Tidal Bench Marks

[Papa-Bear-NYC]

In the last several weeks I've had occasion to recover a number of tidal bench marks.

 

I've often wondered why there is a separate category for these. Why not just use regular bench marks?

 

They always seem to be set in clusters, often with 4 - 6 in one area. And of course they are near the water, often on bulkheads, piers, sidewalks near the shore etc.

 

If anyone can give the whys and wherefors of tidal bench marks, I would much appreciate it.

 

Thanks

[+Kewaneh & Shark]

In function, tidal benchmarks are just like regular benchmarks - a vertical reference point - and they are used in a similar manner. The difference is usually the datum being referenced. The 'regular' benchmarks are now referenced to the North American Vertical Datum of 1988 (NAVD 88). Tidal benchmarks reference a local tidal datum which are defined by a phase of the tide in a local area. NAVD 88 and local tidal datums are different. There are also differences between tidal datums in different areas. The marks are clustered to help define the datum in that local area.

 

- Kewaneh

Edited May 11, 2006 by Kewaneh & Shark

[Papa-Bear-NYC]

In function, tidal benchmarks are just like regular benchmarks - a vertical reference point - and they are used in a similar manner. The difference is usually the datum being referenced. The 'regular' benchmarks are now referenced to the North American Vertical Datum of 1988 (NAVD 88). Tidal benchmarks reference a local tidal datum which are defined by a phase of the tide in a local area. NAVD 88 and local tidal datums are different. There are also differences between tidal datums in different areas. The marks are clustered to help define the datum in that local area.

 

- Kewaneh

Thanks Kewaneh

 

But it seems lilke the local tidal datum elevation is not published on the datasheets. All tidal bench marks that I have seen on NGS datasheets (maybe 20-30) specify an elevation based on NAVD 88. Maybe the agencies that set them up (usually it was CGS or USE) used it when they were on NAVD 29, which is a sea level based datum, but not on NAVD 88 which is not sea level based.

Edited May 11, 2006 by Papa-Bear-NYC

[DaveD]

Tidal Bench Marks are set by the Center for Operational Oceanographic Products and Services (CO-OPS) which is on Office in the National Ocean Service just like NGS. They are responsible for the installation and maintenance of the National Water Level Observation Network (NWLON) which includes approximately 185 long-term (19 year +) tide gauges. Each tide gauge has series of at least 4-6 BMs within a kilometer of the gauge. You can find listings of these marks at http://tidesandcurrents.noaa.gov, and then select "Products" and "Bench Marks" from the drop down menu. About half of these marks have been tied by NGS and are also available from the NGS data base.

[Papa-Bear-NYC]

Tidal Bench Marks are set by the Center for Operational Oceanographic Products and Services (CO-OPS) which is on Office in the National Ocean Service just like NGS. They are responsible for the installation and maintenance of the National Water Level Observation Network (NWLON) which includes approximately 185 long-term (19 year +) tide gauges. Each tide gauge has series of at least 4-6 BMs within a kilometer of the gauge. You can find listings of these marks at http://tidesandcurrents.noaa.gov, and then select "Products" and "Bench Marks" from the drop down menu. About half of these marks have been tied by NGS and are also available from the NGS data base.

Thanks DaveD for the information and that source. It looks like a gold mine. And hundreds of new benchmarks, well documented, to go out and find!

 

I guess the next question is are the guages still in active use? The two I just checked (Brooklyn Bridge and Willets Point) both say "the guage was ...". In all the areas I've visited, I found a proportion of the bench marks, but I have never seen a guage. I guess I don't know what they look like. With the data on this site, I can start looking for them too.

 

Edit: One question to DaveD or anyone who knows: does CO-OPS or NOS have any program by which members of the general public (that's us) can recover and report status on the marks it maintains, but which are not in the NGS network? Either on-line or snail mail or othewise?

 

Thanks

Edited May 11, 2006 by Papa-Bear-NYC

[+Kewaneh & Shark]

The gauges may still be in use. It would depend on whether or not the water would still need to be monitored or not. The only way to know for sure would be to contact the agency that monitors the gauges.

 

I frequently work near the California Aqueduct, a canal that moves water from the San Francisco Bay Area to the LA Basin. It is heavily monitored by the Department of Water Rescources and the Army Corps of Engineers for movement. This is not a small undertaking considering that it's over 400 miles long and portions of it parallel the San Andreas Fault. It is consequently heavily benchmarked, and many of these marks are placed at the bases of gauging/monitoring stations. This is what the monitoring stations look like near the aqueduct and they are very much in use. Benchmarks GU1472 and GU1477 are located at the base of these monitoring stations. Yours may look similar.

 

The view southeasterly down the California Aquaduct showing the recorder station. GU1472 is at the base.

 

The view southeast down the California Aquaduct showing the recorder station. GU1477 is at the base.

 

- Kewaneh

[DaveD]

Many of the CO-OPS sites have operational tide gauges nearby. The priamry network is called the National Water Levels Observation Network (NWLON) and consists of approximately 190 stations that are visited annually by a CO-OPS maintenance team. Most of these sites have already been operational for at least 20 years. CO-OPS also established sites that are referenced as secondary or teritary and may be operational for just a few years or few months depending on the program requirements. Unfortunately, at this time CO-OPS does not have an on-line monument recovery program such as NGS. We are working with them to try and integrate access and updating of our seperate databases with more efficient and seamless systems. You can find information about how the tides are measured and what a gauge looks like at http://oceanservice.noaa.gov/education/kit...oldmeasure.html

[Papa-Bear-NYC]

Many of the CO-OPS sites have operational tide gauges nearby. The priamry network is called the National Water Levels Observation Network (NWLON) and consists of approximately 190 stations that are visited annually by a CO-OPS maintenance team. Most of these sites have already been operational for at least 20 years. CO-OPS also established sites that are referenced as secondary or teritary and may be operational for just a few years or few months depending on the program requirements. Unfortunately, at this time CO-OPS does not have an on-line monument recovery program such as NGS. We are working with them to try and integrate access and updating of our seperate databases with more efficient and seamless systems. You can find information about how the tides are measured and what a gauge looks like at http://oceanservice.noaa.gov/education/kit...oldmeasure.html

Thanks Dave

 

I've started going over the data on the CO-OPS pages on Tidal BMs in my "turf", and I've integrated some finds from the last week onto the GC pages for the associated Primary BM. I have already found some (non-NGS Tidal BMs) that are gone so the folks in that office may be inmterested.

 

Here's a couple of entries I've made (more to come).

 

Horns Hook Tidal Station

 

Brooklyn Bridge Tidal Station