[2] Baron Haussmann, tasked by Napoléon III to modernize the city, appointed Belgrand as Director of Water and Sewers of Paris in March 1855.

The tunnels he designed were intended to be clean, easily accessible, and substantially larger than the previous Parisian underground.

[6] Belgrand remains famous for his works, consisting the Paris sewers, the aqueduct on the Vanne river between Arcueil and Cachan, the aqueduct on the Dhuis river (fr: Dhuis (rivière)) and the reservoir of Montsouris (fr: Réservoir de Montsouris) which stores the water underground.

Public reaction to the improvements was overwhelmingly favourable, supported by tours of the newly constructed sewer system and a series of photographs taken by Nadar,[7] pioneering the use of artificial lighting for photography.

[10] Belgrand's projects remain "one of the most extensive urban sewer systems in the world"[1] and served as a "transitional phase" leading to modern wastewater processing.