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A total of £15m is being invested in a Carmarthenshire town as part of an innovative scheme to manage surface water and help reduce flood risk.

Dwr Cymru Welsh Water's RainScape initiative will reduce the amount of rainwater which flows into local public drainage systems in the Llanelli area.

It will see a swale - a shallow, vegetated channel - installed on a local playing field.

Llanelli currently has a combined sewerage system.

That means that rain falling on roofs and roads is combined with the sewage in pipes.

Traditionally, the company would have built big concrete structures and storage tanks to hold the surface water back.

But Fergus O'Brien, the coastal waters manager for Welsh Water who has co-ordinated the scheme, said Llanelli has so much rainwater that the storage tanks would be enormous and the size of 200 Olympic-scale swimming pools.

"The main thing is that it doesn't deal with the fundamental problem which is that we're putting too much clean surface water run-off into the network, where it becomes contaminated with sewage before it seeps out again," he added.

Instead, he said the swale will separate the rain water and slow it down, with the hope that most will eventually soak back into the ground and go into local natural waterways.

Welsh Water said it was particularly needed in the area as Llanelli saw almost as much storm water in its network as Swansea, which serves three times the number of properties.

It means that some properties in Llanelli can be affected by sewage flooding.

The first part of the scheme saw a swale installed at Queen Mary's Walk football pitch, which will be landscaped with a range of plants and flowers.

The company said the playing field would not be affected by the scheme.

Minister for Natural Resources and Food Alun Davies, who launched the scheme, said it was the first of its kind in Wales.

"As well as providing a practical solution to reducing the impacts of excess surface water in Llanelli, the scheme will also benefit the community through the creation of new jobs and improvements to the local landscape," he added.

Welsh Water said the initiative was similar to schemes in Malmo, Sweden, and Portland, USA, where sustainable drainage systems have reduced flooding, enhanced biodiversity and kick started regeneration.

Nigel Annett, managing director of Dwr Cymru Welsh Water, said: "We expect this innovative and sustainable approach to bring similar benefits to Llanelli and the surrounding area."