OT: materials that might be found of a 1920s strand line.

Oil? Used for lubrication if not propulsion and likely they weren't too careful about it getting into the water.

Was it the kind of river to have shipping?

Also runoff from industrial processes like gas works, tanneries, etc that would end up in the river.

In suitable anoxic conditions, quite possibly. Black organic deposits are often formed anoxically (see coal, peat bogs, etc).

They'll be coal in a few hundred million years...

Theo

International shipping used the river at the time. Going by the recently demolished gasworks site, I've no idea what the ground contamination was, but after rain , some of the ground had a vibrant sort of electric purple colour, impressive but disturbing. I suppose bits of tarry stuff might show up from the then sloppy bunkering of vessels. Also someone suggested that around then they used wads of coconut hairy-fibre brown covering waste material, much as bubble wrap is used today, to protect fragile items in transit.

So, are you asking this for any specific reason? Layering of sediments and the like has always occurred, indeed there are some satellites that have ways of sensing fast changes in this sort of data, as it will point to some change maybe over 100 years or so, not the sort that takes thousands of years. Brian

Although tide gauges have been around for at least 100 years, if the records survive , the datums/calibration procedures tend not to survive as gauging sites tend to move around different sites in a port. It would be nice to have another way , other than newspaper accounts, of the levels of extreme tides in earlier decades. So by nurdle counts, "best before" dates on crisp packets,etc its been possible to correlate recent high tides with the known records In local chart datum terms at 4.95m a strand line for 4.90m tide 23 April 2023 (would have been obliterated last week due to a 5.14m tide 02 Aug 2023) and going up slope

Roman fish farming tanks in the mediterranian were set very accurately relative to sea level because they used waves washing over ramps to provide circulation of water and this only worked properly when the ramps were at just the right level relative to the sea. Original work on this was done by Nick Fleming. There is a lot of literature on this subject now. John

This may be what NOC prof Ivan Haigh was telling me about proxy records for tidal records in the Med, a couple of months ago ,but did not go into detail.

I liked the example shown on a TV prog last month relating to IIRC about

If its a river or and area with moving sand banks then water levels over a decade may be very variable due solely to silting or dredging. The height of a tide may also be influenced by the amount of water flowing down a river when te tide is coming in.

I think you are mistaken, Venice is not being submerged by rising sea levels, it ins sinking into the swamp it was built on

That is the thing to do. give the building proper underpinning so they dont sink sea levels have been rising at ~ 3mm a year for the last 5000 year+ and are not changing rates.

There's another minor point - there's F all tide in the Med.

Andy