I thought I'd devote the first real post in this blog to explaining why the sand berm idea was doomed from day 1. The sciencey parts of this post are for those among my readership who are not professional coastal geologists, but I hope that everyone can get a little something out of this. The material here may be dated by a couple of weeks, but I figure it's best to clear the pipes to make way for some new stuff later.
OK. Berms. Actually, first, a little bit of background: Offshore of the barrier islands, the sea floor takes on a characteristic steepness, or slope, which is largely dictated by the prevailing wave climate and the type and size of available sediment. You can think of that characteristic slope as a sort of geological goal for the island system, and you can imagine that the system would have to work back towards that goal if ever it were pushed away. So if, for example, some enterprising individual were to walk out past the surf zone and dig a hole, then the system would have to find a way to fill that hole back up in order to reattain the desired slope.
So where do you get the material to fill up the hole? To answer that, I introduce the term "depth of closure." Depth of closure is the depth beyond which sediments are not exchanged between the barrier island system and the offshore marine system. Think of it this way: If you stand on the beach, just landward of the breaking waves, you will notice that each incoming wave brings some sand onto the beach, and each outgoing wave takes some sand away. If you walk out a little bit further, you would find that the sand is still moving back and forth, but that it isn't happening quite as quickly as when you're standing right where the breakers are. Eventually, if you walked out far enough, you would get to water so deep that the waves barely affect the bottom, and no sediments are exchanged between the barrier island system and the marine system. This is the depth of closure. Any material that the system uses to fill a hole would have to come from inside the depth of closure, which is to say, from the barrier island system.
This all gets back to berms pretty easilly. The battiest part to the original plan was to dig a trench about a mile offshore of the Chandeleur Islands, and use the excavated material to build a sand berm in front of the islands. We know from the discussion above that digging a hole would be exactly the type of shock that would force the system to work to return to its equilibrium shape. Exactly how the island system would accomplish this is not something that I know to predict but there's a serious risk that the islands themselves would basically sink into the sea as they borrowed sediments from upill to fill the trench.
The idea that digging a trench offshore of a barrier island could threaten the stability of the island is not cutting edge science. It's very old news, and anybody with an undergraduate degree in coastal sciences should have been able to see why digging the trench would have been such a bad idea. The mere fact that the plan was proposed at all was terrifying, and became one of the first indications that the prevailing response to the oil spill was naked panic.
Coastal scientists in Louisiana woke up one morning to read in national newspapers that the state had fast tracked a coastal management plan without consulting any of them. And once the permit application started making the rounds, the situation looked even bleaker. The original permit application was a joke. It was three pages long, and contained almost no useful information. Those three pages were being used to explain a project that was predicted to cost $250 million or more. You can read the permit, along with some very interesting agency comments, here.
So what's happening now?
Well, a certain sort of subdued sanity seems to have prevailed during the permitting process. Knowledgeable individuals at the various reviewing agencies pitched a fit, and were able to take most of the badness out of the plan. There is no trench anymore, and only a small number of the proposed berms were approved. Instead, material for the approved berms is now being dredged from a number of point sources around the coast. This, to my mind, was a much better solution, and has the potential (albeit accidentally) to have some restoration benefits in the longer term.
But the cat is out of the bag. The Governor seems increasingly unhinged as he lashes out at the federales for not doing what he wants(and NOW, dammit. stop thinking and react!) while his top coastal advisor has been relegated to explaining that the lack of thought put into the plan was a deliberate attempt to add flexibility.(link) Meanwhile nobody seems to be in charge, and nobody sees a clear path forward.
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Everybody knows that the boat is leaking
Everybody knows that the captain lied
Everybody got this broken feeling
Like their father or their dog just died.
------------------------------------Leonard Cohen------
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