Some more plants, some less paving; the changes in Theo and Mieke’s garden seem minimal. The biggest intervention is under the ground. An infiltration system was installed there that collects all rainwater. With blocks and crates …
Disconnect the downspout and collect water
The pavement of the garden had been uncomfortable for Theo Keizer, owner of an interior design agency. “I thought that some things had to be ‘worked up’.” His wife Mieke was less happy with the plants. Reason enough to take a closer look at the entire garden. It started with ideas for minor adjustments and ended with the decision to disconnect the two downspouts. Theo: “A design must have depth. In other words: besides being fun, it is also functional and environmentally friendly. “
The infiltration plan was devised in collaboration with Elke Blänsdorf, Anneke Beemer and foreman Robert Koelewijn (Amerongen ornamental pavement). A system of infiltration crates is connected to one downspout, and to the other a system of infiltration blocks made of pressed rock wool. Both infiltration systems form a hollow
the space in which a large amount of water can be collected. In the new situation, all rainwater sinks into the soil.
When installing an infiltration system, you need to know exactly how much storage capacity is needed. This is different for every garden, and it depends on the permeability of the soil, the size of the roof, and the amount of paving in the garden. Theo: “We have sandy, loamy soil and the total roof area is 84 m². That is why we assumed a required storage capacity of 25 liters per m² of the roof surface. This is taken quite broadly so that we can also
To prevent the system from becoming dirty or overloaded, a leaf separator was connected to the downspouts. A leaf separator filters the coarse dirt and also provides
Ventilation. In heavy rainfall, it also serves as an overflow. Theo: ” But that has not happened yet. Even during peak showers of more than 40 mm per hour, the storage capacity was always sufficient. ” A sand trap has been placed between the rainwater drainage and the blocks and crates. It captures the fine particles. The two sand catchers are concealed invisibly under a layer of gravel.
Under the carport
Because underground infiltration systems can even support a car, part of it has been buried under the pavement of the carport. The pavement has been reused and partly replaced by gravel, which is more permeable to water. “We consciously chose river pebbles for this,” says Theo, “because they come from close by.” The pebbles are fixed in galvanized grids and not in plastic honeycomb plates, which are often used for this purpose.
Also, a conscious choice, says Theo. “We found this material to be much better suited to the whole.” Another nice detail is the gravel edge at the house, which makes it ‘separate’ from the environment. Theo: ” Moreover, there will be no splashing water against the facade. The galvanized grids of the garden bench are a nod to the grids used under the carport. ”
Two infiltration systems
The infiltration facilities in Theo and Mieke’s garden do not form a water buffer for the plants. They are for infiltration and drainage only.
The soil above the blocks and crates can even be drier in dry periods.
Two systems have been used:
- Infiltration blocks are made from pressed rock wool. This natural material absorbs rainwater with a capacity of 94% by volume. The blocks are easy to install yourself. There are blocks with built-in pipes that can be connected to the rainwater drainage. There are also blocks that can be placed without pipework, for example at the edge of a terrace or path.
- Infiltration crates are made of recycled plastic with a lot of hollow space in between. They are wrapped in geotextiles. This usually happens in the garden itself. Geotextile prevents sand or roots from entering the infiltration system. Infiltration crates are cheaper than blocks, but placing them requires more expertise.
- The distance from the infiltration facility to the facade must be at least 1.5 m. The bottom of the infiltration facility must be 15 cm above the average height of the groundwater.
- Above the crates a minimum of 50 cm of (crushers) sand must be placed, above the blocks a layer of at least 15 cm is sufficient. A layer of sand must also be placed under the crates and blocks.