São Paulo, Brazil: Rain Gardens

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Photo by Luciana Minami/City of São Paulo

Photo by Luciana Minami/City of São Paulo

Photo by Luciana Minami/City of São Paulo

Photo by Luciana Minami/City of São Paulo

Photo by Luciana Minami/City of São Paulo

Photo by Luciana Minami/City of São Paulo

Photo by Luciana Minami/City of São Paulo

Photo by Luciana Minami/City of São Paulo

AIPH World Green City Awards 2022 logo

City: São Paulo
Country: Brazil
Categories:         Living Green for Climate Change IconLiving Green for Water Icon
Award: Certificate of Merit

* This case study was written by the city and has not been edited by AIPH

Initiative: City of São Paulo’s Rain Gardens

The city of São Paulo has 12.3 million inhabitants and is organized into 32 districts, located in administrative areas with territorial limits established according to socioeconomic parameters and indicators.

São Paulo is a metropolis facing complex issues, and the city’s Municipal Administration is under the need to find effective, timely and economically feasible solutions.

The main services offered by the Municipal Department for Subdistricts [in charge for the Rain Gardens] are related to city-wide management, inspection and land-use and occupation. A connection between sustainable practices and technology is widely encouraged in the provision of these services.

The Rain Gardens are Nature-based Solutions highly efficient in flood control, with other major benefits: (i) retain solid pollutants, chemicals and waste before the water returns to the soil, (ii) control sediments from rainwater runoff, and (iii) prevent the reproduction of vector-borne insects by draining water within 48 hours.

São Paulo develops seven types of Rain Gardens: traditional, green spaces, urban conservation woods, pavements with infiltration wells, land art, green stairs and bioswales.

With the increasing acknowledgement and cost-effective development of this micro-drainage solution, the city of São Paulo mapped locations with historical flooding problems and additional areas for the implementation of the Rain Gardens.

Currently, São Paulo has more than 200 Rain Gardens and has set the goal of achieving more than 400 by 2024

Addressing the urban challenge

Breadth of the issue – How are the problem(s) that are being tackled by your initiative affecting citizens/local businesses or a significant component of the local wildlife?

The environmental impact is evident, as it expands the permeable coverage of the city, slowing down the speed of surface waters and collecting water in the subsoil which can then be reused by the existing vegetation. In the urban conservation woods this situation is easily observed, as the tree seedlings from the Tamanduateí River have shown a vigorous development, not only because of the water available, but also because of the conservation treatment, the use of municipal organic compost and the soil cover, which has made these spaces successful and has enhanced biodiversity.

In the Rain Gardens, the population immediately notices the impact of removing concrete and planting seedlings and ornamental plants as substitutes. The green spaces are gardens and small environments for collective and public use in areas which were previously intended for parking lot. The place turns into a recreation, leisure and landscaping option for the city and creates environmental and community awareness.

The interventions have the approval of the residents who have recently requested the installation of new units in other locations. In some of these cases, the population has planted new seedlings in the gardens, demonstrating its participation and care, key elements for the success of the initiative.

Depth of the issue – How seriously are the problems being tackled by your initiative impacting the life of the citizens/businesses/wildlife concerned?

The Rain Gardens minimize effects of heat islands, increase air and soil humidity, decrease the risks of flooding, and make the city more pleasant, people-oriented, with an increased and diversified vegetation coverage, as well as promoting alongside the population a critical awareness of environmental issues.

The power of plants and natural ecosystems to deliver benefits

How is the initiative shaped by scientific evidence of the potential for plants and natural ecosystems to deliver benefits?

When it rains, water can run off impermeable surfaces such as roofs or pavements, collecting pollutants such as waste particles, fertilizers, chemicals, oil, rubbish, and bacteria along the way. The sediment pollution enters untreated sewage and flows directly into nearby streams and ponds.

The Rain Garden collect rainwater runoff, allowing the water to be filtered by vegetation and infiltrate the soil, recharging underground aquifers. These processes filter out pollutants.

The landscape redesign of the intervention points ensures ideal accessibility conditions, as well as the creation of urban micro-environments in roadbeds, either with a modular size and dimension (2×5 m in the case of green spaces) or tailor-made for specific situations. By replacing sites such as concrete and asphalt pavement to leisure spaces linked to the Rain Gardens, the City of São Paulo aims at complementing the urban surface drainage system using micro-environments and water collectors, as well as enabling unrestricted tree-planting.

The purpose is to ensure that the population reproduces the Municipal Administration’s initiatives in their homes. The proportion of land in residential areas corresponds to 70% of the city’s total, which, together with 30% of public properties (including roads), can make the city more environmentally responsible. In general terms, the programme will reduce the effects of flooding in São Paulo since drainage systems will be able to work in an integrated manner.

How has the city exploited the potential of plants and associated ecosystems to deliver more than one benefit?

The potential of plants was explored when choosing the species, seeking the use of hardy plants, preferably native ones that respond better to climate change, parasites, and weeds, thus reducing the need for maintenance and keeping the conservation of the fauna and flora habitat.

Another key factor that was taken into account was the specific characteristics of each species chosen and how they are used in the project, providing a better performance of the drainage system, better uptake of nutrients, control of erosion, silting, flooding and improved water quality, reducing diffuse pollution of micro basins.

Innovative and Collaborative Solution

How does the initiative show evidence of feasibility, including on-going financial and logistical support?

The Rain Gardens are developed by teams that are already hired by the Municipal Administration to perform other routine services, so there is no need to create a new contract, which facilitates the expansion of the initiative throughout the city.

In what ways is the initiative innovative?

Considering the importance of the management of water resources, it was necessary to develop an innovative program, focused on the protection of the environment, based on green infrastructure works and Nature-based Solutions.

The creation of this programme stimulates the development of new actions and green works that are cost-effective and to maximise the benefits and efficiency of drainage systems and sustainability, since the gardens are pioneers in the use of recycling concrete removed from the street, use of tree pruning waste to compost the soil, thus improving its quality, and is also used as natural coverage, decreasing the growth of weeds, always seeking to improve the quality of life of the population.

How is the initiative supported by collaborative working across disciplines and sectors?

A culture of collaborative work is essential because it helps solve problems efficiently and stimulates innovation. The more integrated, the greater are the chances of achieving good results. In the process of building a Rain Garden, the City of São Paulo relies on:

  • Team of execution of services in public areas – construction sites;
  • Green areas management team – execution of the landscaping projects;
  • Pruning contract – donation of organic material from tree pruning;
  • Agronomist engineer – analysis of hydrographic basins;
  • Civil servants of the Sub districts – analysis of the particularities of the areas and suggestion of new locations for the execution of projects and maintenance;
  • Architect from the Department of City-wide Management – elaboration of the projects;
  • Population – help in the maintenance and preservation of the areas.
How does the initiative demonstrate evidence of community support?          

Execution of the pilot project in the Vila Mariana district planned for Uvaias Street at the corner with Décio Street, in Saúde district. This initiative was part of the Pilot Project for Tree Planting on Sidewalks (PPAC) and was developed based on the collaborative work of the public and private sectors, as well as civil society.

Implementation, Impact and Replicability

How has the initiative had a ripple effect beyond the scope of the initiative itself, thereby demonstrating a change in the city’s and/or its partners’ way of working with plants?

Rain Gardens have the function of increasing urban permeability and minimising the effects of flooding. Through an underground drainage system, the innovative green areas absorb and filter part of the rainwater and avoid accumulation on the surface. The gardens also increase the possibilities for well-being, leisure, and biodiversity.

The interventions have the approval of the residents, who have recently requested the installation of new units in other locations. In some of these cases, the population has planted new seedlings in the gardens, demonstrating its participation and care, actions that are fundamental to the success of the initiative.

How has the initiative had a ripple effect beyond the scope of the initiative itself, thereby demonstrating a change in the city’s and/or its partners’ way of working with plants?

From the outset of the implementation of Rain Gardens and conservation woodlands throughout the city, the project had a lot of support from the population, which has contributed to more people-oriented Nature-based Solutions in São Paulo.

How have other cities expressed interest in the initiative, or what potential does it have to interest other cities and be customised to their own circumstances?

The city of Salvador, Brazil, and Milan, Italy, were interested in the project, since it can be applied in any city that suffers from flooding problems.

Sustainability and Resilience

What efforts have been made to reduce the carbon footprint of the initiative?

Use of the concrete rubble removed and reserved after the excavation to fill the volume and increase the “voids” in the soil, making the process more sustainable.

Use of organic compost from the pruning actions performed by the Municipal Administration to compose the substrate that will receive the planting of specific vegetation, in addition to the use, when feasible, of the soil from the site itself.

How have the anticipated impacts of climate change been considered?

The program promotes the development of actions and projects of urban intervention, green infrastructure and environmental recovery in the city of São Paulo, aiming to increase permeability, biodiversity, afforestation, landscaping, well-being and leisure.

All actions are inspired on Nature-based Solutions, by stimulating natural processes and plants that involve the creation of urban micro-environments such as rain gardens, green spaces, bioswales, infiltration wells, land art and urban conservation woods.

These are components linked to the management of surface and groundwater, as well as the treatment of diffuse pollution, excessive sedimentation and water harvesting from urban drainage lines. In addition, the interventions are intended to reduce events associated with climate change.

The Rain Gardens project act in collaboration with the permeability micro-watersheds created by the urban conservation woodlands, with emphasis on rainwater harvesting and preservation; on increasing vegetation cover; and on creating specific flood environments to test plants of different origins, locations, types, species and varieties, to define the most adapted for such urban conditions, as there is not extensive literature on the subject, especially about tropical regions.

The program uses recycled material (rubble from pavements removed by the Municipal Administration, usually concrete) as the basis for the underground infiltration mattresses, ensuring that the gardens and bioswales are environmentally sustainable, both in their urban function and use of materials.

What processes does the initiative include for it to be considerate in its use of soils and other natural resources?

For the execution of the Rain Gardens, the City of São Paulo reuse the soil coming from the excavation of the place itself with a fertilized addition.

As an attempt to reduce the use of irrigation water, it is applied, in some areas of the gardens, the shredded organic waste from pruning carried out in the city of São Paulo.

The waste has the purpose to reduce the evaporation index of the irrigation water, thus helping to hold humidity and to hinder the growth of weeds next to the ornamental plants.

Monitoring, Maintenance, and Management

How has the initiative been designed and implemented so that long-term needs for management and maintenance are reduced and can be met?

The proposal is to minimise the effects of surface runoff from rainwater – so frequent and costly to the Municipal Administration – by using retention gardens.

These gardens will retain the water and increase the permeability of the streets, helping to minimise the effects of flooding in the city of São Paulo.

This system works as a reservoir for excess rainwater that cannot be absorbed due to the low infiltration capacity of the soil. It also serves as a water filter as it improves water quality by reducing and absorbing pollutants.

Priority should be given to choosing native plants that live in harmony with the surrounding environment and will respond better to climate change, parasites, and weeds. They are more resistant, thus reducing the need for maintenance.

What protocols are in place to facilitate monitoring of results?

The monitoring of Rain Gardens considers the sum of direct precipitation with the volumes coming from impermeable areas – analysis of the monitoring systems of precipitation events and flooding points, in order to estimate the surface runoff (Uranus – predictive of flooding).

The retention function is analysed from the capacity of the system related to the maximum amount of water on its surface.

The infiltration function is analysed by comparing the infiltration capacity of the natural soil with the rain garden.

The storage function was evaluated according to the heights of the water column stored inside the experiment.

The rain garden is shown to be efficient and suitable as a compensatory technique to assist in the management of rainwater, especially water coming from impermeable surfaces.

How has the initiative been enhanced in response to monitoring of results?

Based on the results found from the monitoring of Rain Garden, the City of São Paulo looked for better soil compositions (more suitable for water drainage), to enhance the capacity of the system to retain the maximum water on its surface by increasing the amount of openings that receive the water from the roads or the depth of the plants layer or even increasing the depth of the aquifer. All these are indicators that greatly change the effectiveness of the solution and that were informed by the systematic monitoring performed in relation to the Rain Gardens in São Paulo.