IMPACTS OF HUMAN INTERVENTIONS IN FLUVIAL SYSTEMS: OBSERVATIONS FROM THE EDENVILLE DAM DISASTER IN CENTRAL MICHIGAN

Fluvial systems have served as transportation corridors, municipal utilities, and natural resources throughout human history. In the central and eastern United States, natural river systems were modified throughout the 19^th and early 20^th centuries in response to both local and regional needs. Dams, canals, and impoundment structures provided municipal water sources, irrigation systems, industrial power, local hydroelectric generation, and flood control. On May 19, 2020, an intense rainstorm preceded the failure of the Edenville Dam, which was constructed in 1923 in central Michigan to manage flooding on the Tittabawassee and Tobacco rivers. Such storms have become increasingly prevalent in the upper Midwest in the past decade.

The breach of the Edenville Dam resulted in the rapid drawdown of 44 M-m³ of water from Wixom Lake, the over-topping of downstream Sanford Dam, and an estimated $200 million in property damage in Midland, MI. Subsequent engineering and geological reconnaissance investigations have uncovered complex interactions between human interventions and the natural river system. The initial point of failure of the Edenville Dam appears to coincide with the location of a terrace riser beneath the dam, with the post-breach course of the Tittabawassee River now occupying a former river channel. The ~1-mile-long dam traversed 5 terrace levels established at glacial till/glacial outwash transitions, resulting in significant lateral variations in the thickness of dam fill. The low gradients of the Tittabawassee and Tobacco rivers precluded substantial sediment impoundment near the dam, and the post-breach flood instead scoured at least 2 m into local bedrock and removed ~8,000 m³ of agricultural topsoil further downstream. Sediment deposits >1 m thick covered recreational and industrial facilities built on the Tittabawassee River floodplain, and questions of the remobilization of industrially-contaminated sediment downstream of the breach have been raised.

The legacy of the Edenville Dam disaster will not be measured in the cost of this one breach, but in what we learn about the potential consequences of failure of 1000s of similar dams constructed throughout the US and their resiliency in light of extreme precipitation events related to global climate change.