Randers Shopping Centre is built on former farmland and has 1800 parking spaces distributed over 8.5 hectares of outdoor areas.
Much of the rainwater drainage from the parking spaces (two out of three sections) as well as roughly 1.3 hectares of roof surface are connected to an existing stormwater sewer (ø800 mm) in the street Merkurvej. Although the car park is constructed using SF stones and grassy areas, substantial rainwater runoff is still expected from here.
The existing stormwater sewer in Merkurvej has drainage from basements (basement entrances) that cannot withstand being dammed up. Permission has been obtained to discharge 746 l/s to Merkurvej, 589 l/s of which are already used by drains from existing catchment areas.
As the flow from the Shopping Centre is estimated to exceed roughly 1,100 l/s every ten years on average, the drainage from the Shopping Centre had to be attenuated.
Each of the two sections of parking spaces were connected to separate attenuation basins from Wavin of 220 m3 and 380 m3, respectively. The flow from each basin was controlled by a Mosbaek CY flow regulator with capacities of 123 l/s and 61 l/s respectively.
The damming up on the car park is so brief and occurs so rarely that it constitutes only a minor inconvenience to users. This made it possible to economise on the basin volume, however.
The project dates from 1997 and the consulting engineering company was Abrahamsen & Nielsen A/S.