Water managers may have to ‘spill’ water from Lake Tahoe

Given the amount of precipitation that has dumped into Lake Tahoe in the past handful of months, water officials may have to send “quite a bit” of water over the emergency spillway located in Tahoe City.

That statement from U.S. District Court Water Master Chad Blanchard on Tuesday comes with a caveat: Officials are waiting for an updated forecast that will take into account the impact of the most recent storms on spring runoff.

New information outstanding, the need to release, or spill, some water from the lake is looking likely. As of 2 p.m. Tuesday, Lake Tahoe was at 6,226.66 feet, according to provisional data from the United States Geological Survey. That number puts the lake 3.66 feet above its natural rim and within 2 ½ feet of the lake’s “legal limit.”

“This year it looks like we’ll have to spill quite a bit of water,” Blanchard said in an interview with the Tribune.

Use of the term “legal limit” in a Tribune story about the large rise in lake level between October and mid-February sparked curiosity from some readers who found the phrase unusual.

One reader asked: “What happens if the lake exceeds the limit? Does it get a ticket?”

The legal limit of 6,229.1 (6.1 feet above the lake’s natural rim) and ensuing need to release water dates back roughly 100 years, Blanchard explained.

“It all dates back to 1907. We had another year like this [year], but 1906 had been a big year also, and we went into the winter full. … Then we had this type of winter that we’re having now and the lake rose tremendously,” Blanchard said.

In July 1907, the lake level was at 6,231.26 feet — an elevation that led to a great deal of erosion. With no way at the time of forecasting how the winter weather could impact lake level come spring, and with fear of possible damage to homes around the lake, talks about limiting Lake Tahoe’s level started ramping up around that time, Blanchard said.

Going above the eventually established legal limit was common in the early 20th century. The lake exceeded the legal limit by at least ½ a foot in 1906, 1907, 1914, 1916 and 1917.

There was legal action at some point, and around 1917 was when 6,229.1 feet was established as the upper, or legal, limit of the lake. The number eventually found its way into the Truckee River Agreement of 1935, and it has remained the legal limit since.

There have been instances, such as in 1997, when the lake went slightly above the limit. Only so much water can be released, and in some instances the outflow cannot keep pace with the inflow, Blanchard said. In 1997, the lake exceeded the limit by “a couple tenths of a foot” before dropping back down, he added.

As for this year, the decision on whether to release water (and if so, how much) in order to make room for runoff will need to be made in the near future.

Currently, 50 cubic-feet-per-second — the minimum amount required to be released from Lake Tahoe at this time of year — is running out of the lake. Blanchard noted that even if officials decide to spill water, the amount pales in comparison to that lost to evaporation each year. That number averages 40 inches, he said.

If the lake does manage to fill this year, it will mark a physical increase of 6 ½ feet — a new record. The previous record of 6 feet came in 1995.

“We’ll have to wait for a new forecast. … We very well could be required to start some precautionary release from Tahoe,” Blanchard said.

Correction: The original version of this story used the incorrect unit of measurement when describing the lake’s height above the natural rim. It is feet, not inches.

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