29 October 2019

Various climate-adaptive solutions have been applied in this innovative testing ground in Houten.

Many urban districts have become very grey over the years as gardens have been paved over and there is little greenery left, which means that many of these districts have problems with water storage. The municipality of Houten created a testing area with various green solutions right next to the town hall to gain experience and to apply climate-adaptive innovations.

When designing grey areas (cities and also residential areas), it is important to take into account the increasingly frequent extreme weather conditions. The design must therefore be different. It is important to remove paved areas as much as possible, to make it greener and to create space for water and buffering water for drier times.

Several methods of ‘disconnecting’ (infiltrating all rainwater into the soil or draining it into surface water) have been applied in the experimental garden, as we are used to in the urban environment. In addition, the focus is on step by step ‘coupling’ through effective links to tackle the existing living environment, which has not yet been disconnected. For example, various types of paving grids, more space for beds and the improvement of vegetation with permeable paving.

Installation of a TreeParker as a water absorption system in Houten: optimal combination of green, grey and blue

The benefits of diverting rainwater in TreeParker tree pit
Trees and water infiltration are still too often applied separately. But there are also options where the functions of trees and stormwater management can even reinforce each other. The municipality of Houten shows how multiple functions combined in the TreeParker system lead to a better result.

Multifunctional use of space: green, grey and blue
Uncompacted soil is ideal for the growth of a tree and for the infiltration of water, such as trees in a park. However, in a metropolitan area there is not enough room available for this, as everything is paved. How can we still provide the trees in a paved area with uncompacted soil? This is possible with a TreeParker system, which is a load-bearing construction underneath the pavement, which is filled with uncompacted soil.

Three functions in one location: trees, paving and water storage.

The uncompacted soil in the TreeParker underneath the pavement (grey) ensures that the tree can grow without any hindrance (green) and it allows for water to infiltrate in a natural way (blue).

Optimising the added value of trees
Everyone knows that trees above ground filter our air in several ways. But did you also know that trees purify our soil and water? They do this together with the organisms in the soil and the physical properties of the soil. Rainwater takes a lot of pollution with it as it flows off. Phytoremediation ensures that these pollutants are also broken down and/or absorbed. Phytoremediation is nature’s way of cleaning up pollution, which is often caused by humans. Structural soil cells are ideal to facilitate these natural clean-up operations. In this way, the tree can also offer added value underground for our society and city.

Specific to this application: water absorption system
TreeParkers with a height of 80 cm were installed next to a bicycle shed. There used to be a linden tree on this spot, but it was no longer vital and was therefore removed. The contractor Peek Infra excavated the tree pit to install the multifunctional water storage system. Underneath the TreeParker an extra provision was made to store purified surplus water (water absorption system), which is absorbed by the soil during a dry period so that the tree roots benefit from it. The total system has a static storage capacity of approximately 70 percent.

Artist impression of TreeParker as a water absorption system

Prevent surpluss water
The TreeParker system is fed with water from the roof on the one hand and rainwater on the other hand. This rain falls on the paving and infiltrates the structural soil cells through wide joints. Temporary saturation of the soil is no problem, but it should not last too long, which is why the system is equipped with various overflow facilities. After saturation of the soil, the surpluss water flows through an overflow high up in the TreeParker system directly to the water absorption system underneath the TreeParker units. As soon as this water collection reaches a certain level, an overflow under the TreeParker system ensures that the water is drained away. It is important to know the permeability of the substrate.

Climate-proof design
With this permeable paving and testing ground, the municipality of Houten offers solutions in the field of water problems and responds to floods, but also to longer periods of drought. Space is needed to store this water underground and above ground. It is important to remove paved areas as much as possible, to make it green and to create space for water and buffering water for drier times.