[Tagging] tagging floodplain

John Willis johnw at mac.com
Sun Sep 25 11:40:32 UTC 2016

Would this be used for controlled areas flooded by a river only during extraordinary rains (like a super-typhoon)? 

Here is a river that has never exceeded the bounds of the "normal" flood control measures in the time I have lived here, but these parks are clearly in a contained flood channel that surrounds the river, and extends for the river's entire remaining length to the ocean. Our town is where it emerges from the mountains.


Most of the rivers in Japan are entirely contained in large man-made emergency flood control systems, but rarely do their waters ever extend to their limits. Often, above the "normal flooding" line (but still inside the flood control berms), parks, baseball diamonds, driving courses, and other non-building mappable features are built. 

It would be nice to define the flood control limits that the river sits in, as the riverbank is not mapped to the adjacent berms, as it is covered with scrub or these man-made features, and is not an accurate depiction of the bank's location.  

It could be something that relates the way of the river to the area/way of the top of the flood control system (wall, berm/levee/cliff/bank/ etc. 

Natural=flooodplain wouldn't be good, perhaps waterway=floodplain (or similar), which could share nodes with a  =riverbank way would be good. People who want to map it obviously have an idea of where it's boundary should be (almost all rivers in Japan would be super-easy), as people have made levees and other control measures around most large rivers people would care to map this around. 


> On 25 Sep 2016, at 7:48 PM, Colin Smale <colin.smale at xs4all.nl> wrote:
> Where would the boundary be? How could we describe it objectively? In low lying areas such as the Netherlands there are sometimes so called winter dykes which give a sharp edge to the flood plain. Otherwise it would all be a bit vague around the edges.
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