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Global warming on tide levels
- Thread starter chicopee
- Start date
LittleWheels
Structural
Yes but there can be mechanisms moving tide levels in the other direction locally.
"The rising water level is mostly due to a combination of melt water from glaciers and ice sheets and thermal expansion of seawater as it warms."
"The rising water level is mostly due to a combination of melt water from glaciers and ice sheets and thermal expansion of seawater as it warms."
Yes. It's difficult to sum it up in a nice, tidy, technically precise way that isn't open to nit-picking, but I'll make it as succinct as I can:
Mean Sea Level, still water depth, and the half tide level are all different. Mean Sea Level is a datum based on the previous 19 years of data. So unless sea level rise is linear, it'll be a bit slow on the uptake in reflecting the current conditions. Still water depth is the level at which the surface of the water would be at a given point in time in the absence of wind driven waves. Half tide is the average between the mean high tide and mean low tide.
So the average still water depth would be roughly equal to the half tide level. I say roughly because it also accounts for storm surges and other variations beyond periodic tides. The fundamental premise of sea level rise is that the average still water depth is trending up. Therefore, the half tide level would also be trending up.
Sea level rise isn't necessarily causing a change in the tides - I'm not aware of any research showing that tide ranges are changing, but there's more water out there and so the average level is higher. That's why in coastal cities we're getting more and more nuisance tidal flooding. At high tide, storm water drainage systems don't work as well because they're either being back flooded or their check valves are held shut by higher water levels at the discharge.
Mean Sea Level, still water depth, and the half tide level are all different. Mean Sea Level is a datum based on the previous 19 years of data. So unless sea level rise is linear, it'll be a bit slow on the uptake in reflecting the current conditions. Still water depth is the level at which the surface of the water would be at a given point in time in the absence of wind driven waves. Half tide is the average between the mean high tide and mean low tide.
So the average still water depth would be roughly equal to the half tide level. I say roughly because it also accounts for storm surges and other variations beyond periodic tides. The fundamental premise of sea level rise is that the average still water depth is trending up. Therefore, the half tide level would also be trending up.
Sea level rise isn't necessarily causing a change in the tides - I'm not aware of any research showing that tide ranges are changing, but there's more water out there and so the average level is higher. That's why in coastal cities we're getting more and more nuisance tidal flooding. At high tide, storm water drainage systems don't work as well because they're either being back flooded or their check valves are held shut by higher water levels at the discharge.
And drains taking that flood water away were designed to flow at optimal depth (less than the full pipe diameter), but when flowing full, they lose about 7% of their maximum flow capacity.
A black swan to a turkey is a white swan to the butcher ... and to Boeing.
A black swan to a turkey is a white swan to the butcher ... and to Boeing.
EdStainless
Materials
The local variations in tides are significant, and so are apparent changes in MSL.
I know of places where coastal buildings 150 years old show no change in where the water level is.
While in other places the changes are noticeable.
= = = = = = = = = = = = = = = = = = = =
P.E. Metallurgy, consulting work welcomed
I know of places where coastal buildings 150 years old show no change in where the water level is.
While in other places the changes are noticeable.
= = = = = = = = = = = = = = = = = = = =
P.E. Metallurgy, consulting work welcomed
MTNClimber
Geotechnical
NOAA recently put out a nice little article about sea level rise with an interactive map showing sea level change at a bunch of benchmarks across the US. Interestingly the land along parts of coastal Alaska is rebounding faster from glacial melt than the sea level is rising so it appears sea level is dropping relative to the benchmark.
Could it be that Alaska is still rebounding from the last Pliestocene glaciation? I know Manitoba is slowly rebounding, after approx 20K years...
Rather than think climate change and the corona virus as science, think of it as the wrath of God. Feel any better?
-Dik
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