May 2006 Flooding
While the Merrimack River is prone to minor flooding, on May 15, 2006 rainfall raised the river more than 8 feet (2.4 m) above flood stage, forcing evacuations, damaging property, and breaking the main sewage pipeline in the city of Haverhill, Massachusetts, dumping 35 million gallons of raw sewage waste into the river per day. Reports of total rainfall vary, but most areas appear to have received around a foot of rain with some areas receiving as much as 17 inches (43 cm).
According to The Boston Globe, around 1,500 people evacuated their homes to escape the flood.
This flood also prompted the city of Lowell, Massachusetts to install a modern (albeit temporary) flood control gate comprising square steel beams at the site of the historic Francis Gate, a 19th and 20th century wooden flood gate. When lowered, the Francis gate seals the city's canal system off from its source on the Merrimack. The Great Gate, as it is also called, was built in 1850 under the direction of James B. Francis. Considered unnecessary when it was first constructed, "Francis' Folly" first saved the city in 1852 and subsequently in 1936.
Read more about this topic: Merrimack River