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The ups and downs of Lake Almanor

 

By Dale Knutsen

Special to Plumas News

 

There are two persistently popular discussion topics in the north end of Plumas County: (1) the weather, and (2) the state of Lake Almanor.  Folks will readily engage in conversation about both topics, based on their current observations and recent recollections. Is this a dry year or a wet year? How low is the lake? Has it EVER been this low? Will the water rise this summer? And so forth.

 The lake has definitely been important to the region for the past 100+ years, serving as a reservoir for the extensive PG&E hydroelectric power generation system and creating a recreational magnet for residents and visitors alike.  So it is quite understandable that it might dominate local conversations. But when the discussion gets into seasonal or multi-year changes, recollections and opinions often diverge.  Accurate information on weather patterns and lake levels may not be at our fingertips.  But the information does exist if you are willing to dig for it, and that leads to this brief article on the recent history of Lake Almanor water levels and precipitation.

 The level of the lake’s water is monitored constantly by the California Department of Water Resources. That information is tracked by a local group associated with the relicensing of the dam and lake, and is posted on their website at www.project2105.org .  However, the large array of posted numbers may not be terribly helpful for the average citizen, so the information has been plotted graphically in the figure below to add some multi-year perspective to the matter. A 23-year timeframe from calendar 2000 through 2022 was arbitrarily selected for examination.

The lake water level varies over the course of each season, with the high water mark found in early summer after the rains and snow melt runoff have completed their contributions.  To capture the approximate maximum water level each year, the measured lake level on July 1st is plotted in the upper part of the figure as a solid line.  The fluctuations over the 23-year period are relatively rhythmic, varying from a low of 4479 feet above sea level in 2001 to very near the 4494 feet maximum allowable level on several subsequent years.

Water is drawn out of Lake Almanor to meet PG&E’s power generation and statutory flow requirements through the outlet next to the dam and through the Prattville-Butt Lake tunnel. This results in a gradual draw down of the lake level over the warm season, before autumn rains begin the recharge process.  And sure enough, if you plot the lake level on November 1st of each year, it falls below the July line.  But perhaps surprisingly, the difference between those two lines is relatively small, averaging less than 8 feet over the time period examined.

Local weather patterns are, of course, the dominant factor in how much water is captured by Lake Almanor. One way to illustrate the factor is to plot the amount of total precipitation received in the basin, using our customary July through June “water year.”  Rainfall plus the water content of snowfall is accounted for in this process, with the results shown in the lower part of the figure. The data comes from the PG&E monitoring site at Prattville. It is representative of our general weather pattern, but does not attempt to account for precipitation in higher elevation areas upstream of the lake.

The precipitation patterns show considerably more annual variation than the lake level data, and that is due to the nature of the lake bottom. Lake Almanor is simply a flooded meadow, relatively shallow as reservoirs go.  Its gentle slope (particularly in the western lobe) means that a small change in lake level will result in a very large change in apparent shoreline. This causes significant visual differences over the course of a season or from year to year as the lake level fluctuates.

Now, as to the future, we are definitely in a wet year scenario, and that bodes well for substantial recharge of the lake.  We’ll need to wait a couple of months for the official projection from PG&E, who typically brief the District 3 Supervisor on their estimates sometime in April.  But in the meantime, we are free to guess at the 2023 peak lake level as we continue to complain about the amount of snow and ice we are dealing with.

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