On Fri, Apr 26, 2019 at 3:44 AM Richard Fairhurst <rich...@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 oriented. 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. _______________________________________________ Tagging mailing list Tagging@openstreetmap.org https://lists.openstreetmap.org/listinfo/tagging
