The following are the longest tunnels in the world:
The Delaware Aqueduct Tunnel
The Delaware Aqueduct is the world’s longest continuous tunnel in the world. It serves as the main water supply tunnel to New York City. The 137,000m tunnel was drilled through solid rock and is, on average, around 4 meters wide for most of its course.
Päijänne Water Tunnel
The Päijänne Water Tunnel is the second longest tunnel in the world at just over 120,000m long. It is located in Southern Finland and runs between 30 and 100 meters underground-level.
The tunnel transports fresh water for the millions of inhabitants of Southern Finland’s major cities like Helsinki, Espoo, and Vantaa. Construction began in around 1972 and took a total of around 10 years to complete.
The Dahuofang Water Tunnel
The Dahuofang Water Tunnel is the third longest continuous tunnel in the world and the longest in China. It is located in the Liaoning Province of China and runs for around 85,000m.
The tunnel was built to provide fresh water from the Dahuofang Reservoir to the cities of Shenyang, Fushun, Liaoyang, Anshan, Panjin, Yingkou, and Dalian. Construction began in 2006 and was completed three years later.
Orange–Fish River Tunnel
The Orange-Fish River Tunnel is an irrigation tunnel located in South Africa. Work began on its construction in 1966 and it was finally completed in 1975. When completed, the tunnel’s length of over 82,000m makes it the longest continuous enclosed aqueduct in the southern hemisphere.
The Bolmen Water Tunnel
The Bolmen Water Tunnel is another water supply tunnel in Scandinavia. It was built to transport water from Lake Bolmen in Kronoberg to the Swedish province of Skane.
The 82,000m tunnel supplies water to around 700,000 Swedish citizens and has a cross-section area of around 8m2. Construction began in 1975 and took around 12 years to complete.