Moving coastline and water edge shifts


I read that thread, but it is still unclear how should things should get done ? Mapping waterway changes - adding/losing land - #5 by AndrewS_OHM

I am wondering what is the best strategy to manage “moving” edges of water surfaces in time ?

  • Should we draw each piece of water surface that was present at one time and today ?
  • How does the end_date manages the suppression of a water surface ? (In the example below, it is not working. Could you help me to make it work ?)
  • Where should be tagged the coastline ? (on the farest edge in the sea ?)
  • Is the update of the coastline position still an issue in 2024 ? (before, it was never updated, which will ruin any modification performed with water connected to a coastline)

Not working example (even if end_date is set ?) :

Capture d’écran du 2024-05-17 10-12-41

Link : Query Features | OpenHistoricalMap

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Hi @Stephane_V - great to see you here on the forum!

There are probably a bunch of ways to map the water surface that was present before & now is not. We haven’t put together a best practices doc on that and probably should.

For your example, I think it’s working now, but I didn’t test it as well as I should have before I edited it, so it might have been working?!?!?

The only thing that looked odd to me was that it had start_date=-10000, which should have been fine, but is also optional. Leaving no start_date value just means that it’s been there since as far back as we can tell (without adjust sea levels for the ice age, etc…)

For your questions:

  • I’d draw each piece of water surface separately, but these can change significantly over time, so you may have many versions of the same water area.
  • end_date=* should work like it does for other features - buildings, roads, etc. If something’s not working, please bring it up here!
  • For now, we should probably just leave the current / modern coastline tagged with natural=coastline.
  • Yes, our current coastline process is messed up and needs to be repaired, but that’s a pretty large project that will need some coordination. You’re correct that it will complicate moving shorelines until that’s fixed, but I don’t think it will be impossible.

Please take a look and let me know if it is working for you!

Here is what I can show.

Lake Duwamish and Lake Washington change lake water levels.

I also am working on a lake in the center of America where a dam is built and there is a normal lake level and a high water level. I am not sure what dates there are for the high water but its clear from imagery that the “normal” lake level is far higher than that listed in the USGS TOPO and I am not sure how to edit that change without knowing more about the dates.

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Other examples: