Lake Tahoe drops below its natural rim
INCLINE VILLAGE, Nev. — Lake Tahoe is now terminal.
The UC Davis Tahoe Environmental Research Center on Tuesday night reported that the level of Lake Tahoe fell precipitously over the past couple of days despite the recent snow and has fallen below its natural rim.
The center said the level reached the natural rim at 9 a.m. on Tuesday and then rose slightly a couple of hours later, but by 5 p.m. it was again at the rim and has continued to fall. The water level falling below the rim is six days sooner than the center anticipated.
The center said that the recent storm was not enough to increase stream flows into the lake and that high winds that accompanied the snow showers greatly increased the rate of evaporation from the lake.
“In one 36-hour period, the lake level fell by 1.2 inches due to evaporation,” said an email from TERC. “This is almost four times the annual evaporation rate of about 72 inches per year.”
Expectations are that the lake level will continue to fall about 1-1.5 inches per week without significant precipitation, which is about the same as 4 to 6 billion gallons of water per week, or enough water to meet the daily needs of 48-72 million people.
“That’s not a drop in the bucket,” the center said.
Flow from the lake to the Truckee River will be at zero, although the Truckee River will continue to get inflow from groundwater and from streams downstream of Lake Tahoe.
A terminal lake, sometimes called an endorheic lake, is one that does not have any outflows to streams and other water bodies. Examples in Nevada include Pyramid Lake and Walker Lake, while in California there is Mono Lake and the Salton Sea.
The low water levels are already impacting the Tahoe’s shoreline, with accumulating deposits of rotting algae on the beaches of the South Shore and a scene of docks out of water on the North Shore.
“It is likely that winter will arrive in the next few months and the lake level will rise above the natural rim soon after,” the center said. “But if the 21/22 winter turns out to be below average, next year the lake will fall below the natural rim much sooner and likely stay there for most of 2022. This will impact recreation as many docks and boat ramps will be further away from the shoreline. The growth and the washing up of filamentous algae on the very wide beaches will increase. The sill across Emerald Bay may end up above the water surface, physically turning Emerald Bay into a separate lake, a similar issue that may occur at the mouths of many streams cutting off access to spawning kokanee salmon next fall.”
Source: UC Davis Tahoe Environmental Research Center
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