Oroville Dam ~ Explanation of a historic event

The Cliff Notes Version of this Breaking Story

  • Construction was completed in 1968 of the tallest dam (not the widest) in the U.S.
  • There is a main emergency spillway to the north that has NEVER before carried water until February 11 at 8pm.  IT IS NOT LINED.  (This is very dangerous.)
  • The main emergency spillway is lined with concrete to prevent earth erosion, and thus protect the damn.

  • The main emergency spillway was designed to release water at a controlled rate to reduce flooding.  However the concrete was cracked and when the water release hit it, the crack became a huge gash in the bottom half of the emergency spillway.

  • If damage is allowed to continue it would threaten the whole dam, so emergency crew lined the emergency spillway with rocks to try to slow down the erosion from the alternate drainage site.
  • Engineers DO NOT wish to continue using this auxiliary section of the hill if it can be avoided.
  • The only way they can do this is to continue sending water out the main spillways at the quickest controlled rate possible.
  • On Monday February 13th, nearly 200,000 people were evacuated, but the evacuation order was lifted to a warning on Tuesday.
  • There are 2 other options for getting water out of the reservoir besides this damaged spot.  However these are ALSO compromised.
  • Flooding along the western side of the Sierras could be 10-100 feet high.

Advice from a Survivor

  1. Look at this spill map above and consider your location relative to it (or any major body of water)
  2. Do not wait for official evacuation orders to leave.  If in doubt, get out.
  3. Follow emergency channels carefully until March. (Yes MARCH!)

Friends of Lake County, this potential Sacramento Valley flood doesn’t affect us.  We have a different set of interesting challenges.  Clear Lake, which is the largest NATURAL lake in the US is above flood stage and we are having cluster earthquakes 10 miles east of the lake. (Read more here.)

This long winded geologist gives you a heads up on the increase in earthquake activity.  (Pay attention to 15m15 to 22m15 for how to use Google earth to evaluate your own home and elevation.)

The Longer Version of this Story

Scale of this Dam

Oroville Dam is an earth-fill embankment dam located in the Sierra Nevada foothills east of the Sacramento Valley.

At 770 feet high, it is the tallest dam in the U.S.and serves mainly for water supply, hydroelectricity generation and flood control. The dam impounds Lake Oroville, the second largest man-made lake in the state of California, capable of storing more than 3.5 million acre-feet.

The embankment was completed in 1967 with the last of 155 million tons of material that it required over 40,000 train trips to transport.

Oroville Dam was designed to withstand the strongest possible earthquake for the region, and was fitted with hundreds of instruments that serve to measure water pressure and settlement of the earth fill used in its construction.  There were some strong earthquakes in the region after it’s construction, earning it the nickname “the dam that talks back”.

(In otherwords… Watch for cluster earthquakes over the next month or two!)

Emergency Spillway Use and Evacuation

Shortly after 8 a.m. on February 11, 2017, the auxiliary spillway began carrying water for the FIRST time since the dam’s construction in 1968. Evacuation of Oroville itself was not considered at that time, as officials stated that there was no threat to public safety. The flow topped out at 12,600 cu ft/s, and the water flowed directly onto the earthen hillside below the the auxiliary spillway, as designed.

On February 12, 2017, an evacuation was ordered for in low-lying areas along the Feather River Basin in Butte, Yuba and Sutter counties, due to an anticipated failure of the auxiliary spillway. The flow over the main spillway was increased to 100,000 cu ft/s to try to slow erosion of the auxiliary spillway.

By 8 p.m. on the evening of February 12, the increased flow had lowered the water level, causing the auxiliary spillway to stop overflowing. However, evacuation orders were not rescinded. A damage assessment was expected on the morning of the 13th. By February 13, 188,000 people in the vicinity were reported evacuated. On February 14, the sheriff of Butte County lifted the mandatory evacuation order following assurances by state and federal officials that the dam and spillway were deemed safe.

As of February 15th the Department of Water Resources continues to reduce water levels in the reservoir. At its current drainage rate the dam is predicted to be able to absorb the anticipated inclement weather arriving later in the week. California State Parks has closed all recreation trails near the Diversion Pool and the Department of Fish and Wildlife has closed off all wildlife facilities as they are severely flooded.

Importance of the Oroville Dam Functions

  1. Hydroelectricity – It is one of the largest underground power stations in the United States.    Since 1969, the Hyatt plant has worked in tandem with an extensive pumped-storage operation comprising two offstream reservoirs west of Oroville. These two facilities are collectively known as the Oroville-Thermalito Complex. The Hyatt and Thermalito plants produce an average of 2.2 billion kilowatt hours (kWh) of electricity each year, about half of the total power produced by the SWP’s eight hydroelectric facilities.
  2. Irrigation – Water released from Oroville Dam travels down the Feather River before joining with the Sacramento River, eventually reaching the Sacramento-San Joaquin Delta, where the SWP’s California Aqueduct diverts the freshwater for transport to the arid San Joaquin Valley and Southern California. Oroville-Thermalito hydroelectric facilities furnish about one-third of the power necessary to drive the pumps that lift the water in the aqueduct from the delta into the valley, and then from the valley over the Tehachapi Mountains into coastal southern California.
    Water and power from the dam contributes to the irrigation of 755,000 acres in the arid San Joaquin Valley Westside and municipal supplies to some 25 million people.
  3. Flood Control – During the winter and early spring, Lake Oroville is required to have at least 750,000 acre feet, or a fifth of the reservoir’s storage capacity, available for flood control. The dam is operated to maintain an objective flood-control release of 150,000 cubic feet per second, which may be further reduced during large storms when flows below the Feather’s confluence with the Yuba River exceed 300,000 cubic feet per second.  In the particularly devastating flood of 1997 inflows to the reservoir hit more than 331,000 cubic feet per second, but dam operators managed to limit the outflow to 160,000 cubic feet per second, sparing large regions of the Sacramento Valley from flooding.
  4. Fish Hatchery – Oroville Dam completely blocks the  migrations of Chinook salmon and steelhead trout in the Feather River. In 1967, in an effort to compensate for lost habitat, the DWR and the California Department of Fish and Game completed the Feather River Fish Hatchery. The Fish Barrier Dam, built in 1962, intercepts salmon and trout before they reach the base of the impassable Thermalito Diversion Dam and forces them to swim up a fish ladder to the hatchery, which is located on the north bank of the Feather River. The hatchery produces 10 million salmon smolt, along with 450,000 trout smolt, to stock in the river each year. The salmon smolt are released in two runs, with 20% for the spring run and 80% for the fall run. This facility has been successful enough that there is concern that salmon of hatchery stock are out-competing remaining wild salmon in the Feather River system.


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