|waterway = riverbed|
|area of riverbed|
|Used on these elements|
|Tools for this tag|
This tag is proposed to describe the area of the riverbed together with other optional tags defining the Landcover. As most rivers have fluctuating water levels this area would be typically larger than the area defined by riverbanks and encompass the whole area that is regularly flooded and visibly formed by the river.
It should be useful for rivers with large temporal fluctuations of water flow with a discernible riverbed much larger than the normal area covered by the river such as the Isar around the Sylvenstein reservoir, the Maggia around Giumaglio and Someo, as well as desert streams.
The surface of the riverbed can be already mapped using various natural/landcover tags but not the fact that it is a riverbed and gets occasionally flooded.
Also there are conflicting opinions whether it is a "good practice" and how it is defined when an area is mapped with natural, landcover or similar that is "cut" by a river defined as area between riverbanks. This proposal defines this semantics for the special case of areas inside riverbeds.
How to map
The river (waterway=river) and riverbanks (waterway=riverbank) need to be mapped in addition to the riverbed. If the river course is too variable to map precisely do not map the riverbanks. The river may also be tagged as intermittent=*.
It is assumed that most riverbeds will have a surface similar to natural=shingles and this could be a default property of riverbed (not decided yet).
Islands (areas which are never flooded and distinct from the river bed) can be mapped with multipolygon/inner. In contrast to this vegetation patches within the riverbed that are not true islands should be mapped as areas not part of a multipolygon relation with it.
- landcover=*, natural=*, surface=* - to define the appearance of the riverbed when not flooded
- landuse=* - in some areas parts of the riverbed may be seasonally used for example for agricultural purposes
Riverbeds are areas prone to be flooded and visibly formed by a river flow.
The riverbed covers the whole area except for areas excluded as multipolygon/inner which are defined as islands in the riverbed and not flooded except on extreme occasions.
The river - where defined by riverbanks covers the riverbed.
Where the river is defined only as waterway=river a fuzzy and highly variable river flow may be assumed.
The riverbed area could be rendered with blue circles or similar superimposed to the surface indicating that it is occasionally flooded.