Treasure Beaches Report: Pt. 2. (2020 and Beyond). : 11/11/25 Report - Must Read Study on Scouring and Settling of 18th Century Shipwreck Artifacts. Reader Observation and Finds.

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

Recent Find by Vance D.

Vance D. has been reading this blog and what I've been saying about the movement of sand and things like that and has been watching the beach. He recently ran into an interesting feature that cut into the beach and way back. It sounded like one of those runoff channels that ends as a rip current. It was four or more feet deep and there was a drop off of a similar amount in the water, the bottom of which was covered with shells. He metal detected it and didn't find much. He did however find some things outside of the dip, including a sinker, the above leaf thing (above) that shows no maker's mark and appears to have been once gold-plated, and the darkened nickel, which shows evidence of marine life although it was found just a couple feet from the foot of the dunes.

Nickel Find by Vance D.

Thanks for sharing Vance. I'm glad you are relating what I talk about in this blog to your personal observations on the beach.

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Yesterday, as Part VI of my series I posted a great dissertation on shore stranded shipwrecks. I'll call the following section Part VI of my How Coins Move on a Beach series.

I just ran across a good archaeological research article that fits right in with what I've been saying. The title is Predicting Scour and Maximum Settling Depths of Shipwrecks: a numeric simulation of the fate of Queen Anne's Revenge by Trembanis and McNinch, 2003. It studies scouring and settlement of artifacts of the QAR, which sank about three years after the 1715 Fleet, so in relation to long term effects, should be somewhat comparable to1715 Fleet artifacts. I was glad to find it since it agrees with and supports my own thoughts, which were arrived at primarily through years of personal observation.

The article is not easy to read unless you are familiar with the academic terminology and jargon, which I found a little challenging. I'll try to break it down and relate it to how I've tried to describe the same processes in the past.

I'll start with an excerpt or two from the abstract. I'll skip most of what was said about the model for now. Here goes.

...The ship, which ran aground in waters less than 4 m deep while attempting to navigate Beaufort Inlet, now rests in 7 m of water on the shoals of the ebb tidal delta. Archaeological evidence indicates the wreck has remained in the same location since the initial grounding which suggests that the numerous and varying-sized artifacts scattered around the debris field have settled through approximately 3.5 m of substrate. McNinch et al (2001) hypothesized that this extensive settling through unconsolidated sandy sediment resulted from episodic periods of scour and burial, and that the wreck's recent exposure occurred because the sedimentologic nature of the underlying geology limited continued scour... Queen Anne's Revenge, formerly the French slave ship Concorde, was a three-masted ship of approximately 250-tons (Moore, 1997) with a keel depth that likely extended 3.7 m below the surface of the water (Moore, personal communication). Written documentation by David Harriot, who sailed with Blackbeard, noted that the QAR "ran aground" on the shoals of the ebb tidal delta while attempting to enter Beaufort Inlet in 1718 (Moore, 1997). Beaufort Inlet.

So the wreck is resting in about 22 feet of water. They say it has remained in the same location since the original grounding. Right off, I don't know how they came to that conclusion, but I'll accept it as generally true for now.

The artifacts they are talking about are a cannon ball, a cannon and a rubble pile. That isn't exactly the kind of artifact I am most concerned about, but the general principles will still be somewhat applicable to objects like coins.

They say the artifacts settled THROUGH about 3.5 meters or around eleven feet of bottom material. That is a period of over three hundred years. The material is described as "unconsolidated sandy sediment," which means simply loose material such as sand and shells that are not stuck together.

So why didn't it settle more in all those years under water? The answer is fairly obvious but worth noting. If you read the study, under the loose material was a layer of silty sand which was more sticky or cohesive. Because of its cohesive nature, it resisted suspension by the water force acting on it at that depth. So, the artifacts settled through less cohesive materials and came to rest on a more cohesive layer. In many cases on the treasure coast, items come to rest on coral or rocky bottom materials.

They "hypothesized that this extensive settling through unconsolidated sandy sediment resulted from episodic periods of scour and burial, and that the wreck's recent exposure occurred because the sedimentologic nature of the underlying geology limited continued scour."

So if they are right, and I'm sure they are in this regard, the settling was not a continuous gradual process. It was episodic. Periodic events, such as storms moved bottom material and caused the settling. As I've described many times before, layers of sand or sandy material are removed and replaced periodically. Items, including coins do not sink in stable undisturbed layers of sand. The sand layer must first be disturbed. Since the water is calmer at depth, without bottom currents or something like that, it takes a special event to disturb those deeper layers, so a big storm might come along and disturb enough bottom material for the item to settle down a small distance where the item will then rest until another similar event comes along and the item will then settle to a lower level. It takes quite a bit of force to lift items like coins, and much more to lift cannon balls, so that would be a less frequent occurrence. In some places, it would never occur. Unfortunately, the study did not look at smaller individual artifacts such as coins.

Moving on to the body of the paper, here is another excerpt.

So the forces acting on this site includes currents from the inlet as well as storm wave activity. They were lucky to catch measurement during so many various events over a two-year period.

The bottom sediment at this submerged site was normally stable but was moved when wave size exceeded 1.5 meters.

They found three basic layers. The top two contained artifacts, while the bottom layer of silty cohesive sand did not contain artifacts. It seemed to act as a base on which the looser more mobile material rested. Below is an illustration showing that.

The Drambuie model is the model the study attempted to validate. I was not much interested with the details of the model, but they had the opportunity to study the effects of a hurricane, a nor'eater, a sou'easter and fair weather. Below is the process they observed for hurricane Bonnie.

By the way "scour" here refers to movement of bottom materials.

So, the extreme conditions produced by hurricane Bonnie even in this relatively deep water, buried the artifacts, then exposed them, and then buried them again. That is the kind of thing we often see with a passing hurricane as the wind direction and forces change as the storm passes.

You can read the article yourself for additional information, but I think I should quit for now. Maybe I'll come back to this article and comment on more of the detailed findings tomorrow. Or I can leave it for you to read for yourself. Let me know.

TreasureGuide@comcast.net

Here is the link

(PDF) Predicting Scour and Maximum Settling Depths of Shipwrecks: a numeric simulation of the fate of Queen Anne's Revenge
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