[Tagging] Drain vs ditch
johnw at mac.com
Fri Jan 11 06:35:14 UTC 2019
> On Jan 11, 2019, at 3:00 PM, Marc Gemis <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.
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