Here’s the second and final installment about beach nourishment, as taken from my research notes for an upcoming story. Last time I talked about what beach nourishment is, and why it is needed. Now I’ll talk about the methods and the costs.
So, how to do?
To start with, the sand has to come from somewhere. Although sand can be taken from inland sources, or even from sand trap areas in harbors, it typically comes from offshore deposits. Other sources include inlets, dunes, rivers, and lagoons. The sand grains have to be the same size, or slightly smaller than, the native sand at the beach for the nourishment to be effective. And if taken from an offshore site, it has to be at least two kilometers from the shore. Otherwise the borrow area will just get refilled and cause more erosion.
When sand comes from an inland source, it is brought to the beach via trucks. When it comes from offshore it is brought by pipes. In both cases, as long as the sand is underwater, it is dredged. For offshore dredging there are two methods. Actually there’s a billion, but here are two popular ones—cutter-suction dredging, and trailing-suction hopper dredging.
Cutter-suction dredging is where a barge is anchored in one place, and has a pump extended to the borrow area with a cutterhead on the end. A cutterhead is a big scary drill thing that excavates and sucks up sand. This sand is pumped from the barge, through a floating pipeline to the dump site on the beach. Once the sand in one area is all sucked up, the dredge moves forward along the cut by adjusting the anchors, and continues. This is an efficient system, since it allows for constant pumping. It doesn’t work well in bad weather, what with the floating pipeline and all.
Trailing-suction hopper dredges work by having two trailing arms with dragheads at the end attached to a barge. Dragheads loosen sand and suck it up, putting it onto the barge instead of into a pipeline. The barge motors around in the borrow zone, dragging these arms and sucking up sand until full, and then moves to a mooring buoy with a pipe to the shore, where the sand is offloaded. Although hopper dredges don’t cut as deep, they are more versatile against bad weather, and can go out a farther distance. They’re kind of inefficient, since they have to regularly offload sand instead of moving it continuously.
Howsoever the sand has been dredged up, it can be placed either offshore in a bar that will slowly accrete to the shoreline, or directly on the shore, following the natural profile of the beach. Either way is fine, probably. Although the sand can be uniformly distributed, it’s better to overload it in erosion hotspots, areas where erosion occurs faster.
So who pays for all this? Mostly, the federal government—at least, they provide 65% of funds while 35% are nonfederal. Congress is also the organization that approves nourishment proposals, on a case-by-case basis. These proposals are planned by the United States Army Corps of Engineers, and they do all the design for projects. Now, that doesn’t mean each time sand is added to a beach congress needs to approve it. Typically these projects are long-term, and plan for multiple “episodes” of beach nourishment over many years.
And what is the actual cost of all this? Well, that’s difficult to talk about. Cost differs from project to project for a million different reasons, so there’s no sure answer. That being said, let me give some averages, all calculated by me and taken from information gathered by the fine people at Western Carolina University on this website. All the following dollar amounts are in 2014 dollars.
On average, each episode of nourishment costs $5.1 million. Each coastal state (except Oregon and New Hampshire) has spent, through their whole lifetime, an average of $422 million on these projects. Per foot of coast, replenishment costs $880. Per cubic yard of sand, it costs $10.2. That last figure seems the most relevant, given that everything else is kind of arbitrary—measurements for coastline can vary, and different coasts need different amounts of sand depending on erosion. Episodes are also kind of arbitrary, not some fixed unit.
Now, here’s the state-by-state breakdown, with the highest and lowest of each category bolded.
|STATE||Million $/Episode||$/yd3||$/ft of Coast||Million $ Spent All Time|
It’s worth noting that none of these data deal with cost-effectiveness or cost-reward ratios. For example, beaches in the Gulf of Mexico erode slower than those in the New England area—and a beach next to Miami is obviously much more valuable than a beach next to Apalachicola. It’s worth noting as well that I may have messed up in my calculations, and that this is not a peer-reviewed paper. This was all written by a fiction writer, not an expert or even a journalist. Trust no one.
Except maybe these guys:
Wikipedia – For general info on everything I talked about here
Beach Nourishment and Protection by the National Research Council – For info on dredging methods and government involvement
This post by Jim Namiotka of The Star Ledger – For interesting commentary on beach nourishment
Program for the Study of Developed Shorelines at Western Carolina University – For the numbers, and a picture in the last post
Restoration Systems – For the picture in this post