The Oroville Dam Failure
AGENDA 21 RADIO
BY Scott Cahill, Construction Expert
As I write the Oroville dam in California is eroding back toward a breach of the reservoir. I am a dam contractor. If you ever heard someone say “that dam contractor..” they may have been talking about me.
I have repaired hundreds of dams including ones like Oroville, which were in the process of failure. I know a lot about dams.
The spillway failure is a common type of failure, where phreatic, or surface water entered the spillway, migrating beneath the slabs. (A static element on a dynamic element, A hard element on a live element). The dam is hydrated and dehydrated as water levels rise and fall, moving, as soils swell from pressures and water mass. In times of high rain the phreatic surface (hydrated soils line) moves toward the surface, venting into the void so produced.
This creates a void. Moving water over the years has eroded soils from beneath the slab downstream and left a channel. Now, the spillway has been actuated in a high-flow event and the plates of the spillway have failed into the stream, scouring from beneath them. They will continue to fail as the water continues to flow. The hydraulic jump exacerbates this erosion.
If the flow continues for a long enough time, with sufficient velocity, the reservoir will be voided by the migration of the erosion to the pool (cut-back). I cannot tell if failure is imminent, from Ohio, but it is an unacceptable situation that has been allowed to develop. It is a case of pennies pinched producing dollars spent, perhaps tragedy.
What we can learn as a nation is the information that is being disseminated. Words chosen carefully, to not excite, to not scare. The issue, as it now stands is serious, life-threatening even. The officials, the owners reps, the media will tell us now, that there is nothing to be be frightened about – all under control (remember Katrina??).
We have, for so long, ignored the failing infrastructure of this great nation, Let us hope that a fatal failure is not necessary to get us to act. Past experience does not make me hopeful of that.
Oroville is 770′ high, 6,920′ long. It is one of the 20 largest dams in the world. If Oroville breaks, The city will be flooded.
Eight thousand three hundred and seventy five residents are at risk within the inundation zone. Two hundred thirty critical facilities in the city of Oroville are within the inundation zone, including; Eleven schools, twenty one day care and children service centers, fourteen elder care facilities, twenty six bridges will be lost, the airport, two fire stations, the government administration building, three law enforcement stations, the EMERGENCY OPERATIONS CENTER (brilliant) Two waste water treatment plants, the jail, and the Hospital. (from the City of Oroville local hazard mitigation plan update May, 2013)
We are not talking about a river rising, where people have time to evacuate. We are talking about a wall of debris, mud, and water taking out a city, buildings, roads, bridges, life, in a horrible instant.
When will we, at last mandate proper maintenance and inspection of these high hazard and medium hazard dams? Why are we willing to suffer a loss of hundreds of millions of dollars to save a couple of dollars on proper and responsible dam safety and repairs?
Whatever you may hear, this is a significant event which could be horrible in its scope and its magnitude. Let us pray that it does not breach, and let us hope that, at last people are sufficiently concerned to act.
Scott Cahill
