Tuesday, February 11, 2014

2/11/14 Report - Reading Beaches 101: Required Reading for Improved Beach Metal Detecting

Written by the Treasureguide for the exclusive use of treasurebeachesreport.blogspot.com.

Use link below for source of diagram and web site on sand movement.
An ancient philosopher named Heraclitus said something like "You can never step on the same beach twice."   He didn't say exactly that because he didn't speak English.  But that is what he meant.  He recognized how dynamic a beach really is.   

I have been thinking lately about doing a post on how things move on a beach, but I never got around to making the diagrams that I needed.  Well yesterday I found some diagrams that I can use for the purpose so I'll go ahead and address the topic.

You might wonder why you need this information.  You might think that all you have to do is get a metal detector and wander around on a beach and the detector will find things for you.  You can do that, but you won't find as much as quickly.  In order to increase increase your efficiency and increase the number of finds you make in the time you have available, you need to know how beaches work.  Otherwise you will be searching randomly, or at least less efficiently than you could.

There are miles and miles of beaches out there and treasure is not distributed purely randomly.  That is especially true of treasure that has not been dropped in the last few hours or days.  The trick is to find the hot spots where good things have accumulated.  This information will help you quickly find the most productive spots on the beach.

Many of the same things apply to shallow water, but for now I'm going to talk about beach detecting.

I found this diagram on a web site that you can access by using the following link.  It explains the movement of sand on a beach.  I'll use this diagram and others to show you how treasure moves too.


The sand is moved by wind and water.  I won't talk very much about the wind because its affect on detecting targets is negligible.

One area that is very important is the area between the two thin black horizontal lines just above and below the waves at the right side of the diagram, especially where those lines intersect with the beach.  That is petty much defines the area of wet sand on the front of the beach.

As the tide gets higher and the size of the swells and waves increases more of the beach is affected by the water and to show that the upper black line would be raised.  As the low tide decreases the lower black line would be dropped.

Going back to hurricane Sandy, on the Treasure Coast the water got all of the way up to the dunes or cliff at the back of most beaches.  Most of the time only the front of the beach is directly affected by the water.

A number of years ago I introduced and explained the terms "coin line" and "coin hole" in this blog.  Coin lines and holes are produced by water moving sand and other items, especially coins and some other items, and depositing them, sometimes in a coin line or coin hole.

If you know how to find and work coin lines and coin holes you will be able to dig a high number of items in a short amount of time. 

Coin lines and holes are do not always exist on any particular beach and will be difficult to find on beaches that have few targets.  They are much more apparent and easier to learn about on beaches that consistently have or have had a high number of visitors over a number of years.  On other beaches items move the same way, but it is not as easy to see the patterns simply because there are not enough data points.

Notice the blue arrows in the water going right to left in the diagram.  Those arrows show sand being moved from deeper water to shallow water and from the shallow water to up on the beach.

Other items besides sand, such as coins, also move up onto the beach in a similar manner, but not necessarily at the same time.  Items of different size, weight and shape are moved at different times.

It takes more water energy (generally bigger waves, swells and tides) to move coins than sand.  Other factors are involved too, but I won't overly complicate the basic factors now.

Sand accumulates on the front of the beach sometimes when coins and other items are not being moved onto the beach.  That creates poor detecting conditions, such as what we often see during the summer months, and in fact, the beginning of 2014.  That is when the beaches are building.

But there are arrows moving both directions - on to the beach AND from the beach into the water.  Notice the blue arrows going from left to right under the water.  

Normally there is a pretty good balance between the sand moving onto and off of the beach.  At other times the sand is moving more one way or the other.

Where items other than sand is dropped off depends on several factors including the size, weight and shape of the item plus the shape of the bottom, the tides, currents and where the waves are breaking.

Different objects drop out of the water at different times.  Sand will be moved and dropped off at one location, silt, mud, pebbles and other objects will be moved at different times and dropped off at different locations.  You've seen the results of that, I'm sure.   One time a sand bar will build up, or a shell pile be created or removed, for example.  That is the same way coin lines and holes are created. 

To get more specific, pebbles (defined as around 6 to 10 mm.) are dislodged when water speeds of 100 cm/s are reached, and settle out at around 20 cm/s.

Slower water will get sand moving, and it takes slower movement before the sand drops out and is deposited.

Silt and clay takes more speed to get it moving because it adheres, but once suspended takes very quiet water before it settles out.

The point is that different objects (including coins, rings, pebbles, shells, sand etc.) are picked up at different times depending upon flow of water and are deposited at different times. also depending largely on the amount of flow of water.

This is getting pretty long.  I'll have to cut it off here and pick continue with the topic later.

On the Treasure Coast we have a 1 to 2 foot surf.  It won't change for a few days, therefore expect continued poor beach detecting conditions.

Happy hunting,