Vienna introduced a smart curb. It will help with irrigation.

The first warm days of this year have once again demonstrated the importance of mature trees in urban streets. However, heat and drought also affect the trees. Vienna is therefore developing and implementing a simple device that channels water from the street directly to the tree as needed. This helps the city retain rainwater at the point of impact, provides the woody plants and perennials with necessary moisture, and reduces the amount of water flowing uselessly into the sewer system.

Most passersby or drivers might not notice the innovation at first glance, as it does not significantly stand out among the curb stones. The special concrete block with integrated technology is called "Schwammstein," or sponge stone, by the Vienna City Hall. Inside the square body is a valve controlled by sensors and a control unit that manages the automated opening and closing of the flow from the street to the greenery. The sensor reacts to water and opens the valve after a pre-defined period. "This delay ensures that the first flowing water containing impurities does not reach the tree, but is diverted in the usual manner into the street drainage. The remaining water then reaches the trunks of the street trees," explains Vienna's planning councilor Ulli Sima. The simple idea also contributes to improving the natural cycle of rainwater and the local microclimate due to subsequent evaporation. It also helps during heavy rain, as water from paved areas does not drain away uselessly, but stays in place and does not burden the sewer system or natural watercourses.

A temperature sensor in the "smart stone" prevents the valve from opening at temperatures below eight degrees Celsius. "This ensures that during the cold period, when vegetation is in winter dormancy, rainwater does not flow in," states Vienna City Hall. The flow meter can also close the valve at the moment when the accumulation of water exceeds the infiltration capacity.

The device receives all the necessary energy from a solar panel placed at the top under a sturdy transparent cover, which, according to the city hall, is designed to withstand vehicle passage. Vienna also installs batteries inside the "smart stone." Its compact and simple design, which does not require connection to any network infrastructure, allows for seamless integration into newly created curbs as well as additional installation into existing curbs and root systems.

"Given its special properties, the sponge stone is suitable for use in accordance with the well-known principle of sponge cities," adds Anita Voraberger from the Vienna councilor's team. This provides the trees with sufficient rootable space even beneath paved areas and also allows for connecting individual root systems, contributing to better storage and subsequent distribution of water.

The innovative curb piece was developed by a specialist from the Vienna University of Technology in collaboration with the municipal road management staff. Vienna placed its first sponge stone in autumn 2021 during the planting of trees in the residential district of Währing, and according to the city hall, the testing phase has proven successful. The water supply to the tree has significantly improved, and the device operates without issues. The currently installed "smart curb" is an enhanced version of the original model and will also undergo testing. As part of reducing the area of asphalt surfaces in the city, partially reviving and enhancing the environment, the city hall again placed the "Schwammstein" in a street with traditional dense development, many parked cars, and a lack of greenery. All trees newly placed in Vienna's streets are also carefully selected with respect to the specifics of the urban environment – from temperature fluctuations to resistance to urine or automobiles.