The Black Death was a plague the spread across medieval Europe in 590CE to 1500CE. It was an infection caused by rats and then spread by fleas. The rats were carrying a lot of germs and bacteria at the time so a flea would bite the rat and then would and bite a person.
The average life expectancy of a dam is 50 years, and 25% of the dams in the Army Corps of Engineers National Inventory of Dams are now more than 50 years old.This number is projected to increase to 85% by the year 2020.he Glen Canyon Dam supplies over 5 million people with power (Glen Canyon Dam Adaptive Management Program, 2007). These two dams also have the capacity to store 32,471,000 acre-feet and 27,000,000 acre-feet of water, respectively. In order to harvest hydropower however, dams must be built.
Its output of 84 billion kilowatt-hours (KWh) per year is still surpassed by Itaipu Dam on the border between Brazil and Paraguay. Itaipu's plant has a capacity of 12,600 MW, and has produced 90 billion KWh in a single year. The largest hydroelectric plant in the United States is at Grand Coulee Dam. Its three powerplants have a capacity of 6,809 MW, and it generates, on average, about 21 billion KWh, while Hoover Dam's powerplant has a capacity of 2,074 MW and generates approximately 4 billion KWh a year.