We're talking Wave Attenuation Devices with Fred Dorr today.
Remember, I'm a sportswriter by trade. My entire expertise on the matter we're discussing today boils down to:
1) I grew up on a beach
2) The house was on a seawall
3) I therefore have a base knowledge of waves-crashing-off-walls
4) Even with no scientific/academic training, I have more experience watching waves hit walls than many people who are authorities on the matter.
It's all downhill from there. My science is awful. I taught Science one year, and the highlight there was when I let the kids handle liquid mercury. I had to throw out and then acquire new versions of 10 school desks.
I mention all this because I'm interviewing someone who works in a field that may spark some interest among coastal residents. This is why I am, from this point on, stealing text wholesale from his website.
Also, I conducted the interview via email. It saves me from taping phone calls like a divorcing couple, and it lets Mr. Dorr speak directly to you, in a sense.
This is also why I am not challenging any of his answers. I'm just showing you some new technology, and you can decide if it will work on Duxbury/Humarock/First Cliff/Horse Neck/Scusset Beach for yourselves.
What is a WAD?A WAD (Wave Attenuation Device) is a three sided, hollow, concrete pyramid with holes on all three sides and one on the flat top.
WADs do not come in any one size. They are designed according to the conditions at a shoreline site. If, as in the case of Scituate, "they " wanted to deploy WADs at Minot beach, Peggotty, and Humarock, then quite likely there would be three different designs and perhaps three different sizes.
The design and size depend on the conditions at the deployment site. These conditions include ocean bottom, tide heights, astronomical tide heights, storm surges, weather direction, wind speed, storm intensities/frequencies and other factors.
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| Scituate |
The Science of a WAD:
WADs do two things.
First they knock a high wave down to virtually smooth water.
The second thing they do is to remove energy from an ocean swell. They do this much the same way that the aerator on your sink faucet does. If you didn't have that aerator on the faucet the water would come out in a big blast. The aerator only allows the water in the pipe to get to your sink via very small holes. Therefore each of the water streams contains very little energy.
On the ocean side of a WAD array, the turbulent oceanic swells have picked up some sand and carry it in suspension through the WADs.
However, because the WADs reduce the energy of the wave, the sand falls out of suspension and settles on an eroded beach. If there is sand available in the near ocean, if we have a few nor'easter and if we had an array of WADs, we could over a short period of time (1-3 years) have a new dry high tide beach.
Seafood Farming?
In the background are fish havens they resemble WADs except they do not have a flat top or a hole in it.
They are mass produced in three sizes.
They are deployed in small arrays; circles, squares, triangles, etc. They attract fish and promote organic marine growth.
From what I have read they are very effective in increasing a fisherman's catch.
That's a short question that has a long answer.
1. Waves under cut the sandy edge (TOE) of a seawall
2. WADs knock down high/tall waves to calm water. When I asked Scott Bartkowski if WADs could knock down a 20 foot wave his reply was we have killed 29 foot waves.
3. If there is sand available in the near shore up to 300-500 feet then during storms that sand, with the help of WADs, will migrate to the eroded beach and replenish it.
4. When a beach gets fully replenished, the waves will not reach the seawall. If a wave cannot reach a seawall there can be no damage to shoreline structures.
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| Sandwich, MA |
Q) How do the WADs not get filled up with sand and stone? Would they be more, less or equally effective when filled or partially-filled with sand and stone?
In the course of doing their work the WADs do not get filled up instead they break the wave energy down into little pieces so to speak and the sand actually moves through the WADs. If one snap shot were taken of the entire process then you would say that the WADs were filled up with sand. Go to WADs Work 4 Beaches on face book and look at the video I have posted you will see what I mean.
When a beach is fully replenished then the municipality should get a barge and a crane go out into the sea and move the WADs farther out and make a larger beach.
What sort of impact-force testing did you do on the WADs, i.e. waves picking up Ottoman-sized boulders (see "Bert's, Plymouth") and throwing them off WADs?
1. When Living Shoreline Solutions does their scientific investigation, they look at what's on the ocean floor, ferocity of storms. storm surge, astronomical tide effect, beach slope and a myriad of other parameters. They design four applicable WADs for a specific beach that will do the job of attenuating "its" waves. If there are rocks on the ocean floor then the thickness of the wall of the hollow WAD is increased. Understand that the concrete used is marine grade and reinforced with fiberglass shreds. As regards to the event at Bert's I guess my only answer to that is Poo happens.
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| Ocean Bluff/Brant Rock |
There is no need for keep the fish out of the WADs. The WADS are hollow. Fish can swim in and out of WADs. In the gulf coast LSS makes a series of Fish Havens for commercial fishermen. They have reported significant increase in their harvest due to the effectiveness of WADS. WADs are also used to promote oyster growth.
Do you put these WADs where conventional seawalls stand in relation to the high tides, or do they go offshore some?
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| Duxbury Beach |
Is it possible to perform patchwork repairs on WADs somehow?
I am not sure I know what you mean by patchwork repairs. If you mean to repair a WAD that has been damaged. I do not know the answer because there have not been any cases of WAD failure in seventeen years. Caution must be used because the primary market for WADs is in the south and the Caribbean, where there are no rocks. If you mean can short (25-100 feet) arrays of WADs be put in place. The answer is yes but the overall project must contain several arrays because of a cost/profit problem.
This might be silliest question you've ever been asked in this field, but could a town order WADs in different colors if they so desired?
No it is not the silliest but it comes close. There have been WADs built with rocks imbedded on the top to simulate a nearby breakwater. I suppose if someone wanted a puse colored WAD array that could be done--at a price of course.
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| Green Harbor |
WADs have three purposes--Attenuate waves, replenish beaches, and provide marine habitat. I guess that means that if barnacles are going to grow on a WAD the people will have to deal with it.
Do WADs work if the water level gets higher than them?
Extraordinary question. A swell is essentially rotating water much like a basket ball rolling across a gym floor. If the bottom of a swell collides with the ocean bottom the swell turns into a breaker. When a wave breaks it begins to lose its kinetic energy. Wave height is measured from the bottom of the trough to the top of the swell
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| Kingston |
In the process of losing its energy any sand that was in suspension will be deposited on the beach. That is like trying to stir a glass of iced tea with five teaspoons of sugar in it. As long as the tea is being stirred the sugar will stay in suspension. But, when the stirring is stopped the excess sugar will settle to the bottom of the glass. That is how a beach is replenished.
What sort of aquaculture can someone perform with a WAD?
I know that oysters grow very well on WADs, I have seen pictures of fish in and around WADs. In fact two hours after a WAD array was deployed at Negril Jamaica on a barren ocean bottom there were fish "sniffing" around looking for a good place to stay for the night! I suspect that WADs would make a good hidey place for lobsters
How large of a wave would be required to move a WAD?
The actual answer is no body knows. In the seventeen years that WADs have been deployed all over the world not one has ever been moved from the place it was deployed. That is because of its design. Hollow: water goes through a WAD. A WAD has slanted sides. A WAD is a three sided pyramid. So the water goes up, and through WAD, and can't push it around.
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| Nantasket Beach |
All WADs are site specific. For instance in Scituate, my town. If the town were to WAD North Scituate Beach, Peggotty and Humarock there would likely be three different designs. So far WADs have been as short as four feet and as tall as 12 feet. They have weighed as little as 450 lbs to as much as 21,000 lbs. I asked Ping Wang PHD University of South Florida who has done some Attenuation testing for Living Shorelines, the following question, "Could a WAD be designed to replenish a beach and at the same time prevent any shoreline damage regardless of the height of the waves. His very short answer was "YES".
Is one mile of conventional Massachusetts seawall more or less expensive than the same distance of WADs?
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| Brant Rock/Ocean Bluff |
Another fabulous question. Scituate is or will be building a seawall 700 feet long. It is expected to cost about $4,000,000 That works out to about $5700 per linear foot. I have to stop for a moment here. A seawall is necessary to keep calm high water from flooding the local area. The concerns of sea level rise can be accommodated with a seawall. But an array of WADS attenuate the waves. On the ocean side there might be 12 foot waves. On the shore side of the WAD deployment the waves might be 6 inches high The current cost of a double row deployment of WADs is approximately $1,000 per linear foot. I think that equates to an 80% saving.
Is it possible to buy WADs for personal use like forming a semi-circle in front of your house?
s soon as you said the word "possible" the answer is yes. BUT you would have to ship them from Florida. You would not have a choice in shape, because they do not manufacture them in a factory and then ship them from a stock pile. Living Shoreline Solutions designs a site specific WAD, fabricates the concrete molds in Florida then ships the forms to the site. Once here local labor assembles the forms and a local concrete company provides the concrete. Then someone either has to hire a barge with a crane or a very big front end loader to deploy the finished product.. In addition the state owns the water, you would have to get their permission. From what I understand that takes at least a year.
I have enclosed two files, which are pictures that I plan to use in the article. One picture is of a seawall in Duxbury, which is what I have in mind when I say "conventional Massachusetts seawall." The other is of the White Cliffs Country Club in the Cedarville section of Plymouth. What could WADs do to stop erosion of those sand cliffs?
I have not yet seen your pix but I know that when it comes to cliff erosion, although WADS have not been used in that particular situation. I have to add here that no WADs have ever been deployed in the waters of Massachusetts. I have about 20 years left on this good earth and I intend to use every one of them to get WADs into Massachusetts waters.
Back to your query. Put WADS in the water the scientifically prescribed distance from the toe of the cliff and if there is sand in the near shore then that sand will be transported to the space between the WADs and the toe of the cliff over some reasonable short period of time. Perhaps 1-3 years. In that time the beach level will rise above the height of the WADs and the waves will not reach the toe of the cliff. If the waves cannot reach the shoreline there can be no further erosion except by the rain.
Again go to WADs Work 4 Beaches in face book look at the five videos for proof that they work.
