We all know however that more paving makes it more difficult for rainwater to penetrate back into the earth, particularly in parking areas as they are subjected to more ground compaction from the weight of parked vehicles. This is particularly the case here at Jumbo and snackbar parking lot where a naturally high water table has left the surrounding land, parking and access plagued by surface water. For this reason, the Rockflow water management system was installed around these areas. The system, which is made from 100% recyclable stone wool is installed beneath the parking lot of Jumbo supermarket. The system acts to effectively store rainwater underground during extreme rainstorms. After buffering the rainwater, it will be infiltrated into the subsoil. Groundwater is thus recharged naturally, rather than placing pressure on the sewer system. Here the system buffer measures 12 m x 28,8 m, with a height of 0,5m. The system is equipped with sensors to measure and monitor the system’s operation.
The Rockflow water management system has been designed to buffer a rainshower of 35,7mm per hour. The total paved surface (the roof of the Jumbo supermarket, the parking lot and a part of the street) that has been disconnected from the mixed sewer system (and that has been connected to the Rockflow system) is around 4.500 m2. Due to high infiltration rates of the subsoil, the buffer will be empty and available for the next rainshower within 24 hours (according to water management legislation the system has to be available again within 24 hours). Jan Heemskerk from Jumbo supermarket is enthusiastic about the redesign as the front entrance with additional parking spaces makes the entrance a lot bigger and nicer for patrons as well as the local fishmonger. And certainly, reducing flood and clean-up time and costs is an added bonus for the businesses. The project attracted significant interest and cooperation from residents. Approximately 220 residents were present at the first walk-in sounding board meeting. Zonnemaat has since become a pilot project that is used to encourage other projects of the like.