http://www.bbc.co.uk/news/science-environment-19702450
Report of sea level rise from 93-2010. 17 years by 3mm average is a half a meter, which is 26" wich is 2.15 ft.
You coastal boys should have been making adjustments on sea side developments through these years.
Just how often during this period did cities, counties, utilities, whatever make adjustments to their bench control info???
What is the reality of sea level rise confirmed by private practice LS's along the coasts?? Still using 60's BM's with updated or original data??
3 x 17 = 51 MM, Shot thousands of 40 MM rounds, they were a long way from 2 1/2 feet in diameter.
Could your numbers be a bit off?
jud
How do you know if the sea is rising, the land is sinking or both? Is the earth shrinking or expanding? Is the earth flattening or expanding from pole to pole or any other dimension? There are a lot of factors going on with all this.
I get 17 times 3mm to be like 5cm which is less than 2 inches .. so not to worry just yet... I think
> Report of sea level rise from 93-2010. 17 years by 3mm average is a half a meter, which is 26" wich is 2.15 ft.
NOAA Co Ops site has Nantucket Sea Level Rising at 2.95mm/year. They have helped out by adding that this translates to 0.97 feet per century. I will stand by you for a moment and curse the metric system, then go back to my 3937/1200 and curse the idiots who thought it necessary to create the International Foot.
http://tidesandcurrents.noaa.gov/sltrends/sltrends_station.shtml?stnid=8449130
If you are further interested, it is my understanding that Nantucket is subsiding. The tidal station would be subsiding with it. Unfortunately, we do not have a CORS on the island yet, but when we do, if we find the subsidence to be similar to Chatham (abandoned CORS) or Acushnet (The closest active) we will in fact find that the water is only rising by half the tidal station's estimate and the ground is sinking the other half.
A couple of documented facts can be obtained from the local Museum of Natural History:
1. Approximately 10,000 years ago, the sea level in this area was 100' lower and
2. Since the end of the Ice Age (Approximately 10,000 years ago) the Cape was under the effects of Post Glacial Iso-static Rebound.
Putting these two variables together results in one interesting theory: The water was rising faster than One Foot Per Century to make the relative sea level rise One Foot Per Century.
Fer sure, I screwed the math. 0.25 feet, not much. Not likely to affect much. And certainly as much or much more would be expected in localized areas due to other factors.
NOAA must have a program to update local BM's due to all factors, now that GPS can identify anything like significant changes. New Orleans has been sinking forever and will continue.
Sounds like most of us local surveyors don't need to worry much about this stuff. But if I was practicing on the coastal plains somewhere, I would want to keep some records over decades just as a monitor on my projects.
Lots of stupid regulations require better than 3" max, along with a few that are danged necessary.
I don't think GPS has the capabillities to determine this small of elevation changes. I don't quite understand it all, but the GPS is tied to ground based points that are themselves moving and keep in mind that the total change over 17 years is less than the +- accuracy of GPS elevation...or at least I believe that to be so. Someone would be better informed on this than I would.
Howdy,
FWIW, on the matter of tidal datums and tidal epochs, you might find the following links of interest. The last link is to a specific site here in Texas. It shows how the change in tidal epoch is reflected in changes to different states of tide.
http://tidesandcurrents.noaa.gov/products.html
http://tidesandcurrents.noaa.gov/station_retrieve.shtml?type=Bench+Mark+Data+Sheets
http://tidesandcurrents.noaa.gov/epoch_datum_check.shtml?stnid=8775870
Professor John Hannah of Otago University had an interesting paper on problems with tide measurements. Here in Texas the Texas Coastal Ocean Operating Network (TCOON) has addressed most of the deficiencies the professor noted.
Hannah, J., (2010). "The Difficulties in Using Tide Gauges to Monitor Long-Term Sea Level Change". FIG XXIV Congress, Sydney, April 2010. Selected as the FIG Article of the Month for July 2010. Also published in the Survey Quarterly, December,2010. This article is available on the FIG site.
http://www.fig.net/pub/monthly_articles/index.htm
HTH,
DMM
It did seem a little high
when I was shooting the pipeline at Wells Beach ME. yesterday.
First, as others have mentioned, check your maths.
Second, these sound like eustatic sea levels (I haven't read the article yet,). If your looking at a local area you should be looking at the sea level rise/fall for just that area (or at least making sure the model is at a resolution adequate to determine local effects.)
Read the article now. As noted, the eustatic level of 3mm approx per year is overall. Some regions experience more or less.
I hear some people have really cool technology and methods to enable them to figure out the answers to your questions.
I think they're called surveyors or something.
So...
...does this mean that all the Polar bears haven't drowned yet?
😀
I believe that approx. +0.8 above the NGVD 1929 datum is about right for my area. I'm sure spledeus will chime in if I'm mistaken 😉
It did seem a little high
Just how high was it though? Are you sure it wasn't your benchmark that was low?
From a few years ago, it seemed like the error estimates were higher (or at least as high) as the determined rise in sea level. I don't know if that's still the case, but it certainly didn't seem like the conclusive indication that sea levels were much varied.
> I believe that approx. +0.8 above the NGVD 1929 datum is about right for my area. I'm sure spledeus will chime in if I'm mistaken 😉
About the same here, .7 to .9 since 1934. There's a reason for the 1934 year.
Ralph
New Orleans is subsiding 9-10 mm/year ...
and has been at that rate for over 100 years based on repeated Absolute Gravity observations as compared to 1st Order Invar Leveling in the metro area.
In regard to subsidence with respect to sea level rise, the permanent Tide Gauge at Grand Isle, Louisiana was the significant benchmark for the subsidence study and conclusions published in:
Rates of Vertical Displacement at Benchmarks in the Lower Mississippi Valley and the Northern Gulf Coast - NOAA TR NOS NGS 50
Available in pdf at: http://www.ngs.noaa.gov/PUBS_LIB/pub_vert.shtml
Most of the GPS CORS sites that LSU operates in Louisiana have had Absolute Gravity observed at least once in the past 10 years as an independant check on subsidence rates with respect to the changes in ellipsoid heights observed by our GPS receivers.
In addition to the permanent NOAA tide gauge at Grand Isle, we at LSU continue to install additional CORS antennas at new NOAA tide gauges as part of an ongoing process. (The most recent one was at "Shell Beach, LA.")
You're gonna have to wait two more years to get to the 19 required for a complete tidal epoch. Then you can calculate the new MHWL or MLWL depending how your states define litoral boundaries. 😛
