (the Weerd's sluice gate) currently in use in Utrecht, Netherlands to help protect their delta. The sluice gates should protect the Intracoastal Waterway, the canal gates, and the levees along Lake Pontchartrain from storm surges.

Sluice gates are moveable gates. Metal plates slide vertically into grooves in the sides of the structure. The operation of our gate would be controlled by a hydraulic mechanism.

This solution has actually been proposed in the past but was shot down by environmental groups. They feared the negative environmental impacts on the Lake and the necessity of the tides in the lake everyday to flush out the sewage. However, the gate would only be closed in times of emergency when rising waters in Lake Pontchartrain and threatening storm surges were an issue. At most we predict this to be about a week per year during the hurricane season, so the environmental effects on the Lake would be minimal.

The shipping industry will still be able to use the Lake as usual, except for the short periods of time when the gates will be closed due to threats. The amount of safety and security from storm surges provided by these gates would greatly outweigh any economic loss.

The Governance of the Gate would be given to NOAA (National Oceanic and Atmospheric Administration). This federal agency is in charge of providing “data and forecasts for weather and water cycle events, including storms, droughts and floods” (NOAA). The agency would watch the weather forecasts for the Gulf Region and alert the city of New Orleans when a threatening storm surges or water levels would be present in Lake Pontchartrain. The gates would be closed and remain closed until the water levels subsided.

An important first step must be taken before we build the sluice gate is to rehabilitate the land on either side of the opening to Lake Pontchartrain.  The land has been eroded by rising sea levels and storm so more land needs to be brought in; however, the main problem is the quality of the soil there presently. It needs to be replaced with soil of better quality.

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NOAA Public Affairs. (2006 Nov 2) About NOAA. Retrieved November 18, 2006 from http://www.noaa.gov/.

Closing off the Mississippi River Gulf Outlet

Team 8/9 is planning to create two main distributaries leading to the east and west of the current channel of the Mississippi River. These distributaries would deposit sediment in the surrounding wetlands to help revitalize them.  The eastern distributary channel will utilize the current Mississippi River Gulf Outlet (MR-GO).  This channel was filled in with an average of about 15 ft of silt by hurricane Katrina and is accessible only by small, shallow draft vessels until dredged.  Rather than spending extra money to dredge this channel, it should be filled in from its intersection with the Intracoastal Waterway until the southern tip of Lake Borgne. The funnel effect during Hurricane Katrina that flooded much of New Orleans East and St. Bernard Parish and ultimately caused levee breaches along the Industrial Canal initially came up through MR-GO. Closing of MR-GO end the funnel effect that worsened the storm surge from hurricane Katrina. A distributary from the Mississippi river should be directed into the remaining lower section of the MR-GO.  This distributary will redirect a maximum ¼ of the river’s volume, or about 103,000 ft³ of water during normal water levels.  The intersection of the previous MR-GO channel and the new distributary will be marked by a flood gate that will control the amount of water allowed to enter the channel.  This way, during periods of low water, more of the river’s volume can be kept in the main channel to ensure a navigable channel for ships. 

The impact on the industry and shipping of New Orleans should not be very great. Usually the MR-GO is used by commercial ship as a short cut from the ocean to the port of New Orleans, but closing it off will only add about 40 miles to their journey. The security from preventing another funnel effect by closing off the MR-GO greatly outweighs the frustration caused to any industry.

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Some of above text courtesy of Team 9 website

Brown, Matthew.  (2005).  Corps suspends plans to dredge MRGO.  [Online].  The Times Picayune. http://www.nola.com/newslogs/breakingtp/index.ssf?/mtlogs/nola_Times-Picayune/archives/2005_11_21.html.

Mississippi National River and Recreation Area.  [Online].  General Information about the Mississippi River.  http://www.nps.gov/archive/miss/features/factoids/.

 

Canal Gates and Double Pumps

Unfortunately the very same canals that have successfully drained New Orleans for many years were the reason for much of the flooding in Northern parts of the city. The pumps also were useless because they were unable to pump water out because they were situated in the city below sea level. As a result, the levees along the canals failed and the water was free to flood the city.

To solve this problem we propose installing strong gates at the front of the 7^th Street, London Avenue, and New Orleans Avenue Canals. They would basically be single sluice gates that slide vertically. This has actually already been implemented in New Orleans. Temporary gates are in place already with plans to put in permanent ones. These gates will remain open most of the time to allow the canals to serve their usual function of draining the city, but when there is the threat of a storm surge, the gates would be closed to prevent water from pouring into the canals and putting pressure on the floodwalls and levees.

The same system that will control the opening and closing of the sluice gates on Lake Pontchartrain will control the canal gates.

There is currently work in New Orleans to rebuild the pumping stations and increase their capacity. The pumps are designed to drain the city of water. They were not built to operate during hurricanes. To fix this problem we propose implementing a double pump system, in which pumping stations are present at both the lake shore and in the interior of the city where the canal ends. This would increase the pumping capacity and redesign the city so that it could handle both normal drainage and hurricane floods.

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Levee Re-Construction

The engineering failures and inadequate heights of the levees were major factors that caused the flooding of the city. The levee system in the New Orleans area includes about 450 miles of levee. The map above shows the heights to which we plan to build the levees or maintain them. We plan to rebuild all of the pre-Katrina levees at heights adequate to withstand storm surges from a Category 5 hurricane. We are also lengthening the levee in Jefferson Parish so that it extends all the way to the west to the Mississippi River.

Among our improvements are replacing all I-walls with T-walls. I-walls in many place including in the 17^th Street Canal and London Avenue Canal levees and along the Ninth Ward. T-walls are a much more structurally sound. They are less likely to be pushed over because of the wider, heavier foundation. Floodwalls are rated according to a factor of safety. They should have a factor of safety of 1.3, meaning that they are 33% stronger than they need to be to deal with the water pressure. However, it was found that 17^th Street Canal had only a factor of safety of 1, so there was little question that they would fail.

To protect against subsidence, we have our maintenance and monitoring program that will be described later. We will also look at the subsidence rates at each individual levee site on a small scale. Part of the previous problem was that the Army Corps took the average of the subsidence rate along very long lengths of levees. This system puts the whole levee in danger because it disregards very extreme, dangerous subsidence rates. From now on, however, subsidence rates will be dealt with on an individual basis, instead of averages.

Poor soil quality was another huge issue. The 17^th Street Canal levees were built on top of sand that caused the foundations to be unstable. Also, many of the floodwalls were anchored in soft clay, allowing rising water to push the wall horizontally and a gap to form at the base of the floodwall. If the quality of the soil is poor at the locations of the levees, we will replace it with suitable soil. Although this is an expensive solution, it is the only way to ensure the stability of the levees and floodwalls. Extensive evaluation of the geology of the levee locations is essential.

To protect against erosion from the levees along the 17^th Street, Orleans Avenue, and London Avenue Canals and the Industrial Canal will be armored with concrete on the backside so that overtopping will not erode the backside of the levee and cause a levee failure. They will also be armored on the water-side of the levee at the base of floodwalls so that gaps can’t form at the between the base of the floodwalls and the soil.

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Levee Maintenaince and Monitor Boards

This is a supplemental method of implementation that we have proposed to ensure that our proposals will be correctly implemented. To read more about this click here.

Long Term

Our long term plan is mainly one of vigilance and adaptation to new problems as they arise. In the past, the levees were built and were not taken care of; thus, they degraded and were not adequate to deal with Katrina. The most long-term part of our plan is our maintenance and monitoring program and our plan for governance of the levees explained above. Maintaining the levees religiously will provide a large amount of protection from future floods. Also, the Levee Governance Board is a flexible, powerful body that will be able to institute changes to the flood protection system if unforeseen challenges or problems come up.

 

Cost

We have divided our costs into 6 major categories. As we mentioned, in our Army Corps section, we plan on contracting the work out to private contractors, using a mainly local workforce.

Improvement/Repair	Cost
Sluice Gates Across Lake Pontchartrain	$2.035 billion  (Swenson Times-Picayune)
Closing of MR-GO	$1.47 billion (Dredged Material)
Levee Repair and Construction	$9.425 billion (Wagner)
Interim and Permanent Gates on 17th St., London Ave, and Orleans Avenue Canals	$0.350 billion (Wagner)
Monitoring by Differential Global Positioning System	$1.5 billion (Wagner)
Pumping Stations	$0.345 billion (Wagner)
Total:	$15.125 billion

 

Application to Other Areas

 

Other areas may be interested in using our idea of moveable gates to control water flow, either on canals or on larger bodies of water. Sluice gates are an effective method of controlling water flow because they can be left open in normal circumstances to let regular processes proceed, but if extreme threats or conditions are present, they can be manipulated to protect an area from storm surges.

The flood system failures in New Orleans mainly serve as a wake-up call to all other vulnerable areas in the United States. A federal agency, the Army Corps of Engineers, was responsible for the construction and maintenance of the system; however, it was nowhere near adequate to protect New Orleans. Other cities need to inventory their own flood protection systems to make sure they will be protected in the case of a natural disaster.

They can also look up to our maintenance, monitoring, and governance system as an example to base their own after. Flood protection needs to be constantly on the minds of the residents and governments of susceptible areas, even after the destruction of Hurricane Katrina is forgotten. Any slacking or corner-cutting in the system could come at a huge price of lives and destruction.