So what happens when engineers get it wrong? Bad things can happen.
Usually we think of failing infrastructure as being old, and poorly maintained. But that isn’t the only kind of failure. Case Study: Anita Dam (Montana, 1997). The photos tab on that page is particularly interesting.
The Anita Dam in Montana was built in 1996. It failed in the spring of 1997 mostly because it hadn’t included lessons learned from other dams that had been published in the 1980s. It is 36-ft high and impounds 979,384 cubic meters of water.
Anita Dam is (was?) an earthen embankment dam. It was built to provide water storage and control flooding. (It is currently listed in at least one place as a concrete gravity dam, but photos and video seem to show it is still mostly an earthen dam.)
For a more detailed view of the incident, refer to A Review of the Anita Dam Incident: Internal Erosion Caused by a Buried Conduit and Lessons Learned.
Conduits are one of the very common parts of embankment dams and almost any kind of hydraulic structures. Primarily, conduits convey the water from the reservoir in a controlled manner for various purposes, such as releasing water to meet the downstream requirements
The conduit was supplied with anti-seepage collars, but included no filters. The conduit also didn’t have a continuous support cradle. This resulted in the spring of 1997 of something called piping. Water flowed through the conduit, but also began to flow around the outside of the conduit causing rapid erosion. And increasing the amount of water released downstream. The entire reservoir was emptied in 4 days.
The statistics show that 28% to 46% of dam failures were caused by piping.
Though in this case the dam itself didn’t collapse, it had to be extensively rebuilt to correct the problems that caused this incident. No life was lost, but there was some downstream damage due to the rate of water flow.
What follows is a 2-minute video about the current management of the dam. In the spring of 1997, they didn’t even have an emergency management plan for the dam. (What could go wrong? It is brand new!) And yes, like most things produced by the .gov, that video is fairly self-serving. “See what great things we are doing for the American family!” At lest they are doing something, which seems to be more than they were doing in 1997.