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.Read More »
Well, here’s a post that seems to have nothing to do with anything. Although this is all taken from my research and notes for an upcoming story, it has nothing to do with writing or reading or anything like that. This is just a post about beach nourishment. You’ve been warned.
So, what is beach nourishment?
No, it is not some form of urban foraging, beach nourishment is the process of replenishing an eroded beach by adding sand. It’s done to protect valuable shoreline property from becoming Venice. Alternatives are building a seawall (very common in Europe) or building a breakwater or groin. I don’t know the difference between those last two, but basically they’re large walls of stone or wood that extend into the ocean and collect sediment on the updrift side, like a dam for sand. They’re kind of problematic though, because if they collect too much sand then downdrift beaches aren’t being replenished as much by the natural current of sand that moves along the coast, and might erode very quickly. Another alternative to beach nourishment is a “managed retreat”—basically giving up to the sea and relocating inland.
There’s another thing which I haven’t seen too much written about, called “living shorelines”—the use of native flora to reduce erosion.
So, why is beach nourishment?
Beach nourishment is nice because it preserves the beach without having to build any structure, or move buildings. Sometimes groins are built in conjunction with it, and can be either a series of tapered groins, or adjustable groins—both for the sake of allowing some sand to pass and continue it’s littoral drift. Beach nourishment isn’t a long-term fix though, because the beach is always eroding.
Erosion can be caused by damn humans damn interfering, but it is also caused by storms. Some beaches can recover from storms if they have enough submerged sand to replenish them. Others can’t. This is why during beach nourishment it’s important not just to focus on what’s above the water, but also the swash zone—the shallow area beneath the water. A lot of that sand will return to the beach as it’s carried in by waves.
Erosion is also caused by longshore drift—and mitigated by it. Longshore drift is the process by which sand is carried along the current of the ocean due to the raking angle of the waves. This causes sand to erode, and be deposited elsewhere—then erode again, and be deposited again. The process of sand returning to a beach is known as “accretion.”
Where’s all this sand coming from? River deltas, mostly. Rivers move a lot of sediment out to the ocean. At least, that’s the natural source for sand. With beach nourishment, there are a multitude of other sources. Which is what I’ll talk about next post—the “How” of beach nourishment. The methods used, the problems posed, and some boring-ass statistics about the costs of things.
If anyone wants to do some more research into this, I found these sources very helpful —