Blum and Roberts 2009 - "Drowning of the Mississippi Delta due to insufficient sediment supply and global sea-level rise"

As I referenced earlier, Blum and Roberts 2009 is an extremely important paper published in Nature that deals with feasibility of rebuilding the coast. Here's a presentation I submitted to class with some notes.

That's a really stark title for an academic paper. No messing around, just going for the jugular.


The drainage basin of the Mississippi. The sediment load basically comes from clastic deposits of material washed down from the Appalachian and Rocky Mountains.

"All these lands are drained by the Mississippi" - Armand St. Martin
Louisiana Frenchman

Problem is, the sediment load is not what it used to be. The main loss comes from the damming of the Missouri River.

Here's a snapshot of a few of the dams. Each one pictured generates several hundred MWe's.

From Blum and Roberts' paper, you can clearly see the dropoff after the dams are completed. This data comes from USGS samples of suspended sediment load. Note that we're also losing the coarsest-grain sediment, which is the best at creating new land.

And, to make matters worse, we don't just have a choked off river and low sediment loads. We have to deal with increasing rates of sea level rise. Historical data indicates a rise of ~1mm/yr for most of the 19th and 20th Centuries. We've been increasing to closer to 1.25-1.5mm/yr since about 1970. Future projections are for a MINIMUM of 2mm/yr. There's quite a bit of disagreement on how quickly sea-levels will rise. Here's some discussion on Dr. Jeff Master's blog.

The biggest culprit in sea-level rise? It's not deglaciation. It's thermal expansion.

So, Blum and Roberts put together a mass balance of the sediment coming down the river and what we'd need to keep up with sea level rise. Even if we blew up every single dam on the Mississippi and unleashed the lower Mississippi, we'd continue to lose prodigious amounts of land.

There are some flaws in their model, though. For one, they couldn't come up with a way to count organic buildup of soils due to plant activity. They (as they pointed out in their own paper) said that since they couldn't come up with a way to quantify it on a macro scale, they just neglected it altogether, but admitted that organic buildup could be significant.

This is from the Times-Picayune writeup of the Blum and Roberts paper. Note the slide shows a "no-action" scenario with a 1-meter sea level rise (over 100 years), which is on the middle-to-upper-end of sea level rise projections.

Quite an ending quote. Note that Dr. Harry Roberts might be THE foremost authority on Coastal Louisiana subsidence. He is also from Louisiana, so it's not like he's some grad student on the other side of the country throwing this out. He's right in our backyard. This paper was also published during a major push for diversions to save the coast and he went and said that diversions were nearly pointless (not what you want when you're trying to drum up political support). The paper was extremely contentious within the scientific community.

Also, an honorable mention to Maitri's coastal retreat costume.

Coastal Geology & "Engineered Avulsions"

So, I'm in grad school now and that's eating up a whole ton of time. I'm going to take one of my projects and post a bit of it on the ole blog because I think it's interesting.

The assignment for a class on coastal geology was to take a scientific paper, write your own abstract and make a presentation to the class. Two of my projects were Blum and Roberts 2009, "Drowning of the Mississippi Delta due to insufficient sediment supply and global sea-level rise" (quite the pessimistic title, especially for a scientific journal). Here's a writeup by Dr. Len Bahr and here's the original paper [PDF] as published by Nature Geoscience.

The second one I did was was Mohrig, Kim, et. al. 2009, “Is It Feasible to Build New Land in the Mississippi River Delta?”. Note that the second paper directly references the first. Here's a writeup from Dr. Bahr and here's the supplemental material from Eos / American Geophysical Union (Thanks, Maitri and Helena on the assist!).

Here are my slides with my presentation notes interspersed. I skipped a couple slides in the middle, but this should be the gist of it.


So, the last time I presented, we went through how screwed South Louisiana is. We went through Blum and Roberts' extremely pessimistic projections for coastal rebuilding efforts. Well, now I'm going to present an alternative scenario.

Mohrig, Kim, et. al. presented their paper shortly after Blum and Roberts presented theirs.

We've all heard the dire predictions. 10,000+ km^2 of land loss over the next century. Look at all the red on that map and of course red = bad.

We should just give up and move to Cleveland, right?
Let's take a closer look at one of those "red" maps. You see a bit of green. The Atchafalaya basin is still growing. One lobe is the main Atchafalaya. The other is Wax Lake, which is actually artificially created.


What is Wax Lake? In 1941, there were big river floods and people were worried about Morgan City being inundated, so the Corps cut a channel (the Calumet Cut) to divert ~30+% of the water away from Morgan City. The Corps cut the channel, Morgan City was saved, and everyone forgot about the cut and left it at that. And then something interesting happened...

(Progression of images of delta building; note Belle Isle Salt Mine)




(Some images omitted for post)

Note that all this delta building took place in an area that WAS affected by oil and gas activity, that WAS affected by major erosion from Katrina/Rita, etc.


So, in the paper, Mohrig, Kim, et. al. constructed a model of delta building based off Wax Lake, then backchecked their results on the actual Wax Lake delta. Here's the model results 1941-2005 (the two sets of lines represent variation in % sediment load captured by Wax Lake vs. main Atchafalaya).


Mohrig, Kim, et. al. then modeled two major diversions in Lower Plaquimines Parish. Note that these diversions are AT LEAST an order of magnitude greater than West Bay, which is the largest diversion project built to date.


So, here are the results. From 2010-2110, considerable land is created. One important note: the diversions are only opened during flood events. During low river levels, the diversions are closed. If you "save" New Orleans, but kill the Port of New Orleans, you've sorta shot yourself in the foot. We can both save the city and keep the river navigable.
Another thing to note: everyone says, "we just gotta blow up the levees" and that will fix everything, right? Well, not quite. Mohrig, Kim, et. al. said that wouldn't give you a deep enough channel (to capture the coarsest-grain sediment) and you don't really have enough control over the river dynamics.

They advocated an "Engineered Avulsion" (*I love this term*), like the Old River Control Structure.

Here's another view of an "Engineered Avulsion"



That's the presentation. There was some nice discussion at the end of the presentation. Gotta run to class now.

UPDATE: Fixed some minor typos.

Here's the full progression of images on the Wax Lake building. Found it via this Field and Stream article: Wax Lake Delta: Accidental Eden in the Atchafalaya. I reformatted the images to make them easier to read, but the raw source has a lot more slides on it.

Here's a presentation on "Optimizing Engineered Avulsions". Once again, I love the term "Engineered Avulsion."

Here's the definition of an "Avulsion": In sedimentary geology and fluvial geomorphology, avulsion is the rapid abandonment of a river channel and the formation of a new river channel. Avulsions occur as a result of channel slopes that are much lower than the slope that the river could travel if it took a new course. (Wikipedia)

Recap of recent events

Excellent recap of Oliver Thomas' woes. By the NY Times.

A brief history of the Alphabet Soup organizations in NOLA. COUP, BOLD, GOLD, etc. I find if funny how nobody even knows what GOLD stands for... Required reading to follow New Orleans politics. H/T to Oyster.

Decriminalizing Mental Disorders. Excellent article. Totally ignored issue. From 600,000 beds to 40,000... Amazing.

Chris Rose on corruption. First article of his I've read in a while. Good.

View of Subsidence in New Orleans. Take a look:


Ellois rears his ugly head. Unfortunately, it's not cut off and used as a soccer ball.

2 killed in Treme. This one is close to where I live. Too close for comfort...

Minnesotans: please meet your Michael Brown. He's even got experience with the Corps! No word in the article as to whether or not he's got any experience with the Arabian Horse League or whatever the hell it was.

Speaking of the Corps... Here's their response to Time.

Discovered a new NOLA blogger today. Cliff's Crib.


Vick might be pleading guilty soon. He's fucked no matter what. Hope he gets a cellmate named Spike.

UPDATE- UNLEASH THE EVIL:

(Not photoshopped)