Hey Tom, you should considering doing a video about Chicago’s Tunnel and Reservoir Plan, or  TARP - the “Deep Tunnel” project, which is a massive civil engineering project with 176 kilometers of tunnels up to 10 m in diameter and up to 110 m underground, that store upwards of 7.9 billion gallons (8.7x10 to the ninth liters) of floodwater and sewage. In addition there are numerous reservoirs (old quarries actually) that will hold and store an additional 18 billion gallons! It’s really quite remarkable. All this in a city that also reversed the flow of its river back in the late 19th century.