How to infiltrate rainwater in the face of the triple challenge of a high water table, heavy showers and prolonged dry spells? The municipality of Groessen found a flexible, natural and durable solution in Rockflow.

This was the situation

  • In Groessen, just a stone's throw from Arnhem, a solution was being sought for collecting and infiltrating rainwater.
  • Groessen has a high water table. This means that solutions located deep down would be underwater for much of the year.
  • Underground, existing cables and pipes must be taken into account. A solution involving rainwater discharge requires existing cables and pipes to be relaid, otherwise the drainage pipe ends up deep underground, in the groundwater.

The solution: stone wool

The team in Groessen found an infiltration solution that satisfies all the (special) requirements: stone wool. The existing rainwater discharge was replaced by Rockflow linear infiltration and drainage system beneath the road over a distance of 800 linear metres. Using Rockflow, rainwater is efficiently collected beneath the road. Because where the water falls, it is naturally infiltrated into the substrate.

This Rockflow buffer is made from a natural mineral material – stone wool. This material can very quickly absorb up to 95% of its volume in water before gradually infiltrating it into the substrate. This means that infiltration differs substantially from the original drainage pipe solution, where the water is transported. Rockflow results in less strain on the sewer system and helps to restore the natural water balance.

The project in Groessen is an extensive one. For one thing, the sewage drain is being replaced, then the Rockflow components are installed and rainwater discharges from the buildings and the sink water traps are connected to the buffer. The Rockflow system is installed at the same depth as the cables and pipes. Where these are ‘in the way’, Rockflow buffers are split and then connected together using pipes. So there is a connection and it functions as one system. 

Rockflow - Groessen - Stedelijke klimaatadaptatie

The result

The result of this project meets the challenges represented by Groessen in every respect:

A system above a high water table
The groundwater level in Groessen is high. During wet periods, the groundwater level is just below the Rockflow system. Other forms of water were limited or not feasible.

One solution for all the various k-values
The k-values, or infiltration values of the substrate, vary widely from 0.4 metres to 2.5 metres a day. Rockflow's large infiltration surface means that in Groessen it is also able to infiltrate parts of the substrate with a relatively low k-value.

Large-scale and inexpensive water storage
Rockflow can be used to create storage of as much as 30 millimetres. In the ‘traditional setting’, a large pipe was needed in order to achieve this capacity. That would have made the project many times more expensive.

Together with the foremen, the Rockflow team ensures that the system is properly and quickly installed. This means clear instructions being given in advance, and Rockflow sharing knowledge and experience from previous projects. Rockflow's experts were closely involved before, during and after installation.

Learn more about stone wool for linear attenuation and drainage systems:

Related Rockflow projects:

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Roy Janssen

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