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One year ago Southern California was wondering what happened to El Nino? Outside of a few showers, there was practically no rain to speak of. “Darn those wacky weathercasters!” “Curse those miserable meteorologists!” were common complaints. One year later and we’re inundated with too much rain with more mud flowing, more floods growing and more hillsides sliding than anyone could have anticipated.

Instead of El Nino or La Nina, we have a series of new terms like “atmospheric river,” “rain shadow” or “conveyor belt of storms” to blame for torrential downpours stretching up and down the Golden State. The storms caused the temporary evacuation of almost 200,000 people residing near the Oroville Dam earlier this week when water broke through the emergency spillway causing severe flooding. Locally, Cal Trans was able to reopen a portion of Laurel Canyon Boulevard in the Hollywood Hills after a mudslide sent the backyard of a home crashing down. The Oroville emergency has spurred Supervisor Kathyn Barger to request local crews to conduct thorough assessments of southland dams, spillways and other water-collection and diversion facilities to identify any potential problem areas.

Assessing the local situation

“The Oroville situation reminds us of the need to proactively evaluate our county’s risk with regard to dams and other facilities which may be prone to failure from storms, earthquakes or other foreseeable events,” said Barger who introduced a motion this week directing county agencies to inspect and identify any “potential threats” to public safety. “It is important that we ensure our flood control system is operating safely and efficiently,” she continued, “to assure residents that county engineers are constantly monitoring our dams.”

Mark Pastrella, acting director of the Department of Public Works, said that despite the heavy downpours of the past few weeks, county officials do not expect similar damage to any of its reservoir facilities. In speaking before the Board of Supervisors this week, Pastrella highlighted the cleanup of the Las Lomas debris basin in Duarte, for instance, as an example of an area that has been challenged by heavy rain and the loss of natural flood barriers in last summer’s Fish Fire.

Devil’s Gate in Pasadena is perhaps the county’s “most vulnerable” dam, Pastrella noted, with little to no storage for debris behind it and also because environmental advocacy groups have blocked a clean-out of sediments there. If an overflow does appear imminent, he said county workers are prepared to use an emergency valve on the dam to release water. Devil’s Gate is the oldest of the county’s 14 dams.

Too much rain too fast

State officials were warned that the Oroville Dam emergency spillway wasn’t safe. In 2005, three environmental groups reported notified state and federal officials that the spillway was as risk of collapsing. It really isn’t a spillway but, rather, a 1,700-foot long concrete weir that empties into a dirt hillside. The severe storms have dumped so much water into the dam that environmental fears almost came to pass because the hillside was nearly eroded and posed a threat to nearby communities. Officials spotted a hole on Feb. 12 which led to the evacuation of Oroville’s 16,000 residents and another 180,000 persons in the surrounding area. The evacuation orders had been lifted by mid week.

In March 2016 the rising water in Northern California was good news after a rare weekend of heavy rain. The state had been in the midst of a five-year drought that experts had called the worst in 1,200 years. Dwindling reservoirs, shrinking lakes, and dried-up farm field dominated the landscape and headlines. The snowpack reserves, which typically supply farmers and residents with about one-third of their water, lingered at their lowest level in history in 2015 which resulted in urban conservation mandates requiring residents to use less water while supplies were low. Now there’s too much rain too fast and the resulting damage at Oroville Dam, according to some critics of Gov. Jerry Brown, is the result of not paying enough attention to the state’s infrastructure while focusing too much on conservation measures.

Brown this week was granted federal assistance from President Donald Trump over the “potential failure” of the Oroville Dam emergency spillway citing potential danger to nearby counties: “As a result of the potential for catastrophic flooding, approximately 188,000 residents from Butte, Sutter and Yuba counties were forced to immediately evacuate their homes for life and safety. Officials are aggressively attempting to lower Lake Oroville’s water levels, as another atmospheric river storm system is scheduled to arrive in 48 hours,” Brown wrote.

Powerful storms through Monday

This week, House Majority Leader Kevin McCarthy (CA-23), who is often at odds with Brown on a variety of issues, took stock of the Oroville emergency and looked at the possibility of similar disasters at Lake Success (about eight miles east of Porterville) and Lake Isabella in Kern County. McCarthy was told by the Army Corps of Engineers that the dams at each of these locations were stable and that water levels were well below each spillway. There has been ongoing retrofitting and repair work at main and auxiliary dams at Lake Isabella.

“This weekend’s events at Oroville Dam only further demonstrate the need to expeditiously complete the repair work at Lake Isabella, and also to address raising the Success Dam spillway,” McCarthy said this week, noting that heightening the Success Dam spillway could reserve valuable fresh water.

With two powerful storms expected to hit the southland through Monday, residents can begin to see the end of the drought, but more problems may lie ahead because of the heavy downpours. The atmospheric river (sometimes referred to as the “pineapple express) is described by climatologists as relatively long, narrow regions in the atmosphere (or rivers in the sky) that transport most of the water vapor outside of the tropics. These columns of vapor move with the weather, carrying an amount of water vapor roughly equivalent to the average flow of water at the mouth of the Mississippi River and dumping it as rain as they make landfall. They also talk about a “rain shadow.” This is described as a dry region on the leeward (away from the wind) side of a mountainous area. Take the San Bernardino Mountains for instance. In the case of a rain shadow, Southern California highest chain of mountains will block the passage of rain-heavy weather systems and cast a “shadow” of dryness behind them.

The ‘atmospheric river’

Then there’s the “conveyor belt of storms” which is pretty self explanatory. Climatologists would explain this phenomenon the result of most mid-latitude low-pressure systems tending to develop a network of three distinct coiling air streams as they mature. The air streams act as a conveyor belt or sorts because they transport air in both horizontal and vertical directions. All of these weather systems have made the California landscape virtually knee high in post-drought precipitation—and we’re only in the early days of the traditional rainy season.

The rain has ended the drought in much of Northern California, but the situation may leave the State Water Resources Control Board in a dilemma because it has recommended against eliminating the water restrictions in effect since June 2015, even though facilities like the Oroville Dam—a key depository of fresh water for Central Valley farmers—are at full capacity. By last week, more than seven inches of rain had fallen in and around the Bay Area as the Russian and Sacramento rivers have overflowed their banks because of the rain and melting snow flowing down from the Sierra Nevada Mountains.

With California on pace for one of its wettest winters on record, the biggest deficit remains in Southern California. The recent storms have brought gusty winds and dropped more than two inches of rain in San Luis Obispo and Ventura counties, but lesser amounts due south. There is less runoff from rain in the southland because the soil has yet to recover more moisture after years of drought. As of Feb. 7, representing the latest data from the U.S. Drought Monitor, only 0.73 percent of California remains in “extreme” drought while “exceptional” drought is completely over. For comparison, one year ago 61.4 percent of the state was in extreme drought and 38.5 percent was termed exceptional.

Is drought over?

While umbrella sales have increased, and more roofing contractors are in demand, how much rain has fallen and what can we expect through the spring? Researchers at the University of Colorado-Boulder have been using NASA satellite data and reported that the two biggest storms since January have deposited about 17.5-million-acre-feet of water on the Sierra Nevada range. Compared to averages from the pre-drought satellite record, that amount represents more than 120 percent of the typical annual snow accumulation for this range which is a critical source for the state’s agriculture, hydropower generation and municipal water supplies. They’re keeping eye on the sky at the Jet Propulsion Laboratory (JPL) in Pasadena where scientists report that the winter storms along the U.S. West Coast have resulted in more than 10 feet of snow in just the past three weeks, with some elevations receiving more than 20 feet of snow.

“Early in the January storm, lower mountain elevations received some rain, but the vast majority of the mountain precipitation has come as snow—which is exactly the way we need this precipitation,” said Thomas Painter, a snow scientist at the JPL. “As snow, it released to reservoirs and ecosystems more gradually and efficiently over the summer months.”

What we are experiencing this weekend, according to the JPL, is the collapse of the jet stream southward which results in another temperature drop and moisture flow from the Pacific Ocean. These new storms through the end of Monday could bring more flooding, heavy mountain snow and gusty winds. And this may not be the end of the storm season because we haven’t witnessed the first strong spring storm system.

St. Francis, Baldwin Hills disasters

The Oroville Dam disaster may encourage the state’s congressional contingent on Capitol Hill to back the proposed increase in infrastructure spending backed by President Trump. Of the 1,585 dams in California, 17 are listed in poor condition and 97 in fair condition, according to the National Inventory of Dams, which is maintained by the United States Army Corp of Engineers. Nationwide, there are about 90,000 dams, many of which are privately owned. Lori Spragens, executive director of the Association of State Dam Safety Officials, said the Oroville emergency is an example of “national concern” in explaining that most of the nation’s dams are past 50 years old and many need to be upgraded to current standards.

“It’s the lack of money,” she said. “The whole concern with infrastructure is just not there, as we know.”

The southland has had experience with dam disasters. The worst was the collapse of St. Francis Dam in San Francisquito Canyon (about 10 miles north of Santa Clarita) in 1928 that saw more than 400 people die. An investigation discovered that the dam was poorly constructed and was riddled with code violations. In 1963, five people died and more than 200 homes were destroyed when the Baldwin Hills Dam in Los Angeles collapsed.