Using SuDS to manage surface water from a newly upgraded 19.3-kilometers stretch of the A1 motorway, we incorporated a range of innovative storage systems to treat highway contaminants, improve biodiversity and attenuate flow to reduce any downstream impacts.
As part of the upgrade from existing dual carriageway to three-lane motorway various levels of SuDS were used, including trapped gullies, catchpits, filter drains, French drains and petrol/oil interceptors to filter pollutants before releasing back to the environment. Cut off valves were provided downstream of all outfalls and upstream of ponds to contain pollutants in the event of a significant spillage.
The section of A1 was close to several air bases owned by the RAF that expressed concerns about the risk of wild fowl strikes due to the proposed expanses of open water. Attenuation ponds were therefore designed as two-stage ponds: a first stage wet forebay pond planted with reeds masked the permanent water and dealt with pollutants off the carriageway; a second stage dry pond provided attenuation, enabling the discharge to be restricted into the downstream receiving watercourses.