[Tagging] Drain vs ditch

[Hufkratzer]

https://wiki.openstreetmap.org/wiki/DE:Key:waterway says:
- drain is for rain or industrial water ("Abwassergraben") -> may be 
wastewater
- ditch is just for rain water ("Entwässerungsgraben") -> no wastewater

Am 11.1.2019 07:35, schrieb John Willis:
>
>
>> On Jan 11, 2019, at 3:00 PM, Marc Gemis <marc.gemis at gmail.com 
>> <mailto:marc.gemis at gmail.com>> wrote:
>>
>> was always under the impression that the ones I encounter between
>> farmland and meadows, which typically are surrounded by dirt, ground,
>> plants are ditches. That drains are constructed with concrete or
>> similar material and that there are normally no plants on the bedding
>> of the drain.
>
> TL;DR - the connotation of “drain” is a problem. it is not “draining 
> away” unwanted water, it is merely moving it around, and this 
> connotation causes mapping issues.
>
> ~~~~
>
> I like this summary too. I think the issue is that “drain” has a 
> connotation of moving water “away” from some spot where it is no 
> longer needed or has been used - which is confusing for a lot of 
> irrigation uses.
>
> In places like southern California, which only have large (5x5m) 
> open-air aqueduct systems to move usable water, and further 
> distribution handled almost 100% by pipe for irrigation or drinking. 
> sewer is also piped and handled by treatment plants, and “storm 
> drains" merely channel the occasional rain to the ocean.
>
> This makes mapping “drains” and "ditches” is super easy, because 
> almost all drains/ditches are moving unwanted rainwater to a 
> waterway/ocean.
>
> but in my area of Japan, each neighborhood has several *Kilometers* of 
> tiny concrete roadside “drains” (covered and uncovered) that have 
> little doors or valves that farmers can open to flood ditches that 
> flood rice fields. there are side channels, small storage ponds 
> (3x3m), and other very detailed and intricate water management systems 
> that make a Californian like me marvel at the rain management system 
> they have created.  The drains act merely as storm drains the rest of 
> the year, and integrate “streams” and other natural channels 
> sometimes. but the rain they move is useful for irrigation; rain 
> “drained” away from my area is actually irrigation water for people 
> further downstream.
>
> the other issue is scale. some concrete drains are very tiny measure 
> less than 20cm2, though most are 30cm2 or 50cm2 . most ditches are 
> also roughly 30cm2.
>
> if we go by construction, and try to remove connotation of wastewater, 
> then I think it is easy to map.
>
> Javbw
>
>
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