[Tagging] tagging floodplain

Colin Smale colin.smale at xs4all.nl
Sun Sep 25 22:58:20 UTC 2016


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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