[Tagging] RFC proposed water property key 'ephemeral '

Warin 61sundowner at gmail.com
Sat May 26 06:36:45 UTC 2018

On 25/05/18 20:09, Nick Bolten wrote:
> > The tag provides mapper a way of tagging rivers and streams that is 
> presently not available.
> > That will vary .. year to year and decade to decade ... to much change?
> > This too will vary.
> I think something might be getting lost in translation, since those 
> questions were rhetorical. I'm describing my understanding of the 
> proposal as it exists on the wiki, hoping it matches the intent.
> > Intermittent does not equal ephemeral.
> I now understand that after reading a few reviews, but the wiki 
> proposal does not make that very clear. From the wiki articles, an 
> ephemeral body of water "is only present for short duration", and 
> intermittent "is used to indicate that a body of water does not 
> permanently contain water". From those definitions alone, I'd assume 
> that a river could have both `intermittent=yes` and `ephemeral=yes` 
> and be perfectly valid. However, my new and improved understanding of 
> hydrology definitions would say these are separate and incompatible 
> categories of rivers/streams. Page 6 of this EPA document [1] has 
> definitions that make these things clearer, maybe a similar approach 
> could be taken with the wiki.
The proposal clearly says under 'definition'
"A property key for water that is only present for short duration. 
‘Short duration’ is typically less than 1 day for each flow. The 
majority of the time, at least 90% of the time, the water is not present."

The key thing for ephemeral is 'short duration' ... and 'dry most of the 
time' ... those words do not exist for 'intermittent' nor 'seasonal' in 
the OSM wiki.

> > At present in OSM the tag to indicate an  intermittent flow that only 
> occurs in winter isintermittent=winter
> > The proposal for ephemeral flow in autumn would be
> ephemeral=autumn
> > Combining these would give
> > intermittent=winter
> > ephemeral=autumn
> > I would think that is easy enough to understand and matches the 
> present tagging scheme in use.
> This is actually undocumented, and taginfo has no examples of seasons 
> being used as values for the `intermittent` key. With that said, I was 
> also suggesting that seasons might more appropriately be values for 
> keys describing "frequency/type of flow" like `intermittent` or 
> `ephemeral`, rather than having a separate `seasonal` tag, due to the 
> ambiguity of having more than one flow mode over the duration of a 
> year. Something like `intermittent:seasonal=<season>` might also work. 
> Maybe I'm missing a proposal for seasonal values for `intermittent`?

The key 'intermittent' is poorly defined.
I am not proposing to alter that here (I have another thread on 
seasonal, intermittent and ephemeral, suggest that be used for that kind 
of discussion).

> The idea I'm proposing is that there may be a 'catch-all' key that 
> describes the 'type' of thing that `ephemeral` or `intermittent` are, 
> and to set `intermittent`, `ephemeral`, or otherwise (`perennial`?) 
> values when appropriate. What about `flow=ephemeral` or 
> `flow=intermittent`? Then, if you need to set more specifics, you 
> could use `flow:ephemeral=winter`. This also provides a convenient 
> hint for what is being described: the flow type of the stream.
1) these keys can also be applied to lakes .. where 'flow' is not what 
is wanted.

> > The intermittent tag already exists .. do you want to change it?
> I think we're both considering changes to the `intermittent` tag as 
> potential options.
> > And what if the stream has a seasonal flow in say winter and an 
> ephemeral flow possible in spring?
> > For this proposal this would be tagged
> > seasonal=winter
> > ephemeral=spring
> This is super confusing. Namely, the `seasonal` tag's documentation 
> indicates whether the feature is present, but in this case it seems to 
> be indicating that there is a 'full' flow
No.. is says water is present .. not quantifying the rate of flow or the 
depth of water in a lake. It says water is present ... nothing else.
I can see nothing in the OSK wiki for seasonal that says it is full 
flow. Or any set flow rate.

There is no proposal to tag flow rates .. if you want to do that you 
propose it.

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