Drought Watch – Mar 2016

California Reservoirs Are Dumping Water in a Drought, But Science Could Change That

– KQED  Youtube

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“There’s a rule in California that may seem bizarre in a drought-stricken state: in the winter, reservoirs aren’t allowed to fill up completely.

In fact, even as this post goes up, a handful of reservoirs are releasing water to maintain empty space.

The practice, which has long inflamed combatants in California’s water wars, is due to a decades-old rule designed to protect public safety. If a major winter storm comes in, reservoirs need space to catch the runoff and prevent floods.

But with advances in weather forecasting, some say this preemptive strategy is outdated. A new, “smart” flood control system could save water in years when Californians need it most.

Hitting the ‘Magic’ Line

At one of the state’s major reservoirs — Folsom Lake, east of Sacramento — the volume of water spilling from the dam has swollen eight-fold in the past few weeks, sending billions of gallons downstream, much of it into San Francisco Bay.

Early in February the reservoir reached a key threshold: 60 percent full, which is the highest water level allowed during the winter months, according to rules from the U.S. Army Corps of Engineers and the Sacramento Area Flood Control Agency.

Last year, most of the reservoir was a dry, dusty lakebed.

“What reservoir was left was confined to the old river channels before we built the dam,” says Drew Lessard of the U.S. Bureau of Reclamation, the federal agency that manages the reservoir.

Just an average-size winter storm can send huge volumes of water down the American River into Folsom Reservoir, boosting the lake by 10 percent or more. A major storm can produce dramatically more than that.

“The watershed is pretty flashy and it responds pretty quickly to storm events,” says Lessard. “That’s why we need to reserve a space during those winter months in case that happens.”

Sitting 40 percent empty allows the reservoir to act as a buffer against floods, gulping the runoff without overflowing. In years where the upstream reservoirs are fuller, Folsom Reservoir is required to remain 60 percent empty.

Releasing water downstream does produce benefits, supporting wildlife and endangered fish. It also prevents salt water from San Francisco Bay from backing up into the Sacramento-San Joaquin Delta, which is a drinking water supply for many in the Bay Area.

But preemptively releasing water has its own risks, especially if it doesn’t rain again, as happened in 1997. The reservoir was lowered and, “it was dry the rest of the year and we never really rebounded,” recalls Lessard.

 

 

As California enters a fifth year of drought, seeing operators deliberately dumping water can be disconcerting.

A few weeks ago, Shauna Lorance of the San Juan Water District near Sacramento went to state regulators with a message: when water is disappearing downriver, it’s hard for water consumers to take the conservation message seriously.

“Anything they conserve right now is not held,” said Lorance. “For me to explain to customers, after everything they’ve done, that they need to continue to conserve so it can be spilled is going to be a nightmare.

‘Smart’ Reservoirs

“The rules that govern water in the West were created in the 19th century,” says Marty Ralph, who directs the Center for Western Weather and Water Extremes at UC San Diego. “And yet here we live in the 21st century with its special and new needs: greater population and a changing climate.”

Ralph is piloting a more dynamic method of flood management at Lake Mendocino with the Sonoma County Water Agency.

Instead of a maintaining firm limits on reservoir levels dictated by the calendar, managers would use cutting-edge weather forecasts to gauge how much flood space they need.

“Weather predictions have been improving over the last decades, “ said Ralph. “Particularly on the West Coast, we’ve learned about the phenomenon that produces most flood-producing storms. We call them atmospheric rivers.”

Instead of emptying out a reservoir preemptively, managers would allow the reservoir to stay fuller, keeping an eye on the weather forecast.

If a big storm appears, “they’d have three, four, five days lead time, enough to release that extra water and get it out of the way safely,” said Ralph.

If storms don’t appear, the water would be saved for later in the year.

Ralph says “forecast-informed” operations are becoming possible thanks to major advances in weather research. New weather satellites and more precise forecast models are making predictions more accurate. Researchers are even flying planes into atmospheric rivers to gather information about how they behave.”

Read more of the original article by Lauren Sommer @ KQED Science

More on Marty Ralph:

 

RESEARCH PROFESSIONAL, CLIMATE, ATMOSPHERIC SCIENCE & PHYSICAL OCEANOGRAPHY

Scripps Institution of Oceanography

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From web site:

Interests:

  • Precipitation – diagnosing key physical processes controlling rain and snow formation and developing new methods for precipitation monitoring and prediction
  • Hydrometeorology – exploring atmospheric and land surface conditions that drive streamflow (from weather to climate scales)
  • Water resources – developing modern tools to aid in balancing water supply and flood control in a changing climate
  • Observations – applying new observing strategies (sensors and networks) to water cycle science and prediction
  • Atmospheric chemistry – exploring the role of aerosols in clouds, precipitation and water supply

Marty Ralph @ University of California, San Diego

More on Atmospheric Rivers and aerosols:

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Aerosols influence strength of ARs

“Atmospheric rivers, a relatively narrow band transporting water vapor from the tropics to the West Coast, are responsible for 30-50% of annual precipitation. Some of these events can create major flooding, with the system coming ashore and stalling over an area. A strong AR transports an amount of water vapor roughly equivalent to 7.5–15 times the average flow of liquid water at the mouth of the Mississippi River, according to Marty Ralph, a scientist with Scripps Oceanography/UCSD and co-lead on CalWater2015

Ruby Leung, a scientist with Pacific Northwest National Laboratory and Kim Prather of Scripps Institution of Oceanography, University of California San Diego are flying in the PNNL and NOAA planes gathering data on aerosols. These little particles can be dust from as far away as the African desert or greenhouse gases emitted from fossil fuel burning. Without the presence of aerosols, the water vapor contained in an AR cannot condense into rain, ice or snow, leaving California parched. Too many particles however can have the opposite effect.

Leung and Prather were flying through low-level fog over the California coast on Tuesday morning, collecting samples and analyzing particles before attending the media briefing.”

from @  Yubanet.com