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.ge...@gmail.com
<mailto:marc.ge...@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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