Continuing our column from Sunday, engineer James Francis found success in canal construction and recommended implementing a massive gate to deflect floodwaters from Lowell, Mass. 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 lowered the gate for the first time. On April 23, 1852, the river crested 7 inches higher than the flood of 1785 and the gate, snug in granite, held fast, deflecting the floodwaters and saving Lowell. A day later, a second 28-foot wall of water bombarded the stone-bound gate and again it held. For 161 years, “Francis’ Folly” remains a respected river control structure. Fastcast: Splediforous.