In California, construction crews are trying to lower the level of Lake Oroville and repair emergency spillways at the Oroville Dam, about 75 miles north of Sacramento, to prevent catastrophic flooding downstream.
A secondary spillway was opened Monday after the main spillway, which is supposed to safely release water when the lake level is too high, had developed a huge hole, as we reported.
Rain is forecast for later this week in Northern California, and nearly 200,000 people who live downstream have been evacuated from the area.
As NPR's Richard Gonzalez reported, "The good news is that the water level in the dam is falling and repair crews have been able to drop heavy rocks in key spots of the emergency spillway to prevent further erosion."
For those who were evacuated, hotels in the region were filled to capacity on Tuesday and "evacuation centers are straining to keep up with the demand for shelter," Richard said.
FEMA Acting Regional Administrator Ahsha Tribble said the agency is providing support to evacuated people, Ben Bradford of Capital Public Radio reported.
"We are already moving commodities, and commodities being cots, blankets and water, given the number of people that were actually evacuated last night," Tribble said.
"Officials say a new series of storms coming by Thursday prevents them from saying how long the evacuation could last," Richard reported.
The Los Angeles Times published this diagram of what that catastrophic erosion could look like.
"Meanwhile, local reports are emerging that environmental groups raised concerns about the dam's emergency spillway decades ago," Richard reported.
The Times reported that the the emergency spillways were damaged by far less water than the maximum flow they are supposed to handle:
"Earth and weak rock near the top of the spillway started to erode when peak flows were 12,600 cubic feet per second, compared with the designed capacity of 450,000 cubic feet per second, according to the Department of Water Resources. ... Bill Croyle, the acting director of the Department of Water Resources, said Monday that he was 'not sure anything went wrong. This was a new, never-happened-before event.'
"But during 2005 relicensing proceedings for Oroville Dam, several environmental groups argued that substantial erosion would occur on the hillside in the event of a significant emergency spill. In a filing, they asked the Federal Energy Regulatory Commission to order the state to 'to armor or otherwise reconstruct the ungated spillway.'
"State Water Project contractors, including the Metropolitan Water District of Southern California, were involved in the relicensing. MWD General Manager Jeffrey Kightlinger said Monday his agency deferred to the state and federal agencies on the matter."
At 770 feet, the Oroville Dam is the tallest in the U.S. Although the structure hasn't suffered a catastrophic failure, the excess water dumped by a series of California storms and released through the spillways has nonetheless inundated communities in and around Oroville.
Reporter Paige St. John of the Times tweeted a photo of a drowned cemetery in the town of Marysville downstream of the dam.
An aerial photo shared by the Long Beach Fire Department, which was called in from the southern part of the state to assist local authorities, showed water carving channels through the hills downstream of the dam, carrying mud and debris with it.