Photos: What It Takes to Repair a Damaged Spillway at the Nation’s Tallest Dam

In February 2017, damage to a spillway at the nation's tallest dam placed thousands in the community of Oroville under evacuation due to the threat of flooding. That threat eased as crews shored up the spillway and the clocked ticked down on one of California's wettest winters in years. But the work is far from over in Oroville, where construction crews have been working since February on repairs.

145 photos
1/145
A view of the Lake Oroville flood control spillway in Butte County, California on Feb. 26, 2017 (left) and Jan. 24, 2019.
2/145
The California Department of Water Resources suspended flows from the Lake Oroville flood control spillway after a concrete section eroded on the middle section of the spillway. There is no anticipated threat to the dam or the public. DWR engineers are assessing the options to repair the spillway and control the reservoir water level.
3/145
A contingency plan was prepared for the potential use of the Lake Oroville emergency spillway, as the DWR cleared trees, rocks and other debris from the hillside near the dam where water would flow. Approximately 50 to 100 acres of trees and bushes could have been affected by water releases.
4/145
California Department of Water Resources
Lake Oroville flood control spillway flow was stopped on Thursday Feb. 9 to allow engineers to evaluate the damaged structure.
5/145
Cloudy water led the California Department of Fish and Wildlife to truck 4 million baby salmon from the Feather River Fish Hatchery in Oroville, Calif. to the nearby fish ponds at the Thermalito Afterbay Complex in Butte County.
6/145
Workers move baby salmon from the Feather River Fish Hatchery in Oroville, California to the nearby fish ponds at the Thermalito Afterbay Complex in Butte County.
7/145
Water flows from the Lake Oroville flood control spillway Oroville Dam. Water started to flow over the emergency spillway after the lake level exceeded 901 feet elevation above sea level.
8/145
Waters from Lake Oroville flowed over the emergency spillway and eroded the roadway just below the spillway that leads to the Lake Oroville boat ramp.
9/145
Helicopters carry large bags of rocks to the erosion site below the Lake Oroville emergency spillway.
10/145
Excavators load rocks for helicopters in as part of a repair work airlift from the Oroville Dam parking lot. The rocks are carried by the helicopters to the eroded site below the Lake Oroville emergency spillway.
11/145
Workers inspect erosion just below the Lake Oroville emergency spillway site after lake levels receded on Feb. 13. The outflow from the Lake Oroville flood control spillway remained at 100,000 cubic feet per second at this point in an effort to decrease the lake level by 50 feet ahead of upcoming storms.
12/145
A helicopters carrying a large bag of rocks is seen above the spillway. The rocks helped shore up the eroded area.
13/145
Getty Images
Oroville lake, the emergency spillway, and the damaged main spillway, are seen from the air on February 13, 2017 in Oroville, California. The erosion damage seen below the emergency spillway caused officials to issue evacuation orders a day earlier to nearly 200,000 people in downstream areas.
14/145
Getty Images
Oroville lake, the emergency spillway, and the damaged main spillway are seen from the air on February 13, 2017 in Oroville, California.
15/145
Getty Images
The emergency spillway and the damaged main spillway are seen behind the town of Oroville from the air on February 13, 2017.
16/145
AP
The Feather River flows through Oroville, downstream from the damage area. Crews worked to repair the barrier amid to concerns the spillway could fail and send water downstream.
17/145
Crews prepare for the possible use of the emergency spillway at Lake Oroville. The dam itself was not damaged during the winter, but spillway erosion meant crews would soon use the emergency spillway for the first time in the structure's history.
18/145
The work required a fleet of heavy construction equipment, used to shore up areas around the spillway and dam.
19/145
At one point, more than 125 construction crews were working around the clock.
20/145
A helicopter makes another rock drop at the Oroville Dam spillway site.
21/145
This aerial view looks east toward damaged Lake Oroville flood control spillway with an outflow of 100,000 cubic feet per second. This picture was taken as authorities worked to lower the lake level ahead of another round of powerful winter storms.
22/145
Another aerial view looking east toward Oroville Dam and Lake Oroville, showing the damaged flood control spillway.
23/145
These are diversion pool across from the damaged Lake Oroville flood control spillway. Water was ushered to the pools as work continued to shore up the bank so heavy equipment can remove sediment and debris.
24/145
This photo provides a view of the riverbank across from the damaged Lake Oroville flood control spillway.
25/145
A worker directs the helicopter carrying a bag of material at an eroded spot at the base of the Lake Oroville emergency spillway.
26/145
A survey boat is used to look over the diversion pool between the damaged Lake Oroville flood control spillway and the Edward Hyatt powerplant. Debris and sediment collected at the site, adding another job to the list of cleanup and repair work.
27/145
Here comes the cavalry. A long line of trucks wait on the top of Oroville Dam to deliver concrete for the erosion repair work at the base of the Lake Oroville emergency spillway.
28/145
A view of the erosion below the Lake Oroville emergency spillway.
29/145
Crews construct a barge that was used for hauling excavation equipment to dredge debris and sediment from the diversion pool at the base of the Lake Oroville flood control spillway.
30/145
A worker is airlifted by helicopter to work on the power lines near the Lake Oroville flood control spillway.
31/145
As wet weather continued, rock, aggregate, and cement slurry were placed into eroded areas affected by the erosion.
32/145
Work crews inspect the erosion near Oroville Dam as winter continued to pound the area with rain.
33/145
A view of the damaged spillway about two weeks after engineers first discovered the erosion.
34/145
The damaged Oroville Dam spillway at night, lit up by lights as construction crews continue work.
35/145
Not all the work is done using heavy construction equipment. California Department of Water Resources employee Daniel Sutherland and members of the California Conservation Corps unload buckets of road base material along the walkway on the outer edge of the Oroville Dam spillway.
36/145
Mist rises from the base of the Oroville Dam spillway. At this point, water was discharged at 60,000 cubic feet per second, allowing construction to continue.
37/145
Outflow is reduced to 50,000 cubic feet per second at the Oroville Dam flood control spillway. The decreased water flow allowed crews to get a better look at a large debris field in the diversion pool at the base of the damaged spillway.
38/145
An aerial view of the damaged Oroville Dam spillway. Water flow was reduced at this point, allow workers to remove debris at the spillway’s base.
39/145
An aerial view of the damaged Oroville Dam spillway as winter's strong storms continued to lash the state.
40/145
Once outflow to the spillway was reduced, aerial views provided a better look at the erosion.
41/145
An aerial view of barges loaded with heavy equipment that was moved downstream to extract a huge debris field at the base of the damaged Oroville Dam spillway. Once finished the Edward Hyatt Powerplant can operate, allowing crews to better manage reservoir levels during the spring runoff season.
42/145
Biologists rescue fish stranded by the receding waters of the Feather River after outflow from the damaged Oroville Dam spillway was reduced. The fish were released back into the Feather River.
43/145
A fish stranded by the receding waters of the Feather River. The fish were rescued and released back into the Feather River.
44/145
Heavy equipment removes a debris field in the diversion pool at the base of the damaged Oroville Dam spillway.
45/145
A team of divers seals the eight gates of the Oroville Dam spillway to reduce seepage into the damaged section of the spillway. Kelly M. Grow/ California Department of WaternResources, FOR EDITORIAL USE ONLY
46/145
This shot shows the nearly dry Oroville Dam spillway as sandbags are placed to divert the seepage to one side. It's a dramatic change from about one month earlier.
47/145
Nearly a month after erosion was discovered, workers inspect the damage at Oroville Dam main spillway,
48/145
A view from near the top of the damaged Oroville Dam main spillway. Water flow were stopped for debris removal from the diversion pool below.
49/145
Work crews used heavy equipment on barges to remove the debris field in the diversion pool at the base of the damaged Oroville Dam spillway.
50/145
After repairs beneath the damaged spillway Oroville Dam, scaffolding was removed in early March.
51/145
Water flows were restricted from the spillway as work continued to remove debris in early March.
52/145
Sediment and debris are from the area of the damaged main spillway. By March, about 715,000 cubic yards of material had been removed from the debris pile.
53/145
Cleanup operations continued 24 hours per day as the storm season neared its end. By mid-March crews removed approximately 990,000 cubic yards of material from the debris pile.
54/145
Rebar is exposed in debris and concrete from the damage Lake Oroville flood control spillway.
55/145
A worker uses heavy construction equipment to drop rocks along the diversion pool below the Lake Oroville flood control spillway.
56/145
Water is released from the Lake Oroville flood control spillway at an outflow of 41,000 cubic feet per second. Most of the water flows into a ravine, then enters a diversion pool.
57/145
A helicopter and PG&E linemen install power lines to the shoe-fly temporary lines built to bypass the Lake Oroville flood control spillway and emergency spillway as repair work continues.
58/145
The California Department of Water Resources conducts core drill samples to determine the geological conditions near the damaged spillway.
59/145
Power lines are installed in a temporary reroute of the power line poles below the Oroville Dam.
60/145
An aerial view of the Lake Oroville flood control spillway as water rushes into the diversion pool from a ravine. Water will continue to be released to leave enough storage room for the inflow of spring rains and snowmelt from the Sierra Nevada Mountains.
61/145
California Department of Water Resources utility craftworkers Gary Hage and Chris Williams are lifted to work on a section of Lake Oroville flood control spillway for survey marking.
62/145
A scaffolding walkway is assembled to provide access from the ravine area created by the damaged spillway to the upper section of the Lake Oroville flood control spillway.
63/145
A crew uses shotcrete -- mortar sprayed at high power through a hose -- near the damaged Lake Oroville flood control spillway.
64/145
Dale Kolke/California Dept. of Water Resources
Shotcrete mortar spray is applied just below the damaged Lake Oroville flood control spillway.
65/145
Water flows during reoperation of the Lake Oroville flood control spillway on Friday April 14, 2017. The outflow will be at 35,000 cubic feet per second for approximately 14 days.
66/145
Water rushes into a diversion pool from the ravine carved out from the damaged Lake Oroville flood control spillway. The California Department of Water Resources released an outflow of 35,000 cubic feet per second in mid-April.
67/145
California Department of Water R
Excavation continues just south of Lake Oroville flood control spillway. Spray from the flowing water can be seen in the background.
68/145
This image from a drone shows the damaged Lake Oroville flood control spillway on May 1, 2017.
69/145
Another view from a drone over the Lake Oroville flood control spillway. Outflow at this point on May 1, 2017 was recorded at between 30,000 to 25,000 cubic feet per second.
70/145
California Department of Water R
A wider view from a drone over the damaged Lake Oroville flood control spillway.
71/145
A California Department of Water Resources geologist studies rock in the damage area of the spillway. Photo taken May 8, 2017. Florence Low / California Department of Water Resources, FOR EDITORIAL USE ONLY
72/145
A rainbow spectrum forms in the mist cloud over the Lake Oroville flood control spillway. Photo taken May 15, 2017.
73/145
An aerial view of Lake Oroville at 83 percent of capacity or 104 percent of historical average Photo taken on April 21, 2017.
74/145
Concrete demolition on the lower section of the Lake Oroville flood control spillway. Photo take May 22, 2017.
75/145
A worker inspects the lower section of the Lake Oroville flood control spillway. Photo taken May 22, 2017. Dale Kolke / California Department of Water Resources, FOR EDITORIAL USE ONLY
76/145
An American flag was on display over the Memorial Day weekend. Photo taken from a drone on May 27, 2017.
77/145
A controlled blast on the lower chute of the Lake Oroville flood control spillway in Butte County, California. Photo taken May 30, 2017.
78/145
A controlled blast on the lower chute of Lake Oroville flood control spillway. Photo taken May 31, 2017.
79/145
A controlled blast on the lower chute of Lake Oroville flood control spillway. Photo taken May 31, 2017.
80/145
A controlled blast breaks up remains of the lower chute of the Lake Oroville flood control spillway. Photo taken June 7, 2017.
81/145
Workers prepare to pump concrete between rocks near the diversion pool, part of the first phase of the reconstruction of the lower chute. Photo taken on June 12, 2017.
82/145
Workers prepare the area for concrete placement between the upper and lower chute of the Lake Oroville flood control spillway. Photo taken on June 12, 2017.
83/145
Workers remove concrete broken up by controlled blasts on the lower chute of the Lake Oroville flood control spillway. Photo taken June 12, 2017.
84/145
Excavators unload a barge filled with debris dredged from the diversion pool, part of the recovery of the Lake Oroville flood control spillway. Photo taken on June 19, 2017.
85/145
Kiewit Infrastructure's on-site batch plant for roller-compacted concrete is operational at the Lake Oroville flood control spillway site. Photo taken on June 19, 2017.
86/145
Kiewit Infrastructure has positioned a large crane near the bottom of the lower chute while excavation continues. Drone photo taken June 21, 2017.
87/145
High pressure washers and vacuums are preparing the lower chute of the Lake Oroville flood control spillway for concrete placement. Photo taken June 26, 2017.
88/145
Remaining concrete debris from the Lake Oroville flood control spillway is removed. Photo taken June 26, 2017.
89/145
Concrete forms are constructed on the lower chute, part of a new concrete foundation and drainage system for the flood control spillway. Photos taken June 28, 2017.
90/145
Loose material is washed from recently placed roller-compacted concrete (RCC) on the southeast side of the lower chute of the Lake Oroville flood control spillway. Photo taken July 24, 2017.
91/145
Demolition and debris removal on the upper chute of the Lake Oroville flood control spillway. Photo taken July 24, 2017.
92/145
Workers remove loose rocks and debris before concrete can be placed on the upper chute.
93/145
Rocks are cleaned by water and compressed air ahead of work to place concrete on the upper chute. Ken James/ California Department of Water Resources, FOR EDITORIAL USE ONLY
94/145
Concrete is pumped between rocks in the erosion area between the upper and lower chute.
95/145
An American flag is flown over the Lake Oroville during the solar eclipse.
96/145
A worker walks on the large rock field between the upper and lower chute.
97/145
Crews place leveling and structural concrete near the bottom of the lower chute.
98/145
A view near the bottom of the lower chute at the Lake Oroville flood control spillway.
99/145
Crews continue to place roller-compacted concrete in the erosion area between the upper and lower chute. Photo taken September 15, 2017. Florence Low / California Department of Water Resources, FOR EDITORIAL USE ONLY
100/145
A crane carries a rebar cage to the lower chute of the Lake Oroville flood control spillway. Photo taken September 15, 2017. Florence Low / California Department of Water Resources, FOR EDITORIAL USE ONLY
101/145
A crew places gravel inside a stay-form between the structural concrete on the upper chute.
102/145
An aerial view looking east toward the flood-damaged spillway area.
103/145
This aerial view looks to the southwest over the Lake Oroville flood control spillway.
104/145
Loose rocks are removed before placement of roller-compacted concrete in the erosion area between the upper and lower chute.
105/145
Workers are seen here at sunset, placing roller-compacted concrete onto the sidewall between the upper and lower chutes of the Lake Oroville flood control spillway in Butte County, California. Photo taken October 25, 2017.
106/145
Workers remove bolts from concrete forms used in the construction of two sidewall panels on the upper chute.
107/145
A layer of enriched roller-compacted concrete is placed between the upper and lower chutes at the Lake Oroville flood control spillway in Butte County, California. Photo taken October 30, 2017. Ken James/ California Department of Water Resources, FOR EDITORIAL USE ONLY
108/145
Enriched roller-compacted concrete between the upper and lower chutes at the Lake Oroville flood control spillway in Butte County, California. Photo taken October 30, 2017. Ken James/ California Department of Water Resources, FOR EDITORIAL USE ONLY
109/145
An aerial view of the Lake Oroville spillways recovery site in Butte County, California.
110/145
An aerial view of the Lake Oroville spillways recovery site in Butte County, California.
111/145
An aerial view of the Lake Oroville spillways recovery site in Butte County, California.
112/145
Workers walk on a repaired section of the Oroville Dam spillway.
113/145
The diversion pool just below the Lake Oroville flood control spillway.
114/145
California Department of Water Resources
The first rain of the season falls on the Lake Oroville flood control spillway.
115/145
Workers disassemble the shoo-fly circuit that had temporarily rerouted power lines. Photo taken November 7, 2017.
116/145
A controlled blast clears rock for the placement of the roller-compacted concrete splashpad downslope from the Lake Oroville emergency spillway. Photo taken November 15, 2017.
117/145
After a morning rain shower, crews continue their finishing work on the upper chute. Photo taken November 16, 2017.
118/145
A controlled blast clears rock for the placement of the roller-compacted concrete splashpad downslope from the Lake Oroville emergency spillway, California. Photo taken November 20, 2017. Ken James / California Department of Water Resources, FOR EDITORIAL USE ONLY
119/145
Workers from Kiewit Infrastructure install two baghouse filters on top of the two silos to control dust particles from the roller-compacted concrete (RCC) plant, relocated below the 1,450-foot cutoff wall downslope of the Lake Oroville emergency spillway in Butte County, California. Photo taken December 12, 2017.
120/145
A controlled blast clears rock for the placement of the roller-compacted concrete splashpad downslope from the Lake Oroville emergency spillway in Butte County, California. Photo taken December 12, 2017.
121/145
A row of drilling rigs create holes for the construction of the 1,450-foot underground cut-off wall, downslope of the Lake Oroville emergency spillway.
122/145
Drilling rigs createe holes for the construction of the 1,450-foot underground cut-off wall downslope of the Lake Oroville emergency spillway site.
123/145
An aerial drone view of the Lake Oroville flood control spillway in Butte County, California. Photo taken February 5, 2018.
124/145
A drone view of surveyors from R.E.Y. Engineers, Inc., using a three-dimensional laser scanner to create a 3D map of the lower chute at the Lake Oroville flood control spillway in Butte County, California.
125/145
Workers from Kiewit Infrastructure place leveling concrete into surface depressions near the four energy dissipation blocks at the Lake Oroville flood control spillway site.
126/145
Workers from Kiewit Infrastructure begin construction of a roller-compacted concrete splashpad. Photo taken March 12, 2018.
127/145
A view of work on the Oroville Dam emergency spillway.
128/145
A drone overview of the Lake Oroville emergency spillway construction site, showing the progress of the splashpad. The splashpad will armor the hillside between the emergency spillway and the secant pile wall to prevent erosion if the emergency spillway is ever used again at the Butte County, California site. Photo taken March 12, 2018.
129/145
A drone view of the construction site for a new access road just below the Lake Oroville main spillway and four energy dissipator blocks in Butte County, California. Photo taken March 19, 2018.
130/145
A drone view of the Lake Oroville main spillway. Photo taken March 29, 2018.
131/145
A drone overview of the Lake Oroville emergency spillway construction site. You can see the splashpad that will protect the nearby hillside.
132/145
Excavators appear on both sides of the main spillway prior to the removal of the roller-compacted concrete (RCC) sidewalls in Butte County, California.
133/145
An excavator breaks through a section of the original sidewall on the upper chute of the main spillway at Lake Oroville.
134/145
The sun rises over the Lake Oroville main spillway site. Photo taken July 30, 2018.
135/145
A drone provides an overview of structural concrete work on the Lake Oroville main spillway during Phase 2 of the recovery effort in Butte County, California. Photo taken August 8, 2018.
136/145
Crews place structural concrete on the middle and upper chutes of the Lake Oroville main spillway as a dozen cranes stand ready to support Phase 2 of the recovery efforts at the Butte County, California site. Photo taken August 9, 2018.
137/145
Crews place structural concrete on the middle chute of the Lake Oroville main spillway during Phase 2 of the project at the Butte County, California site. Photo taken September 4, 2018.
138/145
A drone's view of concrete work underway on the upper chute of Lake Oroville main spillway and the emergency spillway during Phase 2 of the recovery effort in Butte County, California. Photo taken September 19, 2018.
139/145
Crews near completion of the placement of structural concrete on the middle chute of the Lake Oroville main spillway during Phase 2 of the recovery effort at the Butte County, California site. Photo taken September 27, 2018.
140/145
Workers prepare rebar panels on the upper chute of the Lake Oroville main spillway. Photo taken Oct. 1, 2018.
141/145
Deer wander onto the Lake Oroville emergency spillway splashpad. Photo taken October 26, 2018.
142/145
A drone provides an overview of the Lake Oroville main spillway. Photo taken October 29, 2018. Crews have finished pouring concrete on the main spillway, but it still needs to cure for a month.
143/145
An aerial overview of the recently completed Lake Oroville main spillway during Phase 2 of the recovery efforts.
144/145
A drone provides a view of the completed Lake Oroville main spillway. Photo taken February 12, 2019.
145/145
More than two years after flood fears gripped the region, a family hikes near the Oroville Dam on quiet spring day.
Contact Us