> On May 30, 2019, at 9:03 AM, Joseph Eisenberg <joseph.eisenb...@gmail.com> > wrote: > > How are the small drainage/irrigation channels tagged currently in Japan? > > Are most tagged as waterway=drain, waterway=canal or waterway=ditch?
they are used for different purposes. based on purpose and construction. I use all three when mapping. (along with many many weirs & sluice_gates). people tag them as streams, drains, and ditches. many streams are re-routed into new (straight) channelized systems, removing them from the old path. aqueducts are usually tagged as waterway=canal canal=irrigation. Here is a drain that pulls off of a stream and supplies water to some rice fields and then dumps back into the river less than 1 KM downstream. you can see how stuff is commonly tagged. I assume there are some errors. https://www.openstreetmap.org/way/621898960#map=15/36.3124/139.3520 <https://www.openstreetmap.org/way/621898960#map=15/36.3124/139.3520> most rice fields are divided into long rectangles, and nominally are separated alternately by access road (alley) and a ditch. here is a picture of the 30-40cm drains that run along most roads to supply and collect water for the fields. https://www.flickr.com/photos/javbw/11091110715/in/album-72157638113676925/ <https://www.flickr.com/photos/javbw/11091110715/in/album-72157638113676925/> These are almost all prefabricated concrete, from 1m2 to 30cm2. the drains have small little plastic doors (metal wood, or a plastic soda bottle jammed in there) that feed fields directly or feed the old ditch system (1m- 50cm ditches) here is a large ditch that enters from the right, goes in a culvert under the road and into a concrete distribution box with a wooden weir board inside to control the water height. The yellow bag is controlling the flow from the box into that field set. It then continues on as a ditch towards camera. https://www.flickr.com/photos/javbw/11091115355/in/album-72157638113676925/ <https://www.flickr.com/photos/javbw/11091115355/in/album-72157638113676925/> the lower fields then feed their water back into the ditches and drains and the drains continue on to the next set and eventually back to the source they were pulled out of (from the weir) it might seem unnecessary to have them re-connect to the river further downstream (often with a sluice gate through a levee), but this system absorbs all of the rain and acts as a flooding buffer, and has to empty back out into the river eventually. they can divert some water into holding ponds for the three weeks in summer when it is really hot and doesn't rain. here is a small one https://www.openstreetmap.org/way/243411132 <https://www.openstreetmap.org/way/243411132> These same drains, in suburban areas, pass through neighborhoods to go from field to field. aqueducts move water from river to river to keep the supply equalized or to supply water treatment plants. One aqaduct pulls water from a giant river about 20KM from my house to a holding lake just above my house. it then feeds water into this stream to take care of farmers down stream. here is quick look at one of these aqueducts (it goes above and underground). https://www.openstreetmap.org/node/3123867846 <https://www.openstreetmap.org/node/3123867846> node where disappears underground in the below pictures. https://blogs.yahoo.co.jp/shsyc511/9073548.html <https://blogs.yahoo.co.jp/shsyc511/9073548.html> here is the beginning to an (old) aquaduct near Nikko https://www.openstreetmap.org/way/685540122 <https://www.openstreetmap.org/way/685540122> here is an aquaduct that goes under a huge river in Nagano. https://www.openstreetmap.org/way/684097406 <https://www.openstreetmap.org/way/684097406> it has bridges over rivers and water control gates and flow control waterways it crosses. https://www.openstreetmap.org/way/401319150 <https://www.openstreetmap.org/way/401319150> it feeds agricultural water to Wasabi farms, which need very clean and controlled water. it grows in ditches that feed water into the riverbed gravel it grows in. https://www.openstreetmap.org/way/684097406 <https://www.openstreetmap.org/way/684097406> Javbw
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