So the city, in 1867, sank an immense cylinder, or crib, 2 miles from shore to pump fresh water back to the inhabitants.

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Then, it would pump out the water, float back to the top and relay its data back to the scientists via a satellite network.

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Hydro dams can be reversed and pump water uphill so that the next day, when gravity pulls the water back down, the turbines spin to make electricity.

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