As what could be, even under normal circumstances, catastrophic levels of precipitation begin in Northern California, and we continue to receive reassurances from the powers that be, there are some people doing some excellent investigation into just how the Oroville dam got into this mess. The particular source of interest today is a British newspaper, The Daily Mail, under the sensationalist headline:
There is a lot of coverage out there with such attention grabbing headlines. I usually go past them pretty quickly because I am more interested in information than in impact – but this piece contained some pretty amazing information. Here’s the meat:
Earlier it was revealed cracks in the main concrete spillway have been included in site reports since 2009 but crews have been resorting to quick-fix concrete solutions to try to stop them from getting worse.
The repairs that have been going on for years were labeled shoddy by Robert Bea, professor emeritus of civil and environmental engineering at University of California, Berkeley.
‘It’s ‘obvious those repairs didn’t work.’ We don’t have details on the repairs, but they put cement into the cracks and troweled it over. I call it “patch and pray.”
Inspectors with the state agency that both operates and checks the dam, the nation’s tallest at 770 feet, went into the half-mile-long spillway in 2014 and 2015 and did not find any concerns.
‘Conditions appeared to be normal,’ the inspector wrote in reports from both years. The most recent report which deemed the dam safe was in August last year when a team of inspectors checked it from only from afar.
The inspection was ordered as California was enduring a five-year drought which meant that until last year, the spillways had gone largely unused.
I would call that repair technique just “pray.” But that takes a little explanation.
Now, before I get into this I want to emphasize that while I know more than the average joe-on-the-street about materials and construction, I am far, far from an expert.
What you really need to know is this – the material we see around us in such great abundance in not “concrete;” it is “reinforced concrete.” The difference is very straightforward – concrete is the stuff we see on the surface, which can be chipped away at fairly easily. But reinforced concrete means that shape of concrete is run through with a reinforcing material, typically steel rod know as “rebar.” As I say, concrete is not all that strong, but you use it to encase a carefully constructed web of rebar and suddenly you have the miracle of construction that built the Hoover Dam – and a thousand other construction miracles that would never work with any other material. It is also important to note that it is the combination of these materials that works these construction wonders – neither steel alone nor concrete alone could do the same job.
Now let’s start with the cracking that they patched. Depending on the severity and amount of cracking these cracks could indicate substandard design or construction of the dam initially, but at this moment there is not enough data to know. Not to mention, I would not be expert enough to say even if the data were available. But fixing reinforced concrete I know a little about. Simply troweling in some concrete is almost useless – it fills the crack, but it does nothing structurally whatsoever.
Here’s the thing, as we said, concrete proper is a fairly weak material and when you put wet concrete on top of dry concrete the new layer of wet concrete will not stick to the underlayer when it drys. It just won’t. If you went and bought a bag of concrete at the hardware store, brought it home, mixed it up and poured it on your sidewalk – the next day, after it dried, you could probably kick the new layer off with your feet. You will have accomplished almost nothing. To really repair a fail in reinforced concrete you have to remove materiel to expose rebar, then tie in new rebar and then apply the concrete over the newly repaired rebar structure. It’s the rebar that ties the fix into the existing structure, not the concrete.
Thus, when the water starts flowing over these ersatz patches, the force of the water is likely to knock the patches out of the crack, like your foot on our imaginary new layer above.
The next thing you need to know about is fluid dynamics. When water flows through those spillways it is supposed to flow over the top of a smooth surface. This results in something called “laminar flow,” which means the water flows more or less straight over the reinforced concrete structure. But when there are cracks in the structure, those cracks create “turbulence” in that laminar flow. Think of this turbulence as little whirlpools around the crack that act as drills, using the force of the water to make the cracks ever larger. Eventually the cracks are going to get large enough to create the mess that we all witnessed last weekend.
Now the article, (BTW, you really should follow the link- the pictures are jaw-dropping) also contains this little tidbit:
The Department of Water Resources declined to answer specific questions about the repair work, saying engineers were focused on ensuring public safety.
That’s probably the right place for the engineers focus at the moment, but I sure as heck hope that someone follows up on this, because this is outrageous.
It’s not hard to speculate on why the repairs were done this way and why everybody passed the buck on it. When the people that make the budget and set the priorities are focused on boondoggle trains and believe that because of “climate change” it will never again rain hard enough for the spillways to be needed, and therefore there is no budget for this kind of stuff, its pretty easy to just shrug your shoulders and move on. Especially in California where you’ll never lose your job and get a very handsome pension to boot, regardless. There are only so many times that anyone is going to be willing to beat their head against the deaf-and-dumb stone wall of elected and appointed officialdom in California before they just stop trying. If their bosses don’t care, why should they? Although it is galling that we are paying them with taxpayers money not to care.
Who knows how many other dams in California are poised to fall apart just like this on has – just waiting like a snake-in-the-grass to bite us.. What I do know is that this particular snake needs to have its head removed. I just pray the voters of California are smart enough to figure that out.