[Tagging] Incorrectly tagging locks on rivers as canals

Kevin Kenny kevin.b.kenny at gmail.com
Fri Apr 26 15:52:12 UTC 2019

On Fri, Apr 26, 2019 at 3:44 AM Richard Fairhurst <richard at systemed.net> wrote:
> On some of the larger American river navigations the lock structures are
> built right within the main river channel - such as this new $3bn (!) lock
> on the Ohio River: https://en.wikipedia.org/wiki/Olmsted_Locks_and_Dam - so
> similar caution to Gloucester would apply, particularly in times of high
> flow. On a major navigation like that you'd be expected to use VHF to keep
> in contact with the lock-keepers, of course.

Yes, indeed! For the one by me, the highest flow is in the spring snow
melt, and the river isn't opened to navigation until that's past, but
the approaches to the locks would be entirely unmanageable at that
time. Obviously, the river is closed to navigation all winter long,
because it freezes over!

The modern Erie Canal is the river itself - the whole length of the
river has been dammed and artificially raised, drowning the old canal
in many places. Before that engineering work, much of its length was
whitewater, and it still plunges over Cohoes Falls.

For the lock nearest me, I tagged only the lock chamber
https://www.openstreetmap.org/relation/7464654 as being separate from
what is now the 'main stem' of the river, in deference to the
sensibilities of the vocal contingent on this list who assert that no
object should ever have an indefinite boundary. (Otherwise, there's a
clearly defined lock channel, and I'd have separated it.) Another
minor complication is that the lock channel is actually the river's
natural channel. Even downstream of the dam, the water is artificially
raised by the next dam downstream. The Thalweg still runs through the
lock, so that winds up being the linear way labelled, 'Mohawk River'.

One thing that I've not yet tried to duplicate in OSM that I see in
NHD there is that NHD has the concept of 'artificial shoreline'. You
can see in https://kbk.is-a-geek.net/catskills/test4.html?la=42.8039&lo=-73.8466&z=15
how much of the lock channel is rimmed in black instead of blue,
indicating the 'artificial shoreline' from NHD. I also haven't tried
to tag the structure that delimits the upstream anchorage. I'm
gathering from the Wiki that OSM wants it to be a groyne, or perhaps a
breakwater. It serves multiple purposes - it does reduce ice jamming
at the lock, and stabilize the shoreline against drift, but it also
creates an area of calm water for barges to anchor off (it used to be
that strings of barges that couldn't fit in the lock all at once were
routinely broken up and locked through one or two at a time.) The Wiki
descriptions of both of those structures are kind of salt-water

You'll see on the north bank how the historic Erie Canal disappears at
the power house. Above the dam, it's under about eight metres of water
and doesn't resurface until Rexford
https://www.openstreetmap.org/way/164420515. Historically, it crossed
the river there on a stone aqueduct and continued on the south side.

The locks here are ... interesting. Vischer Ferry is 66 metres above
the Hudson, and that whole elevation change happens in only seven
locks. For locks 2-6, vessels must lock through the entire flight of
locks continuously, because there's no place to berth or anchor that
wouldn't obstruct traffic.

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