Treasure Beaches Report: Pt. 2. (2020 and Beyond). : 10/28/25 Report - Part IV of How Coins Move on a Beach. Constructive and Destructive Waves. Beach Replenishment.

Written by the TreasureGuide for the exclusive use of the Treasure Beaches Report.

Path of Grain of Sand in Swash Area.

This will be Part IV of my series on how coins move on a beach. On the 24th I did a little clarification. I'll call it Part III b.

Above is an illustration of the movement of a grain of sand in the swash area. That is an idealized case. It doesn't always happen exactly like that, but you can visualize the typical case as looking like that.

The illustration shows a wave approaching the beach at a bit of an angle. It shows the sand being washed up onto the beach in the same direction the wave hits. It shows the wave going up and then the backwash bringing the sand back down the slope. The overall effect would result in a right to left movement of the sand. On the Treasure Coast that would be common. It would typically be a north to south movement.

Other things besides grains of sand would move similarly. When the force is strong enough, stones, shells and other things, even coins, can be moved in a similar way.

I've often found that the best coin and jewelry spots south of the predominate deposition area. In front of many South Florida resorts, there were good coin holes just to the south of the resort.

The movement caused by the swash and backwash goes right along with the littoral drift, which along the east coast of Florida, is north to south.

Besides the surf, there is also a wind effect. You've probably seen strong north winds blowing sand like a stream down the beach. But the wind will also affect the swash. You can often see the backwash being blown along the beach.

On the 24th I posted the illustration below.

So picture this. When there is a north'easter, the swash will move up onto beach and back down with the net movement also being north to south. Combine that with the north to south longshore current, and you have a lot of flow to the south.

As I said in Part III, you can sometimes track the movement of coins in the swash and backwash with your metal detector. And I highly recommend that when possible. Don't forget your test coins.

The swash can move a coin in and the backwash can take it down the slope. Where the coin gets left, depends upon when the force diminishes enough to drop the coin. I've talked a lot about the force gradients. The coin, like grains of sand will keep moving until the force decreases enough to drop them. And we are not talking about a single steady stream, so it can happen in steps. A coin might be moved by the backwash from one wave, be deposited, and then be moved by the swash or backwash of the next wave. There can be numerous steps, but once the coin is covered by enough sand, it won't move again until the sand is also moved.

Another complexity is, the interaction of the swash and backwash. As the swash comes in, it can get hit by the backwash of the preceding wave. At that point the flow gets disrupted and any items being moved can be dropped.

But not all waves are the same.

Constructive waves are waves that drop more sand on the beach.

Source: Wave types - constructive and destructive - Coastal processes - AQA - GCSE Geography Revision - AQA - BBC Bitesize

Constructive waves result in a net increase of sand on the beach, while destructive waves have a stronger backwash and erode beaches.

Source: Wave types - constructive and destructive - Coastal processes - AQA - GCSE Geography Revision - AQA - BBC Bitesize

That seems like a good place to end Part IV.

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The barrier islands keep moving, which we foolish humans label “beach erosion.” We keep trying to bend nature to our will by trucking in lots of sand from somewhere else for millions of dollars.

The people who pay for it often don’t live anywhere near the water...

The barrier islands keep moving, which we foolish humans label “beach erosion.” We keep trying to bend nature to our will by trucking in lots of sand from somewhere else for millions of dollars.

The people who pay for it often don’t live anywhere near the water...

The Corps, the government agency in charge of playing in such big sandboxes, always claims they’re “saving” the beach from disappearing. They aren’t...

“We’re just saving a lot of people’s investments,” he told me...

“Treasure Coast governments have spent well over $100 million during the last five years on beach-renourishment work along our shorelines,” TCPalm.com noted in one editorial...

More than half of Florida’s 825 miles of beaches are now classified as “critically eroded,” thus making them eligible for renourishment...

She calls beach renourishment “a sandy Band-Aid.”

As climate change makes the sea level creep higher, applying that Band-Aid “happens more frequently and is more expensive,” Haydocy told me. Higher seas make even smaller storms more destructive than they used to be, she pointed out...

One thing she said that surprised me is that Florida used to obtain all its sand for rebuilding beaches from offshore dredging — but not anymore.

Now, she said, most Florida beaches are being rebuilt using sand from ancient dunes that form the Lake Wales Ridge, which runs down the spine of the state...

Instead, our “fiscal conservatives” will continue to spend our tax money on rebuilding beaches sure to be washed away in the next storm, which is one step removed from just pouring dollars down the drain....

Here is the link for the much longer article.

Sea level rise makes Florida 'beach renourishment' projects more frequent and expensive • Florida Phoenix

Thanks to Joe D. for that link.

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If you've heard about global warming and the sea levels rising to new levels, consider the following from Wikipedia.

The warmest peak of the Last Interglacial was around 125,000 years ago, when forests reached as far north as North Cape Norway (which is now tundra) well above the Arctic Circle, at 71°10′21″N 25°47′40″E. Hardwood trees such as hazel and oak grew as far north as Oulu, Finland. At the peak of the Last Interglacial, the Northern Hemisphere winters were generally warmer and wetter than now, though some areas were actually slightly cooler than today.

Here is the link for more about that.

The last interglacial period occurred between 130,000 and 115,000 years ago. This period was characterized by a warmer climate than today, with higher global sea levels and smaller ice sheets.

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