The chief engineer chief engineer for Lowell, MA, James Bicheno Francis, constructed a five-mile system of canals in 1848. The Merrimack River provided an uninterrupted source of power to a dozen textile mills. Changes in the river level were controlled by a system of gates and locks. He compiled a history of floods and during a major flood in 1785, the river crested above Pawtucket Falls at 13 feet 6 inches. With the city 30 feet lower than the falls, Francis realized that if crest levels repeated; surging water would funnel through the canals, destroying the heart of the city. He proposed building a massive gate to prevent this tragedy by constructing a gate to deflect flood waters. The project included a gate that would drop and close off feeder canals to the Merrimack River andt was similar to gates used to defend castles in medieval Europe.  Contemporaries ridiculed the idea but in April, 1852, the Merrimack was on-the-rise and Francis decided to lower the gate for the first time. On April 22, 1852, the river crested higher than the flood of 1785 and the gate, snug in granite, held fast. The massive gate worked and 24 hours later, a second, 28-foot wall of water, bombarded the gate. Once again it held. For more than 160 years, "Francis's Folly" is still used.