Stormwater tunnel to alleviate flooding next to Mater Dei

Plans for a 600m-underground tunnel could alleviate severe and increasingly frequent flooding problems in the vicinity of the Mater Dei Hospital, by diverting rainwater from the Taż-Żwejt area in San Gwann and occurring at the main hospital access.

The tunnel will be excavated below Triq Sir Anthony Mamo proceeding towards Triq Dun Karm, to eventually connect with the existing flood relief tunnel below the bypass. Oil and grit separators will treat the stormwater runoff from pollutants before flowing into the proposed tunnel.

The San Gwann industrial estate and Taż-Żwejt residential area, as well as the Life Sciences Park, have limited stormwater systems that cannot keep up with runoff from storms, which are also becoming more frequent due to climate change. The tunnel is expected to reduce flooding at the roundabout junction that leads into Mater Dei Hospital, which would also contribute to a reduction in traffic congestion while improving accessibility to the hospital during storms.

It is hoped the tunnel will divert and collect 20% to 30% of the rainwater catchment of the area, reducing the damage to habitats in the Għollieq valley during flash floods, whilst still keeping 70-80% of the runoff flowing into the valley to sustain the existing biodiversity.