Floods should be a major wake-up call for planners

November 21 2009 04:44 AM

One of the major causes of the flooding is the exceptionally high November rainfall, already well beyond normal amounts for the month and likely to set new records in many parts of the west and south.

Rainfall

In Galway, it has exceeded the highest amount ever recorded for November with 10 days to go until the end of the month and more rain forecast.

Galway's record rainfall for November, until this year, was in 2002 with 211mm.

And by Wednesday of this week, the total had already reached 238.7mm with more to come and is likely to exceed 300mm by the end of the month.

On Tuesday alone, in Galway, 60.8mm of rainfall was recorded and that's exceptional.

As a result, all the river and drainage channels were already full and the ground was completely saturated by the start of this week.

In addition to the ground being saturated to the point where there was no longer any spare capacity, there was also no spare capacity in drains, streams and river channels.

Over the past few days, we've had sustained rainfall dumping high amounts of water into this already saturated environment that was already overflowing in places.

As a result and unsurprisingly, this had led to significant flooding, the likes of which we haven't seen for at least 20 years -- 1986 comes to mind -- and possibly longer.

In addition, for many coastal cities and towns high tides can play havoc with floodwaters in the rivers and streams.

High tides effectively stop rivers removing floodwater into the sea. Instead they cause a build-up of water, and as a result increase the size of the flood-affected area and the height of the floodwater that occurs.

Obviously, there is some relief when low tide occurs but at the next high tide the problem re-emerges.

The combination of these circumstances means many areas that had previous flooding problems were really badly affected. Many areas that hadn't previously experienced floods for a long time or not at all are also being hit.

Floodplains

One of the key issues in understanding the scale and devastation is to assess how much of the affected areas was built on floodplains. There is no doubt that some of the building that took place over the past 20 years was on floodplains or in places which are so low-lying that they were unsuited to development in the first place.

This includes both housing and infrastructure such as roads. A lot of this development took place over a time period and in areas where no major flood events had been experienced, probably as far back as the 1986 flood or even beyond that.

Floodplains, by definition, mean floods. The question is: how often and to what extent?

Clearly, building on floodplains requires careful planning with a long-term view because even if an area hasn't been flooded for a few decades, the threat has not necessarily gone away. A lot of flooding in the west appears to be affecting reasonably new houses in rural areas built in unsuitable locations whether on floodplains or in hollows and other low-lying areas -- areas which are likely to start to fill with water given the meteorological circumstances of the past week in particular and all of this month.

A well-known saying is that "you should never build in places where people haven't built before". The reason is very simple -- these areas were in the past identified as unsuitable for development, and this is something we have not taken heed of.

Global warming

Although we can't say for definite that current events are due to climate change, which is concerned with long-term trends, they are the type of storms and flooding we would expect given the global warming predictions for Ireland.

The predictions are that there will be increases in winter rainfall in Ireland, mostly in the form of more severe individual events, and these are likely to cause flooding. In addition, these rainfall and flood events are likely to become more frequent as the century progresses. The recurrence interval of these events is likely to become much shorter, so a one-in-40-year flood in future might become a one-in-10-year flood or even a one-in-five-year flood.

So there clearly is a need to plan our developments much more strategically and to make sure our key infrastructure is not vulnerable to the weather.

This will present a significant challenge to the Government and the county councils and city corporations to plan long term for the likely consequences of global warming.

It may be the case that this series of floods has shown us where we are already very vulnerable to climate change and they should be seen as a major wake-up call across the board politically.

This brings us to the upcoming Copenhagen gathering where it is hoped that a new global agreement on global warming can be reached that involves all the countries of the world and where Ireland must play a key part.

This is necessary because a replacement is urgently needed for the Kyoto Protocol. This will also set the agenda for dealing with the issue of global warming into the future.

Dr Kieran Hickey is a lecturer in physical geography at NUI Galway and is author of 'Five Minutes to Midnight? Ireland and Climate Change', White Row Press, Belfast

Floods should be a major wake-up call for planners

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