Written by the TreasureGuide for the exclusive use of treasurebeachesreport.blogspot.com.
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Stairs at Seagrape Trail Saturday Morning.
Clipped form video submitted by DJ.
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The posts at the bottom of the stairs at Seagrape Trail were getting washed out Saturday morning. They had recently repaired them, but they were damaged again. I was there that day but forgot to take photos.
Take a look at the stairs and the short posts sticking out of the sand in the photo below. The posts are lower than the bottom step. They weren't showing until the beach eroded.
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Just To The North of the Seagrape Trail Access on 2/20
Clipped form video by DJ
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Also notice the mass of water that is just below the stairs. Just a few yards out is a wave surge behind that mass of water. The surge will push the mass up the face of the slope, and the surge will rush up the slope towards the dunes.
Before I go much farther, I'd like to refer to what I think is the most important thing I've ever learned about beach dynamics. The same principles apply to how things are moved in rivers and streams too, but for now I'm interested in these principles as they explain how sand and other items move on a beach.
Breaking it down, there is a certain amount of force needed to pick up different materials, including clay, silt, sand, pebbles, gravel and other items. It takes more force to start an item moving than is required to keep the same item moving.
There is a certain amount of force required to suspend specific types of sand and other materials. Generally it takes more water velocity and force to suspend clay than it takes to suspend sand, for example. Even though the particles of clay are smaller, they are more cohesive so it takes more water force to pick it up. And it takes more force to move pebbles than sand. Things like the density of the objects, cohesiveness and even shape are important factors. Pebbles are not more cohesive than sand, but they are more dense, so it takes more water velocity or force to get them moving.
There is also a certain amount of force required to keep an object moving once it is moving. It takes less force to keep an object moving than it does to overcome the inertia and other factors that keep a particle or other object stationary.
The above chart shows velocity increasing from left to right on the horizontal axis, and particle size increasing from bottom to top on the vertical axis. The right most red line shows that clay requires more force to suspend than sand, which requires less force to suspend than pebbles (or coins, rings, etc.).
Looking at the left most red line, you see that it takes little force to move already suspended clay or silt, but the force required to transport sand and pebbles or larger objects is greater.
Lets say you have enough water flow to get the sand moving, and enough to keep it moving, but then the force diminishes and the sand settles. The sand will be picked up where the force is relatively high, such as where the wave crashes, and carried up the slope until the water slows enough that the sand drops out of suspension. If the water rushes back down the hill instead of slowly decreasing on the slope, sand can be carried down the hill, resulting in erosion.
The sand is moved when the force is great enough to pick it up and move it, and it is dropped when the force slows. That part seems obvious enough, but there are other factors. You have the tides and interacting multiple waves interacting. Returning waves hit incoming waves, for example. And there are irregularities in the surface of the beach. And there is liquefaction. (That is another topic for another time.)
There are different kinds of objects on the beach in addition to sand. There are shells, and there might be coins and things. Coins have their own peculiarities and methods of moving. I once posted a number of ways that coins move. But that is another discussion for another time.
Without getting into all the variables, sand will be moved differently than coins and things. Different amounts of force are required to suspend and transport different objects.
Lets say you have just enough flow at the base of the slope to pick up and move sand. It will be transported up the slope, and if the force slowly decreases, the sand will drop out and the sand will accumulate. On the other hand, if the water picks up the sand and keeps it moving up the hill, and the water bounces off a cut or dune so the force is maintained at a high enough rate, the sand will wash down the hill again. That is one way you get erosion.
Coins can be picked up if the force is great enough and carried up the hill along with the sand, but since it takes a greater amount of force to keep the denser objects moving, the water can slow enough to drop the coins while the sand continues to move out. If the returning water force is great enough, the coins can be carried down the slope too.
You'll notice that when the water is bouncing off the face of a cut or off the dunes, the returning water can have a lot of force. That means things will be carried down the slope until they drop out of suspension and settle in.
Different objects will settle at different places. Like things will be dropped together. As the water slows, coins and other things will drop out and settle before the sand. That is how coin lines and coin holes are formed. I've talked about that a lot in the past.
So what you are looking for is places where good targets have just been uncovered by eroding sand, or where those targets have been dropped.
After all of the fast moving water is over, slower water will move the grains of sand up the hill and drop the sand, building the beach and perhaps cover denser objects, such as any coins that were left behind. Since you are interested in the areas where good targets are being uncovered or being dropped, you are looking for areas where the sand is being eroded or areas where the water has slowed enough to drop good targets.
It is all a beautiful balancing act. Items are sifted and sorted like they are a gold pan, but on a beach the area is much bigger and there are a lot irregularities and complexities. Still, I think you'll benefit if you get the ideas presented in the above chart.
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PS: I lost the original source of the chart, so if anyone can find it I'd appreciate it. I'd like to be able to credit the source.
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I received some questions and know that some of you might be wondering if your detector might not be working ok because you didn't find anything good last weekend. Your metal detector is probably fine. If you are not sure, test it on some small silver coins. Maybe cut an old silver dime in half, take it to the beach and test your metal detector. If you can detect a small piece of silver like that, you can detect a silver reale unless it is too deep or something is wrong with your sweep. So pay attention to your sweep speed and height when you do your tests. It never hurts to take some test targets to the beach to make sure. But I'd bet that your detector is fine. There is a lot of beach out there and you just have to put your coil over the right spot at the right time. If you understand what I wrote above, that will help you. Finding the spots is the main thing.
I know how it is. When you don't get any hits, you start to wonder if you detector is working well. Usually it is, but you can test it to make sure.
I know how it is. When you don't get any hits, you start to wonder if you detector is working well. Usually it is, but you can test it to make sure.
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Seems like there is some talk about beach privatization again. I received the following emails from DJ.
Thought this bill died a couple years ago.
HB 631 was approved and still on the books, lots of legaleaze
These bills are filed to repeal 631 and protect beach access for the public (as far as I can tell)
I’ll try to get more current info, they don’t make it easy to understand.
Hope we don’t have to face this too.
We had a petition going on this back some time ago. Somebody needs to stay on top of this.
There is also some proposed legislation for the Florida Keys that the Fisher organization is fighting. I've been meaning to post what I received about that, but there has been so much local news lately that I didn't get around to it yet.
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The surf will be small this week.
Happy hunting,
Treasureguide@comcast.net
There is also some proposed legislation for the Florida Keys that the Fisher organization is fighting. I've been meaning to post what I received about that, but there has been so much local news lately that I didn't get around to it yet.
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The surf will be small this week.
Happy hunting,
Treasureguide@comcast.net
