As 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.  Closing off the feeder canals to the Merrimack River, the design was similar to gates defending castles against invaders in medieval Europe.  His contemporaries ridiculed the idea but in April, 1852, the Merrimack was rising and Francis decided to lower the gate for the first time. On April 22, 1852, the river crested seven inches higher than the flood of 1785 and the gate, snug in granite, held fast, deflecting the flood waters; saving Lowell from destruction. A day later, a second 28-foot wall of water, bombarded the stone-bound gate and again it held.  For more than 140 years, "Francis' Folly" is still used.