UC Davis reports Lake Tahoe clarity down in 2015, lake level returns to natural rim | TahoeDailyTribune.com

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UC Davis reports Lake Tahoe clarity down in 2015, lake level returns to natural rim

Lake Tahoe's famed water clarity took a hit last year in part due to California's fourth consecutive year of drought. Researchers from the University of California, Davis, announced this week that average mid-lake clarity dropped nearly 5 feet in 2015 when compared to the previous year.

According to UC Davis Tahoe Environmental Research Center, lake visibility averaged 73.1 feet, a 4.8-foot drop from 2014.

While at face value it may appear to be headline-grabbing news, research center director Geoffrey Schladow said it's not a cause for concern.

"If it declined another 4 or 5 feet next year that would be concerning," he said. "I don't expect that."

Schladow described the change as a relatively normal year-to-year fluctuation that may have in part been influenced by record-low snow and warmer inflow from streams and creeks last year. Both leave fine particles closer to the surface.

The region received 18 inches of precipitation during 2015 and only 5.3 percent of it came as snow — the lowest recorded measurement in 105 years, according to a UC Davis release. In stark contrast, early March storms alone brought around 14 inches of precipitation this season.

Since regular tracking of lake clarity began in 1968, records show that diminishing lake clarity has leveled off significantly. Tahoe Regional Planning Agency, which manages Tahoe-area environmental policy, credits substantial stormwater drainage improvements and watershed restoration for slowing the decrease.

"We're pleased to see that our extensive work to reduce stormwater pollution into Lake Tahoe has contributed to stopping the long-term decline in its water clarity," TRPA executive director Joanne Marchetta said.

In 1968, average clarity was recorded at 102.4 feet. The lake reached its worst average clarity in 1997 at 64.1 feet. Over the last 15 years it has remained around 71 feet, but varies significantly through the year. In 2015 it fluctuated between 86.5 and 59.9 feet.

"The more we can do to reduce stormwater pollution, the better it's going to be," TRPA spokesman Tom Lotshaw said. "It doesn't turn around on a dime, but I think we're making good progress."

Studies by the TRPA estimate that 72 percent of fine sediment pollution reaching the lake comes from existing roads and developed areas.

Caltrans, California Tahoe Conservancy and a number of other agencies currently have efforts underway to reduce sediment pollution through a number of projects, including highway drainage on the West Shore and the Upper Truckee River restoration in South Lake Tahoe.

Federal and state regulators hope to eventually restore lake clarity to 97.4 feet, according to TRPA.

Schladow could not be reached for a follow-up comment on how this year's average snowfall and spring runoff may impact clarity.

LAKE REACHES RIM

Lake Tahoe reached its natural rim earlier this month following the return of average winter snowfall. While it reached the natural rim briefly in June of last year, this year's lake level is expected to remain at or above the rim through late summer. With spring snowmelt continuing, the lake is currently 2 inches above its rim and has begun spilling over into the Truckee River for the first time since October 2014.

National Weather Service meteorologists expect lake level to reach a little over a foot above its natural rim following spring snowmelt.

"It's encouraging," National Weather Service Reno senior hydrologist Tim Bardsley said, adding however, "It's still significantly below average."

In an average year, mid-April lake level would reach around 2.6 feet above the rim.

The lake has already risen roughly 1.6 feet since December, which is a significant recovery — but still far from normal.

"It was the lowest the lake has been since around 1995," Bardsley said of pre-winter conditions.

He added that one significantly above-average winter would bring the lake back to normal levels. Based on his calculations one more average winter would be enough to bring it close, and two average winters would raise it slightly above normal levels.

Bardsley said both scenarios could be realistic, citing past years in which the lake has seen significant recoveries in a single season.