I read this weekend about the reservoir accident at the Taum Sauk Proffit Mountain Reservoir in Missouri. A section of the reservoir wall washed away early on December 14th, allowing a billion gallons of water to cascade down a hillside, washing away a house and nearly killing its occupants. Several cars & trucks on a highway that happened to be in the wrong place at the wrong time were also washed off the road. Nobody was killed, but still; a dang scary deal.
The Taum Sauk reservoir is used in generating electricity by provider AmerenUE; water is pumped into the reservoir at non-peak times (at night) and released to drive turbines & provide additional capacity when needed. The reservoir holds 1.5 billion gallons of water, and AmerenEU officials say that malfunctioning overflow sensors allowed too much water to be pumped into the reservoir, which overflowed and quickly eroded a 700 foot wide section of the reservoir wall. It also turns out that the section that washed away contained substandard fill and dirt instead of the granite that was specified by the engineers who designed it. Uh oh.
It seems strange to me that malfunctioning sensors are at fault in this accident. For one, there had to be more than one system watching over the water level. Something that critical ought to have several levels of redundancy, shouldn’t it?
Now, I have no intimate knowledge of how the water level maintenance system at Taum Sauk was designed or how it’s supposed to operate, but I would think that if one sensor malfunctioned, another sensor with a contradictory reading should have raised some kind of alert to inform an operator that something was up. And if it were me designing a system like that, contradictory readings from two sensors would shut down the pumps until a real live human being could step in and determine what the problem was.
But with this incedent, maybe the operators have seen these sensors malfunction before and have learned that the sensors can be ignored. It’s also possible that an overflow wasn’t considered a critical issue; that nobody envisioned an overflow situation would wash away a huge section of the levee and allow it to drain in 12 minutes. Who knows.
One thing is sure; sensors were in place that should have told someone that things were going wrong, and for whatever reason somebody either didn’t get the message or ignored it. And somebody else is going to be in the hot seat answering some difficult questions about why this happened, and in the end spending a lot of money getting things back to where they were on December 13.