Re: [Tagging] tagging floodplain

[Colin Smale]

On that page it says: 

* In the very common case of rivers subject to seasonal flooding with
much higher water levels for a relatively short period for example
during monsoon season or snow melt and low and relatively constant water
levels for the rest of the year it is best not to map the water extent
during flooding. A useful rule of thumb would be to map the median of
the maximum water levels of all months of the year. For those areas
water covered during floods there are some ideas for tagging like
Proposed features/floodplain [1] and Key:flood_prone [2].

The suggested "rule of thumb" will of course mess up all the rivers in
low-lying areas in OSM, not to mention the difficulty of ascertaining
the location of the line to be drawn (daily aerial photos over a year?).
So it doesn't really deal with the problem at all. 

And on the floodplain proposal it says: 

"There should be some possibility to provide information for this. The
tags should describe who has delineated the flood plains, how is the
probability for flooding, is the floodplain evaluated to be "red"
"green" or whatever zone (this depends on national or regional
regulations) and which type of hazard (torrent, mud-slide, flash flood,
low-land river). Eventually this could be extended to cover avalanches."


I.e. someone (government?) needs to delineate the area, do the risk
calculations and make the classifications. This is potentially open to
political "influence," to prevent or enable development in a particular
area or to justify decisions on flood defences. That is what I mean with
"designated flood risk zones" not being equal to "flood plains". The
former can be mapped - from definitive data with an appropriate licence.
The latter is controversial because of the indefinite boundary, and
belongs in the same category as mountain ranges, where we also don't
have a way of drawing a sharp boundary. 

//colin 

On 2016-09-26 11:02, Martin Koppenhoefer wrote:

> sent from a phone 
> 
> Il giorno 26 set 2016, alle ore 00:58, Colin Smale  ha 
> scritto:
> 
> Problems of defining a boundary exist with river banks too.  
> 
> That is rather obvious - the area which is covered by water can be a 
> continuum, depending on the conditions at any given moment.

yes, that's why there are recommendations how to deal with it:
http://wiki.openstreetmap.org/wiki/Tag:waterway%3Driverbank#Varying_water_level_river


cheers, 
Martin  
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[1] http://wiki.openstreetmap.org/wiki/Proposed_features/floodplain
[2] http://wiki.openstreetmap.org/wiki/Key:flood_prone___
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Re: [Tagging] tagging floodplain

[Martin Koppenhoefer]

sent from a phone

Il giorno 26 set 2016, alle ore 00:58, Colin Smale  ha 
scritto:

>> Problems of defining a boundary exist with river banks too. 
> That is rather obvious - the area which is covered by water can be a 
> continuum, depending on the conditions at any given moment.
> 


yes, that's why there are recommendations how to deal with it: 
http://wiki.openstreetmap.org/wiki/Tag:waterway%3Driverbank#Varying_water_level_river


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Re: [Tagging] tagging floodplain

[Warin]

On 26-Sep-16 06:03 PM, Colin Smale wrote:


On 2016-09-26 09:52, Martin Koppenhoefer wrote:


sent from a phone

Il giorno 26 set 2016, alle ore 02:00, Colin Smale 
> ha scritto:


I don't have my own definition, and I don't want to make up a new 
one. A quick search revealed these:


  * anearlyflatplainalongthecourseofastreamorriverthatisnaturally
subjecttoflooding.
  * an area of low, flat land along a stream or river that may flood
  * an area of land built up from soil left by floods
  * level land that may be submerged by floodwaters

  * a plain built up by stream deposition

They all sound rather open to interpretation, but they are all based 
on natural phenomena, not government classifications.


the definitions you found are all reasonable for natural=floodplain 
and are all describing the same situation, although with different 
focus on which aspect is named.
The definition given above in this thread describing government 
dedication of land is not suitable for the natural tag and should go 
into the boundary tag (and subkeys), if entered into osm at all.
Exactly, problem solved. Despite the title, this thread is not about 
flood plains, but designated flood risk zones. Conflating them with 
floodplains is wrong.


NO!

I gave a link to a document with a map of a sample area... it contained 
that statement.. at NO time was I proposing using that definition (which 
I had not read .. I was simply looking for an example of the area).


But by all mean misconstrue it whatever way you want ...

The problem is how to tag floodplains.. so far this is diverted into;

how to define it ...
how to determine it ... with some accuracy (why? Where is the accuracy 
in determining a woodland? Where is the accuracy in determining an area 
of sand? They are all 'fuzzy' ... they are all indications .. not 
absolutes.
I sure there will be other topics of equal value to someone ... with 
some link to tagging a floodplain.


So ... thanks ... I'll just go do mapping it the way I think would be 
best. Bye.
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Re: [Tagging] tagging floodplain

[Colin Smale]

On 2016-09-26 09:52, Martin Koppenhoefer wrote:

> sent from a phone 
> 
> Il giorno 26 set 2016, alle ore 02:00, Colin Smale  ha 
> scritto:
> 
>> I don't have my own definition, and I don't want to make up a new one. A 
>> quick search revealed these: 
>> 
>> * a nearly flat plain along the course of a stream or river that is 
>> naturally subject to flooding.
>> * an area of low, flat land along a stream or river that may flood
>> * an area of land built up from soil left by floods
>> * level land that may be submerged by floodwaters [1]
>> * a plain built up by stream deposition
>> 
>> They all sound rather open to interpretation, but they are all based on 
>> natural phenomena, not government classifications.
> 
> the definitions you found are all reasonable for natural=floodplain and are 
> all describing the same situation, although with different focus on which 
> aspect is named. 
> 
> The definition given above in this thread describing government dedication of 
> land is not suitable for the natural tag and should go into the boundary tag 
> (and subkeys), if entered into osm at all.

Exactly, problem solved. Despite the title, this thread is not about
flood plains, but designated flood risk zones. Conflating them with
floodplains is wrong. 

//colin 
  

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[1] http://www.merriam-webster.com/dictionary/floodwaters___
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Re: [Tagging] tagging floodplain

[Martin Koppenhoefer]

sent from a phone

> Il giorno 26 set 2016, alle ore 02:00, Colin Smale  ha 
> scritto:
> 
> I don't have my own definition, and I don't want to make up a new one. A 
> quick search revealed these:
> 
> a nearly flat plain along the course of a stream or river that is naturally 
> subject to flooding.
> an area of low, flat land along a stream or river that may flood
> an area of land built up from soil left by floods
> level land that may be submerged by floodwaters
> a plain built up by stream deposition
> They all sound rather open to interpretation, but they are all based on 
> natural phenomena, not government classifications.
> 


the definitions you found are all reasonable for natural=floodplain and are all 
describing the same situation, although with different focus on which aspect is 
named.

The definition given above in this thread describing government dedication of 
land is not suitable for the natural tag and should go into the boundary tag 
(and subkeys), if entered into osm at all.


cheers,
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Re: [Tagging] tagging floodplain

[Kevin Kenny]

There was a proposal a while back for a 'water=intermittent' tag, which
might be revised for the situation, perhaps with some additional tagging to
describe whether the area is inundated seasonally or only sporadically.

For the 'official' flood control boundary, there are also
boundary=protected_area tags of classes 12 and 15.

Either of these could be combined with the appropriate landuse=*, of course.

Just a handful of possibilities - I'm not claiming that any of them is
ideal.

On Sun, Sep 25, 2016 at 8:00 PM, Colin Smale  wrote:

> On 2016-09-26 01:18, Warin wrote:
>
> On 26-Sep-16 08:58 AM, Colin Smale wrote:
>
> On 2016-09-26 00:17, Warin wrote:
>
> Perhaps you could state your definition?
> One definition I saw briefly said something about the maximum expected
> area ... I only skimmed it .. looking for a open source map of the
> floodplain (by whatever definition :) ).
> There are some 'floodplains' on the NSW LPI Base Map - available in OSM
> (similar availability to Bing imagery - but has addresses, parks, forests
> etc).
> The flood level in Forbes was supposed to peak at 10.7 metres .. over the
> 'normal' level of the river? Or over the bed of the river? I don't know ..
> but 10.7 is fairly high!
>
> I don't have my own definition, and I don't want to make up a new one. A
> quick search revealed these:
>
>- a nearly flat plain along the course of a stream or river that is
>naturally subject to flooding.
>- an area of low, flat land along a stream or river that may flood
>- an area of land built up from soil left by floods
>- level land that may be submerged by floodwaters
>
>- a plain built up by stream deposition
>
> They all sound rather open to interpretation, but they are all based on
> natural phenomena, not government classifications.
>
>
>
>
>
> I would expect this to be similar to other OSM 'definitions' like stream
> vs river, monument vs memorial, city vs town vs village .. a bit fuzzy to
> allow for local variations.
> For example in India the definitions of places looks to be swinging to the
> legal/government determined rather than simply population based.
>
> This is also frequently the case in the UK by the way.
>
> The distinction between city and town, and between river and stream, is
> cosmetic, and the fuzziness doesn't hurt. The fuzziness is in whether
> something is "big" or "small" and there will always be debates about
> "medium" things. The fuzziness in these examples does not affect where the
> lines are drawn on the map, only the tagging. I don't see how that
> principle would be applied to flood plains where the location of the line
> itself is debatable.
>
>
>
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>
>
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Re: [Tagging] tagging floodplain

[Colin Smale]

On 2016-09-26 01:18, Warin wrote:

> On 26-Sep-16 08:58 AM, Colin Smale wrote: 
> 
>> On 2016-09-26 00:17, Warin wrote:
> Perhaps you could state your definition?
> One definition I saw briefly said something about the maximum expected area 
> ... I only skimmed it .. looking for a open source map of the floodplain (by 
> whatever definition :) ). 
> There are some 'floodplains' on the NSW LPI Base Map - available in OSM 
> (similar availability to Bing imagery - but has addresses, parks, forests 
> etc). 
> The flood level in Forbes was supposed to peak at 10.7 metres .. over the 
> 'normal' level of the river? Or over the bed of the river? I don't know .. 
> but 10.7 is fairly high!

I don't have my own definition, and I don't want to make up a new one. A
quick search revealed these: 

* a nearly flat plain along the course of a stream or river that is
naturally subject to flooding.
* an area of low, flat land along a stream or river that may flood
* an area of land built up from soil left by floods
* level land that may be submerged by floodwaters [1]
* a plain built up by stream deposition

They all sound rather open to interpretation, but they are all based on
natural phenomena, not government classifications. 

> I would expect this to be similar to other OSM 'definitions' like stream vs 
> river, monument vs memorial, city vs town vs village .. a bit fuzzy to allow 
> for local variations. 
> For example in India the definitions of places looks to be swinging to the 
> legal/government determined rather than simply population based.

This is also frequently the case in the UK by the way. 

The distinction between city and town, and between river and stream, is
cosmetic, and the fuzziness doesn't hurt. The fuzziness is in whether
something is "big" or "small" and there will always be debates about
"medium" things. The fuzziness in these examples does not affect where
the lines are drawn on the map, only the tagging. I don't see how that
principle would be applied to flood plains where the location of the
line itself is debatable. 

  

Links:
--
[1] http://www.merriam-webster.com/dictionary/floodwaters___
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Re: [Tagging] tagging floodplain

[Warin]

On 26-Sep-16 08:58 AM, Colin Smale wrote:


On 2016-09-26 00:17, Warin wrote:


On 25-Sep-16 08:48 PM, Colin Smale wrote:
Where would the boundary be? How could we describe it objectively? 
In low lying areas such as the Netherlands there are sometimes so 
called winter dykes which give a sharp edge to the flood plain. 
Otherwise it would all be a bit vague around the edges.

//colin


Problems of defining a boundary exist with river banks too. 


That is rather obvious - the area which is covered by water can be a 
continuum, depending on the conditions at any given moment.



Here is a document on part of a flood plain .. only about 60 kms long.
http://www.environment.nsw.gov.au/resources/floodplains/120163JemalongCondobolinFMP.pdf
Note that the document is copyright ... Yes boundaries are a 'bit 
vague', they are a 'bit vague' for scrub, wood, sand etc too.


The document gives a definition of "floodplain" as follows: "Any land 
which is so designated by an order in force under section 166 (1) of 
the Water Act 1912." In other words, this need have no relation to 
actual flood risk but it is simply designated as such.


All this is not natural at all. A natural flood plain may or may not 
flood depending on all kinds of things, and the depth of the water and 
the extent of the flood are variable unpredictable. What IS fixed in 
many cases is the government designation of a flood risk area 
(restrictions on building, consequences for insurance etc). But that 
is not what I would call a flood plain in the geographical sense.



Perhaps you could state your definition?
One definition I saw briefly said something about the maximum expected 
area ... I only skimmed it .. looking for a open source map of the 
floodplain (by whatever definition :) ).
There are some 'floodplains' on the NSW LPI Base Map - available in OSM 
(similar availability to Bing imagery - but has addresses, parks, 
forests etc).
The flood level in Forbes was supposed to peak at 10.7 metres .. over 
the 'normal' level of the river? Or over the bed of the river? I don't 
know .. but 10.7 is fairly high!


I would expect this to be similar to other OSM 'definitions' like stream 
vs river, monument vs memorial, city vs town vs village .. a bit fuzzy 
to allow for local variations.
For example in India the definitions of places looks to be swinging to 
the legal/government determined rather than simply population based.


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Re: [Tagging] tagging floodplain

[Colin Smale]

On 2016-09-26 00:17, Warin wrote:

> On 25-Sep-16 08:48 PM, Colin Smale wrote: 
> 
>> Where would the boundary be? How could we describe it objectively? In low 
>> lying areas such as the Netherlands there are sometimes so called winter 
>> dykes which give a sharp edge to the flood plain. Otherwise it would all be 
>> a bit vague around the edges.
>> //colin
> 
> Problems of defining a boundary exist with river banks too.

That is rather obvious - the area which is covered by water can be a
continuum, depending on the conditions at any given moment.

> Here is a document on part of a flood plain .. only about 60 kms long. 
> http://www.environment.nsw.gov.au/resources/floodplains/120163JemalongCondobolinFMP.pdf
> Note that the document is copyright ... Yes boundaries are a 'bit vague', 
> they are a 'bit vague' for scrub, wood, sand etc too.

The document gives a definition of "floodplain" as follows: "Any land
which is so designated by an order in force under section 166 (1) of the
Water Act 1912." In other words, this need have no relation to actual
flood risk but it is simply designated as such. 

All this is not natural at all. A natural flood plain may or may not
flood depending on all kinds of things, and the depth of the water and
the extent of the flood are variable unpredictable. What IS fixed in
many cases is the government designation of a flood risk area
(restrictions on building, consequences for insurance etc). But that is
not what I would call a flood plain in the geographical sense. 

Managed flood areas such as the winter dykes in NL and areas adjacent to
rivers which are intentionally flooded at times of extreme river levels
are another type.___
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Re: [Tagging] tagging floodplain

[Warin]

On 25-Sep-16 08:48 PM, Colin Smale wrote:
Where would the boundary be? How could we describe it objectively? In 
low lying areas such as the Netherlands there are sometimes so called 
winter dykes which give a sharp edge to the flood plain. Otherwise it 
would all be a bit vague around the edges.

//colin


Problems of defining a boundary exist with river banks too.

Here is a document on part of a flood plain .. only about 60 kms long.
http://www.environment.nsw.gov.au/resources/floodplains/120163JemalongCondobolinFMP.pdf
Note that the document is copyright ... Yes boundaries are a 'bit 
vague', they are a 'bit vague' for scrub, wood, sand etc too.




On 25 September 2016 12:30:50 CEST, Warin <61sundow...@gmail.com> wrote:

Hi,

There is a draft to tag floodplains using the key natural.


http://wiki.openstreetmap.org/wiki/Proposed_features/floodplain


My thinking is that this would lead to conflicts with other 'natural'
tags .. like natural=scrub than may be applied to the same area.


So .. what would be the best key to use for this feature/value?

I am thinking that as it is associated with a waterway (it must start to
flood from somewhere and that is usually a waterway) that the key
waterway should be used. It would have rendering similar to a lake - but
'intermittent' so dashed lines rather than a solid colour.


Thoughts?


{There is presently flooding in some areas of Australia, why my thoughts
have turned to this. All too soon it will turn to bushfires}




Sub tags could be used to tag frequency etc. These tags could also be 
used on floodways that are already part of OSM mapping.. so should be 
something like flood:frequency=10 years.
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Re: [Tagging] tagging floodplain

[Martin Koppenhoefer]

sent from a phone

> Il giorno 25 set 2016, alle ore 12:30, Warin <61sundow...@gmail.com> ha 
> scritto:
> 
> My thinking is that this would lead to conflicts with other 'natural' tags .. 
> like natural=scrub than may be applied to the same area.


it's not a real problem, they could overlap. Natural seems fine to me. Although 
these have a connection to waterways, they aren't waterways themselves, hence 
the waterway key seems wrong 

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Re: [Tagging] tagging floodplain

[Mark Wagner]

In the United States, this is usually defined as the "X years
floodplain", indicating how frequently it's expected to flood.  For
example, the 100-year floodplain is the area around a river is the area
that's expected to flood an average of once every hundred years.

-- 
Mark

On Sun, 25 Sep 2016 12:48:10 +0200
Colin Smale  wrote:

> Where would the boundary be? How could we describe it objectively? In
> low lying areas such as the Netherlands there are sometimes so called
> winter dykes which give a sharp edge to the flood plain. Otherwise it
> would all be a bit vague around the edges. //colin
> 
> On 25 September 2016 12:30:50 CEST, Warin <61sundow...@gmail.com>
> wrote:
> >Hi,
> >
> >There is a draft to tag floodplains using the key natural.
> >
> >
> >http://wiki.openstreetmap.org/wiki/Proposed_features/floodplain
> >
> >
> >My thinking is that this would lead to conflicts with other
> >'natural' tags .. like natural=scrub than may be applied to the same
> >area.
> >
> >
> >So .. what would be the best key to use for this feature/value?
> >
> >I am thinking that as it is associated with a waterway (it must start
> >to 
> >flood from somewhere and that is usually a waterway) that the key 
> >waterway should be used. It would have rendering similar to a lake -
> >but 
> >'intermittent' so dashed lines rather than a solid colour.
> >
> >
> >Thoughts?
> >
> >
> >{There is presently flooding in some areas of Australia, why my
> >thoughts 
> >have turned to this. All too soon it will turn to bushfires}
> >
> >
> >___
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> >https://lists.openstreetmap.org/listinfo/tagging  


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Re: [Tagging] tagging floodplain

[Tod Fitch]

> On Sep 25, 2016, at 3:30 AM, Warin <61sundow...@gmail.com> wrote:
> 
> Hi,
> 
> There is a draft to tag floodplains using the key natural.
> 
> 
> http://wiki.openstreetmap.org/wiki/Proposed_features/floodplain
> 
> 
> My thinking is that this would lead to conflicts with other 'natural' tags .. 
> like natural=scrub than may be applied to the same area.
> 
> 
> So .. what would be the best key to use for this feature/value?
> 
> I am thinking that as it is associated with a waterway (it must start to 
> flood from somewhere and that is usually a waterway) that the key waterway 
> should be used. It would have rendering similar to a lake - but 
> 'intermittent' so dashed lines rather than a solid colour.
> 
> 
> Thoughts?
> 
> 
> {There is presently flooding in some areas of Australia, why my thoughts have 
> turned to this. All too soon it will turn to bushfires}
> 

Concur that natural=floodplain will be in conflict with other tags likely to be 
used on the same area. natural=sand, natural=scrub, natural=grassland all come 
to mind for areas I am familiar with which are in flood plains.

On that page there is a link to flood_prone=yes which seems to be a usable tag 
to me, so I don’t see the reason for a new tag. Though “prone” has a 
connotation of fairly frequent occurrences while in the desert areas I am 
familiar with, you can go decades between events that will have enough water to 
cover a flood plain.





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Re: [Tagging] tagging floodplain

[John Willis]

Would this be used for controlled areas flooded by a river only during 
extraordinary rains (like a super-typhoon)? 

Here is a river that has never exceeded the bounds of the "normal" flood 
control measures in the time I have lived here, but these parks are clearly in 
a contained flood channel that surrounds the river, and extends for the river's 
entire remaining length to the ocean. Our town is where it emerges from the 
mountains.

https://www.openstreetmap.org/#map=14/36.3970/139.3324 


Most of the rivers in Japan are entirely contained in large man-made emergency 
flood control systems, but rarely do their waters ever extend to their limits. 
Often, above the "normal flooding" line (but still inside the flood control 
berms), parks, baseball diamonds, driving courses, and other non-building 
mappable features are built. 

It would be nice to define the flood control limits that the river sits in, as 
the riverbank is not mapped to the adjacent berms, as it is covered with scrub 
or these man-made features, and is not an accurate depiction of the bank's 
location.  

It could be something that relates the way of the river to the area/way of the 
top of the flood control system (wall, berm/levee/cliff/bank/ etc. 

Natural=flooodplain wouldn't be good, perhaps waterway=floodplain (or similar), 
which could share nodes with a  =riverbank way would be good. People who want 
to map it obviously have an idea of where it's boundary should be (almost all 
rivers in Japan would be super-easy), as people have made levees and other 
control measures around most large rivers people would care to map this around. 

Javbw

> On 25 Sep 2016, at 7:48 PM, Colin Smale  wrote:
> 
> Where would the boundary be? How could we describe it objectively? In low 
> lying areas such as the Netherlands there are sometimes so called winter 
> dykes which give a sharp edge to the flood plain. Otherwise it would all be a 
> bit vague around the edges.
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Re: [Tagging] tagging floodplain

[Colin Smale]

Where would the boundary be? How could we describe it objectively? In low lying 
areas such as the Netherlands there are sometimes so called winter dykes which 
give a sharp edge to the flood plain. Otherwise it would all be a bit vague 
around the edges.
//colin

On 25 September 2016 12:30:50 CEST, Warin <61sundow...@gmail.com> wrote:
>Hi,
>
>There is a draft to tag floodplains using the key natural.
>
>
>http://wiki.openstreetmap.org/wiki/Proposed_features/floodplain
>
>
>My thinking is that this would lead to conflicts with other 'natural' 
>tags .. like natural=scrub than may be applied to the same area.
>
>
>So .. what would be the best key to use for this feature/value?
>
>I am thinking that as it is associated with a waterway (it must start
>to 
>flood from somewhere and that is usually a waterway) that the key 
>waterway should be used. It would have rendering similar to a lake -
>but 
>'intermittent' so dashed lines rather than a solid colour.
>
>
>Thoughts?
>
>
>{There is presently flooding in some areas of Australia, why my
>thoughts 
>have turned to this. All too soon it will turn to bushfires}
>
>
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[Tagging] tagging floodplain

[Warin]

Hi,

There is a draft to tag floodplains using the key natural.


http://wiki.openstreetmap.org/wiki/Proposed_features/floodplain


My thinking is that this would lead to conflicts with other 'natural' 
tags .. like natural=scrub than may be applied to the same area.



So .. what would be the best key to use for this feature/value?

I am thinking that as it is associated with a waterway (it must start to 
flood from somewhere and that is usually a waterway) that the key 
waterway should be used. It would have rendering similar to a lake - but 
'intermittent' so dashed lines rather than a solid colour.



Thoughts?


{There is presently flooding in some areas of Australia, why my thoughts 
have turned to this. All too soon it will turn to bushfires}



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