Proposal talk:Check dam
Suggestion not to try re-defining waterway=weir
Currently a lot of the examples shown on the proposal page would be correctly mapped as waterway=weir. I would suggest not to try changing that, with nearly 100k features with that tag this is very likely to fail. See also https://wiki.openstreetmap.org/wiki/Talk:Proposed_features/Torrent_control_structures
The definition of the tag also seems to be based on intention of the creation of the structure, not on properties verifiable on the ground.
--Imagico (talk) 15:54, 7 June 2021 (UTC)
- I do not intend to redefine weirs (although the OSM definition of weirs is very vague). Most check dams that I find are not mapped at all. I expect that only a very small portion of objects currently tagged as waterway=weir are actually check dams.
- Check dams are built in very different environments than weirs. Structurally, they are also different from weirs. Both of these can be verified. --Eginhard (talk) 20:43, 24 June 2021 (UTC)
Dam vs weir vs "check dam
Looking at the examples, I think the "solid" check dams where water is designed to flow over the top can be mapped with the current waterway=weir tag.
The "slot" and "slit" kind might be categorized as a sub-type of waterway=dam since they are mostly solid but allow a small amount of water to pass through the dam. Many standard dams have gates, spillways or other channels for a small amount of water to pass through the structure.
However, I agree that the "fin", "rake", "beam" and "frame" structures are not at all like a waterway=dam or weir, since they are not solid structures and do not normally impede passage of water, rather they are designed to catch debris, rocks and logs which might otherwise be swept downstream during flooding. These certainly merit a new tag.
- None of the open check dam types would normally impound any water, so waterway=dam is not appropriate. But during extreme flow events, all of them can become completely clogged with debris and then also impound water, so they should all receive the same main tag.
- I've tried to better clarify the difference between solid check dams and weirs. Mainly, check dams would be completely backfilled with sediment and thus not influence the water level like weirs, also because they are usually found in steeper terrain. --Eginhard (talk) 20:43, 24 June 2021 (UTC)
Correct British / International terminology?
We need to confirm if "check dam" is actually the correct British English term, and if it makes sense internationally. It sounds a bit American to me, or perhaps it is technical jargon? Oxford reference calls this "A small, often temporary, dam constructed across a watercourse to reduce flow velocity and/or counter soil erosion" - this does not look like many of the examples in your photos. Cambridge dictionaries does not have an article on the term at all. --Jeisenbe (talk) 05:38, 8 June 2021 (UTC)
- It is mainly technical jargon I'd say. Check dams are probably not very common in the UK due to the terrain, so I don't expect there to be a different local term. In some areas, check dams to prevent gully erosion can be very basic like in the pictures below (or here: https://www.youtube.com/watch?v=ki1weaf_rMM), better matching the Oxford description. I'm not familiar with those here in Switzerland, but if they are only temporary they should not be mapped.
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--Eginhard (talk) 13:54, 9 June 2021 (UTC)
"Check dam" different from a dam.
I agree with this proposal. Many valleys or rivers in Japan have steep slopes, and there is a danger of flooding when heavy rains fall. Therefore, there are many check dams in the valleys to reduce the speed of flow and retain debris (wood, stone, sand, etc.). Many valleys have water streams, but there are also locations where there is no water stream usually. The main purpose of dams and weirs is to take water for drinking and irrigation or to generate electricity. Thus, check dams and dams ( or weirs ) differ in their structure and purpose. --Tokada (talk) 01:06, 14 June 2021 (UTC)