Non-permanent piers

The following little piers show up on recent ortophotos: ArcGIS Web Application

(Activate the Byortophotos layer to see arial pictures of when they are in use.)

Initially I mapped them in OSM here: OpenStreetMap
But then I removed most of it again, having looked closer at facts on the ground. (They may still exist, if you run into a server-side cached version of the OSM tiles.)

However, they turn out not to be permanent. My guess is that they exist five months each year and are in that period rather practical to have on a map. How are such non-permanent (but potentially of high practical value) structures to be tagged? Should they simply be left out of OpenStreetMap?

Does each of them go back in the same spot each year?

If so, you could possibly map them with opening hours=24/7, 1 Apr-30 Sep, together with a description=pier removed over winter, or something similar.

But if they move to a different spot, then no, I wouldn’t map them.

Here is a bridge that is only available at some parts of the year. Way: 462341136 | OpenStreetMap