> James,
>
> No real reason for the two datums. On both of these surveys there was NO hard benchmark left on the site.
There is a real reason for using 2 datums, in heavy/civil/marine work the dredging/divers/dockbuilders will always revert to MHHW or MLLW and a tide Board. This problem stems from a fundamental lack of communication, it's not your fault Lee. Don't sweat it, the Previous Surveyor obviously didn't have enough experience in this arena to explain to them that they needed to be working to a more consistent repeatable datum.
I had the same situation arise on an outfall project where the DEP tried to relate everything to MHHW of 1935, which was when the USACOE did a study of Jamaica Bay. I backtracked and did a best fit interpolation using Sandy Hook, Willets Point and New York Harbor and correlated it to that years tidal datum. I then submitted a report and I told my client that we would be working in NAVD88, the two Hydro Surveyors agreed with me and we moved on.
Moral of the Story: Unless a Land, Construction or Engineering Surveyor intervenes the water craftsmen and management will default to tidal datum.
> > James,
> >
> > No real reason for the two datums. On both of these surveys there was NO hard benchmark left on the site.
>
> There is a real reason for using 2 datums, in heavy/civil/marine work the dredging/divers/dockbuilders will always revert to MHHW or MLLW and a tide Board.
Aren't these related to orthometric heights? To me, using two datums is using one too many, especially in civil work.
> > > James,
> > >
> > > No real reason for the two datums. On both of these surveys there was NO hard benchmark left on the site.
> >
> > There is a real reason for using 2 datums, in heavy/civil/marine work the dredging/divers/dockbuilders will always revert to MHHW or MLLW and a tide Board.
>
> Aren't these related to orthometric heights? To me, using two datums is using one too many, especially in civil work.
How are they related?
don't get me started....I could write a book. But it is OK. they are licensed.
> ...I then submitted a report and I told my client that we would be working in NAVD88, the two Hydro Surveyors agreed with me and we moved on.
> Moral of the Story: Unless a Land, Construction or Engineering Surveyor intervenes the water craftsmen and management will default to tidal datum.
I would have done exactly as you, work with something solid as you did in your example. In most bathymetry projects that I worked on, there was always survey control, the water craftsmen and management followed instructions, they were not calling the shots with high water marks or other loose datums; even the tide gauges were tied to survey control.
To me, whether the guy is with a back hoe on land or in a dredge on the water, generally, not much is happening until surveyors show up and provide guidance.
> > ...I then submitted a report and I told my client that we would be working in NAVD88, the two Hydro Surveyors agreed with me and we moved on.
>
> > Moral of the Story: Unless a Land, Construction or Engineering Surveyor intervenes the water craftsmen and management will default to tidal datum.
>
> I would have done exactly as you, work with something solid as you did in your example. In most bathymetry projects that I worked on, there was always survey control, the water craftsmen and management followed instructions, they were not calling the shots with high water marks or other loose datums; even the tide gauges were tied to survey control.
>
> To me, whether the guy is with a back hoe on land or in a dredge on the water, generally, not much is happening until surveyors show up and provide guidance.
I'm not sure what projects you've been on, but Dredging Crews come with their own Hydro Surveyors (most of them are really sharp) in addition to the Hydro Surveyor their is a Bathymetric Surveyor. The Hydro guy uses DregePac and Hypac, the Bathymeric guys will use triple beam sonar,multi bea echo, cameras etc. Here's a link to the guy I worked with on this project.
As you can see this isn't some Mickey Mouse operation, there was plenty of legitimate surveying going on. The only issue was the datum and in this case I made the call and had to substantiate why. The Datum to be used was written into the specs and I had to have it changed.
That book would be a great read. Truly.
Every licensed surveyor should be required to read about the mistakes/blunders/negligence of other surveyors!
When I set out a infrastructure site,some clever land surveyors had used non intervisble stations. So no problem, then 2 mile trips to 2 points,then 3 miles to another.
Success.
Then comes the argument.
The survey company agrees approximately with the location of your centre peg for the roundabout,within 1 metre.To cut a story short some buttonpusher was sending crap fro MOSS
> The only issue was the datum and in this case I made the call and had to substantiate why. The Datum to be used was written into the specs and I had to have it changed.
There you go, the specs weren't appropriate so you took the steps to make it right, kudos.
I don't consider a high water mark an appropriate reference datum, that's all. In this here story at the top, a solid defined datum would probably have eliminated the 3ft blunder.
I worked with the Hypack hydrographic software for a few years, enjoyed the software immensely. It is s ery well designed software. Back in the days, when performing a 7-parameters transformation, along with solution, the software would have the following message come up: "The Shaman has spoken"... Hypack's cartoons (by the president) are funny too.
Your story isn't very clear, my good man. What exactly are you saying Stan?
