Around 10 000 people have been forced to flee their homes in parts of central Michigan following the failure of two dams on the Tittabawassee River. The eastern part of the Edenville Dam in Gladwin County collapsed at about 5.45 pm local time on Tuesday 19 May 2020 following days of heavy rain in the area, causing thousands of people to be evacuated from homes in the city of Edenville, about 6 km downstream, as water levers three metres above normal surged towards the town. Shortly after the Sanford Dam, 4km downstream of Edenville and 10 km downstream of the Edenville dam overtopped, sending floodwaters towards the city of Midland, another 9.7 km downstream, where mass evacuations are again underway.
The failure of the Edenville Dam on the Tittabawassee River in Gladwin County, Michigan, on Tuesday 19 May 2020. Dave Petley/Landslide Blog/American Geophysical Union/MLive/Youtube.
The Edenville Dam, a hydroelectric project built in the 1920s, had its licence revoked by the Federal Energy Regulatory Commission in October 2018, following the failure of it's owners Boyce Hydro Power to comply with an order to rectify multiple breaches of safety regulations, including an inability to cope with a potential maximum flood. The dam was subsequently purchased, along with three other hydro-electric projects, including the Sanford Dam, by the Four Lakes Task Force, a 'Delegated Authority' formally created by resolutions passed in Midland and Gladwin counties to administer and oversee the maintenance and operations of the projects.
Flooding on the Tittabawassee River in Michigan following the failure of the Edenville Dam on 19 May 2020. WXYZ Detroit.
Many parts of the eastern United States have suffered extremely high levels of rainfall this week due to the passage of Tropical Storm Arthur, which swept up the eastern coast of the United States without making landfall, and eventually turned east and headed out into the central Atlantic.
Flooding in Sanford, Michigan, following the failure of the Edenville and Sanford dams on 19 May 2020. Michael Connell/TC Vortex.
Tropical storms are caused by solar energy heating the air above the oceans, which causes the air to rise leading to an inrush of air. If this happens over a large enough area the inrushing air will start to circulate, as the rotation of the Earth causes the winds closer to the equator to move eastwards compared to those further away (the Coriolis Effect). This leads to tropical storms rotating clockwise in the southern hemisphere and anticlockwise in the northern hemisphere. These storms tend to grow in strength as they move across the ocean and lose it as they pass over land (this is not completely true: many tropical storms peter out without reaching land due to wider atmospheric patterns), since the land tends to absorb solar energy while the sea reflects it.
Despite the obvious danger of winds of this speed, which can physically blow people, and other large objects, away as well as damaging buildings and uprooting trees, the real danger from these storms comes from the flooding they bring. Each drop millibar drop in air-pressure leads to an approximate 1 cm rise in sea level, with big tropical storms capable of causing a storm surge of several meters. This is always accompanied by heavy rainfall, since warm air over the ocean leads to evaporation of sea water, which is then carried with the storm. These combined often lead to catastrophic flooding in areas hit by tropical storms.
Follow Sciency Thoughts on Facebook.