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.
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.
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.