Working out altitudes after a survey

El Siglo

Howya's folks,

I was doing a saltmarsh survey about a week ago using a dumpy level and rod, just leveling the points that I took samples from. There was no benchmark and I didn't have differential GPS so I instead used the highwater mark at high tide as a benchmark (at 3.9 metres). When I work out my altitudes, do I do them relative to this point (e.g. "point 1 was 0.091 m high relative to the highwater mark) or do I had on the 3.9 and just say point 1 was 3.991 maod?

Cheers in advance.

FesterBeatty

...do it again!

Jimbo

The usual would be 3.991m above temporary benchmark.

You could just call up the levels and then have a note to the side saying 'all levels taken in relation to temporary benchmark at high water mark = 3.900m'

El Siglo

FesterBeatty wrote:

...do it again!

Eh thanks but no thanks!;)

Jimbo wrote: »

The usual would be 3.991m above temporary benchmark.

You could just call up the levels and then have a note to the side saying 'all levels taken in relation to temporary benchmark at high water mark = 3.900m'

Cheers, that's excellent advise so it is!
The usual sounds good, I think that's what I'm supposed to do. I suppose I should then mention how I got these levels, i.e. dumpy level, rodman, no differential gps, no benchmark, highwater taken as 3.9m at 12:20 from Admiralty charts for the area.

Tails142

Well unfortunately your levels wont be correct. The admiralty charts says the HWM is 3.90m0at 12.20 but that doesn't mean it is actually going to be 3.900m due to swell and wind direction etc. High tide times are also only given at certain points i.e. certain harbours/locations and vary at different parts of the coast, so you may need to rethink...

Capt'n Midnight

did you take any measurement of a fixed point that you could re-calibrate against ?