Context
The City of Vienna and its municipal districts aim to enhance the quality of life in the urban environment through green spaces and trees, because they play a crucial role in mitigating heat, especially during the warmer months of the year. However, urban trees typically have considerably less space and the rainfall available is too low to ensure optimal growth conditions. Due to the effects of global warming, there is also an increase in the occurrence of heavy rainfall events, which pose a challenge for the city’s drainage systems and sewer infrastructure. Currently, surface water in urban areas may not be simply allowed to flow into green spaces, as the water may be contaminated. Therefore, a solution is needed to make the best possible use of rainwater as irrigation for green spaces to create better growing conditions and simultaneously relieve the strain on the sewer system during heavy rainfall.
The Schwammstein (English: sponge stone) consists of a concrete body that can be seamlessly integrated into the kerb edging of a tree slice. The dimensions of the stone match the dimensions of the granite kerbs used in the federal capital Vienna. A valve is located in this concrete body, which is controlled by sensors and control electronics. A sensor detects the presence of water in the event of a rain event and opens the valve after a precisely defined time. The power supply is independent of the grid using solar energy, including a battery.
Objectives
Given these limitations on natural water sources and the need to manage storm water run-off, the Schwammstein – sustainable irrigation of green spaces – was developed. The overarching goal is to ensure a pleasant microclimate in the city with efficient means. Maintaining green spaces and irrigation systems is generally labour-intensive, causes costs in both construction and ongoing operation, and has a relatively high consumption of drinking water. By using the Schwammstein, the city intends to save both natural and financial resources. On one hand, it aims to reduce the use of drinking water for irrigation while simultaneously increasing water supply to the soil and vegetation, which can – in the long term – contribute to supporting the natural water cycle and groundwater replenishment. On the other hand, the goal is to save costs in water consumption, water disposal and infrastructure.
Implementation
The Schwammstein emerged from a collaborative effort between the City of Vienna – Road Management and Construction (specifically, Municipal Department 28), and Schwammstein one GmbH, a start-up company. The project team, comprising three dedicated employees, has been working on this initiative since 2019. To ensure seamless coordination and planning, additional personnel from Vienna Parks and Gardens (Municipal Department 42), Water Management (Municipal Department 45), and Waste Management, Street Cleaning and Vehicle Fleet (Municipal Department 48) were engaged as needed. In 2021, the inaugural Schwammstein pilot took place in in Vienna’s 18th district. The subsequent months of testing proved successful, with no significant dirt accumulation or blockages observed in the inlet area. Additionally, there were no incidents of vandalism. Most importantly, the water supply to the tree pit experienced noticeable improvement.