CONTROLLING THE FLOW
California’s Water Supply Eroding under Pressure
Silt built up during 19thC. gold-panning days was used in early 1960s, alongside local sandstone, to construct a backup system for California’s second-largest [electricity-generating] dam at Oroville, despite knowledge that sand and silt from river erosion takes years to settle. And preferably a series of dry years, without rain storms. When it rains, the emergency—earth sluice—is expected to handle any excess.
This year at Oroville both main spillway and emergency failed.
Dammed if we Do and Damned if we Don’t
Department of Water Resources has charge of maintaining an adequate water system for agriculture in the adjacent Central Valley, but it is also responsible for maintaining water aqueducts and two pipelines to supply 3.8million households in Southern California.
In addition to the bonus of the Dam’s production of hydro-electric power for the State.
But background to this important water resource reveals shaky foundations.
Despite a crucial rainstorm flood over Christmas 1964, the incomplete dam was launched by Gov.Ronald Reagan in May 1968, during a week-long festival in Oroville attended by 50,000 visitors.
Ten years later, a massive series of earthquakes hit Oroville in August 1975.
Lori Dengler, Professor Emeritus of Geology at HSU, then a graduate student at UC Berkeley, was obsessed with the seismic ‘swarm’ that shook the dam and its surrounding “surface faulting”—a cluster of fault lines—similar to Petrolia. To her, earthquake reaction came after water levels were dramatically changed.
During the winter of 1974-1975, the lake was drawn down to its lowest level since inauguration, to repair the intakes to the power plant. It was then rapidly refilled and followed by the earthquake sequence of 1975.
August 1, 1975 a Mag.5.8 earthquake hit Oroville. Quakes of this size can occur anywhere in the state, so its size was no surprise. This had been a seismically quiet area, however, and those of us working in the lab noticed when seven earthquakes in the Magnitude-3 range occurred in a tight cluster near the lake. On August 1st, the seismicity ramped up—a Mag.4.7, a Mag.5.8 and 35 additional tremors in the Magnitude-3 range. Vigorous aftershocks continued with over 200 earthquakes in the magnitude-3 range recorded over the next 18 months. Then things quieted down and no earthquakes of Magnitude-3 or larger have been recorded near Oroville since 1992.
It’s not unusual for an earthquake sequence to pop up out of the blue, but the difference in Oroville was two factors linking the earthquakes to the filling of the reservoir. The first was the proximity to the lake, the location of surface faulting and the tightly clustered epicenter locations. The second factor was that the earthquakes followed an unprecedented seasonal fluctuation in lake levels.
Lori Dengler, Prof. Emeritus, Humboldt State University
Time Travel to the Tertiary
For more than a century, the Foothills were considered seismically inactive. That changed with the 1975 Oroville earthquake. The temblor did not cause much damage outside the sparsely-populated Oroville area, but it did have a major impact.
The scientific community had to reassess the large Sierra Foothills area as seismically active, according to the California Geological Survey.
“The Auburn Dam was being built at the time and for design purposes we were asked to estimate how large an earthquake the system could generate. We estimated a Magnitude-6.5 Richter, capable of displacing the dam’s foundation by about three-quarters of a foot. That sent the dam back to the drawing board. The cost multiplied over time, and the dam was never built.”
Michael Reichle, Asst. Director Dept. of Conservation
California Geological Survey
Oil and Gas Wells in Sunken Bedrock Add Instability
Data from a number of (USGS) sources indicate that the Willows fault is far more extensive and complex than previously thought and that Tertiary deposits in the Foothills are in motion. The first clue that the Willows fault branched into a multistrand fault system was provided by an analysis of seismicity of the northern valley and Sierra foothills after the Oroville earthquake. USGS (in 1978) located a number of small-magnitude earthquakes along a zone that originated near the Marathon “Capital Company No. 1” well in the Willows-Beehive Bend gas field and extended north, rather than following the northwest trend of the Willows fault. A slew of seismic events suggested that a north-trending fault splayed off from the main stem of the Willows fault and passed west of the Corning domes.
On the east side of the valley, Upper Cretaceous sandstone and shale rest uncomfortably on metamorphic and plutonic rocks of the Sierra Nevada.
These bed companions are not made any more comfortable by the instability of the great seismic rift which stretches from Mariposa (Yosemite) in the south to Chico and Cottonwood, just S of Redding, in the north. The bedrock first went through onset of marine sedimentation (W to E) in the late Mesozoic era, and through intermittent periods of uplift and subduction the sand and shale—along with their mountain bedfellows—tilted to south and west. In late Cretaceous the reverse occurred and the sand/shale deposits slid westwards—’marine regression’ (E to W).
During these upheaval and subsidence cycles, four submarine canyons developed—cut and then filled, rifting and then flooded with sediment. Where they meet, near Sutter Butte cinder cone, above, movement both east and west continues.
Riverbank Collapse on Dam Shutdown Leaves Salmon Floundering
In the Corning gas fields, analysis of well records by the Sacramento Petroleum Association (1962) showed an anticlinal fold in the area of the Corning domes, with about 121m of maximum closure on the base of the Tehama Formation in the north dome and a steeply dipping southeast-trending fault located at the north end of south Corning dome, but it did not identify a fault west of them.
California Geological Survey
With a new gap in the main spillway now stretching like a fifteen-lane freeway across the cement foundation, immediate closure of Oroville Dam was announced this week. Such a drastic move is in part attributed to safety of those displaced valley residents who have since been allowed to return to their homes and orchards.Salmon young and riverine residents are now without a river bed, as most of the banks have collapsed. Almond, peach orchards and fruit farms, dependent on a seasonal flow of water, were unprepared for such extreme measures, their irrigation systems now high and dry. Salmon fingerlings and immature Chinook die in stranded pools, life-expectancy zero.
Children from Oakdale Heights school, above left, releasing babies last fall into the river, expected their hatchlings to have at least a one-percent chance of survival, on their return from the ocean, are now dismayed by the zero percent outcome for the salmon after dam failure.
Governor Jerry Brown has pledged financial help for storm-affected communities, but the state of California has already unmet infrastructure costs of $187 billion, not including roads. While $2.7 billion has been approved [Prop.1, 2014] for new water storage, that doesn’t cover old dams.
Remembering the warning of seismologists Reichle and Dengler, above, against any sudden changes in water body movement—which can trigger volcanic fault movement—we await the outcome of the shutdown decision with anxiety. It’s not only the salmon spelt, rescued manually from puddles, it’s the water supply for most of the Great Valley.
At times of flood and deluge like these, the slow approach to dam containment—like that of the Klamath River tribal community, with four Atlas Copco dams to maintain until they are dismantled and removed—seems preferable to acting on impulse.
Where Mother Nature rules, we mortals are still fallible.