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Climate change adaptation

Nature based solutions


Rockflow for water management – natural solutions for sustaining water resilience

22. November 2019
Rainfall, rockflow

Solution provider


At ROCKWOOL, we transform volcanic rock into stone wool and our products contribute to address many of society’s biggest climate change challenges, creating new opportunities to enrich modern living and build safer, healthier, and more climate resilient communities.

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Due to climate change, we see more and more heavy rainfall. In addition, more land is being paved or surfaced, and as a result water can no longer drain into the soil and must be disposed via the sewer systems. Especially in urban areas, stormwater causes streets to flood more frequently. The main reason for this is the insufficient capacity, of the existing sewer system, to transport the water.

Rockflow is an innovative water management system that buffers the stormwater quickly and effectively. Depending on the local legislations and situation, the water infiltrates the soil or is gradually discharged to the sewer system . The solution prevents flooding and helps to restore the natural water balance in urban areas.

The Rockflow elements are made of natural stone wool, which can absorb up to 95% of their volume in water without losing form or strength. At the end of their life span, the elements can be fully recycled in one of the ROCKWOOL factories into new stone wool products.

In September 2017 Copenhagen experienced cloudbursts, where sewage systems gave out and while basements and roads were under water. As a result, Rockflow was installed in the city. At Langelands Plads in Frederiksberg, near Copenhagen, Rockflow, is used for collecting and diverting excess water at a controlled pace - thereby countering flooded cities.

The violent cloudbursts that has hit cities around the world in recent years are not a passing phenomenon. They are part of the new reality that cities, citizens and all aspects of the building and construction value chain must take into account. Unfortunately, the infrastructure in many cities are not built to handle the rising waters, which results in flooded roads, cellars and insurance claims in the millions.

Climate change is here now and will still be here tomorrow. The likelihood of bad cloudbursts within the next 50 years is great - and especially in big cities.

A flexible product with high performance

Rockflow is similar in appearance to the well-known insulation material that ROCKWOOL Group is known for, but the product's properties are significantly different. Rockflow has a void volume of 95 percent, which means that a block with a volume of 1 liter of Rockflow can absorb and retain 950 millilitres of water. Furthermore, the Rockflow elements are strong enough to hold the weight of daily traffic when placed under a road. Additionally, the material is extremely flexible and suitable for renovation projects in the cities, where existing underground infrastructure, such as cables and piping, increases the need for a solution that can be adapted to all situations. Although construction is planned from official records of cables and other installations, often another reality is encountered when the excavation work begins. In these cases, it is an advantage to be flexible.

Langelands Plads shows the way

There is a need for urban renewal projects as well as for new construction to think about water retention rather than just diversion. The reason being that the current network of sewers, especially in existing urban areas, is not able to handle the amounts of water generated by the most severe cloudbursts, which only become more frequent.

Before, T-100 incidents statistically only occurred once per 100 years, but today it is not unrealistic to experience three of that kind of cloudburst in a year. The project at Langelands Plads has therefore been built to handle a 100-year incident, as evaporative basins on the parking garage and two large delay pools under the roads have been made.

The solution improves wellbeing and supports a liveable city. It saves cost of damages to buildings and infrastructure caused by cloudbursts in a sustainable and futureproof way.

The installation

The project at Langelands Plads was divided in four sections that interact with each other in case of rainfall. Rainwater is being led to Rockflow buffers, which are strategically located under the road on both sides of the square. The Rockflow buffers absorb the water and gradually release the water over time to the existing sewer system. As runoff water in Denmark is considered polluted, the water will be transported to a nearby filtration plant. By using this mechanism of delayed discharge, the sewer system can transport the water over a longer time-frame using the existing infrastructure.


Rockflow benefits

Rockflow is utilised for water nuisance in streets, in squares and in suburbs, when decoupling areas from the sewer system and when (re)designing water retention areas.

  • Rockflow is custom designed
  • Smart water management using Rockflow from Lapinus is always custom designed. In its simplest form, it consists of buried and covered stone wool elements which release buffered water into the soil in a regulated manner. For more complex problems, for example in intensively built-up urban areas, or beneath roads or industrial estates, the system is designed, dimensioned and calculated in conjunction with engineering agencies. In that case, the stone wool elements are connected to a carefully-designed system of pipes, drains, gullies and (stone wool) filtration cassettes.
  • High drainage and buffer capacity
    Rockflow stone wool elements can absorb 95% of their volume in water within a very short time and have a throughput speed of 200 metres per day.
  • No loss of urban space
    The basic material is stone wool, which has all the properties of rock. Vehicles can park on top of the system without the elements becoming deformed or losing any functionality. All urban functions therefore remain unaffected.
  • Self-filtration
    The structure of the stone wool elements filters any contamination from the incoming water, as a result of which the system never becomes clogged. The system continues to infiltrate from the bottom, even without the use of geotextiles. Furthermore, stone wool filtration cassettes can be applied at the entrance into the system or in filtration pits. The elements are easy to replace and are fully recyclable.
  • Custom design
    The stone wool elements are easy to adapt, without loss of functionality during and after installation (without harming quality and performance), so that any pipes or other obstacles in the ground do not represent a hindrance.
  • Sustainable
    Stone wool is a natural material (made from natural rock) which is produced sustainably by ROCKWOOL. Stone wool is 100% recyclable.