The Miami Conservancy District is a river management agency operating in Southwest Ohio to control flooding of the Great Miami River and its tributaries. It was organized in 1915 following the catastrophic Great Dayton Flood of the Great Miami River in March 1913, which hit Dayton, Ohio particularly hard. Designed by Arthur Ernest Morgan, the Miami Conservancy District built levees, straightened the river channel throughout the Miami Valley, and built five dry dams on various tributaries to control flooding. The district and its projects are unusual in that they were funded almost entirely by local tax initiatives, unlike similar projects elsewhere which were funded by the federal government and coordinated by the U.S. Army Corps of Engineers.
The 1913 flood has been ascribed in part to the 1912 eruption of Mount Katmai and its daughter volcano Novarupta in Alaska. In one of the greatest recorded volcanic events, Novarupta emitted enough fine ash into the atmosphere to block sunlight and cool the climate of the Northern Hemisphere that winter.
The success of the Miami Conservancy District helped to inspire the development of the much larger Tennessee Valley Authority during the Great Depression.
The district manages five dry dams. They are hydraulic fill dams constructed from 1919 to 1922 using fill trestles.
Located near Englewood, Ohio, Englewood dam is the largest of the dams maintained by the district. It regulates the flow of the Stillwater River into the Great Miami River. It consists of 3,500,000 cubic yards (2,700,000 m3) of earth, is 110 feet (34 m) high and stretches 4,716 feet (1,437 m). U.S. Route 40 crosses the top of the dam. The dam can contain 209,000 acre feet (258,000,000 m3) of flood water over 6,350 acres (26 km2). It was constructed in 1919 and consists of as much earth as the Great Pyramid of Giza.