It’s no secret that a vast amount of American infrastructure is in great need of upgrades, repairs or replacements. The repairs that are desperately needed will come, and they will come in one of two ways. Either proactive repairs can be made when problems are first discovered, or repairs can be made at considerably greater cost after catastrophic failures have occurred. As was the case with the I-35 bridge collapse in Minnesota, we often pay in lives as well. Part of the problem is that infrastructure isn’t very exciting or newsworthy to many people outside of the civil engineering community which leads to complacency and apathy. As a result, it’s likely that you may not have heard about the latest struggle currently playing out in California even though it involves the largest dam in the United States and its potential failure.
Surprisingly enough, the largest dam in the US isn’t the famous Hoover Dam but the Oroville Dam at the base of the Sierra Nevada mountain range in California. At 235 meters, it is almost 15 meters taller than the Hoover Dam. It can store over four cubic kilometers of water but whether or not it will keep storing that water into the future is currently under question. In February of this year during a flood control operation damage was observed on the dam’s spillway where a massive hole had formed which only got larger as the dam was forced to continue releasing water. The hole quickly grew, and the floodwaters eroded much of the lower half of the spillway embankment, forming a canyon.
The greater threat to the dam itself wasn’t simply the damage to the main spillway, but the use of the dam’s emergency spillway. It was used for the first time after the main spillway had to be shut down, but once the water started flowing, the amount of erosion behind the emergency spillway was much higher than anticipated. It was thought at one point that the erosion might undermine the strength of the dam itself which would have let loose a 9-meter-high wall of water down the Feather River, destroying many communities in its path. An evacuation order was issued for residents of the area during these series of events, but luckily the main spillway stabilized (although heavily damaged) and was able to allow Lake Oroville to drain enough to alleviate concerns of a total dam failure. The snowmelt in the Sierra Nevada isn’t finished yet, however, so the dam and the engineers working on it aren’t quite out of the woods.