Tunnels are underground passageways dug through an enclosed area like soil or rock. A tunnel may be used as a foot passage or for vehicles, trains, or as a canal. They often serve as an alternative to bridges. Some tunnels are used to supply water for consumption or hydro-power. In fact, many of the longest tunnels on this list exist to carry water, and may also be known as aqueducts. The length of a tunnel is determined by its purpose and the nature of the enclosed area in which the tunnel is dug.
The Top 4
1. Delaware Aqueduct - 85 Miles
The Delaware Aqueduct is the name of a water tunnel in New York City. It takes water from Rondout Reservoir to the Hillview Reservoir. The construction of the aqueduct began in 1939 and was completed in 1945. The tunnel carries almost half of the New York's water supply every day. The tunnel is 85 miles long and has a width measuring 13.5 feet. It goes through the counties of Ulster, Orange, Dutchess, Putnam, and Westchester. The water tunnel leaks about 36 million gallons of water daily through the leaks. A $1 billion project was initiated in 2013 to repair the leaks. A 2.5 mile long bypass tunnel is also being constructed to address the leak problem. The Delaware Aqueduct is expected to be shut down to connect the bypass to the main aqueduct. Shutting it down will deprive the city nearly half of its water supply.
2. Päijänne Water Tunnel - 74.6 Miles
Päijänne Water Tunnel is a 75-mile long water tunnel located in Southern Finland. It supplies water to thousands of households in the cities of Helsinki, Vantaa, and Kerava among others in southern Finland. The tunnel starts at Lake Päijänne, the second largest lake in Finland, and slopes downhill to allow water to flow naturally. The tunnel ends at Silvola reservoir in the Greater Helsinki Area. The water is then pumped into the water treatment plants. The building of the tunnel began in 1972 and was officially opened in 1982. The tunnel went through extensive renovation in 2008 with the southern part of the tunnel reinforced to avoid curve-ins.
3. Dahuofang Water Tunnel - 53 Miles
Another water tunnel on this list, the Dahuofang Water Tunnel is responsible for bringing water to cities around northeast China around the major city of Shenyang. Construction of the tunnel began in 2006 and was finished in 2009.
4. Orange–Fish River Tunnel -
The Orange–Fish River Tunnel supplies water for irrigation and household use in central South Africa. The Eastern Cape Town experienced a water shortage for a long time because of such little rainfall in the area. The reduction of the water levels in the nearby dam only worsened the situation. The Orange–Fish Tunnel was constructed to make irrigation of the large farms possible. The construction of the Orange–Fish River Tunnel began in 1966, and it was officially opened in 1975.