I think describing these as "flood prone" in some way is a good idea.
I imagine you've already mapped the individual features: the levees (man_made=dyke), the individual basins and so on. I wouldn't want to map the whole area as water + intermittent=yes because the water is only rarely present. Perhaps we need a new tag to map a whole area as flood prone? I've seen that on French and Australian topo maps there is a specific rendering for areas that are "subject to inundation". -Joseph On 10/24/19, John Willis via Tagging <tagging@openstreetmap.org> wrote: > I am aware of the underground basins that are dedicated to the task, but I > am wondering how to map above-ground basins that are used as regular land > 360+ days of the year - something you don't have to deal with when mapping > the underground tanks. > > ~~~~~ > > > The rest is not important, but read on if you Want. > > > Yea, Thats in Tokyo on the Arakawa/Edo rivers, the the Tokyo metro area. The > start of the Edo river is a lock-controlled flow from the Tone - as the > larger Tone goes off to the Pacific 70 Km north of Tokyo (it doesn't > discharge into Tokyo Bay). > > As I understand it, those tanks manage the water going into the system in > Tokyo itself, absorbing the flow from the smaller channels/rivers in Tokyo > (Tokyo is big and flat) and buffering it before it gets discharged into the > rivers, absorbing what would normally be trapped behind the River levees. > The Tokyo tank system couldn't handle the river flow directly (it's immense) > - The rivers channeling water down through the region just use extra-wide > and tall 8-10m levees to provide ~ 10-15x normal flow volume to the sea. > (The river goes from 1-2m deep to 8-9m deep, and doubles in width) > > Small towns in my area (pictured) were flooded not by a levee breach, but by > water trapped outside the levee that couldn't get into the river through the > normal gates. > > The Tokyo system prevents that from happening - though I wonder if it could > absorb even a quarter of what the Usuichi trapped. The Usuichi is gigantic. > > > Javbw > >> On Oct 24, 2019, at 9:08 PM, Paul Allen <pla16...@gmail.com> wrote: >> >> >>> On Thu, 24 Oct 2019 at 10:56, John Willis via Tagging >>> <tagging@openstreetmap.org> wrote: >>> >> >>> Inside, there are three “retarding basins” (numbered 1, 2 & 3), with #1 >>> having with a large traditional reservoir, parks, golf course, and sports >>> grounds inside. >> >> There is more to the system than that. There are also underground holding >> tanks and >> tunnels: https://www.youtube.com/watch?v=cfJOW2PtrGk >> >> -- >> Paul >> > _______________________________________________ Tagging mailing list Tagging@openstreetmap.org https://lists.openstreetmap.org/listinfo/tagging
