[Public-List] Charts and depth sounding

[Stephen Gwyn]

Hi Jim and Gord,

While the Canadian Hydrographic Service does resurvey
continually, they, just like the Americans and the British have
relatively limited budgets and don't survey everywhere on regular
basis. Some parts of the bottom, particularly those with lots of
commercial operations get survey quite often. Other parts,
relevant only to pleasure craft, get survey rather
infrequently. Some charts of the west coast that I have are based
on surveys from the 1950s to 1970s. Maybe the rocks haven't
moved, but the sand has, and some of the rocks were
missed the first time round. When I was in Haida Gwaii in 1990,
some parts were still only sketched out. Some bays had one line of
soundings going in, and one line of soundings going out, and a
shoreline. Haida Gwaii was resurveyed (or more accurately
properly surveyed for the first time) in the mid-to-late 1990s,
but I don't think anything has happened since.

For a lot of coastlines the best, most up-to-date surveys are
actually done by private outfits using crowd-sourcing, by
collecting data from regular users who have keep their GPS and
sounder running continuously.

On a related note, in some places, the current tables provided by
Navionics are better than those from the Canadian Hydrographic
Survey. For Johnstone Strait in particular, the CHS predictions
are completely useless. No idea how that's possible. I asked
Navionics, but they just responded that is proprietary
information.

SG