As extreme rain events have become more frequent in the 21st century, Wisconsin ranks second nationally in the number of documented dam failures since 2000, with most of them occurring in just the last few years.

Since 2019, however, the condition of our state’s most critical dams has improved, according to a Wisconsin Policy Forum analysis of publicly available data.

A recent dam failure in the central Wisconsin city of Manawa raised broader questions about the condition of the more than 4,000 dams across our state, spread across all of its 72 counties. They range from massive hydroelectric concrete dams, such as the Prairie du Sac Dam on the Wisconsin River, to small earthen dams that create farm ponds.

While the state devotes considerable resources to inspecting and maintaining its dams, if rainfall and weather events are extreme enough, they can fail. A dam failure is an unintended release of water from the body that the dam controls. This could range anywhere from a catastrophic collapse to a much less consequential event in which a dam is overtopped or releases a small amount of water.

According to data from the Association of State Dam Safety Officials, (ASDSO) from 2000 through 2023, Wisconsin recorded 34 dam failures, the second-most nationally behind South Carolina. It is important to note that these rankings could be affected by state-to-state differences in dam inspection and reporting practices, that in turn may affect what is reported to ASDSO.

Nonetheless, these data make clear that dam failures in Wisconsin also are becoming more frequent: 28 of the 34 happened since 2018. More than half, 18, have occurred since 2020.

Most of these dam failures did not have catastrophic consequences: none resulted in loss of life, and none caused property damage exceeding $100,000. However, initial reports indicated the Manawa dam failure in July, and the rainfall event that caused it, resulted in the evacuation of about 100 nearby residents and caused an estimated $6 million in property damage.

For any dam, the consequences of failure depend in part on how much water it holds back and what lies downstream. The Army Corps of Engineers’ National Inventory of Dams classifies them into three categories of downstream hazard potential – low, significant, or high. Dams assigned high hazard potential are those for which “failure or mis-operation will probably cause loss of human life,” according to the inventory. Of the 34 dam failures that occurred in Wisconsin over the last 23 years, three were high hazard potential dams.

Of Wisconsin’s 206 high hazard potential dams, five were found to be in poor or unsatisfactory condition, according to the most recent data. This amounted to about 2.4% of the state’s high hazard dams. This marks an improvement for Wisconsin relative to 2019, when 10.1% of the state’s high hazard potential dams were in poor or unsatisfactory condition.

Our analysis suggests that recent funding levels have been sufficient to improve the condition of the state’s most critical dams since 2019. However, the state has also experienced more dam failures in recent years. A changing climate – triggering more frequent and more severe extreme rain events – could pose new and greater tests to our dam infrastructure.

This information is a service of the Wisconsin Policy Forum, the state’s leading resource for nonpartisan state and local government research and civic education. Learn more at wispolicyforum.org.