Urban Planning, Ecological Transition, Urban Services and Housing

The municipal drains network covers 1648 kilometres, more than 1000 km of which can be visited. Every year some 115 hm3 of water pass through the network. The municipal drains network serves some 1,540,000 inhabitants in the city and the commercial and industrial establishments located on more than 81,500 properties covering the 98 km2 of the municipal area.

The inherent characteristics of the city of Barcelona complicate the process of evacuating the water generated both by rainfall and industrial and domestic use.

The drainage system is required because of the combination of various circumstances:

· Periods of intense rainfall. Although the city has on average a low level of rainfall, the Mediterranean climate often brings intense downpours (40% of the total annual precipitation has on occasion been recorded in a period of just 2 or 3 days).

· The topography of the city. Barcelona has steep inclines in the upper part (up to 40%), which are more moderate as one reaches the shoreline (less than 0.1%).

· Impermeability of urban land. Non-urbanised land filters 70% of rainwater, while roads and pavements filter only 5%.

· High population density generating industrial and waste water. Barcelona is home to 16,200 inhabitants per square kilometre.

City drains make up an extensive underground network covering the whole urban area. The city of Barcelona has a length of more than 1,800,000 metres of drains, including pipelines, collectors, etc.

The current network also has auxiliary elements (some 40,000 m of inspection shafts, around 60,000 m of gutters, ancillary constructions (siphons, sedimentation pits, pumping stations, dissipation chambers), and 391,200 m3 of rainwater retention tanks.