Am 27.09.2016 um 19:10 schrieb Markus Bärlocher:
I look for this: "Elevation in metres above 'mean high water spring' level."
Which means the geographic hight above MHWS: https://en.wikipedia.org/wiki/Mean_high_water_spring
By clicking on "Wikidata Item" in the sidebar of that page, I get to https://www.wikidata.org/wiki/Q6803625 ("highest level that spring tides reach on average over a period of time")
Is that what you need?