This innovative system is used under built-up areas, such as squares, roads, streets and industrial sites, that suffer from severe flooding during heavy rainstorms. The system consists of thin (standard element 100 x 120 x 15 cm), light (less than 20 kg) stone wool elements that absorb the rainwater and then infiltrate it in a measured manner into the soil layer or drain it to the sewers. Lapinus is the first producer to apply stone wool elements as a water management system and to bring them onto the market. "The Rockflow elements provide an optimal water balance during heavy rainfall," says Daan de Kubber, Marketing & Business Development Manager at Lapinus.
Flooding can occur on stone surfaces during and after a heavy rainstorm because the excess water cannot drain away into the soil and through the sewer system quickly enough. If the rain is coming down in buckets over a short time, a huge amount of water has to be collected and drained. The sewage system cannot handle this enormous amount of water, which is why streets and cellars flood. Capturing and draining the water faster avoids flooding. The stone wool elements can absorb 95% of their volume of water and have a throughput of 200 metres a day. A cubic metre of Rockflow system can take up 950 litres of water in 8 to 10 minutes. "This is more than enough to create water management systems that meet local standards," says De Kubber. Once saturated, the stone wool element can allow the water to infiltrate the substrate or drain to the sewer gradually, spread over 24 hours.
De Kubber has been involved in the development of Rockflow from the very beginning. He says that buffering water with stone wool is a method that is widely used in greenhouse construction. "In greenhouses, it’s used for growing plants on. We have developed stone wool elements that can not only store huge amounts of water very rapidly, but are so strong that they can cope with the load of a full parking deck or trucks that drive over them.”
More and more municipalities are becoming interested in this innovative water management system. Within each municipality, there tends to be an area that is regularly flooded. "Not only has the rain become more intense due to climate change, the current design of the sewer system also contributes to the problem. The sewers in the Netherlands were built eighty years ago and were not designed for the capacity that is necessary today. The problem of excess water is becoming increasingly urgent.' De Kubber: “Rain showers are becoming more extreme due to climate change; the sewers can no longer drain away the water and the streets become flooded. This is happening while more and more surfaces are being hardened in the Netherlands. Resulting in even more damage. Municipalities are often liable for the damage caused by flooding. These municipalities thereby know that they need to take strong measures in the short term to combat increasing flooding."
Replacing the sewers is an expensive process. It is much cheaper to capture the surplus of relatively clean rainwater and to gradually drain it away or allow it to infiltrate the soil. Many urban areas in the Netherlands suffer from a lack of water. "It’s a waste to guide the relatively clean rainwater through the sewers to a water purification plant. Rockflow allows the collected clean rainwater to slowly seep into the soil, causing the water balance to be slowly restored,” says De Kubber.