Quote of the Day
Amateurs practice until they get it right. Professionals practice until they can’t get it wrong.
— Special Operations Credo. I hear doctors say something similar. It is true in Engineering and Software as well. For a professional, it is about far more than getting things right – that is a given. It is about having personal processes that reduce the possibility of mistakes and ensure that you can handle any contingency that might arise.
I was on the phone this morning with a coworker who lives in California, about 150 miles south of the Oroville dam (Figure 1). This dam has recently been in the news because of concerns that spillway erosion could cause a dam failure. At one point, nearly 200K people were evacuated from the potential flood zone.
My coworker was quite familiar with the situation in Oroville, and he mentioned that warnings had been given in years past that this situation could occur. People are now asking how could something like this occur. I will leave that for the politicians to explain.
I was surprised to hear that the Oroville dam is the tallest dam in the US – I guess I remember hearing as a child that Hoover Dam was the tallest – it is now second tallest after Oroville. This got me curious as to what are the tallest dams in the US and where they are located. The Wikipedia has an excellent list of the 86 tallest dams in the US. I used Power Query to grab the list and pivot tables to examine the data. For those interested, my source is here.
Figure 2 shows the top 10 tallest dams in the US and their locations. Height is expressed in feet.
I also was curious about when most of these 86 dams were built, which I show in Figure 3. It looks like the 1960s was a big decade for dam building.
I also looked at where the dams were built (Figure 4). By region, the Pacific Contiguous (coast) and Mountain West regions had the largest number of dams by far. I used the US regions as defined by the Department of Energy.
Figure 5 shows that California has the largest number of these tall dams.
As a Californian in the nation's most populous state, I'm not surprised to learn that California is the number 1 "tall dam" state. Thankfully, our state does have a state-run dam inspection program. My "go to" source for news about the state's dams is "Maven's Notebook." Here's the 17 February 2017 update: https://mavensnotebook.com/2017/02/17/this-just-in-oroville-dam-friday-noon-update-flows-to-further-reduce-as-work-continues-to-get-hyatt-power-plant-back-in-operation/. I was surprised to learn that Hyatt Power Plant can operate in a "pumped storage" mode. https://mavensnotebook.com/wp-content/uploads/2017/02/Hyatt-Powerplant-Oroville-Dam.pdf
The biggest California pumped storage facility is PG&E's Helms Pumped Storage facility, located in the Sierra foothills to the east of Fresno. http://www.pgecurrents.com/2014/08/01/helms-at-30-hydroelectric-plant-delivers-safe-clean-affordable-energy/ "The generators can produce a total of 1,212 megawatts of electricity or enough to power the cities of Fresno and Oakland.
Nearly four miles of 28-foot diameter tunnels connect the powerhouse and two reservoirs." (At 6 hours/day of power production, Helms annually releases 2,656, 098 MWh of power [2.67 TWh/year output with 3.54 TWh/year input - Helms is 75% efficient for utility-scale energy storage.])
I did not know about the pump storage mode on some of these dams. Thanks for the information.
Having a state-run inspection program is important. In Minnesota, we learned a sobering lesson about the importance of thorough inspections when we had the I35 bridge collapse. Like so many disasters, it ended up being caused by a confluence of unlikely events: (1) math error in the design of a number of gusset plates, (2) construction on the bridge that put a 300-ton point load over a faulty gusset plate, (3) increased load caused by thicker than planned concrete roadway, and (4) heavy traffic load. Investigators asked why some of these issues had not been caught in 40 years of inspections. No one has given an answer yet.
'Dollars to doughnuts' that it was a set of 'cost avoidance' measures. That seems to be the case for the so-called "emergency spillway" at Oroville Dam, which is a large "zoned earth-filled dam."