There are many rivers which are heavily silted. Should the visible silted areas be drawn separately and tagged as [shingle]s or combined with the entire [riverbank] polygon?

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asked 22 Dec '17, 17:35

JAT86's gravatar image

JAT86
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Braided rivers are common in many areas of the world: particularly those where natural river courses have not been altered by people.

I don't think waterway=riverbank is the appropriate tag for the following reasons:

  • It gives a misleading idea of the actual normal size of the river, for instance in assessing fordability.
  • Many riverbeds will be used in times of normal flow as part of the transportation network.
  • The flood events which create the riverbed may be comparatively rare. In places at high latitudes or high altitudes it takes decades for plants to re-colonise the flooded areas.

For these reasons I have used natural=riverbed which is documented on the wiki.

Of course you can then, in addition map areas of shingle and sand ; the width of the normal channel of the river (although beware that these may change rapidly causing aerial photos to be outdated), etc.

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answered 24 Dec '17, 12:30

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SK53 ♦
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The wiki page for riverbank states the following:

In the very common case of rivers subject to seasonal flooding with much higher water levels for a relatively short period for example during monsoon season or snow melt and low and relatively constant water levels for the rest of the year it is best not to map the water extent during flooding. A useful rule of thumb would be to map the median of the maximum water levels of all months of the year.

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answered 24 Dec '17, 13:36

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Tordanik
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AFAIK the current practice, and I do this myself in Alaska where many of the rivers look like your example, is to make the riverbank extend to the maximum size the way it appears in the lower part of the screenshot. I've occasionally tagged rivers with very large dry areas with natural=sand.

There are so many unmapped rivers in Alaska that I've used this scheme in part because of the time that would be needed for a finer grained, and perhaps more correct, tagging scenario but you may feel differently about this.

I'll be interested to learn what others have to say.

Cheers,

AlaskaDave

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answered 24 Dec '17, 00:14

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AlaskaDave
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question asked: 22 Dec '17, 17:35

question was seen: 1,090 times

last updated: 24 Dec '17, 13:36

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