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They resemble an ordinary garden, but are a much more complex design. They consist mainly of plant species that are not only decorative but also purify water. The main purpose of rain gardens is to collect and utilise rainwater from nearby areas, including hard surfaces. They can be designed either as a rainwater filtration system or as a sealed system, serving primarily a retention function. Rain gardens enhance biodiversity, as they become a welcoming habitat for small animals and insects.
Rain gardens in urban areas improve people’s quality of life and health by reducing the formation of urban heat islands in summer and decreasing the volume of rainwater flowing into overloaded drainage systems. Through the use of appropriate vegetation and filtering layers in the substrate, a rain garden can pre-treat the water and allow it to infiltrate deeper into the soil. In this way, rainwater is retained within the landscape. If ground conditions are not conducive to water infiltration (e.g. where there is clay soil or another impermeable surface), a rain garden can be created in a container or as a sealed system in the ground.
The locations of rain gardens are not chosen at random – we select sites where there is a problem with the proper management of rainwater. That is why we create gardens along streets, such as Płochocińska Street, whose purpose is to capture water from the road surface.
We have also created a rain garden in the area of Olszynki Grochowskiej Street by the Kawęczyński Canal (Praga-Południe). Here, rainwater from hardened concrete surfaces used to be drained directly into the canal and on to the Vistula. In this way, we lose water from the city instead of managing it. This garden captures water from the pavements, supplies the plants in the garden, and only the excess water generated during heavy rain is drained into the canal. We deliberately placed the garden near the footbridge, where many residents walk – in this way, we educate people on how to conserve urban water.
We have created such gardens in areas including Białołęka and Praga-Południe, as well as in road verges and parks that have undergone redevelopment – Pole Mokotowskie, the Park of the Cichociemni Paratroopers of the Home Army, and the ‘Burza’ Operation Park – also as part of projects funded by the participatory budget.
In 2022, as part of the Participatory Budget, we implemented two projects involving rain gardens, in the form of planters fed by rainwater from building gutters. Six locations were selected, for which over 50 rain garden planters were installed. The locations are mainly schools and public urban spaces.
A rain garden and a meadow in bloom on Rosoła Street.
We are installing weirs and flow control devices on selected canals. In doing so, we are changing the function of the canals from drainage (water discharge) to irrigation. The weired-up canals create a water reservoir that is vital for nature and the habitats of plant and animal species. In doing so, we supply water to plants in the riparian zone, reduce water runoff from the city, replenish groundwater and increase retention. However, we must remember that climate change also leads to more frequent occurrences of torrential downpours. The canals must therefore be prepared to drain rainwater and cope with sudden floods. That is why the water levels we create are not high, so that the remaining capacity of the canal allows for the absorption of any sudden downpours.
We limit the outflow of water from Warsaw’s canals into the Vistula, redirecting the water flowing through the canals to places where it is more needed. Water reservoirs are, to a large extent, interconnected vessels – by damming water in the canals, we can influence water levels in lakes and ponds, which also has a positive impact on the environment.
We are building sluice gates to aid water retention. Water retention is important because, by limiting water drainage from the soil, it improves groundwater levels and, as a result, increases groundwater reserves. This benefits wildlife. Retaining water in the soil not only improves the natural conditions of the area but is also important for mitigating the negative effects of climate change.
Where there is a low risk of local flooding, we do not mow aquatic plants.
We ensure an adequate water supply to reservoirs and maintain them, whilst minimising water outflow.
When filling artificial reservoirs in parks and squares, it is particularly important to minimise the loss of water drawn from the municipal network as much as possible, so as not to exacerbate the difficult situation caused by hydrological drought. In order to minimise the strain on the water supply network caused by increased water consumption, reservoirs are filled over an extended period, using the minimum possible water flow.
We ensure the water in the reservoirs remains clean. We carry out regular water quality tests, which enable us to take measures to restore the biological balance of the aquatic environment.
Planting of aquatic plants to support water purification in the Brustman Ponds.
As part of ZZW’s tasks related to the restoration of water retention in the city, we carried out a project with GPOOS in 2021–22 entitled “Construction of water intakes from the bed of the Służewiecki Stream to restore the retention function of 10 ponds in the Służewiecka Valley, located within the Mokotów and Ursynów districts of the Capital City of Warsaw. Restoration of water retention in the Służewiec Valley reservoirs through the construction of two water intakes feeding from the Służewiec Stream. Restoration of water retention capacity to 27,000 m³”.
