Need Help with Surveying a River Crossing

I can't give you a best practices procedure. I don't know what exact problems in surveying a river crossing that you are trying to resolve. Surveying a river crossing involves the same problems as any other survey but with some additional problems. Traditionally, the reflection/ refraction caused by the water was the biggest culprit. One method consisted of using two high precision instruments, such as Wild T2 theodolites and placing one on each side of the water body. Repetitive angles were turned, horizontal & vertical so that the error & direction could be computed & the true value determined. It has been a long time but essentially, that's it. If I were asked to perform such a survey today, I would use a high quality GPS base to establish control on both sides. The exact procedure & the software used would depend on the distances involved & the accuracy requirements of the survey. Long distances and high accuracy would likely require that the mapping angle be considered. The grid distance is not the same as the distance on the surface of the earth & a rectilinear survey is not the same as a GPS survey. I would use both. I would compare the distance determined by GPS with that measured by an EDM. It would depend on how much water you are crossing and/or what you are building. The best thing is to try to talk to somebody that has done surveys similar to the one you are contemplating. Next best thing is to try to find some technical articles. You can likely find some good discussions / articles in pubs like ACSM & the American Surveyor or their equivalent where you live. I have probably raised more questions than answers but hope this gets you started in the right direction. Getting started is generally the hard part.

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CHARLIE B. AYCOCK, III June 21, 2016 at 4:46pm

I can't give you a best practices procedure. I don't know what exact problems in surveying a river crossing that you are trying to resolve. Surveying a river crossing involves the same problems as any other survey but with some additional problems. Traditionally, the reflection/ refraction caused by the water was the biggest culprit. One method consisted of using two high precision instruments, such as Wild T2 theodolites and placing one on each side of the water body. Repetitive angles were turned, horizontal & vertical so that the error & direction could be computed & the true value determined. It has been a long time but essentially, that's it. If I were asked to perform such a survey today, I would use a high quality GPS base to establish control on both sides. The exact procedure & the software used would depend on the distances involved & the accuracy requirements of the survey. Long distances and high accuracy would likely require that the mapping angle be considered. The grid distance is not the same as the distance on the surface of the earth & a rectilinear survey is not the same as a GPS survey. I would use both. I would compare the distance determined by GPS with that measured by an EDM. It would depend on how much water you are crossing and/or what you are building. The best thing is to try to talk to somebody that has done surveys similar to the one you are contemplating. Next best thing is to try to find some technical articles. You can likely find some good discussions / articles in pubs like ACSM & the American Surveyor or their equivalent where you live. I have probably raised more questions than answers but hope this gets you started in the right direction. Getting started is generally the hard part.
Billy Brooks June 17, 2016 at 8:52pm

Hi Kweku,Read my discussion on Crossing a River with Differential Levels.You may have GPS or not,either way it might help, a lot of good links

http://landsurveyorsunited.com/group/hydrographic-surveyors/forum/t...

billy

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