Written by the TreasureGuide for the exclusive use of the Treasure Beaches Report.
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| Walton Rocks Beach Friday Near Low Tide. |
I ran into a discussion about if beach erosion could be predicted.. Since the discussion was between detectorists, I assume that is not the question they were really interested in. I think what they really wanted to know is when they could make good finds - not when there would be erosion. The first thing you have to do is ask the right question.
Erosion and metal detecting beach conditions are not exactly the same thing. You can have big erosion and no finds, or you can have very little erosion, but be able to find good things. Predicting erosion is only one part of the problem. It would take me quite a while to explain all of that, but I will give one quick example now. You can have big erosion on beaches like those right after the beach renourishment in the Vero area but still not get good finds. Not all erosion produces good metal detecting finds. It depends not only on the amount of erosion, but the previous state or condition of the beaches. You can have huge erosion and no finds, simply because there was nothing there to start with. It helps to ask the right question. Are you really interested in erosion or are you interested in the probability of making finds. Again, there is some correlation, but they are not the same things. \
Big erosion can actually wash away coins just like it can wash away sand. If you watch Gold Rush on TV, you know that too much water through the sluice box will wash the gold away as well as the sand. Predicting erosion is not the same thing as predicting beach conditions, although predicting erosion is part of the problem.
Here is one article that will facilitate this discussion.
Predicting beach erosion. - Free Online Library (thefreelibrary.com)
Here is an excerpt from that article.
But the model [Bruun rule] does not take into account the enormous complexity and uniqueness of natural environments, according to Orrin Pilkey of Duke University and Andrew Cooper of the University of Ulster.
Predicting erosion involves a lot of factors and beach environments are unique and complex. Predicting erosion, if that is really what you want to do, is complex, but we have accomplished it to a large extent.
I quit giving my beach conditions rating not because it didn't work, but because much of the time beach conditions were too predictable. Take this summer. This summer on the Treasure Coast, you would have been correct most of the time if every day you simply said beach metal detecting conditions are poor today. It was a long summer with almost no significant erosion. The surf was running one or two feet most days and the beaches had just received tons of renourishment sand. There was erosion, but those days were few and the erosion was not significant even though there was a lot of it because there was so much sand to start with. Big erosion during times when there is way too much sand to start with is more likely, but not significant. Renourishment sand is easily eroded for various reasons. (I should add that eroding renourishment sand can produce finds if good things were in the sand that was dumped on the beach.).
Here is another excerpt from the same source.
Unfortunately, the alternative to the Bruun rule, extrapolation of past beach behavior, also has problems: Past data may be incomplete, and different parts of a single beach may erode at different rates.
Knowing past beach behavior will help the detectorist, but that is difficult, if not impossible, to quantify. And it is true that different parts of a beach can erode at different rates. I've said that many times. Sand can move one direction or another. One part of the beach will be eroded while another nearby part will accrete. The sand can move north/south or east/west. The front beach can erode, while the high beach remains untouched, or the sand from the high beach can be washed down and dumped on the front of the beach. This can happen to large areas and amounts of sand or much smaller areas and smaller amounts of sand.
You are not starting with a static beach. Some changes are long term, taking years or decades, while other changes are short term - taking weeks, days, hours, or even minutes. I've seen a mid-beach cut washed away in a few minutes. When talking about erosion, you are probably talking about relatively large changes to a continually changing beach. I've said many times how important it is to know the history of the beach, including where it was and how it changed in the past.
If you look at the picture at the top of the post, it looks very eroded, doesn't it. It eroded, but only a few inches in the last three days. This beach was producing old things back a year or two ago. It got more sand, then less sand, and then more sand, over and over for the past year or two. The lowest part (most eroded spot) moved north and south several times as well. So, is this beach eroded? Yes, but most of the erosion was not recent. The recent erosion, due to Earl, was minor and there was a time a year or two ago when much more significant erosion occurred, and beach conditions were much better.
Not all erosion is the same. How do you quantify erosion? Amount of sand lost? In my opinion, that is not the most relevant thing for the detectorist. The detectorists really wants to know when he can find good targets. Again, that is not the same thing as the amount of erosion. Where the erosion happens, and when it happens, are important factors.
Erosion to the front or mid-beach might be productive, but only if it is in an area where desirable targets can be found. A beach that erodes three feet deep, may or may not produce good targets. If the good targets are under four feet of sand, two feet of erosion won't get you there. If the same beach was eroded four feet in the past, fills up again, and then erodes two feet, it likely won't get you there, but it could, depending upon a variety of factors. One interesting thing about dune erosion in good areas, is that the eroded targets can end up right on top of newly accreted sand near the base of the dunes.
So, can beach erosion be predicted? Yes, but not perfectly. It is very much like predicting storms, which have also become more accurate in the past ten years or so. They are more accurate, but there is still some uncertainty. The same thing is true of surf predictions. It seems that the MagicSeaWeed predictions have improved. Not many years ago there was an obvious error in the model. When a big surf was predicted seven days out, a lot of the time that big surf prediction would decrease or disappear. That doesn't seem to happen nearly as often now.
In my opinion. beach erosion predictions are pretty accurate now. Not perfect, but pretty good, You can't predict for every part of the beach though. One part will erode when another part does not. There is always some erosion somewhere. The question should be more specific. Erosion is local and may or may not be signficant for the detectorist in the areas of interest. On top of that, the detectorist must be in the right place at the right time. A detectorist can be off by an hour or less or a foot or less. There might be erosion at one place that produces good finds, and the detectorist can simply be at the wrong place at the wrong time. In fact, he might walk right over a good target and miss it because of poor technique or equipment and conclude the predictions were wrong.
And erosion is not always easy to identify. There can be very significant erosion that does not produce any cut at all. The entire slope of the beach can change, and that might not be obvious but still be very significant. I've talked about those things before.
In my 9/9 post I said, "As you can see, Walton Rocks Beach is low and wide. It has been down for quite a few months." I showed a photo of Walton Rocks as it was on 9/9. In the same post I showed a photo of John Brooks. The two beaches were very different. Brooks was built up, while Rocks had lost a lot of sand over the past year or two and was low and firm.
In my 9/13 post I said, "Yesterday there was some movement of sand on beach fronts which were at a good angle.. This wasn't a lot of sand moving, but in areas where the sand was already low, could be significant. So it will help if you know the beach angles, and where the sand is low or built up a lot.
At Walton Rocks, the sand was low. It was renourished back some years ago but had been losing sand for years. Of course, there were times when sand was added and lost again and again, but the general trend in recent years has been sand loss. A big event occurred when we had a big surf combined with big tides back in the Fall of 2020, I think it was. It hasn't recovered significantly since then.
The rocks shown in the photo above were visible back in (2020 I think) and from time to time since then. They provide a good measure at that spot. In 2020 the dune face was hit good and eroded. In the past week or two the water only barely touched the foot of the dunes there. The erosion to the slope has been progressing back towards the dunes very slowly in a step-by-step fashion.
That beach looks very different from John Brooks, for example, where even a few feet of erosion is much less significant. So my point is that the beginning state of the beach is an important factor - not just the recent erosion. And the angle of the beach and waves will erode one beach while not another. A foot of erosion might be significant at one place but not at another. It gets pretty complex, but you need to know the beach, the current state of the beach, the history of the beach, and the various areas of the beaches. An inch of erosion at one beach can be worth a foot of erosion at another.
So, can we predict erosion? I'd say we can predict it fairly well, but not 100%, just like with storms. We knew all summer long there was going to be little erosion, and there was little, and when there was some, it wasn't very productive for the detectorist because it was mostly in renourishment sand.
Productive erosion for the metal detectorist is a relatively rare event. Since the Thanksgiving storm of 1984, we've had only a few similar events - 2004, for example.
When I was doing my beach conditions ratings on a regular basis, it was not often that I was able to give a 3, 4 or 5 rating. Most of the time it was a 1 or 2, which got boring. Only a few times a year do we get an overall improvement in beach conditions. You can go out and find some modern coins or jewelry any day and have some chance of finding something old if you hit just the right spot at the right time but finding treasure coins on the beach is a relatively rare event. How many times a year do you find treasure coins. It doesn't happen every day, or even every month. But you don't want to miss it. My polls showed that if you found one, you probably found more than one. When it is hot, it is hot.
Back to the question of predicting erosion. I think it is pretty good. I'm seldom surprised by what I see when I go to the beach. It happens. I missed one erosion even about a month ago, but I'd say I'm at least 90% accurate.
If you take into account the surf height, wind and swell direction, tides, and very importantly the shape, history and condition of the beaches, you can predict erosion fairly well. First of all, if you only have a one- or two-foot surf, as we had most of the summer, you are not going to get significant erosion no matter what else is going on. Once you get up to five or six foot surf, it gets questionable, and then you have to consider other things, such as the angles and tides. You also have to consider, though, the state or condition of the beaches. A lot of sand in front of the beach can protect the beach from the force of water. so that kind of thing also has to be considered.
Once again, whether erosion results in finds is another question and involves other factors. It can also be confined to small areas. While most of the beaches are poor, you can get individual beaches or smaller areas of individual beaches that produce.
I'm sorry that wasn't more commplete and better organized, but I hope that discussion helped some.
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Funny that the rich liberal elites (black, brown and white alike) in places like Martha's Vineyard who are all for illegal immigration won't open their grounds and guest houses for the poor people. Just like energy. They'll fly private planes while you are supposed to walk or ride a bicycle. The elites safely maintain power as long they keep the common folk against each other.
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| Source: nhc.noaa.gov |
The NHC is still showing Fiona staying out east of the Bahamas.
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| Source: MagicSeaweed.com. |
Looks like we might get some bigger surf next week. Watch to see how that develops.
Good hunting,
TreasureGuide@comcast.net
