Can anyone help with these?

Can anyone help my friend’s query, I have no idea but I’m sure someone at SYC will know or even where he can find the info out.
thanks and hope you’re all keeping well and not suffering too much with the lack of sailing. Sue

I'm trying to tie the tidal levels for topsham or Lympstone into the ground levels for a development by the river exe. The problem is tidal levels and ground levels use a different starting point for zero, tidal levels use 'Chart Datum' while ground levels use 'Ordnance datum' and so can't be compared. The difference between the datums is listed for large settlements but nowhere near topsham or even Exmouth. The Environment Agency have stated local sailing clubs are our best bet, as the only sailors i know would you know what chart datum level Starcross use? Or better yet Topsham? Thank you for any help!

Hi Sue

It is a while since I looked at this stuff.  But if I remember correctly the chart datum used for all UK charts is LAT  (Lowest Astronomical Tide - lowest tide predicted from gravitational effects only (i.e. may not be the lowest tide seen under some meteorological conditions)).

The LAT is referenced to a fixed point on land through the VORF (some technical details here  www.ucl.ac.uk/civil-environmental-geomat...eference-frames-vorf ).  But easiest to give the Hydrographic Office at Taunton a call to get the difference between LAT and a land reference closest to Exeter.  Your friend might want to ask them what corrections he should make due to climate change sea level rise.

regards

Mark

Thanks Mark, I’ll pass that info on.

Hi Sue also try  ntlf.org  The conversion from od to cd at devonport Plymouth is - minus 3.22metres   the national tide and sealevel facility should have info on Lympstone l would guess.  Cheers Graham  keep safe.

Graham and Mark
Jamie says thank you very much, your info has helped his research.
Sue