13 Havenstraat

Urban tree pit system to prevent flooding and enhance tree growth


Scheidam, NL


Scheidam Local Authority


Urban tree pit system

Products used

BD 340 standard density blocks

Total volume

2.25mᶾ infiltration per hour per tree pit.

A Hydrorock natural aquifer block tree pit system that gave the council  an extremely cost-effective solution capable of effectively dealing with large rainfall events, without any need to connect to the sewage system.

Site issues and requirements

13 Havenstraat is a street in the old harbour city of Schiedam, and was recently renovated. The existing, old rain water sewerage system was failing and damaged, leading to flooding in the area during continuous or short bursts of heavy rain.

The area is commercial, surrounded by either carparks, buildings or roads.

The Local Authority needed an innovative solution in which the existing sewerage system would be made obsolete, flooding would be resolved, and the street appearance and atmosphere would be improved  by greener, healthier trees and shrubs.

The Hydrorock solution

A Hydrorock natural aquifer block tree pit system was adopted to meet all Local Authority requirements.

Each tree pit sub-system was required to buffer and infiltrate/irrigate the rainfall on a 7.5m2 section of road and to buffer and infiltrate 30mm rainfall within one hour. Giving a water volume of 2.25mᶾ  per hour to buffer per tree pit.

Hydrorock provided the Local Authority with the only solution that was able to buffer the rainwater and irrigate trees in a completely green way. For Local Authorities, sustainability is a key specification criteria and in this project, the LA was strongly against placing large volumes of plastic in the ground, due to potential contamination of the nearby sea with micro plastics.

The Hydrorock solution deals with excess water from high rainfall events, filters run off from the road, and the natural aquifer blocks chemically bond many pollutants, cleaning the water before it finally infiltrates into the soil.

Installation and spec

The project was undertaken with minimal disruption, with one section of the road dealt with at a time.

The trees were located between the existing parking spaces and the system was installed around those trees, underneath the spaces to avoid root disturbance. The installation process is relatively simple and even allowed the existing pavers to be re-used.

Because the area was not subject to heavy vehicular traffic, standard-density blocks were used, which have a lower cost per litre than high-density blocks. These were placed with 300mm of over burden, allowing a loading of 3000Kg per m3.

For each sub array, three BD 340 blocks were used at a depth of 1300mm, arranged to the side of the tree under the parking spaces, and one directly in front of the tree. The blocks were connected to ensure fast filling of the sub array.

Not only did the system cause minimal disruption installation but it is also maintenance free throughout its life time.

System design

Click to enlarge.

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