The gates are too short
You are reading that right. The gates are too short.
I'm referring to the three outfall canal gate structures that the Corps built in 2006 and 2007. When the gates drop, their tops are 16 feet above the lake. That matches the top of the adjacent protection in Orleans Parish.
However, that does not meet the Corps' own design guidelines, which have been in effect since October 2007. From page 23 of chapter 1 of the Corps' Hurricane and Storm Damage Risk Reduction System Design Guidelines:
"Structural superiority is incorporated in the design elevation for those structures that would be very difficult to rebuild, if damaged, because of disruption in services. Examples are major highway and railroad gates that require detours, pumping station fronting protection that requires reductions to pumping capacity, sector gated structures, etc. These structures are to be constructed to the 2057 levels plus 2 ft. for structural superiority."
And then on page 3 of chapter 5:
"Structural Superiority – All new structures that are difficult to construct due to their nature, such as railroad and highway gates, pump station fronting protection, sector gates, utility crossings, etc., shall have a minimum 2 ft. overbuild."
The Corps is incorporating structural stability into all its major flood protection structures, like the IHNC-Lake Borge surge barrier, the West Closure Complex, and the Bayou Dupre gate in St Bernard Parish. In fact, Karen Durham-Aguilera crowed about it at the November 5, 2009 City Council hearing (at 2:09:09) when describing additional factors on top of the Corps' 100-year design heights:
"We project subsidence out over 50 years, we add numerous factors of safety so that we add more for that. We add more for what we call structural superiority if it's a hardened structure that we would have to rebuild that it would be too hard to add on to."
Most obviously and relvantly, the extra two feet show up in the proposed design criteria for the new permanent pump stations which will replace the current gates and pumps. On pages 9, 10, 15, 21, and 48 of those criteria, the height of the gates at all three future stations is required to be a minimum of 18 feet, or two feet higher than the current gates. Here's the reference on page 15:
On page 48, a full explanation is given, explicitly citing the structural superiority requirement:
"5.5.9 Structural Superiority
Any PPS [Permanent Pump Station] facilities, structures, civil works, or other components that form a structural portion of the storm surge barrier, or that will be located in areas subject to direct storm surge, shall include structural superiority design features as described below. Structural superiority is required to enhance the ability of the structure to survive potential overtopping events. Structural superiority refers to adding structure height to prevent overtopping of structures.
Structural superiority shall be included as follows:
1. Where structural superiority is required, tops of structures shall be a minimum of two (2) feet above the design grade of the adjacent levees/floodwalls. For this project, minimum structural superiority elevation shall be 18.0 feet."
So despite knowing
a) that the future gates will be 18 feet off the water,
b) what the current flooding threat is, and that it requires gates taller than 16 feet, and
c) that the current gates are 16 feet,
the Corps has not done anything to address this increase in risk. That is, they haven't moved to add two feet to the top of the current gates to protect the city in the intervening years before the permanent pump stations are built. Keep in mind the current gates are scheduled to be in service for at least four more hurricane seasons, and all that time the Corps apparently believes having gates that are too short is okay.
The Corps even knows that 18 feet probably isn't enough for the 100 year criteria. Earlier in the document, they call out the 100 year "still water elevation," (i.e. the surge without waves) in the lake as 10.2 feet. Then they call out the lake wave run up on vertical walls (how much above the still water level waves will wash) as 9 feet. Thus, they are expecting a 100 year storm (which roughly corresponds to a category 2 or 3) to have water go over even an 18 foot wall. Imagine what happens on the other side of a 16 foot one.
The scary thing is that when the gates were in the design phase, they were actually going to be two feet shorter than they are now. Take a look at this early design sketch of the 17th Street closure structure (likely from late 2005), taken from a 2007 presentation given by the design engineers on the closure strucutres, URS and Linfield, Hunter, and Junius:
That drawing shows the gates as topping out at only 14 feet. Scary.
Also, this is not simply an academic difference. There is a reason more height is required at structures like these gates. In this case, they need to protect the actual guts that make the gates work. The extra height would also help protect the equipment that locks the gates in place during a storm. Two extra feet would go a long way toward that protection.
But even without that extra two feet, there are robust systems in place to make sure the gates are protecting the city properly during a storm, right? I mean, surely those locking mechanisms are always operated correctly, right? It's not like the Corps would simply leave the gates unsecured and violate their own procedures, would they?
Um, yes, they would. More on that coming up...
Update - 8/25/12
The Corps is actually planning on following this same strategy - i.e. violating their own guidelines by installing gates that are too short - with the permanent pump stations, as reported in the Times Picayune on May 14, 2012. At the very end of an article about the restarting of the bid process on the permanent stations after the first bids were thrown out as a result of successful protests, there's this mention of changes in the bid specifications:
"Three separate investigations by corps officials found no impermissible conflict of interest created by CBY's hiring of Richmond Kendrick, the former corps official. But the GAO found the other complaints were valid, and in October 2011, the corps decided to request the five finalists to respond to a proposal changed to reflect the GAO's recommendations. The changes included language that now says only that proposals over $700 million would not be accepted.There's only one reason to do this: cost.
Also removed was a request to minimize impact of construction on the Coconut Beach volleyball complex, which had been located within the footprint of the proposed 17th Street Canal station. The complex is moving to Kenner's Laketown area.
Several other design changes, including reducing the required height of surge protection to 16 feet above sea level, from 18 feet, were included.
The corps' decision to reopen the bid process prompted CBY to file suit."