Erosion has created a 300-foot-deep hole in the concrete spillway of Oroville Dam and state officials say it will continue grow.
State engineers on Wednesday cautiously released water from Lake Oroville's damaged spillway as the reservoir level climbed amid a soaking of rain.
Situated in the western foothills of the Sierra, Lake Oroville is the second-largest manmade reservoir in California after Shasta....
I also suspect that the state dam operators were victims to some extent of the 'drought mentality' in California these past several years.
A year ago, during the 2015/2016 rainfall season, we were supposed to get an unseasonable amount of rain due to the so-called 'El Nino' effect, but it never really materialized. The levels of the major reservoirs were allowed to fall in anticipation of the heavy rainfall that never came and so it was a struggle all summer to keep water available for the farmers and the municipal water districts (which some politicians used to make their case, particularly with farmers, for getting rid of state and federal water conservation rules, with one candidate going so far as to say that if elected he would simply declare the drought over which would solve everyone's problems). Then when the rains started this past fall, the state's water managers gave orders to allow the reservoirs to fill again so that could capture as much of this early rainfall as possible in anticipation of another dry year like that last several, but as we all know now the rains continued to come in and much heavier than anyone expected, and before you knew it, places like Oroville were topping out. Granted, perhaps someone should have been keeping a better track of what was happening and been quicker to adjust their assumptions but looking back on what we had experienced statewide the last 5 or 6 years you can't help but have at least a little sympathy for the water managers and what they were confronted with. I hate to state what some will suggest is a pun, but what we had here was a "Prefect Storm".
IRstuff, sure one could certainly imagine that the sudden switch from extremely dried out conditions to extremely wet could well have led to erosion or subsidence or similar but I don't know about 'had to have' quite yet.
All I was intending to say is that cavitation is a cumulation of stress and time; the fact that the surface failed under relatively low flow and duration would suggest that cavitation itself was not likely to have been the problem.
TTFN (ta ta for now)
I can do absolutely anything. I'm an expert!
What d-ya suppose is the reason for the quarry drill making a drill hole just up hill from the main failure. I sure hope they are looking to remove any crappy stuff under the slab in the zone above that failure and replace it, full length with hard stuff, like concrete. Take the bull by the horns there and do it right this time.
Sure, but the entire hillside is like that, so even if that section is backfilled, a different year with heavy rains might washout a different section of spillway.
TTFN (ta ta for now)
I can do absolutely anything. I'm an expert!
Just a observation from studying the various photo's ,it is clear that the composition of the material in that hill is not stable, nor solid granite. So whatever one built on top, will need a solid man made foundation. I agree with a previous poster, now it is time to redo that whole Shute. With either piling or layered compacted material at least 3 meters deep. We had tremendous success with that in other parts of the world before. The same counts for the emergency spillway. I think whatever cosmetics they apply now, will in due time, should this happen again, wash away. I just cannot see how only a layer of cosmetic cement will solve the problem there(emergency spillway). I understand what they trying to do now by filling the area up in steps, but that will be gone in no time, should there be a heavy flow again over the emergency spillway. This can be a very interesting project. I like this kind of problem, as you surrounded with obstacles and yet, there is a way out. Sort of putting a puzzle together. The other issue is to harnass the flow in the main shute. That on its own is interesting as one face various problems as you slowly increase the flow there. I just simulated it on a flow program.
We can agree on doing it right this time, but there are the factors called money and politics. At least they are kind enough to keep us posted on the job in general. They could keep it a secret, hiding their past mistakes.
Yes this is an example of the thesis put forward by Prof Henry Petroski, currently of Duke University where he teaches Civil Engineering and History, that since most civil engineering projects are paid for with taxpayer's dollars that the requirement to let the contracts to the lowest bidder will eventually result in the inevitable engineering failures. It's the nature of the process, but that we can learn from this because when a failure does occur, it establishes what it meant to go "one step too far", and that engineers need to learn from these failures to determine what is the appropriate level of safety that has to be laid down as the minimum below which no project can be taken irrespective of what the political or monetary pressures might be. He covered this in a series of books, several of which concentrated on public works such as bridges and public structures, like arenas and such.
Note that I've read several of his books including 'To Engineer Is Human: The Role of Failure in Successful Design' and 'Design Paradigms: Case Histories of Error and Judgment in Engineering' both of which included extensive discussions about the limitations imposed on public works projects and how engineering failures are often the result of compromises having been made by public officials and/or to live within the funding of such projects.
I've long figured that we'd save money on projects and get a better result in the end by going with somebody other than the lowest bid. Even taking the second low bid would save a tremendous amount of heartache;
nobody would be able to buy the project, the best they could do would be to get out of somebody else's way. Even better, with a good field of bidders, would be ignore the bottom and top bids and then take the bid
closest to the median (or mean) of the remaining bids. At that point you're getting somebody that spent some time trying to understand the project and put some effort into trying to coming up with a number that
makes sense. It seems to me that it would be impossible to game that without extensive collusion among (nearly) all of the bidders.
Even better might be to have the resources to properly review the bids for things like technical compliance, past performance history and all the other stuff beyond simple price. Then out of acceptable bids determine which is the best value.
Of course, doing so objectively and thoroughly is pretty tricky.
These last few posts raise the issue of awarding construction contracts to the lowest bidder. The builder of this dam may indeed have been the lowest bidder, but I don't think we have any evidence at hand to suggest that the construction was not accomplished in accordance with the design.
The most successful major project tender evaluations that I have seen have split the process into two teams - Technical Evaluation, and Commercial Evaluation.
Bids are received in two separate packages - Commercial, and Technical.
The Technical Evaluation team don't know the prices of the bids they are looking at - they simply assess whether the Tenderer has the capacity to undertake the work, whether the bid is conforming, and if not, whether the non-conformance is acceptable. If it is considered to be unacceptable, a request is sent out for a revised offer which conforms with the requirements - and again, any price adjustment is passed on to only the Commercial Evaluation team, NOT the Technical Evaluation team. If a non-conforming offer is deemed acceptable, all Tenderers will be notified of the nature of the non-conformance, to allow them to adjust their offers so as to not be disadvantaged. Only conforming or acceptable bids are considered further.
The Commercial Evaluation team assesses only the contractual and commercial matters, including any price adjustments required to bring the bid to technical conformance. Any bid which has suspect commercial capacity, IR, Safety, QA, etc is eliminated from the evaluation process.
Only bids which are both technically sound and commercially sound are left on the table - and the lowest-priced, commercially acceptable, technically-acceptable bid wins the contract.
This process has worked very well on large projects I have seen (power stations, dams, etc), but it does require a level of competence and diligence that seems to be missing in many public projects these days.
jhardy, even there the issue of 'best value' isn't fully addressed.
Consider a vendor who perhaps proposes a design with a higher life or some such spec beyond the minimum required for a relatively small price delta compared to a company that barely meets all specs for a slightly lower price.
There's a good chance the former is actually better 'value' but even your process may not appreciate that.
In all honesty, you really need to read Petroski's books (or at least the second one I referenced earlier) to understand what his thesis is and it doesn't really have to with sloppy construction or even that the lowest bidder was under-qualified to do the job, but rather that until something fails there is very little that we can learn about what it would have taken to not fail. In other words, we learn much less than we think we do when something does NOT fail and works exactly as it was expected to. It's only when something fails that we learn that we have gone too far. His thesis basically postulated that over a period of time, as public works projects are completed, say a series of similar large bridges over a 70 or 80 year time span, that each subsequent contract bid will be based on the success of the last bridge but with the added pressure from those who will be financing it that perhaps that last project was a bit over-designed and so the tendency is to trim the 'margin of safety' just enough to demonstrate an appreciation for the need to get the most bang out of the taxpayer's dollar. But eventually you will trim it just a bit too much like, in that old adage about "the straw the broke the camel's back".
One of the examples that Petroski used in his book was the Tacoma-Narrows Bridge (AKA "Galloping-Gerty") in Washington state. Up until that bridge was built NOT a single large suspension bridge had ever failed. And NO large suspension bridge has failed that was constructed AFTER they learned why the Tacoma-Narrows Bridge failed. After nearly 60 years of successful construction of suspension bridges, starting with the Brooklyn Bridge in 1883, with each subsequent suspension bridge becoming more elegant and lightweight, until 1940 when the Tacoma-Narrows Bridge was finished. It doesn't take much of an expert to look at how suspension bridges evolved over that 60 year time span to see that Petroski's thesis has been borne out.
I seriously doubt that anyone dealing with a multi-million dollar project is simply going to take the lowest bid without doing some level of due diligence. While few go to the levels outlined by Julian, we, as professionals, have to go through the technical proposals to ensure that the proposer is at least competent, and at least compliant to the KPPs. And certainly, in government, CYA is a major factor, so lowest bid is not guaranteed to win unless there's an extremely high confidence that the contractor can pull it off. If anything, CYA automatically dictates that lowest bid gets tossed out, along with highest bid.
Examples from aerospace/defense that I'm aware of
> We bid against a competior for the very last buy of a large subsystem and underbid the competior by a significant amount, and they had never built anything in that class of subsystem before. Nevertheless, they won, and wound up having to get help from us afterwards. CYA says that we were a totally bad risk for the contracting officer in charge because we had just gotten fined for falsification of test records in the year leading up to the RFP.
> We bid on a system and were probably 50% higher than the incumbent, but we won. CYA says that the incumbent had serious issues in the past, and we were later told by the customer that our proposal was substantially superior to the incumbent's, particularly in the area of a single KPP that was actually erroneously specified by the customer, which we caught and proposed a much tighter requirement that was correct for the intended application.
> In one case, our dreaded BD folks decided to drastically underbid on an effort that we had previously briefed a higher amount to the customer. The contracting officer did not do their due diligence, and didn't listen to CYA and awarded us the contract, which we promptly overran. The contracting officer was summarily fired from the program, although our BD folks escaped unscathed. To make it worse, the contracting officer took his windfall and funded a competitor, who later ate our lunch, and the program itself wound up getting mothballed.
TTFN (ta ta for now)
I can do absolutely anything. I'm an expert!
Engineering can be a gamble to some extent, can't it? I read 'To Engineer Is Human: The Role of Failure in Successful Design' some years ago. But I recall a basic premise being that lots of people can design/build big strong (i.e. expensive) things that won't fail. But the art of engineering is designing things that are right on that edge (with acceptable factors of safety of course). Which is one of the main reasons we have failures.
Another fun read I covered at about the same time, while not directly related to this incident, was Mark Eberhardt's 'Why Things Break: Understanding the World By the Way It Comes Apart'. It was a good bridge for me to a better understanding of the principles of materials science.
"All I was intending to say is that cavitation is a cumulation of stress and time; the fact that the surface failed under relatively low flow and duration would suggest that cavitation itself was not likely to have been the problem."
How well was the spillway inspected for damage after the prior usages, and were repairs made? How good were the repairs?
This is an open flow channel at a very steep grade, flow will be supercritical at almost any discharge (see the capillary waves running down the slope at near-shutoff when the inspectors are futzing in the chasm?), velocities of the flow will be high enough, somewhere on that steep grade, to reach cavitation at small surface aspherities. I.e., it's a given, not a maybe. The thing would have to be smoother than glass to avoid cavitation, and even then I'd not be certain.
I don't disagree that other factors could be involved (subsidence of underlying layers, lack of reinforcement, loss of seal at expansion joints...) but without due consideration of fluid mechanics, fixes that ignore it won't work.
Almost like you would want to begin designing these style "open-flow" unconstrained spillway floors and walls like an inverted planing surface: Complete with multiple, small-height, slightly-angled but sharp-edged "steps" with air flow allowed back underneath the liquid mass possible from the sides.
Instead of a high-speed small boat continuously but steadily "bouncing" off of a still (ideally smooth) water surface, you'd have a still surface with a high-speed water flow going over it.
If the instruction to bidders contains the methodology for acceptance, it may be easier to disqualify an unsuitable bidder. The owner can be exposed to litigation without a 'real' reason for rejecting a bid, after a contractor has invested a substantial cost in preparing it.
