cause of flooding

hiwayman

Not sure if this is the right forum for this, so mods, feel free to move.
The floods are all over the media at the moment. and we have climatologists tell us that this will become more frequent because of global warming.
I have another theory. In my local area, over the last 10 years of rapid development, I have seen a number of swamp or winter lakes which are normally dry but fill into lakes after heavy rain, filled in or built on.
These areas are on higher ground, the water that normally lies in these lakes/ponds is now piped away down hill rapidly and does'nt get a chance to soak slowly and naturally into the soil.
I don't think there's anything unique about my area, so how much has this happened elsewhere in the country?

cian1500ww

Here's a concrete reason:

as above illustrates perfectly we were building massive amount of property over the last few years as much as 88,000 in one year alone. This massive change in land use must have played some part.


Oh yeah and cork city is built on a flood plain

cough cough

syklops

IMO, Any climatologist who goes on air and says the floods are caused by global warming/Climate change is a fool or a liar.

Where I grew up there were fields which always either got water logged or flooded every couple of years. Those same fields flooded this year and there are houses there now with mahogany dressers floating down the hall.

My home town has had the worst floods in over a hundred years since records began, and while we had very bad rain about 10 years ago which caused flooding in the area, the town did not flood that year. What has changed in that time? Some say the earth got warmer, some say it got colder, some say it stayed about the same temperature. The only thing I know for sure that happened is 24 houses were built inside that 10 year period, on a piece of land that no-one ever thought of building on in well over a hundred years.

Birdnuts

The massive destruction of natural wetlands like raised bogs, turloughs etc. over the years has removed huge areas of natural soakage which means water runs straight into rivers at much faster rates then would otherwise be the case leading to increased frequency and potency of flooding. The farming community, Bord Na Mona etc have to share the blame on this one, so too various government agencies and indeed the EU under the flawed CAP regime who grant aided such activities.:(

hiwayman

cian1500ww wrote: »

Here's a concrete reason:

LOL I like the frontage onto the shannon bit

Arnold Layne

And you probably killed Kenny as well. YOU BASTARD!!!:eek:

octo

hiwayman wrote: »

Not sure if this is the right forum for this, so mods, feel free to move.
The floods are all over the media at the moment. and we have climatologists tell us that this will become more frequent because of global warming.
I have another theory. In my local area, over the last 10 years of rapid development, I have seen a number of swamp or winter lakes which are normally dry but fill into lakes after heavy rain, filled in or built on.
These areas are on higher ground, the water that normally lies in these lakes/ponds is now piped away down hill rapidly and does'nt get a chance to soak slowly and naturally into the soil.
I don't think there's anything unique about my area, so how much has this happened elsewhere in the country?

I agree - but where did you hear climatologists say this? Here's what Met Eireann had to say which contradicts that:

Is this part of climate change and can we expect further wet years?

The rainfall pattern, being extremely variable anyway, is very difficult to judge. There is no doubt that Ireland has had three extraordinary years of rainfall, both in terms of the overall amounts of rain and in the number of very intense spells of heavy rain. Such events have happened before and are within the realms of “natural variability” so it is not possible to say that these events have been directly caused by climate change. However, such events have rarely occurred so close together in time or over so many locations so it is reasonable to wonder if this is a feature of a changed climate.

Our best knowledge of climate change and what it may bring comes from computer models of the atmosphere. These models have predicted that, by mid-century, we will see increased rainfall in the West of Ireland and a change in the character of our rainfall to include more frequent heavy falls. However, they have also predicted that we would see significantly drier summers in the East. Long-term climate models are not expected to provide year-to-year detail of rainfall but rather the long-term patterns so it is too early to say that they are correct or not.

In terms of the rainfall detail over an area as small as Ireland, it is not possible to predict how the next few years will go though, as stated before, the expected long term trend is towards a wetter west of Ireland and more frequent heavy falls generally. There is no reason to expect continued very wet conditions over the coming few years.

mike65

Being old enough to have a longish memory of the weather and rainfall I feel there has been a change in the nature of the delivery of rain - the good old days of misty constant drizzle is pretty much over and has been replaced by more pronounced precipitation over shorter periods. If that is the case, add in the concreting over of Irelands river valleys (see pic above) and more frequent flooding instances will surely follow.

The state needs a complete rethink based on a hydrological survey. I haven't heard anything from the Greens on the current flooding and would have expected to by now.

Deep Easterly

This sums up how climate change is predicted to impact in Ireland over the next 50 years or so:

- Temperature: general warming with mean monthly temperature increasing by between 1.25ºC and 1.5ºC. The largest increase will occur in the South- East and East, with the greatest warming occurring in July.

- Precipitation: most significant changes will occur in June and December. Rainfall in June will decrease by about 10% compared to the present while December values show increases in the range of 10-25%.

-Storms: increased frequency of severe storms over the North Atlantic in the vicinity of Ireland by about 15% compared to current conditions.

From IRELAND: National Climate Change Strategy 2007-2012

kerry1960

Indeed Pat, an increase of temperatures might not be welcome by some of us , the chance of increased storminess would not be welcomed by most of us ,and the possibility of a big increase in winter rainfall is something not wanted by anyone , but judging by the reaction of our government to this months disaster in the west and south it could well be time to check your local items for sale ...ie life rafts and arks .

Deleted User

Deleted User wrote: »

as above illustrates perfectly we were building massive amount of property over the last few years as much as 88,000 in one year alone. This massive change in land use must have played some part.


Oh yeah and cork city is built on a flood plain

cough cough

Turns out it was over 93,000 in 2006 alone and over 700,000 since 1998.

Now thats a hell of alot of concrete.

http://www.environ.ie/en/Publications/StatisticsandRegularPublications/HousingStatistics/FileDownLoad,20957,en.pdf

and

http://www.finfacts.com/irelandbusinessnews/publish/article_10008758.shtml

Danno

What measurement of land are those figures?

Danno

Danno wrote: »

What measurement of land are those figures?

The publications dont include that but you would have to discount for apartments and that but still a serious amount of land use change in the past 10 years.

eoinor

Some more info on the causes of flooding:
http://www.opw.ie/hydrology/data/speeches/National%20Hydrology%20Seminar%202001%20No%209%20-%20FLOOD%20RISK%20MANAGEMENT%20-%20STORAGE.pdf
http://www.opw.ie/hydrology/data/papers/Floods%20-%20Causes%20Management%20and%20Relief.pdf

driveshaft

I'm no expert on climate change, hydrology or anything of the like, but one thing I am not short of is local knowledge and the management and behaviour of the River Shannon in county leitrim.

It is accepted that the shannon floods riverside lands in the wintertime, particularly the low lying bogs along the non-navigable section Between Drumshanbo and Leitrim Village. However, when there have been 'exceptional' floods in the area (ie. areas flooded that would not under normal circumstances), and this has been attributable to the holding of water by the ESB in the Shannon system. One interesting point that is always raised is that the flooding experienced on the Shannon is never to be seen on the Erne system 30 miles away, and the only logical reason for this is the fact that the river flows mostly through another jurisdiction and the political problems that would lead to.

It is clear to me that the ESB's policy of holding water in the shannon is the primary reason for the horrendous flooding experienced along the Shannon and likewise in the Lee and Liffey. Water ought to have been released well before the wet spell set in, the fact that this did not happen shows a failure to do as much as watch the weather forecast.

Over the past few days I have been observing the Lough Allen Sluice Gate at Ballintra, which is the first control on the river. It would appear that at that location, by the time it was realised there was a problem, the sluice was in danger of destruction and the only option was to close the suice and allow the water to flow over the top, this resulted in the shannon which is normally 8ft below the level of the lake, becoming the same level as the lake. I have also heard that a similar problem arose at Tarmonbarry, where it was impossible to raise the sluice due to the amount of water flowing over the top.

I also feel that the volume of water entering the river between Ballintra and Leitrim Village is underestimated. There is a large amount of bogland in this area and with the level of rainfall, there would be biblical amount of water entering the system. There is also the River Feorish, which flows from near Sligo Town entering the system at this point.

When you apply this type of mis-management along the length of the Shannon, it is very apparant why the mess ensued. I accept that there was a severe amount of rain and that an element of flooding was to be expected, but if the ESB were actually managing the river (ie looking at rainfall predictions) the problem would have been far less severe.

To cap it off, there is a section of road near Leitrim which floods from heavy rain. It even flooded in July this year. This area flooded when the rain fell, but disappeared without assistance withing 48 hours. If a natural flood could disappear this quickly, could the shannon have done the same if it weren't artificially held back?

octo

driveshaft wrote: »

It is clear to me that the ESB's policy of holding water in the shannon is the primary reason for the horrendous flooding experienced along the Shannon and likewise in the Lee and Liffey. Water ought to have been released well before the wet spell set in, the fact that this did not happen shows a failure to do as much as watch the weather forecast.

Well said driveshaft, there's a good letter to the Indo along similar lines about this the other day, pointing out "Hydropower is more profitable if the reservoirs are full, while flood management is easier if they are empty."

force eleven

Undoubtedly, there has been record rainfall in November,which is a major factor. However, if you check out the site below, it shows ordnance survey maps from the 19th century (historic tab) and early 20th century (25i maps) and overlay the latest 2005 aerial maps onto these. I checked out Ballinasloe for example,where the new Lidl and Hotel were built recently, and you can see they used to be part of the river system and liable to flood. I haven't had time to look at other areas, but recent planning must be a factor in some cases.

http://ims0.osiemaps.ie/website/publicviewer/main.aspx#V1,708536,728158,6