The history of one problematic dam in Oregon teaches how not to manage risk
Were the scientists' concerns justified? It's difficult to say. Leakage has diminished considerably and is now estimated at less than 1 cubic meter per minute. Only patches of wetness are currently visible on the dam face, perhaps validating the engineers' claim that dams made of roller-compacted concrete eventually stop leaking because of their self-sealing tendency.
Still, confidence in the dam's infallibility within the Corps was never complete: Even after the official safety assessment was made, Corps engineers continued to monitor leakage flow and chemistry for the next 15 years at a cost of several million dollars. In 2004, an aeration system was finally installed. The Corps insists that its use is unrelated to dam safety and represents only a measure to control algal blooms by reducing the nutrient loading that results from deep-water anoxic conditions.
Thankfully, the dam didn't collapse, as I and others once feared it might, but the margin of safety under which it operates is not really well known. Indeed, in the two decades since the Willow Creek story unfolded, much has remained unclear. Yet some things are for sure: The public had a right to know about any anomalies in the functioning of the dam; the press was obliged to investigate; and Congress had a duty to protect local citizenry from a structure that it had put in place. But as the history of events shows, the process of technical study and public discourse went awry, beginning with the sensationalized news story, which naturally enough triggered a quick-fix Congressional demand for immediate answers. Under tremendous political pressure, the Corps scrapped a promising scientific investigation and, with only an abiding faith in roller-concrete construction to support its position, arbitrarily declared the dam "reliably safe," a strange phrase that perhaps reflects the fact that the verdict was not without uncertainty.
At that point, though, a more straightforward statement by the Corps that the dam could conceivably become unsafe would have likely required some dire—and discreditable—measures, the most drastic being a forced evacuation of the townspeople and even removal of the dam. So when the troubling news broke, the strategy the Corps adopted was not to admit to any possibility of risk. In a more rational world, all parties would have acknowledged that absolute safety would be impossible to guarantee instantly. The Corps could then have temporarily drained the reservoir to ease concerns and to allow a better examination, and it could have been open about its ongoing studies and efforts to ensure that any dangerous deterioration of the dam would be detected and remedied well before it had a significant chance of endangering lives or property.
I like to think that scientists and engineers faced with a similar problem today would tackle it in such a mature and sensible fashion. But I fear they might well repeat the mistakes made at Willow Creek a couple of decades ago, which is why it's useful to look back on the episode—not just as an amusing piece of history, but also for the (excuse the expression) concrete lessons it can provide to those people whose job it is to assess, communicate and manage risk.