Urban Cisterns, Public Space and Temporary Housing

As large cities continue to expand, impermeable surfaces dominate their landscapes, reducing natural infiltration and creating flooding. Preventing the accumulation of stagnant water — with infrastructures where rainwater is stored for later use — and transporting the excess towards natural water bodies or, ideally, treatment plants has been a constant challenge. The installation of cisterns in urban areas has provided some response to the problem. However, these systems often limit themselves to a simple resolution of the water issue, without considering the design of public space.

The issue of flooding in the Alcântara area, particularly at "Boca do Vale", where the canalized Alcântara stream – Caneiro – meets the Tagus River, represents a recurring challenge for the city of Lisbon. This confluence point, historically prone to flooding due to its low topographic elevation and the insufficiency of the storm water drainage network, becomes even more vulnerable during periods of intense rainfall, when surface runoff exceeds the capacity of existing infrastructure. The rapid urban growth and high soil impermeability in the Alcântara watershed exacerbate the problem, reducing natural water infiltration and increasing the risk of flash floods. The situation is further exacerbated by the pressure on the drainage system, which fails to efficiently absorb excess water, resulting in frequent floods that impact traffic, built heritage, and residents’ safety. Additionally, the area’s proximity to the Tagus exposes it to increased flood risks during high tides, further complicating storm water drainage. The proposed sustainable drainage system – which reduces the amount of rainwater entering the municipal drainage system, moderating the need for centralized treatment plants and promoting decentralized water management practices – offers clear environmental benefits. The prefabricated and replicable element allows for the creation of high-quality public spaces during seasonal collection intervals – both above and below street level, and sometimes integrated as infrastructure within existing public buildings. These spaces not only improve air quality, reduce urban heat island effects, and promote biodiversity, but also facilitate access to vacant buildings, enabling their reintegration as new temporary housing solutions.