If land is surveyed from ocean shoreline (high-tide). How is it figured years later when tides have changed?

Question

Meaning, does the constant change in the oceans shoreline (over time) effect land suveys and measurements for mountain altitudes?

Answer 1

Tidal gauges are used to determine mean high tide. These instruments are either pressure type, which have to be corrected for barometric pressure or sonic type, which measure water depth using sonar. They record the measurements at freqent intervals over long periods of time and the resulting measurements give a mean average sea level.

This in turn is used to generate a vertical datum for surveying purposes. Because it is such an involved process it is not adjusted very often, but is is changed periodically, and most countries in the world have some sort of a national survey or group that keeps track of this sort of thing. As I have said in your other questions, the current datum for North America was established in 1988 and is used for Canada, US, and Mexico.

To give you another example of how this data is derived see one of my previous answers about determination of sea level in India:
http://answers.yahoo.com/question/index;_ylt=AngYwJx55EGpZEYY1rva_dzsy6IX?qid=20060614075708AA95YEy

Answer 2

Yup. The high tide will always be there. If it erodes away part of your land, you lose it. If a new survey was done, the records would reflect a new measurement. If it is not re-surveyed and the land comes back, you should get your land back because they won't even know it was gone. Although this topic is being debated amongst legislators at the state levels.

Answer 3

You do not have to measure sea level at any particular time or tide level. If you take lots of measurements and then average them you will get the average sea level. The accuracy will be determined by the number of measurements you take. It is simple statistics. Take a look at the plot labeled "Recent Sea Level Rise" in the link below and you will see what I mean.

Answer 4

in case you look on a U.S. Geological Survey topographic map you will see the assertion, "Datum is advise sea point." this suggests that the 0 elevation line is on the component this is the advise (ordinary) point of the sea whilst all variations of tide point are taken into consideration. For substantial reference factors steel plaques stated as benchmarks are oftentimes placed to mark the spot. If all the international's polar ice melted and the sea point rose of course the advise sea point would upward thrust. for this reason the map references won't likely substitute because of the fact it would be too plenty artwork and fee to make the mandatory variations. There would probably be purely a notation asserting subtract this variety of super style of inches or ft from the previous measurements.