Unionville used Farmington River water power from the late 1700s onward. Its first dam, built circa 1780, stood 200 yards upstream from the Route 4 bridge, with a canal on the west side of the river powering a mill next to Riverfront Miniature Golf. Early industrial growth was limited by the lack of modern transportation until the Unionville Feeder Canal opened in 1828. Built to provide most of the water for the Farmington Canal and also to serve as a transportation canal, it allowed barges to dock downstream of the South Main Street bridge so raw materials could be imported and finished goods exported to New Haven or north to the Upper Connecticut River Valley. Rising demand for water power led to a larger crib dam, completed in 1832, 300 yards upstream from the first dam; it was much taller and included a major canal system with a holding basin for the east side of the river, and Richard's Mill received power through a canal from the new dam. That same year, the Hartford Courant advertised water privileges at the head-race of these canals for sale or lease. The arrival of the railroad in 1850 brought year-round transportation and further increased demand for water power. In 1856 James Cowles built a new dam farther upstream, later upgraded several times to increase capacity and known as the Big Dam. By 1878 Unionville was a thriving community whose water-powered industries stood alongside churches, hotels, a public school, and a post office. Paper production became the major industry because of water power and the abundant supply of soft water from underground aquifers, while other industries produced metal products and wooden furniture, and saw and grist mills also operated there. The Big Dam included an earthen section 1,000 feet long to prevent flooding of the railroad tracks, two major abutments supporting a wide gravity dam, and a surface layer of concrete. The Flood of 1955 exceeded the structural capacity of all the dams, destroying much of the Big Dam and all the dams downstream, though parts of the west and east abutments and remains of the power canal and dam still survived afterward.