Not far, and it does not keep going. Waves turn over the top layer of a beach and then stop, so a ring lost weeks ago is usually still in the same shallow layer as a ring lost yesterday.
That has been measured on a real coastline. Here is the number, and here is what nobody has measured.
On a gently sloping sandy beach a one metre wave turns over roughly the top 10 centimetres of sand. A storm reaches about half a metre. Below that the sand mostly sits still, and a ring sits inside the layer that moves.
Which makes the common assumption wrong. A ring does not work its way deeper year after year, because the depth has a ceiling. Centimetres, not metres.
A one metre breaking wave turns over roughly the top ten centimetres. The ring is in this layer.
A storm reaches about half a metre. The maximum is about 1.8 times the average.
There is a ceiling. A ring does not work its way deeper year after year.
Coastal scientists call it the sediment mixing depth: how deep the waves actually turn the sand over, as opposed to how deep the sand goes. It was measured directly, with rods pushed into the beach, across seven field experiments on steep and gentle foreshores of the Algarve coast in Portugal.
“The mean mixing depth is 1.86 times the breaking wave height multiplied by the beach slope, and the maximum mixing depth is about 1.8 times the mean.”
Put an ordinary day through that and a one metre breaking wave on a gently sloping beach gives about ten centimetres. Put a storm through it and the same beach gives roughly half a metre. The worst case is around 1.8 times the average, so a bad day goes deeper than a typical one, but not without limit.
Ten centimetres is a typical case, not a constant. The beach slope sits in that formula right next to the wave height and multiplies in exactly the same way: twice as steep is twice as deep. So the same one metre wave turns over several times more sand on a steep foreshore than it does on a flat one, which is what the seven experiments were built to compare.
The paper draws the line at a beach face slope of 0.08. Steeper than that counts as a steep beach, flatter counts as a gentle foreshore. That is roughly a metre of drop over twelve and a half metres, which is something you can judge standing on one.
It also explains why earlier answers to this question disagreed so badly. The relationship measured here matches what earlier work found on steep beaches, and is about eight times larger than what earlier work found on gentle ones. Same question, same physics, answers a factor of eight apart, because nobody had put the slope in the formula. Worth knowing before you trust any single number on this subject, including the ten centimetres above.
So the honest answer is a range rather than a single number. On a flat beach on a calm day it is a few centimetres. On a steep beach in a storm it is a good deal more. What does not change is that there is a ceiling at all, and that on most days it is measured in centimetres.
Sand is not a liquid. It moves when something moves it, and on a beach that something is the wave. Below the depth a wave can reach, nothing is stirring the grains, so nothing is carrying the ring any further down.
Beaches are pulled apart and rebuilt by storms, but even that has a floor. Encyclopaedia Britannica on beaches describes a depth below which the strongest waves no longer sort or move the sand at all.
The question people actually arrive with is whether it is too late. On the evidence above, depth is not the reason it would be. A ring lost a month ago is in the same layer of sand as a ring lost yesterday, and that layer is well within the reach of a metal detector.
What gets worse with time is the area, not the depth. Sand travels along a beach as well as up and down, and the person who lost the ring remembers the spot a little less precisely every week. That is the real cost of waiting, and it is much larger than the few centimetres.
Gold is among the least chemically reactive elements there are. It does not rust and it does not tarnish, which is why Egyptian gold comes out of the ground after roughly 3,300 years in nearly perfect condition.
An 18 carat ring is 75 per cent gold. The rest is usually copper and silver, and those are the parts that can dull. So it may come up looking duller than it went in. It will not have corroded away.
Waves sort sediment by density. Lighter grains are carried off and heavier ones are left behind, which is why heavy minerals concentrate in dark bands on a beach. Gold is 19.3 grams per cubic centimetre, by a long way the heaviest thing on a sand beach, so it behaves like the heaviest grain there rather than like something the water takes away.
Two things on this page would have been easy to invent. Neither is known, so neither is claimed.
Retrievly does not search. It is where you post what you lost and roughly where it happened, so that somebody near you with a detector can pick it up.
The people who do that are hobby detectorists. They go in their own time, and the part they are actually in it for is handing the thing back.
In public only a rough circle is shown. The exact point goes to the one person you choose, and only after you have chosen them.
No money goes through Retrievly. A thank-you is arranged directly with whoever goes out, and a genuine thank-you is enough.
We are new, so there may be nobody signed up near you yet. That is when we go looking and send them your request. Retrievly does not vet or check anyone, so read the profile and meet somewhere public.
Post a requestBrowsing needs no account. You only sign in to post.
Kenny built Retrievly. He has snorkelled the Danube for years and keeps bringing up things that belong to other people: wallets with the ID still in them, phones, keys. That is where Retrievly came from.
More about Kenny