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I searched the Wiki to find the tag to use for one waterway crossing another one. The bridge over it is called aqua duct, but the option going down lacks a specific tag. The used tunnel culvert is widely used for straight forward waterways crossing other ways. I found no tag for a U-shaped tunnel crossing underneath another waterway, a so-called syphon with extra tags for the construction such as level or layer ? Has anyone ever used tags like it to specify this item ?

asked 03 Feb '18, 10:45

Hendrikklaas's gravatar image

accept rate: 5%

edited 04 Feb '18, 20:09

aseerel4c26's gravatar image

aseerel4c26 ♦


To understand the situation better.

alt text

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Canal Syphon:

In a canal syphon, drainage is carried over canal similar to a super passage but the full supply level of canal is above than the drainage trough.so the canal water flows under syphonic action and there is no presence of atmospheric pressure in canal.

You ment a culvert under water? Working as a syphon.

(03 Feb '18, 23:59) Allroads

Where is the word syphon used on a way. overpass way

syphon in value

Link to example way: link 1, link 2 GM example Link example on node: link node 1 link node 2

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answered 04 Feb '18, 01:20

Allroads's gravatar image

accept rate: 10%

edited 05 Feb '18, 19:49

I've mapped similar structures to this, though I didn't know this term. They are not uncommon in the mountainous areas of India.

The approach I've taken, has been to follow the convention used with highways: If it's unclear if the upper road is a bridge, or the lower road is a tunnel, due to embankments with overhangs or other unusual structure, pick one or the other tag but not both.

Or as the wiki says "It is sometime, however, a matter of judgment as to whether to tag a particular situation using a bridge or a tunnel. Do however avoid using both a bridge tag for the upper way and a tunnel for the lower way for the same crossing."

In the case of the syphon you show the diagram of, I'd probably put a tunnel=culvert tag on a section of the canal, but I'd not worry too much about it, just don't use both the tunnel and bridge tags.

While this may not be as detailed as we'd hope, there seems to be nothing inaccurate about my suggestion. I hope that is helpful.

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answered 05 Feb '18, 08:48

keithonearth's gravatar image

accept rate: 13%

My opinion tunnel=yes level=-1. put level=0 on upper channel. Bridges normally go up and over things they cross, therefore bridge tag is not needed.

(03 Apr '20, 19:19) andy mackey

Hi Andy why not using tunnel=culvert, waterway=drain, layer=-1. I would not use level since the structure is not one. There are 2 as fare as my knowledge reaches. It is made by blokking the canal, build the culvert (syphon), bring or reconstruct the upper waterway as canal, river or whatever.

(05 Apr '20, 12:54) Hendrikklaas

Yes Nick that sounds ok. Layers and levels are confusing https://wiki.openstreetmap.org/wiki/Layer

(06 Apr '20, 00:50) andy mackey
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question asked: 03 Feb '18, 10:45

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last updated: 21 Oct '21, 05:38

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