Parts of Michigan were inundated with heavy rain from the morning of May 17, 2020 through the afternoon of May 19. A low pressure system and front stalled across the region. Per the NWS Detroit, widespread rain totals of 5-8 inches were observed in the Tri Cities region (Saginaw, Bay City, Midland) and into parts of northern Lower Michigan. This rain amount overwhelmed the Tittabawassee River.
Per the NWS Detroit, “Exacerbating this issue was an already stressed dam system at Edenville and Sanford, which helps control the downstream flow along the Tittabawassee River into the city of Midland and eventually the Saginaw River. With increasing elevation heading north into northern lower Michigan, the heaviest rain totals (7-8 inches in Gladwin and Arenac counties), resulted in excess runoff flowing in a general north to south direction towards the Edenville and Sanford dams.”
During the evening of May 17, “catastrophic dam failures” occurred at Edenville and Sanford. The result was historic flash flooding in both towns and in the city of Midland. Much of downtown Midland was inundated. Many homes were destroyed and several roads were closed due to washouts and destroyed bridges. Approximately 10,000 people were evacuated from the area. The NWS Detroit issued a rare flash flood emergency for the event.
https://youtu.be/qBuQMEvqGH4
The NWS Detroit describes the impact of this event this way, “To help further understand the historic nature of this event, the rainfall recurrence interval for the Tittabawassee River watershed is estimated to be a once in a 200 year event. To explain this in a different way, each year this amount of rainfall has a 0.05% chance of occurring across this basin. These values are estimated, however, as recurrence intervals are calculated for point locations, not an entire watershed. However, the cumulative effects of the dam failures on top of the heavy rain resulted in a much greater historical effect to the magnitude of flooding experienced in the city of Midland and nearby surrounding areas. At the very least, the flooding that occurred will be remembered as a generation-defining event for those who experienced it firsthand.”
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