Proposal:Tidal Rivers

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Tidal Rivers
Proposal status: Rejected (inactive)
Proposed by: Chrismorl
Tagging: ?=?
Applies to: ?
Definition: ?

Rendered as: ?
Draft started: 2007-05-19
RFC start: -
Vote start: 2007-11-02
Vote end: -


Whether a river is tidal or not is a feature well worth recording. It would probably be rendered as two different shades of blue with the tidal river colour being the same as the sea. At present (May 2007) t@h uses the two different blues with a junction between them at an arbitary place - see the Thames or Severn estuaries. Instead, it would be better if the junction was at the upper limit to the tide, which for many rivers would be at a weir (e.g. Teddington on the Thames, Chester on the Dee) - a more satisfactory dividing line since it corresponds to something physical. This means that the banks of the tidal river would be natural=coastline - a tidal river as a long sea inlet.

But there would also be a linear waterway=river down the middle, as suggested previously. If it had a tag tidal=yes and then by default renderers could only render only the name, not the blue. For the less prominant tidal rivers and streams that are too small to be represented by an area, we would still use waterway=river, tidal=yes, but renderers could act on an explicit osmarender:render=yes tag.

Implementing this proposal would add extra useful tidal information, would add names to large rivers and estuaries, would tidy up current inconsistencies and would give prettier maps, while still maintaining proper separation between mapping data and rendering hints.


Seems sensible to me. Only slight disadvantage perhaps is that in places like the Thames in Central London it is generally thought of as a river bank, not a coastline... but how far east do you have to go before it is thought of as coastline? I dont know. -- Harry Wood 15:57, 2 November 2007 (UTC)

I'm opposed to the idea of tagging a river with coastline, but if we add a tidal key, where does a river stop being tidal then? And I know what tidal means, but is there some way you can look at the river and see where it stops being tidal without needing to wait a few hours to see if the water level went up or down? And if it did go up or down 5cm, does that make it tidal? --Eimai 21:10, 14 January 2008 (UTC)

Where does a land/water boundary stop being coastline and start being riverbank? In the Thames estuary, here does the sea end and the river begin? The position is arbitrary and when Osmarender had rivers and sea different shades of blue you used to get a silly straight line at some point in the estuary. I realize that the limit of the tide in a natural river could be ill-defined but is in a position where the river is narrow and less conspicuous. Navigable rivers often have a weir and a lock above which the river is non-tidal; the position is fixed. Using coastline for a tidal river bank reduces the arbitrariness.

The effects of tide are most noticeable on the shore (mud flats, etc.), making it logical that the tag should be there. (This why it makes sense.) The old and new ways are compatible, so whatever is used could be easily changed later. Chrismorl 14:13, 22 January 2008 (UTC)

I was just looking at the way the Thames is actually tagged. The current situation is actually a lot more confused than I thought it was. We have waterway=riverbank in addition to waterway=river as per the Waterway/riverbank. But the Thames river bank is tagged as both riverbank and coastline up to point when it ceases to be tidal to the West of London.
The banks continue to have both tags throughout London, out towards the sea. The riverbank tag stops at this arbitrary point, and here we also have a way across the river tagged natural=old_coastline, which Mapnik seems to actually be paying attention to (blue area to the West is currently broken though) All very weird.
Should the bank be tagged with both? Seems wrong to me. It should be one or the other. Then again, tagging it with both does kind of settle the argument! (that's probably why it's ended up like that) -- Harry Wood 10:34, 8 February 2008 (UTC)
That's because I added the tag earlier :-) Yes, it does seem wrong to have both, but I can't imagine it'll make much difference to the current users, and it will fix the Thames on the Mapnik rendering when new coastlines get updated. Until this gets sorted out properly it seemed a reasonable way to patch things up. I only went as far as the tidal Thames (although I might have overshot slightly by accident). The Mapnik rendering does need a proper fix for rivers you couldn't possibly decide are coastline. Randomjunk 11:59, 8 February 2008 (UTC)

This page mentions a tidal=yes tag, other pages suggest water=tidal. Can we clarify the difference between these tags? I assume water=tidal means that the land will be flooded at high tide and dry out at low tide, whereas tidal=yes indicates that it is flooded at all times but the water level is affected by the tide? -- Steve Hill 14:54, 14 April 2008 (UTC)


This is a proposed change to the way we might use existing tags. Just as with normal Proposed Features, we could have a vote on it.

So vote here. Do you approve or disapprove of the idea? : River areas should be tagged as natural=coastline inland up until they cease to be tidal (as opposed to the current arbitrary cut-off point)

  • I approve - seems sensible to me - Harry Wood
  • I reject this proposal - While I agree that it is desirable to mark the extent of the tidal river, it simply doesn't make sense to tag riverbanks as coastline. The banks of the Thames in the City of London plainly aren't coastline, nor is the river sea. If this proposal is approved, I think a lot of rivers will still get tagged as riverbank because it's the logical thing to do. Please can we just use riverbank and tidal=yes. I acknowledge that the point where we switch from riverbank to coast is somewhat arbitraty, but nonetheless, a river is distinct from the sea in having fresh not salt water. I would suggest that we transition at Sea Reach, south of Canvey Island, which is the suggested westerly extent of the Thames Estuary on the wikipedia Thames Estuary page [1]. Daveemtb 19:54, edited 14 January 2008 (UTC); Daveemtb 12:11, 2 September 2008 (UTC)
    Except that the Thames *is* salt water up to the tidal limit - albeit progressively less salty the further you go towards Teddington Lock. Richard B 12:52, 2 September 2008 (UTC)
    Well, you learn something every day! After looking into it, it seems that it is classed as "freshwater" (though no doubt somewhat saline) up to Westminster, "brackish" from there up to just past Tilbury, and "marine" from there onwards. Anyway, I was clearly wrong about the saltwater thing, but I still maintain that it is nonsensical to tag the banks of the Thames as coastline right into London! What's wrong with tidal=yes? Daveemtb 15:25, 4 September 2008 (UTC)
  • I approve Chrismorl 14:13, 22 January 2008 (UTC)
  • I reject this proposal: it's unclear where to stop marking a river as tidal, and rivers shouldn't be tagged with coastlines. --Eimai 15:10, 22 January 2008 (UTC)
But in the vast majority of cases, it *is* entirely clear where to stop marking a river as tidal. As pointed out above, most are at weirs or locks. If you say that rivers shouldn't be tagged as coast - where does the coast become a river? On the Thames, and most other tidal rivers, the flow of water can go in either direction, depending on the tide - it's got a degree of salinity etc. Perhaps it's worth pointing out that the Ordnance Survey in the UK mark tidal rivers in the same ways as coastlines. Richard B 12:45, 8 February 2008 (UTC)
  • I approve Richard B 12:45, 8 February 2008 (UTC)
  • I reject: before we don't have a valid definition of coastline concernig geoid, ellipsoid and sea level, it is not possible to describe a dynamic systems like tide in a static map like OSM. --Markus 22:27, 14 January 2009 (UTC)
  • I approve this proposal. Agree with RichardB; also local knowledge is usually the best definer of when the tidal area ends. I do think we need a river way through the tidal section out to open water, as rivers often follow a non-obvious line down their estuaries (cf the Exe and Teign, down here). Andygates


I'm going to tag the tidal portion of the Hudson River estuary=yes. RussNelson