Stadsarchief commercial project

Infiltrating rainfall from a 4000m2 roof with no connection to sewerage system




Municipality of Amsterdam


Large unitary infiltration module

Products used

BD Blocks used for infiltration

Total volume

Dynamic capacity of over 200 m3

A high capacity infiltration system offering ease of installation, sustainability and longevity.

Site issues and requirements

For new commercial buildings in The Netherlands, it is compulsory to discharge rainfall directly into the ground (and the local water table) by infiltration – no sewage connection is permissible for rain water.

The Hydrorock solution

The roof area of this commercial project is 4000 m2 and the defining rainfall event was established as 200 m3 of rain in 1 hour (50mm per m2) during a downpour.
The entire parking area has been used to install multiple modules of Hydrorock natural aquifer BD HD 220 blocks.

There are 800 blocks in total, in modules 5 blocks wide and 160 blocks long, with an overall footprint of 384 m2.
Together, the modules have an infiltration surface area of 420m2, a static capacity of 176 m3 and a dynamic capacity of over 200 m3, ensuring the blocks can deal with the heaviest of rain events.

The K value of the soil is 1.5 meters per day, allowing infiltration of 62.5 litres per m2 per hour, per m2 contact surface area. In total, the modules infiltrate 26,250 litres per hour.
At these rates, the entire infiltration module system is ready for the next rain event in just under 8 hours.

Out-performing plastic

  • The Hydrorock infiltration method provided a constant infiltration area (including the bottom of the blocks) of 420 m2 ( infiltrating 26 m3 per hour)
  • Plastic crates, in an identical configuration and size, only achieve an infiltration area of 70 m2 (infiltrating 4.3 m3 per hour), making it impossible to infiltrate 200 m3 within the required time frame.
  • In order for a plastic system to empty for the next rain event, the contact surface area would have increase so much that it became obvious that Hydrorock was the only solution – on size, functionality and price.
  • Hydrorock natural aquifer blocks are made from stone wool and are 100% recyclable. This meets City of Amsterdam sustainability policy which has turned away from specifying non-functioning buried plastics in the soil.

System design

Click to enlarge.

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