Like sand through the hour glass, so are the dunes of our lies.
by Len Bahr, PhD*
Bobby Jindal’s coastal barrier project resembles a love letter to south Louisiana – written in the sand.
This is my fourth (but probably not final) post on an obsessive push by Governor Jindal to force the feds to rubber stamp and BP to squander $360 building fragile sand berms parallel to the deltaic coastline of southeast Louisiana. This pipe dream would presumably repel surging oil from BP’s out-of-control Macombo well. IMHO this project is as likely to keep BP oil out of Louisiana marshes as the Maginot line kept the German army out of France during WWI.
I seem to have become as obsessively opposed to this project as the governor is determined to build it. Nevertheless, I harbor no unrealistic expectations as to the winner of this one-sided contest. The national media are treating the emergency sand berms as a fait accompli. For example see this otherwise excellent account of the causes and responses to the BP Blowout from June 5 in The New York Times, which discusses federal delays in permitting the Jindal sand berms without mentioning any scientific controversy.
The emergency sand barrier concept seems to have been broached initially by Plaquemines Parish President Billy Nungesser and I believe that Mr. Nungesser’s support is sincere and motivated by righteous desperation. On the other hand I believe that Governor Jindal’s support is motivated more by national ambitions than belief in the project.
As I have reported in previous posts, no coastal scientist of note supports the sandy Band-aids. I have cussed and discussed the sand berm concept with a number of technical authorities, not one of whom has been invited to proffer recommendations on the state’s ambitious plan.
These experts include, among many others, Dr. A, a petroleum geologist with extensive experience on the Mississippi River delta; and Dr. B, a senior coastal engineer and modeler. They relayed their respective opinions on the concept, after reviewing various official state planning documents. Some of their thoughts are as follow:
A: As I watch helpless like everyone else, and silent because of my current position, I cannot help but despair about the governor’s plan to build the sand band-aids. There are many unintended consequences that project advocates are almost certainly hearing about but either overlooking or ignoring because of a belief in an alternate universe of knowledge.
I made some calculations on sand requirements for this concept that your readers might find interesting.
Assume 130 km (80 miles) of barrier, 2 m (6 ft) high. Achieving this would require filling in low spots and creating a strip wide enough to be stable at 2 m above the surrounding landscape. Assume a berm 10 m wide at its base, tapering from a peak thickness of 3 m to account for filling in all the holes, to zero at the edges, for a mean thickness of 1.5 m. This yields a cross-sectional area of 1.5 x 10 = 15 m. Now multiply by 130 km, and you would need an absolute minimum of almost 2 million cubic meters of sand.
Remember that the Mississippi River delta suffers from a serious sediment deficit. Although we cannot know for sure, two million cubic meters of sand might be roughly equivalent to 2 years’ worth of total sand (see Editor’s note, below) delivered to the mouth of the river.** Considering that beaches in the Mississippi delta consist of of a very narrow range and specific size of sand grains, this could equal 5 years or more of total sand supplied by the river. Sediments outside of the size range ‘preferred’ by the beach and its wave climate will wash away almost immediately.
To illustrate the serious sediment deficit of the Mississippi River delta, I’ve adopted your proposed Superdome Equivalent (SDE) unit of measure, 5 million cubic yards, or about 4 million cubic meters of sediment. If massive river water diversions are not built soon to rebuild the delta, every year of delay will increase the deficiency by 15-20 SDEs.
According to the above assumptions, the proposed sandy band-aids would require about 0.5 SDE. This is not a trivial amount, especially when compared with the total amount of actual sand in the river’s sediment load (>90% is silt and clay). It also adds to the long-term sand deficit….which will be further exacerbated if these guys are allowed to do this!!
To get the 50 million cubic yards called for in the documents I’ve seen*** you would need a strip of sand 86 miles long by an average of 2 yards high by 165 yards wide. That would be a more stable Band-aid than the one I used for calculations. However, it also means a lot more sand. This is about 38 million cubic meters, about 9.5 SDE’s, or an equivalent of 20-50 years of the optimum size sand arriving at the river mouth.
I’m not saying that all the sand can or should be mined from the river; I’m only using the river load as a base for comparison. The big question is the possible sources of sand. It’s not as though unlimited sand exists out there on the shelf in readily accessible locations.
In short, I think the ‘Sandy Band-aid’ concept is a terrible idea that would have a marginal short-term gain, with a huge long-term cost. The gain, if any, would benefit marshes that will be submerged in 25 years anyway, sad to say.
B: I have seen nothing in state presentations and proposals that address my four primary concerns:
1) the availability of sufficient sand resources (and the possible waste of what little resources there are if the plan is not properly conceived);
2) the time that it would take – it is closing the barn door after the horses have escaped – the oil is already in the marsh; and
3) even if there were sufficient sand and time – the berms would no keep the oil out of the estuary, as the tidal passes would bring the oil that is in the Gulf into the interior;
4) even if the passes were successfully boomed off – that would only last until storm waves pushed the oil over the booms or, more likely, washed them away.
What is needed is a massive effort to soak up and collect the oil (and to stop the gusher!).
A: I agree with B’s 4 issues. I reviewed the presentation (by Garret Graves, Governor Jindal’s coastal advisor), which I feel is worthless, as well as the application to build the berms. On the surface, the berms look like a reasonable idea if there were a lot of sand laying around on the inner shelf – as off the coasts of Alabama and Florida. They would take a long time to build and would do little but put a decoration on the barriers with the opportunity cost of consuming much of the sand resources availability for longer-term restoration.
B’s point about tidal passes is absolutely crucial, as any changes to tidal prisms will result in unintended consequences as the shoreline adjusts to accommodate the prism elsewhere. And all bets are off if there is a significant storm later this season. As I understand it, the total length of berm segments now being proposed is much greater than the 85 miles that we discussed last week…according to the current permit request, the design includes 128 miles of berm, and 102 million cubic yards of sand, or ~20.4 Superdome Equivalents!
If they actually pursue the plan of taking sand from the nearshore system, with the intent to replace it at a later date, I don’t see how they can predict what will happen without serious modeling over periods of months to years – and it won’t be good. I don’t think there is much sand there anyway, except for near the modern river mouth and the older mouth bar sands the modern channel now cuts through south of Boothville.
Sand thickness off of the Chandelier Islands and the Isle Dernieres-Grand Isle chain is pretty minimal. I saw a recent report by the US Geological Survey (USGS) on sand near the Chandeleurs, which was deposited by a variety of processes (from old distributary channels and through longshore and offshore drift from the islands themselves). Restoration of the Chandeleurs must use the natural sand transport trends to make efficient use of sand. Spreading sand out evenly, as proposed by the state, will mean much of it will just go to waste.
B: There is also the issue of the ‘spaghetti’ of oil and gas pipelines on the shelf, where even the owners don’t know exactly where their pipes are! In other words, without a detailed (and time consuming) magnetometer-based survey of all the borrow areas mining sand for barrier berms would risk nearshore pipeline ruptures.
*Founding editor (email@example.com)
**Dr. A’s first comments on sand volume requirements were sent before the original permit proposal submitted to the Corps of Engineers was modified from 80 to 86 miles of berm segments. Current proposals call for up to 128 miles!
Editor’s note 1: Since posting this article around 9:00 AM CDT a sharp-eyed reader spotted what appeared to be a major discrepancy re the average annual sediment load of the Mississippi River. He cited a 2009 paper by Bob Meade, retired from USGS and the acknowledged ‘dean’ of historical changes in Mississippi River sediment loads, who uses the figure of 145 million tons of sediment/year. This strongly contrasts with Dr. A’s number of about 2 million cu meters (roughly tons) of sand/year. The apparent discrepancy is explained by the fact that Meade’s figure includes the total river sediment load, including roughly 30% of the load that flows into the Atchafalaya River and the total suspended fraction (silts and clays) not just sand.
Editor’s note2: an alert reader just forwarded this link to a new report on the sand berm project by scientists with the US Geological Survey.