For the first time, Lapinus, part of ROCKWOOL, has installed their Rockflow water storage and infiltration system under residential streets as a rainwater drain, commissioned by the municipality of Maasgouw (Limburg). The municipality previously installed Rockflow buffers beneath playgrounds and car parks with great success. The rainwater drain used has a total length of almost 3 kilometres. Rainwater from the roofs and streets is channelled via drainpipes and gutters to the underground water storage units, made from Rockflow elements. With an absorption capacity of 95%, the stone wool elements store the water quickly and release it gradually into the ground within 24 hours. Rockflow ensures that stormwater no longer enters the wastewater sewer, thereby preventing flooding in the event of extreme rainfall. With Rockflow, Maasgouw municipality is opting for more effective water buffering and infiltration than gravel or lava cases and crate systems offer. The innovative system stores twice as much water as lava and/or gravel. On top of that infiltration is faster since the bottom surface area of the buffer is available for water to percolate through. “Stone wool has such a high density (pore size less than 40 µm) that sand grains cannot infiltrate the system”, explains Lowie Eijkelhardt, civil technology project leader at Maasgouw Municipality. “The high absorption capacity of Rockflow also ensures that less material is required to achieve the intended buffer volume. Compared with lava cases this is a factor of more than 2. With Rockflow, less than half the amount of soil needs to be excavated.”
Maasgouw Municipality is proactive in Limburg regarding the disposal of stormwater. Rainwater is no longer transported to a purification installation via the wastewater sewer but is infiltrated via infiltration elements in the ground. This has two benefits: wastewater treatment plants perform better if the waste water to be processed is less diluted by rainwater, and infiltration improves the water balance and counteracts depletion of groundwater. The municipality has been replacing old wastewater drains and is placing new infiltration systems since 2008, increasingly relying on Rockflow for these systems. Furthermore, Rockflow has a high load-bearing capacity, as a result of which coverage of only 35 centimetres in depth is sufficient, which is an additional benefit” states Rob Driessen, business developer at Lapinus. “Due to this, the system can be installed very close to the surface of the road, which means it is one of the few systems suitable for locations with a high groundwater level.” Rockflow is also an environmentally friendly system. “Stone wool is made from volcanic basalt rock; a natural substance that is fully recyclable.”
BLM Wegenbouw of Wessem started installing Rockflow from the middle of this year. Engineering bureau Ducot Engineering & Advies of Herten created the Rockflow design and wrote the specifications on behalf of the municipality. A strip of Rockflow 1 metre in height by 120 - 150 cm in width is installed in excavated trenches. The total volume for all the streets is around 2,500 cubic metres. 50 to 70 centimetres of infill sand, a 30 cm foundation of mixed granulate, 5 centimetres of road sand and finally a hard surface of concrete blocks are placed on top of the Rockflow packages. The rainwater from the front of the roofs and the streets is discharged to the stone wool packages via drainpipes, drainage gutters and underground pipework. The packages fill up from the bottom. Driessen: “A stone wool package of 1 m3 fitted with inflow channels fills with water in 10 minutes, which is six times faster than the norm in this project.” The release of the water takes place within a maximum of 24 hours. “This depends on the moisture level of the soil. With relatively dry soil this can be 4 to 5 hours. In the event of full saturation, infiltration is no longer possible and the water is then discharged into the Maas river at four outlets.”
Lapinus was involved in the project from design to implementation. Driessen: “We spent a great deal of time explaining the system beforehand. There were some questions, particularly concerning the load bearing capacity. Clients, consultancy bureaus and contractors don’t usually expect rockwool to be very strong, because it is a light and porous material. In order to fully convince them, we showed them our test location. A year ago, we installed Rockflow in a range of element strengths on our own industrial estate. Every day, 60 to 120 trucks drive over the test surfaces; in that time, not one element has sunk even a millimetre.
That says it all.” Jean-Philippe Janssens, senior water advisor at Ducot Engineering & Advies, confirms this. “At the time the system was being designed, this test was still running. To be absolutely sure that the Rockflow elements would not sag, we did not design one package, but two narrower ones. In retrospect, this appears not to have been necessary and the design was adapted to a single strip, 1.2 to 1.5 metres in width.”
By the end of 2019, all the streets in Old Maasbracht will be fitted with Rockflow. Lowie Eijkelhardt has been very satisfied with the system up to now and doesn’t rule out the conversion of other streets in Maasgouw to the innovative water management system. “I don’t want to put Lapinus on a pedestal, but I am an absolute fan of the product.”