[Tagging] Drain vs ditch

[Eugene Podshivalov]

Michael, thank you very much for such in-depth analysis. I would conclude
the following from it.

There are distinctions between these two terms, otherwise they would not be
defined separately.
In simple words, a ditch is a small open-air man-made or self-formed
channel in the ground for absolutely any purpose, both lined or unlined
entirely or partially.
If the purpose of a ditch is to carry away suporflous water be it
industrial discharge or rain water or wet land water or any other liquid it
can be called a drain (or drainage ditch).
Tagging such drains with e.g. waterway=ditch+usage=drainage would be normal.
But it would sound nonsense if you call an open-air overground drainage
construction a "ditch", e.g. http://landscapenashville.com/STA75559.JPG
I would tag such things as man_made=* though.
Drainage overground or buried pipes can be tagged with the
existing man_made=pipeline tag.

Cheers,
Eugene


вс, 3 февр. 2019 г. в 04:14, Michael Patrick <geodesy99 at gmail.com>:

> A survey of international and some national lexicons indicates that the
> two terms 'ditch' and 'drain' are equivalent used in the context of liquids
> from the smallest to largest scales.
>
> The term 'drain' however seems mostly to apply at the interface where the
> water transitions from the substrate ( soil ) to free running water, down
> flow from that the water is 'channeled' through ditches, fluves, shutes,
> spillways, canals, and a multitude of functional confinements. One of the
> earliest ( 1920 ) legal references to British and American law notes this
> equivalence, and the following an extract from a 2017 global standard
> saying basically the same thing.
>
> UNESCO-WMO International Glossary of Hydrology at
> https://unesdoc.unesco.org/ark:/48223/pf0000221862 -World Meteorological
> Organization, United Nations Educational, Scientific and Cultural
> Organization:
> "...will be useful to national hydrological services as well as
> educational and research institutions throughout the world – especially for
> those who require more than one language for understanding or communicating
> information about the field of hydrology. In establishing recognized
> international equivalents of hydrological terms, our goal is also to
> minimise misinterpretations and consolidate the foundation for stronger
> international cooperation."
>
> 407 ditch see also drain
> Man-made small open channel constructed
> through earth or rock for the purpose of lowering
> and/or conveying water
>
> 415 drain see also ditch
> Conduit or small open channel by which water is
> removed from a soil or an aquifer, by gravity, in
> order to control the water level or to remove
> excess water.
>
> Ditto with the USGS and the UK Ordnance Survey:
>
> For example, OS MasterMap Topography Layer User guide - "Water - Water
> features are defined as features that contain, delimit or relate to
> real-world objects containing water. The physical water features shown in
> OS MasterMap Topography Layer include: ...  drains and ditches; ... Dam,
> ditch, dock, double, down,  drain  D, Double ditch or drain DD" ... a look
> see at a lot of OS web map products show the same thing. In the case of the
> UK, a vast amount of property lines are encoded as these ditches and
> drains, so they formalized this equivalence to accommodate whatever the
> locals called them.
>
> There is no dependence on the size, width, depth, etc. A perhaps extreme
> example ( due to heavily mechanized agriculture in the U.S. ), but still
> illustrative is that the USDA construction guidelines make the following
> distinctions:
> Small ditches ( maximum top width 15 feet )
> Medium-sized ditches ( top width 15 to 35 feet )
> Large ditches ( more than 35 feet top width)
> In SE Asian rice production, their largest ditches probably would be in
> the 'small' category compared to the U.S.    I don't read Chinese,
> Japanese, Korean, etc. but I'm sure they have a couple thousand years of
> established vocabulary for their field water handing.
>
> The modern agricultural water handling industry ( what you would get if
> you asked somebody to install a 'ditch' or a 'drain' in a field makes a
> distinction as follows ( echoing the 'interface' idea above ):
>
> Ditch — A man-made, open drainage-way in or into which excess surface
> water or groundwater drained from land, stormwater runoff, or floodwaters
> flow either continuously or intermittently
> Drain — A buried slotted or perforated pipe or other conduit (subsurface
> drain) or a ditch (open drain) for carrying off surplus groundwater or
> surface water.
>
> Ditches aren't restricted to water use. Sometimes they are there because
> the material was sued to form an embankment, or used for road surface (
> 'borrows' in the USA ), animal control barriers, access control, boundary
> marking, spill prevention and control of loose soils and aggregate slides.
> And in all the water literature, in the U.S, and U.K., they pretty much
> also freely used 'drainage ditch', not just simply 'ditch.
>
> Predominantly, if the cut is not further improved from the native
> material, it seems to be called a ditch, if structure is added like
> concrete lining, wooden bank sides, maybe it will get a more specific term.
> Economics dictates that for the most part these enhancements only occur
> over limited lengths for flow control, erosion, obstacles, evaporation, etc.
>
> Drainage structure means a device composed of a virtually non-erodible
> material such as concrete, steel, plastic or other such material that
> conveys water from one place to another by intercepting the flow and
> carrying it to a release point for water management, drainage control or
> flood control purposes.
>
> Looking at the aerial photography majority of 'drains' in the OS based web
> maps, they are pretty much 'swales' (
> https://en.wikipedia.org/wiki/Swale_(landform) ), without the distinctive
> edges of a 'ditch'.
>
> In conclusion:
>
> For legacy tagging, ditch/drain should be left alone because of
> equivalence.
>
> For new tagging, ditch or drainage_ditch, ditch:drainage, or 'whatever'
> scheme should indicate it is a ditch for conduction of water, and
> 'drain_open' or some such to distinguish it from subterranean drains (
> despite being buried, these are actually sometime more visible than the
> ditches on aerial / sat photography ). Anything 'drain' should be confined
> to where the ground interfaces with a open channel. But  a singular 'ditch'
> would suffice.
>
> Because of global variety and local conditions, there should be no 'size'
> distinction, or distinction because of structural presence, materials, etc.
>
> Local terminology takes precedence, at the highest level it is available.
>
> While a dictionary might be a useful start for determining a meaning,
> there is almost always some better source of definitions in a specific
> domain, culture, and region, and location. The U.N., E.U., U.K., Scotland,
> and down to Renfrewshire all have documentation of what terms mean in those
> local contexts, for example.
>
> Almost always, a single word will be immediately overloaded when used
> world wide.Human languages have compound words, adjectives, verbs and
> adverbs for a reason, and tagging schemes have equivalents.
>
> Michael Patrick
> Data Ferret
>
>
>
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