Written by the TreasureGuide for the exclusive use of the Treasure Beaches Report.
I went for a a couple days ago to do a little scouting around and found the bottom half of an older straight-side Coca Cola Bottling Company bottle from Fort Pierce. I really wish it was not broken. I love to find old Coca Cola bottles, especially those from Fort Pierce and local areas.
While on that subject, here is a link to a great article for dating and identifying older Coca Cola bottles.
https://www.fohbc.org/wp-content/uploads/2012/07/DatingEarlyCocaColaBottles.pdf
I continued on my walk , looking for a good metal detecting spot. I finally found one. I noticed the larger rocks scattered around the wet sand area so took a closer look and found a piece of an older copper case of some sort, kept eye-balling and found a piece of an old watch band (see below) and a couple other promising metal items. I intended to return to the spot with my metal detector, but the wind changed, and the spot deteriorated. Too bad. It was a small area, but seemed like it would hold at least a few coins, and maybe an older one or two. I'll check once in a while to see if that spot opens up again.
The finds are not of value other than the information they provide. One suggests the possible presence of older bottles in the area, and the metal objects indicated a good spot for metal detecting.
Even though I didn't get in any good metal detecting I did locate some spots to watch and possibly search in the future.
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I wanted to bring your attention back to the article I referrred to on 9/2: SIMPLE GENERAL FORMULAE FOR SAND TRANSPORT IN RIVERS, ESTUARIES AND COASTAL WATERS by L.C. van Rijn.
(Here is the link. https://www.leovanrijn-sediment.com/papers/Formulaesandtransport.pdf)
That is a great article. It considers most of the factors that determine how sand moves on a beach, which is what you need to know in order to understand not only erosion and accretion, but also how other treasure moves on a beach.
Other items are moved by the same forces and according to the same physical principles as the sand. The other items, including coins and rings, simply are of different sizes and shapes and metallic composition.
I didn't finish the topic when I introduced the paper in my 9/2 post, so today I'll comment on a couple more excerpts from the paper. Here is the first.
Flume and field data show that the sand transport rate is most strongly related to the depth-averaged velocity. The power of velocity is approximately 3 to 4. The bed material in natural conditions consists of non-uniform sediment particles. The effect of the non-uniformity of the sediments will result in selective transport processes (grain sorting). Grain sorting is related to the selective movement of sediment particles in a mixture near incipient motion at low bed-shear stresses and during generalized transport at higher shear stresses...
I often talk about items being sifted and sorted by water. Everybody knows that it happens, but few people understand the details concerning how it happens.Ever since I discovered the Heezen and Hollister chart, I've been talking about this. Actually before that, but since then in more specific terms.
I talked about the point at which the water velocity reaches a force that particles overcome the forces that keep them in place so they are lifted and trasnported. In previous posts I called the force required to get an item moving as the "trigger point."
Here is an excerpt from my 8/30/15 post on that subject.
That provides an excellent example of how what I have named "trigger points" are important. In case you haven't read what I've said about trigger points, a trigger point is the amount of water movement or force needed to get different objects to start moving.
Little force is needed to move silt or fine sand and more force is needed to move small pebbles and even more force is needed to move things like gold coins. Every object has its trigger point. If you know where each object lies on the scale, you know in what order things will be moved as the amount of force increases. If you think about that continuum and how the various trigger points are met as the amount of force increases, you'll understand how some objects are moved and others left behind as different amounts of force are produced.
The other important thing is the "drop point," which refers to the point at which different items drop out of moving water and settle. As water movement decreases, different objects settle out at different times.
An important thing to watch is when and where the amount of force changes. For example, there will be a lot of force directly in front of a breaking wave and less as the water goes up the slope on the front of the beach. If the trigger point for an object, such as a coin was exceeded at the base of the slope, the "drop point" might be reached at some point as the water slows as it goes up the slope. Objects that are less easily moved will generally settle out first, but it is not a straight line function.
It gets more complicated since you also have to take into account things such as the back flow, which may have enough force to move sand or other objects back down the slope again.
Up to 600 rpm the force produced by Frogfoot's blowers moved the sand, but above 600 rpm the coins were also being blown around. What they wanted was to blow the sand but not the coins, which would then tend to settle down into the hole.
Particle movement will occur when the instantaneous fluid force on a particle is just larger than the instantaneous resisting force related to the submerged particle weight and the friction coefficient. The degree of exposure of a grain with respect to surrounding grains (hiding of smaller particles resting or moving between the larger particles) obviously is an important parameter determining the forces at initiation of motion. Cohesive forces are important when the bed consists of appreciable amounts of clay and silt particles. The driving forces are strongly related to the local near-bed velocities. In turbulent flow conditions the velocities are fluctuating in space and time. This makes together with the randomness of both particle size, shape and position that initiation of motion is not merely a deterministic phenomenon but a stochastic process as well....
Notice here the acknowledgement of the importance of an objects size, shape and initial position. The longstanding and oft repeated myth of weight determining where an object will be found on a beach neglects those variables. As I've often said, density is better predictor than weight, but there are other important variables, including the objects shape, to mention one.
I have demonstrated in the past by my own informal experiments and by reference to formal studies that the shape of the object will help determine how an object will be moved by water. The amount of surface area presented to the force of water is important, therefore a ring will move differently from a coin, for example, even if the objects are made of the same material and have the same weight.
The Rijn paper acknowledges the importance of the objects original position too. Everyone knows that objects hiding in bedrock crevices, for example, will be protected from the force of water and will tend to remain in place.
While the Heezen and Hollister chart provides a lot of important information about how sand and other objects are moved on a beach, the Rijn paper supports and adds to that.
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| Source:nhc.noaa.gov |
The red and yellow areas at this point look like they will head up into the Atlantic. At least one model is currently showing that. So there is nothing right now that looks like it will change our current beach conditions much.
Happy hunting.
TreasureGuide@comcast.net