Kicking the Inner Harbor Navigation Canal anthill…
by Len Bahr, PhD*
I recently posted an article on an innovative suggestion by a highly credible hydraulic engineer that could benefit the entire Pontchartrain basin. The concept is that the replacement of the lock in the Inner Harbor Navigation Canal (IHNC) offers a golden opportunity to convey river water into the basin to help mitigate damage caused by the notorious Mississippi River Gulf Outlet (MRGO).
I’m happy to report that the article garnered broad interest and comments, both positive and negative.
The concept was cited in On the Hill by Bruce Alpert and Jonathan Tilove in The Times-Picayune on March 7, 2010. I could not find a link to the article at nola.com, so I’m quoting directly from a newsprint copy with real ink:
Len Bahr, a coastal advisor in Gov. Mike Foster’s administration, said that one way the Army Corps of Engineers might overcome near unanimous opposition from environmentalists to the lock project would be to reconfigure the design so that it isn’t merely a navigational project but one that also helps “mitigate the enormous environmental destruction caused by the Mississippi River Gulf Outllet.” The idea…would be to use the lock project to move a significant volume of river water and sediments to restore wetlands destroyed by the MR-GO. Bahr acknowledges it would be hard to get the necessary bureaucratic approvals from the corps, and perhaps Congress, but says the effort is worth it.
In addition to remarks posted at the end of the piece, I received some comments in the form of emails and some were whispered directly in my ear. My favorite was in the latter category: “Len, you really kicked an ant hill!”
Provoking discussion is perhaps the most important function of this blog, so evidence of success in this regard is music to my ears. Garrett Hartley, whose talented toes helped send the Saints to the Superbowl, is from Texas, where fire ants are as common as cows and I can imagine him kicking ant hills as a kid. Metaphoric ant hill kicking is not in the same league as sending the Who Dats to Miami – but it sure feels good.
At any rate, the possibility of adding an environmental thrust to the sole navigation bennies of the IHNC project warrants more discussion so this post includes some of the emailed comments received directly and/or copied to me (edited to remove authorship and clues to the sources).
To avoid confusion I must point out that the IHNC replacement lock itself would not serve as the diversion control device(s), which would be added for a modest cost during the construction of the lock. A third post on the IHNC diversion concept will include more detail.**
A classic folk song describes a fiddler happily bowing away on his front porch during a downpour in which his roof is leaking badly. A curious bypasser, The Arkansas Traveler, points to the rooftree leaking like a waterfall and suggests that the resident patch his roof after the rain ends. The fiddler’s nonchalant response: “My cabin doesn’t leak when it doesn’t rain.” This reminds me that during periods of abundant rainwater in south Louisiana, e.g., this winter, few folks talk about our desperate need to divert river water into the delta.
The year 2000 brought what should have been a huge wake up call and a premonition of future bizarre weather incidents to be expected under global climate change or, as Thomas Friedman calls it, ‘global weirding.’ That was the year during which 19,000 acres of salt and brackish marshes in coastal Louisiana became ‘perched and parched’ by low sea level, low river flow, no local rainfall, clear skies and baking temperatures. Some areas of vital coastal forest even caught fire that year.
I was then advising Governor Foster on coastal issues and I recommended cataloguing every water control structure in south Louisiana, beginning with the Old River Control Structure, to see how river water and local sources of freshwater, including treated sewage, could be distributed into dying wetlands. This would include all womanmade devices for managing water levels in south Louisiana: locks, pumped drainage canals, flap gates, etc.
Now, with the brown marsh year ten years behind us we’ve almost forgotten the need. John Lopez with the Lake Pontchartrain Basin Foundation has resurrected this idea of the beneficial use of existing structures. He has created a list of existing coastal water management devices that he calls “legacy structures.”
A. I like the idea but am cautious as I do not necessarily understand the concept of allowing the Lock to also divert River water. I would be in favor of having a functional deep-draft lock and could see how a pulsed or controlled release system could have benefits. I would think there are concerns related to deposition when the water flow slows and am trying to imagine the getting the water flow and sediment into the proper areas with the Lake and GIWW entrances.
B. This is something I have been asking people about for a while too since I have been in coastal restoration. I seems like it is one of those things that is so simple that everyone tends to overlook thinking that well someone has probably already looked at this because it is too obvious. In my inquires the answers that I have gotten is that Corp won’t want to mess with these operations. We’ll why not. I would also suggest looking at the Algiers Lock. Take a look at a map. This could be capable of serving as a significant diversion into parts of the Barataria Basin. If the IHNC can be done, it makes sense to look at this too.
Concerns about using the IHNC as a diversion structure
A. I’d have to see the engineeering behind it. Onthe surface it looks like smoke and mirrors by the navigation interest to gain suport for the lock project to say it has an environmental benefit.
The location for the proposed lock is in the turning basin. Water flowing from a constricted channel (i. e. the existing location of the lock) to a less restricted channel (the turning basin) should cause some of the suspended sediment to deposit as a result of slower velocity at the expanded area.
Not sure the sediment will get where they say it will go. Look at the locks up river how often they have to dredge sediment from accumulating near the locks. Also sediment will fill in int he channels (IHNC, and GIWW) which would reduce storage capacity for flood events and increase maintenance costs (dredging) these channels.
Also, not sure what water elevation they are proposing to allow in the channel, but we will have to look at the design of the surge barrier to see if a water pressure due to increased head on the protected side is OK for the structure. And we will have to look at the changes to design loads on the supports for the gates also.
B. Siltation will be the biggest problem. Dredged material will have to be barged out. Locks do not allow for a large quantity of exchange of water. Water from the upper elevation fills the closed lock to raise ships up to the upper elevation or water that has filled the lock is let out to to lower ships to the lower elevation. It seems to me that this exchange is very restrictive. Relatively speaking, the amount of water moved from the upper elevation to the lower is quite small, environmentally insignificant. The volume of water, silt bearing water, requires a flow that is more river-like with an area to spread out and drop the silt. Shipping and wetland ecology are not easily done in combination. Kind of like large cities and wilderness areas, it is a hard combination to accomplish.
C. I agree with the (above) concerns…The idea of using the lock to divert water is an old idea, not new. It has been eliminated from consideration due the reasons enumerated.
*Founding editor (firstname.lastname@example.org).
**An additional post on this subject is under development, in which my source for this concept will (I hope) flesh out some details and respond to the above comments.