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December 2015 flood facts

Some fact about the dangers of flooding and a summary of the 2015 flood event


There are:

  • 208,500 properties at risk of river or sea flooding, around 11% of all properties,
  • 163,000 properties at risk of surface water flooding (some overlap with above)
  • 73,000 of these benefit from flood defences
  • 2,000 properties at risk from coastal erosion in the next century

Costs and investment

  • Flooding in Wales cost an estimated £71 million between Nov 2011 and March 2014
  • Dec/January storms of 2013/14 caused £8.1 million of damage to flood defences but costs avoided due to flood defence investment is estimated at £3 billion
  • £165 million invested in flood and coastal erosion risk management in Wales between November 2011 and March 2014 reducing the risk to 6,700 properties

Assets

  • 319 miles of defences maintained by Natural Resources Wales (NRW)
  • More than 4,000 flood defence assets owned by NRW

Flood awareness

  • Flood forecasting service delivered for 173 locations in Wales
  • More than 97,000 people registered to receive free flood warnings via Floodline Warnings Direct (a shared service between NRW and the Environment Agency)
  • More than 1,000 communities and individual businesses in Wales now have their own pre-prepared flood plans in case the worst was to happen

Severity of December 2015 event

Met Office records, backed up by NRW data indicate that Wales had the wettest December on record, going back to 1910. Despite that, we have not seen comparable record widespread flooding in Wales which you might expect for – there have been far worse winter months for flooding. Our records show, for example

  • 996 millimetres of rain at Cwm Dyli, Snowdon, in December
  • our rainfall gauge in Bala shows it was the wettest since records began in 1961
  • river levels on the Conwy, Glaslyn and Dyfi peaking at record levels

Investment in defences, warnings etc over last few decades has had a positive impact, but the pattern of rainfall in Wales last month also probably played a significant role:

  • the worst was focussed over NW Wales, much less in the South
  • it was persistent and sustained in duration rather than being more concentrated in a short time period

River levels

December 2015 was an exceptionally wet month resulting in exceptionally high river levels at several gauging stations, particularly in North West Wales with several rain gauges in North Wales recording more than 200% of the long term average for that month. The highest river levels on record were experienced at:-

  • Afon Seiont at Peblic Mill - the highest peak since records began in 1976 (the previous peak was in November 2009)
  • Afon Llyfni at Pont y Cim - the highest since records began in 1995 (the highest recent peak was in November 2012)
  • Afon Gwyrfai at Bontnewydd - the highest since the gauging station rebuild in 2009

The 2nd highest river levels on record were experienced at:-

Afon Conwy at Cwmlanerch – second highest since records began in 1964 (the highest peak was in November 2009)

Afon Elwy at Pont y Gwyddel - second highest since records began in 1973 (the highest peak on record was in November 2012)

Afon Elwy at St. Asaph - second highest since records began in 1997 (the highest peak on record was in November 2012). 

Case study – Dolgellau

Improvements to existing walls and building new defences and floodgates, has increased protection from flooding for over 300 properties in the town.

Work on the £5.6 million scheme began in September 2014 and completed in Autumn 2015. In December 2015 the river Wnion rose to levels which were higher than the previous defences and without the new scheme properties in Dolgellau would have flooded. The Minister for Natural Resources is due to officially open the scheme on 25 February 2016. 

We are encouraging people who live or work in the area to register for free flood warnings. Around 150 people have already done so, providing essential time to prepare and take action if a flood threatens.

Case study – Llandudno Junction

Although only 3.2 kilometres long, the Wydden has a total of 41 flood defence assets, 4 flood storage areas and one major asset along its length. The scheme, completed in 1996, and which was upgraded in 2012, provides added protection to 200 properties from both fluvial and tidal flood.

Over Christmas 2015 the flood defence system on the Afon Wydden operated four times. Without the system many homes would have been flooded on each occasion. The most recent flooding resulting in significant damage to property occurred in 1993. No serious flooding has occurred since the completion of the flood defence scheme in 1996. 

Other sites

Our data shows that properties in Porthmadog, St Asaph, Beddgelert, Aberdaron, Lanfair Talhaiarn, Bangor, Bangor on Dee and Bala would have flooded this December without their defences. Defences in Conwy Valley in Llanrwst also prevented worse flooding from happening here. In south Wales NRW defences helped prevent flooding in St Clears, Tregaron and Abergwili.

Flood warnings

NRW issued 55 Flood Warnings and 178 Flood Alerts in Wales during December. 

Developments in flood risk areas

NRW assess approximately 900 planning applications in flood risk zones each year. Our work supports Welsh Government policy to steer development away from areas at flood risk wherever possible and if there is no alternative then the development’s location and design should mean that it is safe for people.

Around 96% of Planning Authority decisions are in line with our advice, either in rejecting the application or amended to meet our advice. We object to developments that fail to show the flood risk, either to or from a proposal, can be managed.

The aim is to guide development away from areas at high risk of flooding. This is easier to achieve at the strategic planning stage where alternative sites, at lesser risk of flooding, can be identified.

Roles of different agencies

NRW is clear about which rivers, drainage channels and assets it is responsible for and has a maintenance programme in place to check these before a major rainfall event to make sure they are working as well as they can. We were out regularly over the Christmas period making sure that trash screens were clear, pumping stations in good working order etc. Smaller watercourses and surface water flooding is the responsibility of Local Authorities. We work hard to join up with Local Authorities, emergencies services in a multi-agency response.

Dredging

NRW has an annual programme to de-silt water courses which it is responsible for and where it can make a difference.

We regularly undertake watercourse maintenance in communities which are at high flood risk, both rural and urban communities. This includes removing sediment from channels, managing in-channel vegetation and clearing obstructions and gravel. Examples from 2015 and 2014 include

  • the River Severn at Llanidloes
  • the Camarch at Beulah, Powys
  • the Thaw at Cowbridge
  • the Usk at Brecon
  • the Clwyd at Llandyrnog
  • the Wnion at Dolgellau

However dredging is often not the answer, and can make the problem worse by simply transferring water quicker to cause flooding downstream. It can also increase erosion of river banks and flood defences, damage the environment and impact other land users and rural businesses. The number of places dredged varies from year to year according to need and the level of flood risk.

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