Must be a lot of snow in those Welsh mountains and some rain to fall as well?

On Thu, 14 Jan 2010 22:46:43 +0000, Trevor wrote:

Must be a lot of snow in those Welsh mountains and some rain to fall as
well?

It'll take something very impressive to flood the Severn here in Bewdley:
it's currently a long way below its usual winter level, and not that
different to what I'd expect in the summer. Unfortunately I don't know
what the level was here in early March 1947.

I can't speak for areas further upstream, of course, and I think that
many of the smaller rivers (the Wye, for one) might be at considerable
risk, but I think we'll probably be okay here. Perhaps up to "Flood
Warning" status, but I'd be surprised to see "Severe Flood Warning".

I now wait to be proved wrong!

--
Bewdley, Worcs. ~90m asl.

On Thu, 14 Jan 2010 17:33:41 -0600, David Buttery wrote:

On Thu, 14 Jan 2010 22:46:43 +0000, Trevor wrote:

Must be a lot of snow in those Welsh mountains and some rain to fall as
well?

It'll take something very impressive to flood the Severn here in
Bewdley: it's currently a long way below its usual winter level, and not
that different to what I'd expect in the summer. Unfortunately I don't
know what the level was here in early March 1947.

I can't speak for areas further upstream, of course, and I think that
many of the smaller rivers (the Wye, for one) might be at considerable
risk, but I think we'll probably be okay here. Perhaps up to "Flood
Warning" status, but I'd be surprised to see "Severe Flood Warning".

I now wait to be proved wrong!

Further to the above: here's a photo I took in Bewdley this afternoon.
Not a brilliant one, but it gives the idea: in January I'd expect the
level to be up to around halfway between the current water level and the
quayside. What you see here isn't exceptionally low, but it's well below
average for the time of year.

http://i49.tinypic.com/mj4jk2.jpg

--
Bewdley, Worcs. ~90m asl.

On Thu, 14 Jan 2010 17:33:41 -0600, David Buttery wrote:

It'll take something very impressive to flood the Severn here in
Bewdley: it's currently a long way below its usual winter level, and not
that different to what I'd expect in the summer.

Depends how fast any thaw takes. I reckon there is a good 3" or more
of rain stored up as snow lying around here ATM. If that went in 24
to 48hrs it would certianly give the rivers something to think about.
It would probably be worse than a normal 3" of rain over that time
scale as the ground is frozen and won't be doing it's normal sponge
impression.

--
Cheers Dave.
Nr Garrigill, Cumbria. 421m ASL.

On Fri, 15 Jan 2010 00:14:09 +0000, Dave Liquorice wrote:

Depends how fast any thaw takes. I reckon there is a good 3" or more of
rain stored up as snow lying around here ATM. If that went in 24 to
48hrs it would certianly give the rivers something to think about. It
would probably be worse than a normal 3" of rain over that time scale as
the ground is frozen and won't be doing it's normal sponge impression.

Yes, that's all fair comment. I can't actually remember a "super-thaw"
situation (heavy rain combined with rapid melt of deep snow upstream)
happening here, so I'm guessing a bit. I still think that the sheer size
of the Severn will play in our favour, as it does have a lot of "space"
to fill up at the moment: it's not like July 2007, for example, when it
was already quite high after the rains of June.

--
Bewdley, Worcs. ~90m asl.

On Thu, 14 Jan 2010 19:53:55 -0600, David Buttery wrote:

Depends how fast any thaw takes. I reckon there is a good 3" or
more of
rain stored up as snow lying around here ATM. If that went in 24
to
48hrs ...

Yes, that's all fair comment. I can't actually remember a "super-thaw"
situation (heavy rain combined with rapid melt of deep snow upstream)

It happens, we are up to 1.6C now with a F6 SSW'ly breeze . It feels
decidely warm out (of the wind, wind chill is -15C). Thaw slowed over
night and there is a lot of ice about from frozen melt waters but
that is now thawing as well.

I still think that the sheer size of the Severn will play in our favour,
as it does have a lot of "space" to fill up at the moment:

Not sure what the catchment of the Severn is, Mid to North Wales?
They have snow there but I think most of it in South Wales. It's not
so much how much "space" there is but flow rates. If a point on a
river can only carry X thousand cubic meters of water per hour
without flooding and the flow into that point is X plus a bit the
"plus a bit" will cause a flood.
Simplistic but you get the idea.

--
Cheers Dave.
Nr Garrigill, Cumbria. 421m ASL.

In article ,
David Buttery writes:
On Thu, 14 Jan 2010 22:46:43 +0000, Trevor wrote:

Must be a lot of snow in those Welsh mountains and some rain to fall as
well?

It'll take something very impressive to flood the Severn here in Bewdley:
it's currently a long way below its usual winter level, and not that
different to what I'd expect in the summer. Unfortunately I don't know
what the level was here in early March 1947.

After a prolonged period when presumably almost nothing was flowing into
the river, I'd have expected it to be fairly low then too.

I can't speak for areas further upstream, of course, and I think that
many of the smaller rivers (the Wye, for one) might be at considerable
risk, but I think we'll probably be okay here. Perhaps up to "Flood
Warning" status, but I'd be surprised to see "Severe Flood Warning".

I now wait to be proved wrong!


Fingers crossed for you.
--
John Hall
"Acting is merely the art of keeping a large group of people
from coughing."
Sir Ralph Richardson (1902-83)

On Fri, 15 Jan 2010 09:59:52 +0000, Dave Liquorice wrote:

snip
Not sure what the catchment of the Severn is, Mid to North Wales? They
have snow there but I think most of it in South Wales.

I can't actually find a catchment map, which is a bit disappointing. I
thought the EA might have one, but if they do it's not obvious. There's
this from the Geographical Association:

http://www.geography.org.uk/resource...hmentoverview/

I'm sure an old (1980s) copy of the Guinness Book of Records had a map
showing the catchments of the main British rivers, but I don't have that
edition and can't remember any further details.


It's not so much
how much "space" there is but flow rates. If a point on a river can only
carry X thousand cubic meters of water per hour without flooding and the
flow into that point is X plus a bit the "plus a bit" will cause a
flood.
Simplistic but you get the idea.

Yes, understood. But surely if less water is flowing through than usual
(as now) there's more scope for an increase of X without the river
bursting its banks. That's really what I meant by "space": if the river
were already close to lapping the banks, less rain/snowmelt would be
needed to provide the conditions to push it over the top.

--
Bewdley, Worcs. ~90m asl.

In message , David Buttery
writes
On Fri, 15 Jan 2010 09:59:52 +0000, Dave Liquorice wrote:

snip
Not sure what the catchment of the Severn is, Mid to North Wales? They
have snow there but I think most of it in South Wales.

I can't actually find a catchment map, which is a bit disappointing. I
thought the EA might have one, but if they do it's not obvious. There's
this from the Geographical Association:

http://www.geography.org.uk/resource...hmentoverview/

I'm sure an old (1980s) copy of the Guinness Book of Records had a map
showing the catchments of the main British rivers, but I don't have that
edition and can't remember any further details.

There was a Readers Digest Atlas of the British Isles with one as well.
However, on the web, see

http://www.hydroclimate.org/foto/Figure1.jpg
http://www.after-oil.co.uk/Severn_Catchment.jpg

It's not so much
how much "space" there is but flow rates. If a point on a river can only
carry X thousand cubic meters of water per hour without flooding and the
flow into that point is X plus a bit the "plus a bit" will cause a
flood.
Simplistic but you get the idea.

Yes, understood. But surely if less water is flowing through than usual
(as now) there's more scope for an increase of X without the river
bursting its banks. That's really what I meant by "space": if the river
were already close to lapping the banks, less rain/snowmelt would be
needed to provide the conditions to push it over the top.


--
Stewart Robert Hinsley

On Thu, 14 Jan 2010 17:45:32 -0600, David Buttery wrote:

Further to the above: here's a photo I took in Bewdley this afternoon.
Not a brilliant one, but it gives the idea: in January I'd expect the
level to be up to around halfway between the current water level and the
quayside. What you see here isn't exceptionally low, but it's well below
average for the time of year.

http://i49.tinypic.com/mj4jk2.jpg

Well, there we are... it looks as though the EA are not particularly
concerned by flood potential this weekend:

http://news.bbc.co.uk/1/hi/uk/8462372.stm

Their predictions are actually milder than I'd expected.

--
Bewdley, Worcs. ~90m asl.