Water & Drought

Sacramento agencies ask: Why release water from Folsom Lake during drought?

Folsom Dam, shown in June 2015, can hold 977,000 acre-feet of water. Its current level is above normal but nowhere near capacity.
Folsom Dam, shown in June 2015, can hold 977,000 acre-feet of water. Its current level is above normal but nowhere near capacity. Sacramento Bee file

Northern California’s El Niño winter has been on pause lately, with this week’s storm representing the only significant rainfall so far in February. Yet federal dam operators recently increased the flows out of Folsom Lake by thousands of acre-feet a day as a precaution against flooding. They did so even as the reservoir sat 40 percent empty.

The dam operators weren’t acting on their own initiative. They were adhering to a nearly 30-year-old manual, drawn up by the U.S. Army Corps of Engineers, that requires them to release water when Folsom Lake rises to a specified height. The requirement holds even if no major storms are forecast and the state is trying to conserve water during the fifth year of an epic drought.

Similar operating manuals, all created by the Corps, govern flood-control releases at 54 dams in California. The majority haven’t been updated since at least the 1980s; Folsom’s manual was last updated in 1987.

Now, a small but growing chorus of Sacramento-area water managers and hydrology experts says it’s time to rework the guidelines at Folsom and other reservoirs to permit more flexibility on water storage, particularly given a warming climate expected to bring more frequent and longer dry spells.

“When April rolls around, it’s … likely we’ll look back and say, ‘Gosh, I wish we hadn’t made those releases,’” said Jay Lund, director of the Center for Watershed Sciences at UC Davis.

The ramped-up releases didn’t occur in a vacuum; they followed a remarkable surge in which the lake’s water level tripled in less than two months. Officials with the Corps said flood safety remains a paramount concern, particularly with hundreds of thousands of Californians living on floodplains below dams.

Christy Jones, chief of water management in the Corps’ Sacramento district, said every dam’s flood-control manual provides some wiggle room to account for recent weather patterns, forecasts and hydrological conditions, but reservoirs must have ample space during the wet season to ward against unforeseen floods.

“If they say that (a storm) is going to be really small, and it ends up being much bigger than what they forecast, then we don’t we keep enough space in the reservoir, then we’ve not done our duty to help reduce that flood risk downstream,” she said.

The increase in water releases from Folsom, which began Feb. 5, spilled enough water to supply the Sacramento region for weeks, much to the chagrin of water managers who remain under orders from the state to meet stiff conservation targets. They say it’s difficult to get people to take shorter showers and rip out their lawns when extra water is flowing out of Folsom even amid prolonged forecasts of sunny skies.

“If we can’t trust people to make forecast-based decisions, then you need new staff,” said Shauna Lorance, general manager of the San Juan Water District, which relies on Folsom Lake to supply its 160,000 retail and wholesale customers.

Some environmentalists take issue with the idea that water flowing down the American River is wasted, saying the flows help with fish populations and other needs. But at the Fair Oaks Water District, the heavy releases from Folsom represent an opportunity lost.

“Customers see water being dumped down the river,” said General Manager Tom Gray. “If we’re in the dire straits of a drought, shouldn’t you be looking at actual (weather) projections? Shouldn’t you maybe not use the regular playbook?”

Jones’ response: “Well, the difference between a water district and the Corps of Engineers is the district is looking at how much water can we save. The Corps of Engineers is looking at how much can we protect the downstream communities.”

Local water officials don’t take issue with flood control in concept. The last major Northern California flood, in January 1997, killed eight people and caused $1.8 billion in damage. And even ringed with levees, Sacramento remains among the nation’s most flood-vulnerable regions. Worries over flood risks were so pervasive that in the mid 1990s, the Sacramento Area Flood Control Agency worked out an agreement with Folsom’s dam managers to add more flood-storage space in the lake, on an as-needed basis.

The U.S. Bureau of Reclamation has primary responsibility for Folsom Dam operations. Water is released year round, in varying amounts, to meet downstream water quality standards and other needs. Reclamation officials must abide by Corps manuals once the water levels in Folsom rise to a certain point.

The flood-control threshold is a moving target and will gradually rise through the rest of winter and into spring, enabling more water to be stored, as the rainy season winds down.

The Corps’ original flood-control guidelines, created when Folsom Lake opened in 1956, called for keeping the reservoir no more than 60 to 80 percent full through March, depending on recent precipitation. Flood-control operators made two major updates over the next three decades: once after a prolonged drought, once after a horrific flood, according to Corps documents.

The manual was first updated in 1977, following a massive drought. That update dictated the lake not rise above 60 percent capacity in early winter, but it allowed operators to start increasing water levels past that amount beginning each January, hedging against the possibility of a dry winter.

Then, after a huge flood in 1986, the guidelines were updated again, but with later-season flood risks in mind. Mid-February became the point when the lake level could rise past 60 percent.

The flood-control manual hasn’t been updated since, Jones said, but will get its first update in 30 years next year as part of the construction of a $900 million auxiliary spillway. The new gates will be 50 feet lower than the main gates. That would allow for earlier and safer water releases from Folsom Lake during periods of high water, federal officials say.

Jones said officials are discussing the possibility of revising the manual to allow for more forecast-based decisions at Folsom. But, so far, nothing has been decided.

Joe Countryman, a retired Corps engineer in Sacramento, said Folsom is an ideal candidate for incorporating short-term weather forecasts into operational guidelines. The reason? The river channel below the dam is wide enough to accommodate sudden gushes of flood-control releases when storms are spotted developing over the Pacific Ocean.

“We have the great advantage here where we can see out in the Pacific and we can tell when a large storm is coming in,” said Countryman, who sits on the Central Valley Flood Protection Board. “It’s not a secret. It can’t sneak up on us.”

Corps documents discussing the spillway project show officials are torn on the issue of using weather forecasts to keep more water in storage.

A report in 2013 by a Corps consultant on the spillway project said Sacramento area water agencies have been pressing the Corps to store more water during winter, but the consultant said: “The balancing act of neither releasing water ‘too late’ nor ‘too early’ from Folsom Reservoir is not an easy one. Even when more is learned about accurately predicting such parameters as precipitation and basin wetness, there will always be uncertainties. … Exactly how to balance these uncertainties in the manual update could be an area of tension among stakeholders.”

Some critics say the federal dam managers have been slow to use improved science, engineering and weather data.

Ann Willis, a researcher at the UC Davis Center for Watershed Sciences, said the flood-control manuals at many of California’s dams are too rigidly tied to outdated weather models. For instance, the flood-control manual at Folsom cites weather patterns prior to the 1990s. The manuals, Willis said, say reservoirs need to stay comparatively empty in winter to make way for heavy snowmelt in the spring – a philosophy that gradually could be rendered obsolete by climate change.

“When the spring season comes along,” the UC Davis scientist said, “there’s no snowmelt to capture.”

Changes to Folsom’s operating manual could lead to significant water savings. Under current guidelines, federal officials aim to keep Folsom at or below 575,000 acre-feet, or 60 percent of capacity during much of winter. As an example, allowing the lake to hit 65 percent of capacity before making flood-control releases would permit an extra 50,000 acre-feet to remain in storage.

That 50,000 acre-feet would be equivalent to all water used in 2015 by the roughly 220,000 retail customers in Roseville, Folsom and the San Juan Water District, the three agencies most reliant on Folsom Lake for drinking water.

This month’s ramped-up releases weren’t the first time that extra water poured out of Folsom during the current drought to guard against a flood that never came.

During the week of Christmas 2012, Folsom Lake was well below capacity. Nonetheless, the Bureau of Reclamation opened up the Folsom Dam gates, based on the Corps’ guidelines, and let tens of billions of additional gallons flow out.

It was the highest sustained flow recorded between 2012 and 2015, according to records kept by the California Department of Water Resources. While it did rain 2.4 inches in Sacramento over the next two weeks, that was the last of the significant rain until the following October.

Lund, the UC Davis watershed sciences director, said there’s strong institutional reluctance to a sweeping reworking of the agency’s dam guidelines.

“Nationally, the Army Corps of Engineers takes a look at this and says, ‘Wait a minute, if we open this little can of worms in California, there’s another 600 reservoirs across the country, each of which have their stakeholder groups who are just itching to fight to see if they can ... get something else out of the system,’ ” Lund said.

“Bureaucracies are risk-averse anyway, so this puts them all in a bad situation. We should be making these changes, but there are real human reasons why there’s reticence to do it.”

Jones, the agency’s flood manager in Sacramento, said changing any flood-control manual requires complex and costly engineering and environmental studies. Each time a dam’s flood-control manual is updated, the reviews “can easily cost several million dollars per project” and funds require congressional approval, she said.

“We do things as we are authorized and funded to do,” she said.

Ryan Sabalow: 916-321-1264, @ryansabalow

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