The Great Dayton Flood of 1913 resulted from flooding by the Great Miami River reaching Dayton, Ohio, and the surrounding area, causing the greatest natural disaster in Ohio history. In response, the General Assembly passed the Vonderheide Act to enable the formation of conservancy districts. The Miami Conservancy District, which included Dayton and the surrounding area, became one of the first major flood control districts in Ohio and the United States.The Dayton flood of March 1913 was caused by a series of severe winter rainstorms that hit the Midwest in late March. Within three days, 8–11 inches (200–280 mm) of rain fell throughout the Great Miami River watershed on already saturated soil, resulting in more than 90 percent runoff. The river and its tributaries overflowed. The existing levees failed, and downtown Dayton was flooded up to 20 feet (6.1 m) deep. This flood is still the flood of record for the Great Miami River watershed. The volume of water that passed through the river channel during this storm equaled the monthly flow over Niagara Falls.The Great Miami River watershed covers nearly 4,000 square miles (10,000 km2) and 115 miles (185 km) of channel that feeds into the Ohio River. Other Ohio cities also had flooding from these storms but none as extensive as the cities of Dayton, Piqua, Troy, and Hamilton, along the Great Miami River.