Per tagging mail list on "waterway=wadi problem" one suggestion was to extend the values of intermittent to include:
If the tag is missing on a waterway the assumption is intermittent=no. Winter, spring, summer, autumn should be self explanatory.
- I am strongly against adding additional values beyond "yes". New tag would be significantly better Mateusz Konieczny (talk) 07:49, 1 October 2015 (UTC)
Ephemeral indicates water flow happens only for short periods of time and may not happen every year. (Wed Jan 21 16:15:31 UTC 2015)
- Since seasonal=* is widely used for tagging saisonality of features - introducing a second possibility to do the same does not seem like a good idea. Also with something like intermittent=summer it is not intuitively clear if the waterway is intermittent in summer and permanent otherwise, if it is dry in summer and carrying water otherwise or if it is only carrying water in summer. Suggesting intermittent=ephemeral as an option seems fine though (but it needs to be documented what ephemeral means).--Imagico (talk) 17:12, 21 January 2015 (UTC)
what's the difference between this and using http://wiki.openstreetmap.org/wiki/Key:seasonal ?
- IMO intermittent features can "exist" possibly only for some hours at a time (but could be up to a week or so), whereas for "seasonal" objects the timespan is always at least a week, usually a month or more (possibly even 11 months?) 14:05, 12 June 2013 (UTC)
Seasonal: occurs on a yearly basis.
Intermittent: occurs randomly. Might be once every 100 years, once every 3 years.
- Tagging with seasonal=yes is not a good reason to remove intermittent=yes Mateusz Konieczny (talk) 07:48, 1 October 2015 (UTC)
In recent edit regular (seasonal) changes were excluded. What is the justification for this. According to what I found "intermittent" is not excluding regular changes - see for example "Intermittent streams flow seasonally in response to snowmelt and/or elevated groundwater tables resulting from increased periods of precipitation and/or decreased evapotranspiration." from "Temporary streams" by Margaret Palmer, or https://en.wikipedia.org/wiki/Perennial_stream " "Perennial" streams are contrasted with "intermittent" streams which normally cease flowing for weeks or months each year, and with "ephemeral" channels that flow only for hours or days following rainfall." or https://en.wikipedia.org/wiki/Stream#Intermittent_and_ephemeral_streams .
- For now I reverted this edit in http://wiki.openstreetmap.org/w/index.php?title=Key:intermittent&diff=1223403&oldid=1223341 and http://wiki.openstreetmap.org/w/index.php?title=Key:seasonal&diff=1223404&oldid=1223343 Mateusz Konieczny (talk) 07:11, 1 October 2015 (UTC)
The meaning of intermittent? irregular, random. The meaning of seasonal? regular, on a yearly cycle. To say that intermittent=seasonal is wrong. Much more on the talk mailing list. Warin61 (talk) 11:53, 1 October 2015 (UTC)
- intermittent=yes simply means non-permanent, nothing more, nothing less. If you want to be more specific on the nature of the intermittency you can either consider additional values or other supplementary tags - like seasonal=yes Practically the vast majority of intermittent waterbodies are seasonal of course.--Imagico (talk) 12:14, 1 October 2015 (UTC)
- "intermittent=seasonal" is clearly untrue, but I am not sure why it is supposed to be relevant. intermittent waterbody/waterway means non-permanent waterbody/waterway (as it is already defined on Key:intermittent) Mateusz Konieczny (talk) 15:13, 1 October 2015 (UTC)
For additional clarification on the semantics here: In hydrography there are generally the following distinctions:
- perennial streams which carry water permanently along their whole length
- seasonal streams where waterflow occurs in a seasonal pattern
- ephemeral streams where waterflow occurs only during certain weather events within the catchment area
- intermittent streams which in the strict sense refers to a purely spatial and no temporal variation, i.e. surface waterflow is intermittent along the course of the waterway and is below the surface otherwise.
In this scheme combinations of all the three non-perennial variants can occur and are also common in reality. The OSM use of intermittent=yes does traditionally not follow this distinction but applies to all non-perennial waterways. There is currently no distinct established tagging for ephemeral waterways (53 occurences of ephemeral=yes) --Imagico (talk) 09:02, 3 October 2015 (UTC)
Intermittent vs. ephemeral definitions
For what it's worth, the NHD and other sources have fairly explicit definitions for both "intermittent" and "ephemeral" where it concerns waterways. In places I've found it, the distinction is pretty clear.
- contains water for only part of the year, but more than just after rainstorms and at snowmelt
- have flowing water periods during the wet season (winter-spring) but are normally dry during hot summer months. Intermittent streams do not have continuous flowing water year-round
- contains water only during or after a local rainstorm or heavy snowmelt.
- have less flow than intermittent streams, are typically shallow, and have flowing water for brief periods in response to rainfall. Ephemeral streams and ditches are normally dry for most of the year.