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USC&GS Tidal Bench Marks

NGS Surveyor

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I'm trying to confirm the type of USC&GS disks that were used for tidal bench marks during the 1960s. Tidal bench marks were connected to tide gauges by differential leveling and are normally within 1.2 mile or so of a tide gauge. Does anyone have any photos, preferably with dates from the later part of the 1960s?





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Great, thanks for all the posts. We've now confirmed that the disk with the single, crossed slash was used in the late 1960s, what about the early 1960s and even the late 1950s? I have a drawing from 1961 that shows the single slash disk, but it doesn't indicate what year it was first used.





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The great and amazing and wonderful members of the TheBeanTeam found this 1956 station that is a Tidal Bench Mark: OA0708


Hi TillaMurphs,


I was just about to ask if you posted the wrong link, when I saw it. The very first line on the Data Sheet: :blink:


OA0708 ***********************************************************************

OA0708 TIDAL BM - This is a Tidal Bench Mark.


OA0708 PID - OA0708





OA0708 ___________________________________________________________________

OA0708* NAD 83(1991)- 43 58 00.59399(N) 124 06 30.36401(W) ADJUSTED

OA0708* NAVD 88 - 10.494 (meters) 34.43 (feet) ADJUSTED

OA0708 ___________________________________________________________________


Both the Horizontal and Vertical are adjusted. I wonder if it was a Triangle Station that was adopted for a Tidal Station Mark?



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Before your range, both with a single slash, NOT crossed:

1936 - FV0898 ... pic

1946 - FV0733 ... pic


hmm.. from Ventura county to Monterey county (Ca) there are only a couple in the late 50's to early 60's that are not DNF'd.


How can you tell if a station was originally set as a tidal bench mark? Could a station that was originally a vertical control be adopted as a tidal bench mark? For example EW3748 does not have tidal in the designation but the datasheet says it is a tidal bench mark.

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Billwallace and All, The disk with the center symbol of a circle with a slash across the diameter was used beginning c1916. Circa 1924 to c1961 this design was used to mark tidal bench marks.


“How can you tell if a station was originally set as a tidal bench mark?” Here are several clues:


1. Distance from an ocean, tidal river, or Great Lakes – Usually within ~1 mile, see reference in #2, below.


2. Distance from a tide gauge - The present specification for tidal bench marks states “all bench marks should be within a radius of about 1.6 km (1 mi.) from the (tidal) gage…” (from “User’s Guide for the Installation of Bench Marks and Leveling Requirements for Water Level Stations”, October 1987, at: http://tidesandcurrents.noaa.gov/publicati...Bench_Mark.pdf).


Note, the one mile is not only from where a tide gauge exists now, but also everywhere that USC&GS/NOS ever had one. Since thousands of hydrographic surveys have been conducted along the shoreline of the U.S., and almost all surveys required one or more tide gauges, there have been many tide gauge sites along the U.S. shoreline, and usually tidal bench marks at each one. Some of these tide gauges were only in place for a few months and some have been in place for many years. The tide gauge at San Francisco was installed in 1854 and has been recording ever since, see articles: http://www.magazine.noaa.gov/stories/mag139.htm ,and

http://tidesandcurrents.noaa.gov/publicati...rs_of_tides.pdf , and: http://celebrating200years.noaa.gov/founda...ome.html#record .


3. The type of disk – Normally, pre-1971, USC&GS disks (center symbol of circle with slash or crossed slash) would be used. From 1971 to the present, NOS disks have been used. But, if a USC&GS/NGS disk already existed in the area, it may have been used as a tidal bench mark if it met the stability specifications and the one mile spacing requirement. So as we have seen in a posting above, a mark originally set as a Triangulation Station later became a tidal bench mark.


4. Stamping – The current specification for stamping tidal bench marks reads: “new (tidal) bench marks will be stamped and designated with the last four digits of the (tide) station number, a letter, and the current year. For example, five new (tidal) bench marks set at station 905-2058 would be stamped 2058A, 2058B, 2058C, 2058D, and 2058E…” (from the same, above pub.) This is similar to the naming of geodetic bench marks, see below.


Designations for geodetic bench marks (vertical control) are issued for each project in blocks, here is a quote from a recent project: “The designation series for any new bench marks set for this project shall be 1010, 1011, 1012, or 1013. Each designation series includes the use of 24 new designations. Stamping format shall be: sequential letter of the alphabet, designation series, year set--e.g. "A 1010 2008". The year is not considered part of the designation in the description file. The letters “I” and “0” shall not be used and shall be skipped in the sequence of letters. “Z” is the last possible letter to use in the series and a new series will need to be started beginning with “A” and the next number series after the use of “Z”.” Of course, the “1011, 1011…” will change for each project.


5. Database – All tidal bench marks for current tide gauges, and many tidal bench marks for historic tide gauges, are on-line on the CO-OPS web site at: http://tidesandcurrents.noaa.gov/, look under “Products” then “Bench marks.” All historic tidal bench mark descriptions are not on-line. Tidal bench marks that have been tied into the vertical geodetic network will also be in the NGS database.


Hope all this helps,




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Thanks for all the info. I clicked on the link and had fun looking for all the tidals we found in the Florida Keys. Boy, they really have the Keys broken down too. I bookmarked the site and will certainly print off the relevant info sheets so when we go back in February we will have some extra info to hopefully help us out in our recoveries.

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I know this one isn't in the date range you wanted, but I am curious about it. AA0267


It is listed a D70 Reset and yet it is also stamped as Tidal No 2 as well. Was/Is this common to have one disk have dual purposes and stamped as such? Or am I just being dense and missing something here. (Which wouldn't surprise one bit).

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AstroD-Team, It looks like this mark is both a geodetic bench mark (vertical control) and a tidal bench mark. Looking at the Datasheet, the first line clearly states that its Tidal. The 8th line has the NAVD 88 elevation to mm and the 12th line states "VERT ORDER - FIRST CLASS II" - both indicating that this mark is a geodetic BM.




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Hi all - maybe alittle offf subject - but....


In a few days I will be going for AG7451 and 4 others in VERY close proximity.


Can someone tell me the significance if Tidal marks - why so many so close together, if there is anything special I need to know or look for or log etc etc?!


These will be the first of their kind I go for.......


(and - are any of y'all in the vicinity and want to go with me?)

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Frex3wv, Re your question, “Can someone tell me the significance of Tidal marks - why so many so close together…”


USC&GS/NOAA has two types of bench marks (I’m discussing only vertical control points). The first are “geodetic bench marks,” and the second are “tidal bench marks.” Geodetic bench marks are surveyed with respect to the current national vertical datum which is NAVD 88. These are spaced along lines surveyed by spirit leveling and are normally not close together. Tidal bench marks (BM) are surveyed with respect to their nearby tide gauge. Since ocean water levels vary from place to place, each tide gauge usually has a slightly different “zero.” Three to ten tidal bench marks are set and leveled to at each tide gauge location. These tidal BM are normally set within one mile of the tide gauge. The reason for having multiple tidal BM is to help ensure a permanent record of the datum (zero) established from the tide gauge observations at that location. For the detailed specifications for tidal BM, see: http://tidesandcurrents.noaa.gov/publicati..._Bench_Mark.pdf . For descriptions of the different types of disks, see my paper on USC&GS and NOAA survey disks at: http://www.ngs.noaa.gov/web/about_ngs/hist...ey_Mark_Art.pdf .




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