[Talk-us] Waterway directionality in drainage canals

Paul Norman penorman at mac.com
Sat Apr 28 20:23:23 BST 2012

> From: Nathan Edgars II [mailto:neroute2 at gmail.com]
> Sent: Saturday, April 28, 2012 2:24 AM
> To: Tag discussion, strategy and related tools; OpenStreetMap talk-us
> list
> Subject: [Talk-us] Waterway directionality in drainage canals
> It's the standard to draw a waterway in the direction of flow. I've
> questioned this several times, but it's an ingrained default.
> My question is more specific: what happens to a drainage canal that
> reverses direction? I offer the Everglades and surrounding agricultural
> land as an example. There are huge "water conservation areas" that store
> water. When it rains, gates are closed and opened to direct water into
> these. During a drought, gates send water back out into the canals for
> local use. When there's a big storm, water will instead go directly out
> to sea.
> So there are a lot of major canals that have no fixed direction. How
> should these be mapped? Is there any existing scheme that can show how
> water flows under different conditions?

The same issue came up with minor drainage ditches and cranberry fields
here. They're used to drain sometimes and sometimes to flood the field for

I came up with the proposal
http://wiki.openstreetmap.org/wiki/Proposed_features/directional for
directional=* but it's abandoned. 

One weakness with the proposal is that unknown values are a special case of
directional=no, not directional=yes

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