Rain gardens, or therapy for gated cities

Water can be too much, too little or it can be too polluted. These are the three main problems we face, especially in urban areas. In recent years, we have increasingly been experiencing the alternation of two, one might say opposing phenomena: periods of drought interspersed with heavy rainfall, creating urban flash floods.

It seems paradoxical – on the one hand, water is scarce to the point that urban greenery has to be watered with this tap water, while on the other hand, heavy rains flood streets, overload sewers and cause flooding. The reason? The sealed surface of cities and the lack of space to hold this water and slow its runoff. Climate change is only exacerbating this water paradox, and local governments, urban planners, and the many NGOs and community groups coming out with grassroots citizen initiatives, are facing a huge challenge today: how to restore water to its rightful place in the urban landscape.

Rain gardens, a blue-green answer to a gray problem

More and more experts are speaking out: if we want to strengthen cities’ resilience to climate change, we need to bet on nature-based solutions (NBS). This is not just a fashionable buzzword, but a concrete strategy for planning space using natural processes. According to municipal climate change adaptation plans (MPAs), every city in Poland should increase the area of greenery-related land capable of retaining water. Warsaw, for example, envisions in its strategy to increase local retention by 10 percent by 2030, and Wrocław to create 100 new green retention points within a decade. Łódź has included the ecohydrological concept of the Blue-Green Network in its development strategy [1] and plans to plant 50,000 new trees and renaturalize by 2030. 10 sections of rivers within the city.

Among the many NBSs, rain gardens – small but effective pieces of blue-green infrastructure that can retain rain and make use of it locally – occupy a special place. It is increasingly possible to obtain funding for this type of investment, as exemplified by Lodz’s Collecting Rainwater program.

Energize nature, not storm overflows

A rain garden is a specially designed piece of greenery designed to capture and treat rainwater. It can take the form of a depression in the ground – a natural basin into which water from roofs, sidewalks or parking lots is directed. Due to limited space, an alternative may be rain gardens in containers (container gardens), which operate on a similar principle, but work well where it is not possible to incorporate a new system into the ground, such as in highly compact urban areas, in courtyards, backyards or against the walls of buildings.

This is a good choice, among others, for schools, universities, public facilities where mobility is important and interference with already existing infrastructure is impossible. In both cases, rainwater soaks into a specially prepared substrate of filtering layers (e.g., sand, gravel, nonwoven fabrics) and is treated in the process of phytoremediation, thanks to the presence of appropriately selected native hydrophytic plants (e.g., common sedge or yellow scythe).

Importantly, a rain garden is not just a “wet garden.” It’s a well-thought-out structure that collects water during rainfall, filters it through the ground and plant roots, retains some for the needs of fauna, and gives back the excess in a controlled manner or allows it to infiltrate into the ground. It is worth noting that such gardens also have a symbolic dimension – they combine a modern approach to water management with the tradition of urban gardening, known in Poland since the pre-war era. Thanks to such solutions, water – commonly treated as a threat – is returning to cities as a valuable resource.

Small retention – big effect

From an environmental and water management perspective, rain gardens offer a whole range of benefits. They retain water, reducing the risk of flooding and sewer overloading, purify water from pollutants flowing off paved surfaces, and promote biodiversity by creating habitats for insects, birds, nectariferous plants. Thus, they influence the improvement of the microclimate: they cool the environment (reduce the urban heat island effect), improve air quality and humidity. An important advantage of rain gardens is also their role in environmental education and improving the visual aesthetics of our surroundings.

Examples from the University of Lodz campus

Lodz, a city struggling with both water scarcity and heavy rainfall, is becoming a laboratory for blue-green infrastructure. Two interesting examples of rain garden solutions are located at the University of Lodz.

The water corner built on campus is a student initiative, implemented as part of the university’s civic budget. It was created as a response to the need to stop water running off roofs and show how it can be used locally. It consists of a basin with water-loving and nectar-loving plants that not only filter water, but also attract pollinating insects. Surrounding the garden is a zone of natural wood decomposition (enriching the quality of the soil), a turf of herbs and grasses (intended for free and creative use of the area by the academic community), and educational boards so that the space also serves as a living, ecohydrological classroom for learning about the natural environment around us.

On the other hand, by the buildings of the Faculty of Biology and Environmental Protection of the University of Lodz, within the framework of the NCBiR-funded Springness [2](Water4All) project, whose partner is the UNESCO Chair of Ecohydrology and Applied Ecology, innovative hybrid rain garden systems were constructed, combining hydrological and natural solutions. The space was designed to capture all the water from the roofs of nearby buildings, and then treat it in designed filtration tanks, using various sorptive materials such as dolomite, limestone, Bioporiff or the BioKer formulation developed at the UŁ Department of Biosciences.

These systems are geared to efficiently remove pollutants, i.e.: phosphates or ammonium ions, which can contribute to the degradation of aquatic ecosystems. As a result, water devoid of these substances is retained in an environmentally safe manner in ponds or infiltrates into the soil through absorption basins or rain gardens. Numerous plantings of native plant species support local biodiversity. In addition to retention itself, the garden serves an educational and social function – integrating students, researchers and the community around the topic of water conservation. The goal of the project is to develop tools for managing retention and reuse of rainwater on the university campus, which thus became a demonstration area for NBS implementation, This type of action minimizes the negative effects of climate change in urban space.

Summary

Rain gardens do not solve all the water problems of cities, but they are an important system component in rainwater management. They have the advantage of simplicity, low maintenance costs and can be implemented almost anywhere: at schools, offices, on housing estates and even in home gardens. Each such garden is a place whereby we direct our gaze toward rain as a valuable resource, rather than a threat or unnecessary waste associated with urban operations. It’s a step toward a more resilient and welcoming environment, and at the same time proof that water can stay where it falls, instead of disappearing into drains.

More and more rain garden companies are appearing on the market, and interest in them is growing steadily. Given that most gutters could be effectively connected to rain gardens, the demand for NBS solutions in Polish cities is virtually unlimited.

Authors: Konrad Budziński, Kamil Osumek, Weronika Misztal, Dagmara Radziszewska, Wiktoria Kujawa, Anna Wieczorek, Anna Jaskulska, Hubert Krzyszkowski, Adrianna Domańska, Patrycja Trusewicz, Paweł Jarosiewicz

Footnotes:

1. The Blue-Green Network is a concept developed by the teams of the UNESCO Chair of Ecohydrology and Applied Ecology at the University of Lodz and the European Regional Ecohydrology Center of the Polish Academy of Sciences.
2. Project Managing urban rainwater runoff to counter extreme hydroclimatic events (Springiness),NCBiR, WATER4ALL, 2024-2027 – https://www.ehaeunescochair.org/springiness