Dam Trouble

California Megaflood: Lessons from a Forgotten Catastrophe

A 43-day storm that began in December 1861 put central and southern California underwater for up to six months, and it could happen again

In 1861, farmers and ranchers were praying for rain after two exceptionally dry decades. In December their prayers were answered with a vengeance, as a series of monstrous Pacific storms slammed—one after another—into the West coast of North America, from Mexico to Canada. The storms produced the most violent flooding residents had ever seen, before or since.

Sixty-six inches of rain fell in Los Angeles that year, more than four times the normal annual amount, causing rivers to surge over their banks, spreading muddy water for miles across the arid landscape. Large brown lakes formed on the normally dry plains between Los Angeles and the Pacific Ocean, even covering vast areas of the Mojave Desert. In and around Anaheim, , flooding of the Santa Ana River created an inland sea four feet deep, stretching up to four miles from the river and lasting four weeks.

If the Great Flood of 1862 happened again most of the dams would probably fail as all of the emergency spillways are based on the same wishfull analysis as Oroville.

If the Great Flood of 1862 happened again most of the dams would probably fail as all of the emergency spillways are based on the same wishfull analysis as Oroville.

Eh', maybe but not due to sh#t construction. My Wife is a leading Dam Safety Engineer for the State of Colorado here in Glenwood Springs, CO. Pretty sure they pay her a f*#kton and she runs a really tight ship.

We supply Lake Mead with a ridiculous amount of water, Parts of California and all of Las Vegas would go full Road Warrior in a month without it. Colorado seems to be on it, but then I'm a moron married to a Hydrologist/Dam expert..

Making use of part of the old diversion tunnels that were used when the dam was built, the spillways were thus more economical to construct, but have less capacity and must have at least 30 percent clearance between the water level and the tunnel ceiling.[
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At the onset of the flood in 1983, several false weather predictions made the Bureau of Reclamation late in opening the spillways.[citation needed] At first, as inflows exceeded normal levels, the penstocks were opened to full release, and as inflow continued to rise, the river outlet works were also opened, discharging more water into the river below. The reservoir, however, continued to rise, and Reclamation finally decided to raise the floodgates. Other than test runs, this was the first time that the spillways had ever been put into operation for practical reasons, this time running at 20,000 cubic feet (570 m3) per second per tunnel. In several days, noticeable vibrations began to make themselves felt in the dam wall and surrounding rock. A close examination of water exiting the spillways revealed noticeable debris, including sandstone, which signaled severe erosion taking place. Reclamation responded by reducing releases by half, however, the rumblings continued, and it was not long before the spillways were shut down completely for examination.[14] The rumblings were so notable that a worker in the employee dining room, located near the power plant, was reported to say that it "sounded like the barrages that he had experienced in Vietnam".[16]

Subsequently, inspection crews were lowered down the spillway tunnels in a small cart to assess damage. What they found was that at tunnel bends, the force of the water, by means of cavitation, had damaged and eroded the lining of the tunnel, which was 3-foot (0.91 m)-thick concrete. At some places the erosion had completely worn away the lining, exposing the soft sandstone underneath; this was the source of much of the debris. The tunnels could not be closed for long, however: the National Weather Service was reporting more rainstorms in the Colorado River Basin,
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Reclamation was worried that the water would eventually erode around the diversion plug altogether, creating a connection to the reservoir floor. This uncontrolled spillage would cause the reservoir to drain.