A Century of Topological Coevolution of Complex Infrastructure Networks in an Alpine City

Table 1

Narrative changes of the infrastructure networks [32–34].

Years	Narrative
Before 1910	WDN for about 23,000 inhabitants; total population 49,727 in 1900; design demand 150 liters per capita and day, transporting a significant amount of water in the city; also the massive amount of waste water had to be transported out of the city by a newly build combined sewer system; a mandatory connection of the consumers to both networks was enforced by law
1910-1929	world war; maximum recorded water consumption of 500 liters per capita and day in 1927 due to unaccustomed consumer behavior (still used to the central supply of running wells); 30% of the current WDN structure (year 2017) existed already in 1910; opening of the airport at the eastern part of the city in 1925
1930-1949	world war; massive influx of refugees, infrastructure mainly unaffected; opening of a new airport at the western part of the city in 1948; supply deficits; reduction of water consumption below 300 liters per capita and day through information campaigns
1950-1969	Strong population growth, city and road network expansion; construction of the WWTP (mechanical treatment) in 1966; strong UDN expansion in western and eastern direction; biggest growth rates for the WDN between 1960 and 1970.
1970-1989	380 liters per capita and day; construction of the motorway and connection with the city (1970s); construction of the biological treatment at the WWTP in 1974; connection of neighboring villages to the WWTP; maximum loads of 330,000 people equivalents (PE) in 1987; production industries with high water demand and waste water accumulation leave the city
1990-2009	Further connection of neighboring villages; expansion of the WWTP to 400,000 PE; minor network expansions, increased pipe and sewer rehabilitation
2009-present	Steady population growth, urban expansion is limited by the topographic boundary conditions; densification of city districts (from detached houses to apartment blocks); approximately 250 liters per capita and day (domestic water demand is app. half of it); actually connected people equivalent to the WWTP: 270,000 PE (2011); roads: 476 km; WDN: 320 km; UDN 244 km.