Urban Drainage Systems in Sant Cugat

The growth of cities and urban areas implies increased construction of buildings and paved streets, subsequently, creating more impermeable surfaces. In nature, the amount of rain water absorbed by the earth is approximately 95% while the excess water that overflows is 5%. However, in low-density urban zones, the amount of water absorbed by the earth drastically drops to only 30% while 70% of the rainwater becomes overflow. In high-density urban zones, it is the complete opposite of what occurs in nature with 95% of rainwater overflowing. The need to redirect this water into aquifers is vital in order to responsibly use this natural resource, to maintain a balanced ecosystem both at the urban scale and the global scale, and to achieve a sustainable management of water.

In recent years, an alternative way of designing and managing drainage infrastructures developed worldwide. Building systems allow water to pass through the surface layer to its interior where it is stored temporarily to be filtered if the soil permits after a natural purification process or to be transferred to another point of infiltration, purification, lamination, or retention in a controlled manner.

The establishment of the Sustainable Urban Drainage Systems (SUDS) implies a profound reconsideration the city-territory relationship, incorporating prominent values to its sustainable urban model. These systems not only facilitate the treatment of surface water, but also create awareness in the community, helping to restore the citizens’ active role in the management of green spaces in streets, squares, and parks. Therefore, SUDS is not just a preventative system in water management, but also a mechanism for reusing water and, at a decentralized level, using water to irrigate green zones. The objectives of SUDS is especially applicable to the urban makeup of Sant Cugat, a city whose urban growth respected its relations to the water movements and included them in the green structure.

This management of the sustainable reuse of water for the irrigation of green zones is especially important. By managing the rainwater in the surface and not channeling it through the sewage system, it benefits the management of wastewater as well by avoiding overloading the sewage system which could generate flooding and contaminate the environment. This new system will return the same amount of water extracted back to the natural environment, satisfying a key component of the Water Framework Directive which ensures a healthy ecological status of natural water courses beginning in 2015.

The study examines the viability of implementing a sustainable drainage criteria to the Sant Cugat territory. It explains the difficulties of the current urban drainage system and an alternative sustainable drainage system in order to improve rainwater management in the urban environment. Through the analysis of the land, it allowed for the characterization and diagnosis for the management of rainwater. The objectives are to take advantage of resources that generate opportunity zones as well as to offer resolutions and intervention strategies related to the objectives included in the agreement with the Government.

The study was a collaboration between the Government of Sant Cugat del Vallés and the University Polytechnic of Catalonia – Vallés School of Architecture.


Cíclica [space·community·ecology] i Isabel Vega


Ajuntament de Sant Cugat del Vallès i Universitat Politècnica de Catalunya

Project year



1 de January de 2013


Territory and landscape