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15-01-2010, 07:00   #1
M.T. Cranium
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Friday 15th -- flood risk rising, milder

Friday 15th -- flood risk rising, milder
____________________________________

We need a new focus for the general interest discussion, methinks, as the cold spell ends for the time being in a wave of mild, moist air drawn up from the latitude of the Azores.

I'll just make a brief starting post here, the details can be found in the forecast thread.

The combination of rain today and tonight, with melting snow that is still quite widespread in many areas (central, eastern, northwest especially) seems capable of bringing some moderate or even severe flooding in spots. Any place that streams drain highland areas especially in Wicklow, Dublin, Laois, Carlow, Kilkenny, Tipps, west Cork and Kerry, as well as possibly Mayo and Donegal, need to be closely watched for rapid water level rising.

In other places, the flood situation may be more from waterlogged fields and bogs not releasing standing water but oozing out the excess onto roads and nearby areas. And there could be some flooding in cities and towns in a few spots because water is unable to drain away through clogged drains.

Anyway, if you doubt the potential for flooding, have a look at the photo threads on this forum and realize that there is much more snow available for melting than it may appear in lowland areas. Reports of several feet of snow, some of it already moisture-laden, with rain to come, have me concerned that by tonight or Saturday, there can be some serious flooding.

And add to that dense fog and the odd mudslide, you've got a lot of things to watch out for on the roads today, tonight especially, and through the weekend.
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15-01-2010, 09:27   #2
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Important thread MT - thanks.

With in some places having in execss of 1 metre of snow in the Dublin/Wicklow Mountains at the moment in conjunction with temps now nudging 9.0c here, that 1 metre of snow has the potential to release the equivalent of 100mm of rain (in addittion to what rain may fall today and tonight). Potential for flooding should not be underestimated.
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15-01-2010, 11:31   #3
 
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Density of Snow =
Snow, freshly fallen 160 Kg per Cubic metre
Snow, compacted 481 Kg per cubic metre


Snow water equivalent (SWE) is defined as the depth of water (in millimetres) of snow cover on a horizontal surface area if that snow cover is completely melted. SWE is related to snow depth and density by

SWE (millimetres) = depth (metres) x density (kilogram per cubic metre).

I am going to assume 5 Cms of Snow cover coz I am lazy and its easy to multiply

10 cm = .1 of a metre
5 cm = .05 of a metre
Compacted
.05 * 481 = 24 mm

Fresh fall

.05 * 160 = 8 mm

These are some back of envelope calculations I did for a thread I started on this earlier this week...

In short I think it would be wise to be prepared for some water if you live in a prone area
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15-01-2010, 11:34   #4
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Please take care; a few years ago I waded in to rescue 5 ewes and their ten lambs from a sudden flash flood in a different but high situation.

It was a terrifying sight and can happen anywhere there is flowing water; this was a mountain stream suddenly overwhelmed.

Please God that that at least is one thing we are safe from up here. I hope.. the snow is melting gently and we are not in the lee of any great height. The hill opposite us is almost clear now.And drainage seems fine

Last edited by Graces7; 15-01-2010 at 11:36.
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15-01-2010, 11:36   #5
 
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I am going to guess that the water is not going to be much 1 or 2 degrees so best to stay out of it
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15-01-2010, 11:56   #6
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15-01-2010, 13:01   #7
 
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Can Jen ask a stupid question please ?

When the snow all melts up the Dublin & Wicklow mountains which river will it run down into ?
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15-01-2010, 13:26   #8
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the nearest one
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15-01-2010, 13:26   #9
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Quote:
Originally Posted by jenzz View Post
Can Jen ask a stupid question please ?

When the snow all melts up the Dublin & Wicklow mountains which river will it run down into ?
All the riveres that have their sources in the Dublin & Wicklow mountains.
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15-01-2010, 13:31   #10
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Met Eireann has now issued a weather warning for this :




Issued at 15 January 2010 - 13:00

Weather warning

Rain Friday night will produce falls of 20 to 30mm in parts of south Munster and south and east Leinster, with some thawing of mountain snow also. This may cause localised flooding. Strong winds countrywide also, with gusts 80 to 100 km/hr locally.
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15-01-2010, 13:55   #11
 
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Quote:
Originally Posted by jenzz View Post
Can Jen ask a stupid question please ?

When the snow all melts up the Dublin & Wicklow mountains which river will it run down into ?
The Liffey for one, Watch out strawberry beds
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15-01-2010, 14:13   #12
 
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Quote:
Originally Posted by jenzz View Post
Can Jen ask a stupid question please ?

When the snow all melts up the Dublin & Wicklow mountains which river will it run down into ?
The dargle number two
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15-01-2010, 14:28   #13
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The dargle number two
The Dodder number three.
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15-01-2010, 15:29   #14
 
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Quote:
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Can Jen ask a stupid question please ?

When the snow all melts up the Dublin & Wicklow mountains which river will it run down into ?
The River Dodder starts at the foot of kippure, will flow into bournabreena and on through dublin, So does the liffy start at the other side of kippure and on into kildare and dublin.
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15-01-2010, 15:34   #15
Elmer Blooker
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I hope they're filling the sand bags in Carlow Town and Enniscorthy, with deep snow melting in Wicklow feeding the Slaney and Barrow you can throw in heavy rain and southerly gales piling the tides up against the south coast.
I made this point elsewhere on some other thread about a week ago maybe.
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