Oroville Dam
| Oroville Dam / Lake Oroville | |||||||||
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| Coordinates | 39 ° 33 ′ 0 ″ N , 121 ° 28 ′ 0 ″ W | ||||||||
| Data on the structure | |||||||||
| Construction time: | 1957-1968 | ||||||||
| Height above foundation level : | 235 m | ||||||||
| Height of the structure crown: | 281 m | ||||||||
| Building volume: | 59 635 000 m³ | ||||||||
| Crown length: | 2 317 m | ||||||||
| Crown width: | 15 m | ||||||||
| Power plant output: | 819 MW | ||||||||
| Data on the reservoir | |||||||||
| Altitude (at congestion destination ) | 274.5 m | ||||||||
| Water surface | 63.98 km² | ||||||||
| Storage space | 4.364 billion m 3 | ||||||||
The Oroville Dam is a debris dam north-northeast of Oroville in Butte County of the US state California . It dams the water of the Feather River in the foothills on the western slope of the Sierra Nevada to Lake Oroville , generates electricity and, as part of the California State Water Project, supplies central and southern California with irrigation and drinking water. The dam also functions as a pumped storage power plant for energy storage and is also used for flood protection and recreation.
The Oroville Dam is part of a series of hydraulic structures on the Feather River, the Oroville-Thermalito Complex , a chain of dam structures, reservoirs and power plants that are operationally linked.
Building
Dam structure
The Oroville Dam is the tallest dam in the United States , ahead of the Hoover Dam, and among the 20 largest in the world in terms of structure height and dam volume. The dam is a 235 meter high and 2317 meter long zonal earth dam that holds back 4.36 cubic kilometers (= billion cubic meters) of water. On the right-hand side and somewhat separated from the actual dam body, there are devices for flood relief on a ridge that seals off the valley. They consist of a structure with movable weir gates with a subsequent chute and stilling basin , as well as an emergency overflow with a drainage of the water over a natural bed in the area.
There is a bottom outlet at the cavern power station under the dam structure . If the lake level falls below 195 m, this drain is the only way to feed the 1.05 cubic kilometers of water still in storage into the lower reaches of the Feather River. This is particularly important in drought conditions, as the river bed would otherwise dry out.
Both the operational overflows, flood reliefs, drainage devices and the power plant runoff of the Oroville Dam flow into the Thermalito Diversion Pool , another reservoir that is dammed in the original bed of the Feather River by the Thermalito Diversion Dam a few kilometers downstream .
pumped storage power plant
In the rocky mountains on the left, below the foot of the embankment, there is a cavern power plant that uses the hydropower potential of the dammed up reservoir. Six machine sets are installed in a cavern built in the rock with the area of two football fields, three of which have a generator output of 132 megavolt amperes and three have 141 MVA, which corresponds to a total installed generator output of 819 MVA. The construction head is approx. 187 meters, the variable head depending on the water level in the reservoir is 125 to 206 meters. The nominal flow rate is 480 m 3 / s at maximum output . The headwater is fed to the power plant through two pressure lines, each 6.70 m in diameter from the inlet structure on the reservoir. The processed water is drained via a gravity line and a pressure pipe into the Thermalito Diversion Pool .
Three of the six machines are designed as pump turbines so that the system can be operated as a pumped storage power plant during off- peak periods . To do this, the functional principle of these three pump-turbine machine sets is reversed and water from the underwater , the Thermalito Diversion Pool , is pumped back into the reservoir with the excess electrical energy available in the power grid . The design pump head is 180 meters, with a volume flow of 53 m 3 / s per machine set; the total pumping capacity of the system is 159 m 3 / s. The machines have an output of 129 megawatts each in pumping mode
Fish pass
The Feather River Fish Hatchery was built in Oroville to compensate for the impairment of fish migration caused by the transverse structures . This is a fish farm where king salmon and rainbow trout ( "steelheads" ) are raised and used in the Feather River to preserve the natural species . On the fish ladder or fish ladder of the facility, you can watch the salmon migration through underwater windows in September and October .
history
The construction work began in 1957 with road relocation and ended with the inauguration in 1968. Most of the building material (clay, sand, gravel) was transported to the construction site by bucket wheel excavators, belt conveyors and shuttle trains from a former dredging field, where gold was extracted south of Oroville.
Since 1975, when an earthquake with a magnitude occurred 5.7 at Oroville, you know that the dam on an active geological fault was built.
In 2005, three environmental groups asked the Federal Energy Regulatory Commission (FERC) to secure the dam's emergency overflow with concrete instead of leaving the unsecured earth dam overflow. The environmental associations declared that the earth dam overflow would not meet modern safety standards. If the emergency overflow had to be used, this could lead to severe erosion on the earth dam overflow and this in turn to flooding in localities below the dam. The FERC and other authorities, who would have to bear the costs of securing the emergency overflow with concrete, considered this unnecessary and the concerns exaggerated.
Accident at the bottom outlet in 2009
On July 22, 2009 of the occurred in the underground valve chamber bottom outlet an accident when it was created a strong negative air pressure in the discharge line at the test point opening the bottom outlet valves, which completely broke up acting as a pressure bulkhead partition and devastated the operating platform of the drain valves. One worker was seriously injured and several others were slightly injured. The valve chamber is located under the dam near the power station cavern of the Hyatt Power Plant in the course of a bypass tunnel that was created during construction. The two bottom drain valves could only be operated from the damaged platform. A baffle ring provided in the outlet tunnel below the mouths of the Howell Bunger valves to calm the flow was removed by the operator in spring 2009 because it was damaged. The water jets shooting into the tunnel at high speed generated such a turbulent flow that the tunnel's ventilation failed and the negative pressure was created that caused the damage. As a result of the accident, the operation of the bottom outlet valves was prohibited, as they could not be operated without endangering the personnel. The bottom outlet was renovated between 2014 and 2015. For this purpose, the valves were removed and completely overhauled and a new control system installed, the control room of which is now located in the turbine hall of the power plant and allows remote actuation of the valves. Due to the still missing bluff, the bottom outlet was operated with reduced flow in the dry summer phase of 2014 and 2015. In 2016 a new baffle ring was installed that allows the valve to open without restriction. At full water level, a water discharge of 153 m 3 / s could be achieved. However, at the beginning of the flood problems in spring 2017, the bottom outlet could not be used again, as work to improve fire protection in the underground facilities was carried out from January 2017, which meant that the valves could not be operated.
Failure of flood relief in 2017
In February 2017, after weeks of rain, the dam reached its maximum storage target . As planned, the adjustable flood relief , which consists of a barrier structure at the height of the dam crest and a concrete chute, was put into operation.
From February 7, 2017, parts of the concreted channel erupted. In order to delay the destruction of the channel, which progressed further up to the barrier, the flow rate was reduced again, which led to a further rise in the water level in the reservoir and finally to the overflow over the emergency overflow area to the side, which, however, has no erosion-preventing water drainage. This overflow, which was supposed to relieve the controllable flood discharge, became active for the first time in its 48-year existence. In order to prevent a catastrophe by undermining the emergency overflow, the amount of water flowing off via the concreted flood relief channel of the dam was increased again, which caused the water level of the reservoir to drop, but led to massive progression of damage to the weft channel. Parts of the water from the firing channel now flowed next to the channel and led to massive erosion on the slope.
evacuation
On the evening of February 12, 2017, residents of Oroville and the counties below the dam were ordered to evacuate immediately. With helicopters, boulders were dropped in big bags below the emergency overflow to stabilize the slope in front of the wall. The reason for the evacuation were fears that the concrete wall crest of the emergency overflow could be so undermined and weakened by regressive erosion that its stability can no longer be guaranteed and that if it breaks, up to 10 meters of the dammed lake level could spill over the slope downstream. At this point in time, around 2800 m 3 / s were again drained through the badly damaged chute in order to prevent flushing at the emergency overflow. The situation was made worse by the fact that, as a result of the damage to the relief structures, enormous amounts of rubble and debris were washed into and deposited in the Thermalito Diversion Pool , the artificially dammed up river bed of the Feather River below the barrier. This led to a damming of the underwater of the Hyatt Power Plant , which is located in a cavern at the foot of the earth dam, and therefore had to be shut down. Its flow capacity of around 370 m 3 / s was no longer available for flood relief. More than 160,000 residents of Yuba , Sutter and Butte Counties were affected by the evacuation.
On February 14, 2017, residents were allowed to return to their homes, but a readiness to leave the affected areas was recommended. On March 22, 2017, all warnings and readiness recommendations regarding a new evacuation were lifted by the Sheriff of Butte County.
Backup work from February 27, 2017
After the emergency overflow had been in operation for two days, water was continuously drained from the reservoir via the damaged chute in order to lower the water level. In the course of February 27, 2017, after the lake level was lowered by about 19.2 meters, the discharge through the firing channel was throttled to zero. This served to carry out safety measures, in particular to dredge the deposited debris at the foot of the drainage channel to lower the water level of the Thermalito Diversion Pool in order to bring the hydropower plant back into operation. On March 3, 2017, one of the power plant's six turbines was successfully put into operation on a trial basis after the high-voltage pylons of the power lines were secured in the flooded slope area of the emergency overflow and a drainage channel in the gravel landing at the foot of the firing channel was dredged. On March 4, 2017, the power plant operation was temporarily stopped again in order to deepen and widen the dredged drainage channel so that the plant can return to full operation in a few days. The volume of the rubble washed in was estimated at 1.3 million cubic meters. From March 5th, individual turbines of the power plant were put into operation again, on March 8th three of six were in operation. The discharge was slowly increased in order to be able to assess the influence of the current on the safety and efficiency of the ongoing dredging work.
After the majority of the debris washed in at the foot of the firing channel had been removed, the PWR announced that it would restart the flood relief system at noon on March 17 with a flow rate of approx. 1420 m 3 / s in order to provide storage space for the snowmelt to create the expected increased lake inflow in the Sierra Nevada. The lake level rose to approx. 263.5 m MSL when the firing channel was not used (with a maximum storage target of 274.20 m MSL). In addition to the dredging work, safety work was carried out on the largely intact upper part of the firing channel and the demolition edge during the period with no drainage. Among other things, the part of the base plate above the demolition edge was pegged to the surrounding rock with numerous rock anchors in order to prevent further settlement and movement of the channel.
Damage further down the Feather River
On March 4, 2017, the San Francisco Chronicle reported that in the vicinity of Yuba City, the Feather River embankments slid into the river for several miles after the water level dropped very quickly due to the throttling of the outflow. Since the water no longer pressed against the river banks, the soil saturated with pore water slid under its own weight, tearing trees, dirt roads and farmland with it. As a further consequence of the lowering of the river level, the migration of young king salmon ( Oncorhynchus tshawytscha ) and rainbow trout ( Oncorhynchus mykiss ) into the Pacific was prevented, as many fish were caught in residual water ponds and puddles that were separated from the rapidly receding main stream. This resulted in a rescue operation by employees of the California Department of Fish and Wildlife and the California Department of Water Resources .
Determination of causes
On March 15, 2017, the composition of the official investigation commission, which is to investigate the causes of the failure of the flood loading systems, was announced. The commission is made up of experts from the United States Society of Dams (USSD) and the Association of State Dam Safety Officials (ASDSO).
On April 17, 2017 it was independent report of at the University of Berkeley settled Center for Catastrophic Risk Management published. This report considers deficiencies in construction, construction and maintenance to be the cause of the failure of the chute. The concrete slabs that form the bottom of the channel are too thin, have too little reinforcing steel and are insufficiently anchored in the bedrock. In addition, the sealing at the concrete joints would be inadequate, and the non-positive connections of the reinforcing bars at the joints are deficient. At the points where the clay drainage pipes and especially their plug- in sleeves are under the base plates, the concrete thickness is only 10 to 15 cm. Over the decades, a crack pattern developed at these weak points that matched the position of the drainage pipes. Through these cracks, which were only sparsely repaired, and the leaky building joints, water seeped under the base plates, which the drainage systems could no longer adequately drain away. Likewise, in the area of the later break of the channel, the drainage gravel and soil were flushed out of the foundation area, which led to the formation of water-filled cavities under the slabs. Due to the inadequate anchoring in the rock, the forces of the water masses flowing at high speed resulted in tilting and rotating movements of the individual channel segments that were washed out and ultimately on February 7, 2017, the bottom fracture and failure of the concrete structure in the middle part of the total length. The water now running wild over the area from the break point led to massive erosion and scour formation on the slope and further destruction.
On January 5, 2018, the final investigation report of the investigative commission was published.
New construction of the flood relief systems
On March 1, 2017, the Department of Water Resources (DWR) , which operates the plants, convened an independent panel of experts, the Board of Consultants (BOC) . This supports and monitors the plant operator and the approval and supervisory authorities in the repair and reconstruction work.
On April 6, 2017, the responsible Department of Water Resources published a concept and schedule for the new construction of the chute. This concept envisaged repairing the upper area of the channel between the flood gates at the dam crest up to the point of fracture to a length of around 490 meters in the summer of 2017 as far as possible, and in areas where this should no longer be possible, dismantling and after to rebuild current standards including the building foundation and drainage. This construction phase had to be completed by November 2017 in order to safely discharge the precipitation in winter 2017/18.
This should then be done in the lower area, as practiced in spring 2017, as an interim solution for one year through the canyon created on the left by the water, leaving out the lower, largely destroyed channel area. These temporary should raid -edge the upper trough, the resulting naturally stilling basin at the fracture site and the further course of the channel in the rock, among others, by RCC are backed plies, prevent a further erosion. The rolled concrete construction method was also intended to finally bridge the rinsed and eroded areas in order to create a level subsurface for the final construction.
Depending on the construction progress achieved in the upper area, the lower part of the chute is to be completely demolished in the following construction window in summer 2018 and then rebuilt with the previous geometric dimensions.
On April 17, 2017 it was announced that the construction company Kiewit Infrastructure West Co. had won the bid for the reconstruction of the firing channel with its bid of 275,443,850 US dollars.
The area of the emergency overflow at the northern end of the dam was strengthened by a 442 m long bored pile wall , which was built approx. 228 m down the slope parallel to the dam crest. The bored piles of this wall were tied 10-20 m deep into the bedrock. The area between the bored pile wall and the existing overflow dam is to be protected against erosion, as occurred in February 2017, with rolled concrete in the 2018 construction window.
On May 19, 2017, the last lowering of the water level in the 2016/17 flood season was ended by the chute. Immediately afterwards, the demolition work of the remaining structural parts began in the lower area and the renovation of the upper part, which will only be renewed in 2018, as well as the renovation of the area below the emergency overflow. The original concept was converted into a final plan with a specific timeline and published on July 26, 2017.
On November 1, 2017, the firing channel was provisionally completed for the safe discharge of 2860 m³ / s in the 2017/18 rainy season. Contrary to the original plan, two sections were completely rebuilt - already in the final version in reinforced concrete - and in the rinsed middle part a temporary solution with a rolled concrete substructure was built on the original route in the final gradient and laterally closed with approx. 4 m high rolled concrete walls.
On May 8, 2018, the demolition of the sections of the firing channel that had not yet been renewed in 2017 and the temporary rolled concrete side walls of the central part began. The rolled concrete base was milled off, after cutting drainage ditches, the rolled concrete surface of the temporary chute will become the substructure of the final version to be built in 2018, made of reinforced concrete base plates and side walls along the entire length. Likewise, the top section between the defensive gates and the middle section, which was renovated in 2017, will be completely rebuilt using this construction method, including a new foundation.
In a press release at the beginning of September 2018, the Department of Water Resources (DWR) announced that the construction work was on schedule. The total costs of the accident and of restoring and upgrading the damaged facilities amount to approximately $ 1.1 billion.
On November 1, 2018, work on the completely renewed firing channel was completed on schedule. The work on the stepped rolled concrete sealing of the site between the incised bored pile wall and the crest of the emergency overflow and the retrofitting of these existing structures lasted until spring 2019. On April 2, 2019, the spring damming target was reached and the firing channel for the first time since the accident in February 2017 Put into operation.
See also
literature
State of California - The Resources Agency - Department of Water Resources: Volume III - Storage Facilities In: Bulletin Number 200, November 1974, pp. 63 ff. ( PDF; 32 MB ).
Web links
- Lake Oroville - Oroville Dam
- YouTube video: The Birth of Oroville Dam - contemporary short film about the construction of the dam
- Current fill level
- Oroville Spillway Incident , Department of Water Resources (DWR) topic page on events from February 2017
- Webcam of the California Department of Parks and Recreation of the construction site of the destroyed flood relief
Individual evidence
- ^ Oroville Dam ( English ) In: Geographic Names Information System . United States Geological Survey . Retrieved August 2, 2017.
- ↑ Lake Oroville ( English ) In: Geographic Names Information System . United States Geological Survey . Retrieved February 13, 2017.
- ^ "River Valve Outlet System" , Presentation of the Department of Water Resources, 2015 English language, PDF file, accessed March 10, 2017
- ↑ Oroville Facilities Overview , Department of Water Resources, with map display, English language, accessed on March 1, 2017
- ↑ Edward Hyatt Powerplant
- ↑ Feather River Fish Hatchery , Homepage, English language, accessed March 10, 2017
- ^ McDowell Wellman: Construction of the Lake Oroville Dam. Periscope Film, August 1964, accessed May 7, 2020 .
- ^ Paul Rogers: State was warned about inadequacy of emergency spillway. In: Oroville Mercury Register. February 12, 2017. Retrieved February 17, 2017 .
- ↑ Inspection: 313228637 - Ca Water Resources , Occupational Safety and Health Administration (OSHA) investigation report , accessed March 10, 2017.
- ↑ DWR planning study on worrisome river valves blamed in 2009 Oroville Dam accident , report on OrovilleMR-News, accessed on March 10, 2017.
- ↑ Key Oroville Drain Plugged as Heavy Storms Pounded the Reservoir , report on Newsdeeply.com, accessed March 17, 2017.
- ↑ Matt Hamilton and Shelby Grad: Too much water: How Oroville Dam problems became a crisis , in: Los Angeles Times of February 12, 2017, last accessed on February 12, 2017.
- ↑ DWR Increases Oroville Spillway Flows , California Department of Water Resources (DWR) press release dated February 9, 2017 (PDF)
- ↑ a b c Ryan Sabalow and Sam Stanton: BREAKING: Spillway collapse threat from Oroville lessens as 160,000 evacuate, clogging roads , In: Sacramento Bee of February 12, 2017, last accessed on February 12, 2017.
- ↑ tagesschau.de: Heavy rains: Biggest dam in the USA damaged. Retrieved February 13, 2017 .
- ↑ Oroville Dam: Tens of thousands flee from the impending dam disaster In: Spiegel online from February 13, 2017
- ↑ Video of the flooded dam on February 12 and 13, 2017 on YouTube (removed)
- ↑ Relaxation, but no all-clear , Spiegel Online from February 14, 2017
- ^ Oroville Dam: 'The threat level - it is much, much, much lower' . In: Sacramento Bee . February 16, 2017 ( sacbee.com ).
- ↑ Concern At Oroville Spillway Triggers Evacuation Orders , press release of the California Department of Water Resources (DWR) dated February 12, 2017 (PDF)
- ↑ Eric Kurhi: Oroville: Thousands evacuate as authorities warn of dam failure , in: Mercury News of February 12, 2017, last accessed on February 12, 2017.
- ↑ Sheriff Allows Oroville Dam Evacuees To Go Home. In: CBS SF Bay Area. February 14, 2017, accessed March 8, 2017 .
- ↑ California residents forced to flee Oroville Dam emergency may return home. In: CNBC . February 14, 2017. Retrieved February 25, 2017 .
- ↑ Butte County Sheriff Lifts All Evacuation Advisories & Warnings Previously Issued for the Oroville Dam Spillway Incident , press release of the Butte County Sheriff's Office of March 22, 2017 (PDF)
- ↑ Spillway Incident Update 02/27/17 , press release of the California Department of Water Resources (DWR) dated February 27, 2017 (PDF)
- ↑ Hyatt Power Plant at Lake Oroville Update - Temporary Shutdown to Increase Future Flows , press release of the California Department of Water Resources (DWR) of March 4, 2017 (PDF)
- ↑ Oroville Spillway Incident Update , press release of the California Department of Water Resources (DWR) of March 8, 2017 (PDF)
- ↑ Lake Oroville Releases and Feather River Flows to Increase Friday , California Department of Water Resources (DWR) press release of March 17, 2017 (PDF)
- ↑ a b c Kurtis Alexander and Tara Duggan: Riverbanks collapse after Oroville Dam spillway shut off , in: San Francisco Chronicle of March 4, 2017, last accessed March 4, 2017.
- ↑ DWR Selects Forensic Team to Investigate Oroville Spillway Incident , California Department of Water Resources (DWR) publication March 15, 2017 (PDF file)
- ↑ Preliminary Root Causes Analysis of Failures of the Oroville Dam Gated Spillway , Center for Catastrophic Risk Management (CCRM) report, RG Bea, April 17, 2017 , published in the Los Angeles Times
- ↑ Independent Forensic Team Report - Oroville Dam Spillway Incident , published on the Association of State Dam Safety Officials (ASDSO) website, PDF file January 5, 2018
- ↑ Reports from the Lake Oroville Spillways Recovery Project Board of Consultants , California Department of Water Resources (DWR) publication of March 10, 2017 (PDF file)
- ↑ Oroville Spillway Recovery - Plans under Design , California Department of Water Resources (DWR) publication April 6, 2017 (PDF file)
- ↑ DWR Awards Contract for Oroville Spillways Repair , California Department of Water Resources (DWR) publication April 17, 2017 (PDF file)
- ↑ Final 2017 Construction Plans for Lake Oroville Spillways Project Approved , California Department of Water Resources (DWR) publication of July 26, 2017 (PDF file)
- ↑ Oroville Spillways Construction Update May 9, 2018 , California Department of Water Resources (DWR) publication May 9, 2018
- ^ Oroville Spillways Construction and Cost Estimate Update , published by the California Department of Water Resources (DWR) on September 5, 2018
- ↑ DWR Uses Oroville Main Spillway , California Department of Water Resources (DWR) publication dated April 2, 2019