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| Evacuation Order Is Lifted as Crews Race to Shore Up Oroville Dam | Evacuation Order Is Lifted as Crews Race to Shore Up Oroville Dam |
| (35 minutes later) | |
| Crews in Oroville, Calif., worked rapidly on Tuesday to lower a reservoir and shore up an eroded emergency spillway in hopes of preventing flooding in the valley below. As the reservoir fell, the authorities told more than 100,000 people who had been evacuated from the area that they could return home. | Crews in Oroville, Calif., worked rapidly on Tuesday to lower a reservoir and shore up an eroded emergency spillway in hopes of preventing flooding in the valley below. As the reservoir fell, the authorities told more than 100,000 people who had been evacuated from the area that they could return home. |
| “The risk that we faced when we initiated those evacuations has significantly been reduced,” said Kory Honea, the sheriff for Butte County, which contains the dam. | “The risk that we faced when we initiated those evacuations has significantly been reduced,” said Kory Honea, the sheriff for Butte County, which contains the dam. |
| But Mr. Honea did not rule out the possibility of future evacuations if circumstances change at the dam, a 770-foot-high embankment along Lake Oroville in the foothills of the Sierra Nevada. He said the area was still under an evacuation warning. | But Mr. Honea did not rule out the possibility of future evacuations if circumstances change at the dam, a 770-foot-high embankment along Lake Oroville in the foothills of the Sierra Nevada. He said the area was still under an evacuation warning. |
| New storms are expected to send more water into the lake this week. The authorities are hoping to drain enough that the emergency spillway will not need to be used, but they are lining it with rocks and slurry nevertheless. | New storms are expected to send more water into the lake this week. The authorities are hoping to drain enough that the emergency spillway will not need to be used, but they are lining it with rocks and slurry nevertheless. |
| “We need to prepare for all contingencies,” said Bill Croyle, the acting director of the California Department of Water Resources. “If we have to use it, we want to make sure it’s in a condition to take higher flows.” | “We need to prepare for all contingencies,” said Bill Croyle, the acting director of the California Department of Water Resources. “If we have to use it, we want to make sure it’s in a condition to take higher flows.” |
| The lifting of the mandatory evacuation order brought at least a temporary end to a crisis that led Gov. Jerry Brown to seek an emergency declaration for Yuba, Butte and Sutter Counties. | The lifting of the mandatory evacuation order brought at least a temporary end to a crisis that led Gov. Jerry Brown to seek an emergency declaration for Yuba, Butte and Sutter Counties. |
| “This is about engineering, it’s about construction, it’s about repair,” Mr. Brown said on Monday. “We’ll get a lot of eyes on the problem, now that we have a problem, and the problem is big.” The dam was completed in 1968. | “This is about engineering, it’s about construction, it’s about repair,” Mr. Brown said on Monday. “We’ll get a lot of eyes on the problem, now that we have a problem, and the problem is big.” The dam was completed in 1968. |
| President Trump is monitoring the situation, Sean Spicer, the White House spokesman, said at a news briefing on Tuesday, calling it “a textbook example of why we need to pursue a major infrastructure package in Congress.” | President Trump is monitoring the situation, Sean Spicer, the White House spokesman, said at a news briefing on Tuesday, calling it “a textbook example of why we need to pursue a major infrastructure package in Congress.” |
| “Dams, bridges, roads and all ports around the country have fallen into disrepair,” Mr. Spicer said. | “Dams, bridges, roads and all ports around the country have fallen into disrepair,” Mr. Spicer said. |
| It has been a wet winter in Northern California, and the water level at Lake Oroville was high after it received six or seven inches of rain last week, in addition to the runoff from 12 to 20 inches of rain that fell in the basin above it, said Jim Mathews, a meteorologist with the National Weather Service in Sacramento. | It has been a wet winter in Northern California, and the water level at Lake Oroville was high after it received six or seven inches of rain last week, in addition to the runoff from 12 to 20 inches of rain that fell in the basin above it, said Jim Mathews, a meteorologist with the National Weather Service in Sacramento. |
| Last week, crews observed a hole in the dam’s concrete spillway, which drains water into the Feather River. The cause of the hole is not yet known. Water was diverted to an earthen emergency spillway. But major erosion was detected there over the weekend, prompting fears that the spillway could collapse, sending a 30-foot wall of water into the valley below. | Last week, crews observed a hole in the dam’s concrete spillway, which drains water into the Feather River. The cause of the hole is not yet known. Water was diverted to an earthen emergency spillway. But major erosion was detected there over the weekend, prompting fears that the spillway could collapse, sending a 30-foot wall of water into the valley below. |
| “We determined that although efforts to mitigate potential failure needed to take place, we couldn’t guarantee that they would be completed in the time frame necessary to ensure that people could be evacuated,” Mr. Honea said. People were told to leave immediately. | “We determined that although efforts to mitigate potential failure needed to take place, we couldn’t guarantee that they would be completed in the time frame necessary to ensure that people could be evacuated,” Mr. Honea said. People were told to leave immediately. |
| The authorities decided to lower the lake’s surface by sending 100,000 cubic feet of water per second over the main spillway, which is holding up despite the damage. That kept the water out of the emergency spillway. | The authorities decided to lower the lake’s surface by sending 100,000 cubic feet of water per second over the main spillway, which is holding up despite the damage. That kept the water out of the emergency spillway. |
| The authorities have continued to release water from the lake to make room for water from more rain, which forecasters say is expected later this week. | The authorities have continued to release water from the lake to make room for water from more rain, which forecasters say is expected later this week. |
| “We’re still looking at another series of storms right through the next week or so,” Mr. Mathews said, adding that heavy runoff from melting snow was also expected later in the season. By Tuesday afternoon, the lake level had dropped by eight feet. | “We’re still looking at another series of storms right through the next week or so,” Mr. Mathews said, adding that heavy runoff from melting snow was also expected later in the season. By Tuesday afternoon, the lake level had dropped by eight feet. |
| On Tuesday, work crews were also scrambling to repair the emergency spillway, in case it is needed. | |
| “They’re using rocks, boulders, sandbags and a slurry trying to fill it in, and that’s with helicopters, and that’s around the clock until the engineers deem it’s adequate,” said Al Duncan, a public information officer with the Oakland Fire Department. | “They’re using rocks, boulders, sandbags and a slurry trying to fill it in, and that’s with helicopters, and that’s around the clock until the engineers deem it’s adequate,” said Al Duncan, a public information officer with the Oakland Fire Department. |
| The authorities turned the evacuation order into an evacuation warning on Tuesday afternoon, which meant residents who had huddled in Red Cross shelters, a fairground and a Sikh temple were allowed to return home. | The authorities turned the evacuation order into an evacuation warning on Tuesday afternoon, which meant residents who had huddled in Red Cross shelters, a fairground and a Sikh temple were allowed to return home. |
| But, Mr. Honea said, “an evacuation warning considers the possibility that future inclement weather or increased lake levels or problems associated with the existing damage to the spillway could elevate risks in the future and necessitate immediate evacuations.” | But, Mr. Honea said, “an evacuation warning considers the possibility that future inclement weather or increased lake levels or problems associated with the existing damage to the spillway could elevate risks in the future and necessitate immediate evacuations.” |
| Experts say that the combination of concrete and earthen spillways is not unusual, and that some erosion can be expected. | Experts say that the combination of concrete and earthen spillways is not unusual, and that some erosion can be expected. |
| “That’s a pretty standard design for many dams around the country,” said Mark Ogden, a project manager with the Association of State Dam Safety Officials. “What makes this one unique is the fact that it’s one of the largest dams in the country.” | “That’s a pretty standard design for many dams around the country,” said Mark Ogden, a project manager with the Association of State Dam Safety Officials. “What makes this one unique is the fact that it’s one of the largest dams in the country.” |
| Nonetheless, the authorities seemed to suggest on Monday that the scale of the crisis had emerged suddenly. | Nonetheless, the authorities seemed to suggest on Monday that the scale of the crisis had emerged suddenly. |
| “I’m not sure anything went wrong” with the auxiliary spillway, said Mr. Croyle, who called the use of the spillway a “new, never-happened-before event.” | “I’m not sure anything went wrong” with the auxiliary spillway, said Mr. Croyle, who called the use of the spillway a “new, never-happened-before event.” |
| In 2005, environmental groups requested that the state line the earthen emergency spillway with concrete, warning that erosion could become a problem if it were used. That action was not taken, and Mr. Croyle said he was not familiar with the request. | In 2005, environmental groups requested that the state line the earthen emergency spillway with concrete, warning that erosion could become a problem if it were used. That action was not taken, and Mr. Croyle said he was not familiar with the request. |
| Mr. Mathews, the meteorologist, said there was not a straightforward answer. “I would say for Northern California, obviously we have flooding, so there is no drought,” Mr. Mathews said. | Mr. Mathews, the meteorologist, said there was not a straightforward answer. “I would say for Northern California, obviously we have flooding, so there is no drought,” Mr. Mathews said. |
| But a hydrologist looking at groundwater in Southern California, where conditions are drier, might answer differently. And Governor Brown has not declared an end to the drought. | But a hydrologist looking at groundwater in Southern California, where conditions are drier, might answer differently. And Governor Brown has not declared an end to the drought. |
| “We go from several years of below-normal precipitation, and then we go to several years of above-normal precipitation,” Mr. Mathews said. “That’s basically how it works in California. It’s either feast or famine in the water.” | “We go from several years of below-normal precipitation, and then we go to several years of above-normal precipitation,” Mr. Mathews said. “That’s basically how it works in California. It’s either feast or famine in the water.” |