On Thu, Sep 13, 2018 at 10:02 AM Martin Koppenhoefer <dieterdre...@gmail.com> wrote:
> you’ll have to put the ridges to map the watersheds anyway, the catchment > basin is implicit with the waterways, coastlines and ridges. > > If there are names or other properties for the watersheds and catchment > basins in play, it could make sense to have dedicated objects nonetheless, I > agree. > > > > 2), while a ridge has to have a certain amount of slope to be called a > > ridge (perhaps at least 5 or 10% grade?), watershed boundaries are > > sometimes very shallow > > > how can we observe those sheds in shallow areas? Can it be done on the ground > or does it require additional elevation data? Maybe in the context of shallow > land the sheds aren’t stable? Definitely there are exorrheic wetlands and ponds in which the watershed line is entirely indefinite. I know of a number of wet areas that have distributaries into multiple major river basins; e.g., the Grand Gorge area in the western Catskills drains into both the Delaware and the Schoharie (and thence via the Mohawk to the Hudson); the Preston Ponds area of the Adirondacks drains to both the Hudson and to the Cold River (thence by the Raquette to the St Lawrence), and so on. The nearest the US has to an authoritative source is the National Hydrography Database (NHD) which does have watershed boundaries, with a hierarchical reference numbering system identifying them and tying them to the 'reach codes' of the rivers that drain them. ('Reach code' is a persistent identifier of up to 16 (?) digits, identifying branches of a river from mouth to headwaters. (I've never investigated what reach codes do with distributaries - I simply haven't needed to know.) There have been projects in the past to import NHD data in bulk. I was tempted to do it in my area once - I have the good fortune of living in a place where the data quality of NHD is pretty good. While some bulk imports from NHD have been highly successful, I stumbled on conflation issues and abandoned the idea. I still occasionally copy-n-paste a stream from NHD into JOSM, but that's always onesie-twosies, and compared with data that are already in OSM and with aerials. (Severe storms in the last decade or so have caused some fairly major watercourses around here to shift, and NHD still hasn't caught up.) _______________________________________________ Tagging mailing list Tagging@openstreetmap.org https://lists.openstreetmap.org/listinfo/tagging