Protecting properties from flooding (inc. coastal defence)

With over 9,500 buildings in the County Borough identified by the Environment Agency as being at significant risk of flooding, this is a key strategic issue for Conwy County Borough. This is the highest number of properties in significant risk of flooding for any local authority area in Wales. A further 8,900 properties are at moderate or low risk of flooding^[i]. Conwy CB also contains the longest section of artificial coastal defences in Wales at 23km.

Based on a National Flood Risk Assessment in 2012, 16,750 properties in Denbighshire were in a flood zone, which is between 20% and 30 % of all properties in the area. The ‘Flooding in Wales’ report identified 3,250 properties as being in severe risk of flooding, with a further, 13,200 at moderate or low risk.

Conwy County Borough is exposed to the combined potential risk from river, tidal and coastal flooding. Urban drainage and surface water problems have also contributed to the county’s long history of flooding. Most of the flooding occurring inland is from the River Conwy and its tributaries. The towns of Trefriw and Llanrwst are located on the banks of the River Conwy; flood risks here are from surface water run-off, sewer systems and also tidally influenced river flooding.

The eastern extremes of the town of Abergele are potentially influenced by the Ffynnon-y-Ddol watercourse and the tidal River Clwyd. Abergele is also at risk from the River Gele.

Conwy, Llandudno Junction, Mochdre, Colwyn Bay and the Ganol Valley are mainly urban areas and are partially exposed to the coast and estuary of the River Conwy and the River Ganol. This is an area of significant importance due to its road and rail networks. In this area there is also a risk of flooding from the River Wydden and the River Gyffin. Surface water and sewer flooding have also been an issue in Conwy.

There is risk of tidally influenced flooding along the whole of Conwy and Denbighshire frontage especially in the urban areas, the main areas of concern are; Llanddulas, Llanfairfechan, Kinmel Bay, Llandudno, Old Colwyn (rail embankment), the town of Conwy, Rhyl and Prestatyn. Risk from tidal flooding also extends up the Clwyd estuary beyond Rhuddlan.

The majority of historic flooding data collated by Denbighshire County Council relates to flooding from ordinary watercourses. The floods in November 2012 were due to the combination of a prolonged period of intense rainfall on already heavily saturated ground in the Clwyd and Elwy river catchment areas which led to these main rivers overtopping as well as some surface water flooding and flooding from ordinary watercourses.

Modelling of future flood risk in Denbighshire using Natural Resources Wales national mapping datasets, estimates that 5,140 properties are at risk of surface water flooding to a depth of 0.1m and 1,579 properties at a risk from flooding to a depth of 0.3m. 89% of these properties are residential properties.

Fluvial flood risk within Denbighshire is located along the main watercourses of the Clwyd, notably Ruthin, the Elwy, St Asaph and, in the south of the county, Corwen affected by flooding from the River Dee. In addition there is flood risk associated with numerous smaller watercourses throughout the county. Communities that have been affected in the past include Ruthin, Denbigh, Llangollen, Corwen, Gwyddelwern, St Asaph, Dyserth, Llanbedr Dyffryn Clwyd and Pwll Glas

[i] Flooding in Wales: a national assessment of flood risk (2009), Environment Agency

Conwy and Denbighshire have both experienced some extensive flooding, from the Towyn floods in 1990 which affected 2,800 properties to the more recent events in Ruthin, St Asaph and Rhyl in 2012/13 that affected almost 700 properties. The last 20 years have seen more than 20 significant flooding incidents affecting this area

In particular the heavy rainfall and stormy weather of winter 2013/14 and subsequent years have highlighted the problems that flooding can cause for homes and commercial properties, with breaches in the coastal defences along the North Wales coast, repeated flooding events in the Conwy valley and closures of major transport routes including the A55 trunk road. Flood prevention is now high on the national political agenda, and with scientists predicting more such extreme weather events in coming years as a result of climate change^[ii], this remains an area of key concern for the Public Service Board.

[ii] ”UK storms: Hammond says climate change ‘clearly a factor’”, BBC News article, February 2014 http://www.bbc.co.uk/news/uk-politics-26213919

Floods are natural events and will continue to occur, regardless of any efforts to prevent them. The danger from flooding will never be eliminated and therefore it is important to focus as much on reducing the disruption that flooding causes as on measures to prevent it.

Flooding already poses a serious risk to the people, economy and environment of Conwy and Denbighshire, and it is likely that changes in our climate, such as increased severity of storms and wetter winters, will increase the risk, as well as the rate of coastal erosion, in the coming decades^[iii]. Communities at risk of flooding and coastal erosion can expect to see those risks realised more frequently and the magnitude of the impacts to be increased. It will not be possible simply to continue to build more and bigger drainage systems and defences in response to this increased risk; the response has to be rooted in the principles of risk management, providing a holistic approach to identifying flooding issues, and managing the risks, and their consequences.

The 2004 Foresight Future Flooding report suggested that the annual economic damages in Wales will rise from £70 million in 2004 to £1,235 million in the 2080s under the most likely scenario.

[iii] Adapting to Climate Change: Guidance for Flood and Coastal Erosion Risk Management Authorities in Wales, December 2011