[env-trinity] Trinity Journal- Wet year, lower diversions boost lake

[Tom Stokely]

Wet year, lower diversions boost lake

http://www.trinityjournal.com/news/2011-11-16/News/Wet_year_lower_diversions_boost_lake.html 
BY AMY GITTELSOHN THE TRINITY JOURNAL
As forecast, the 2011 water year was a wet one for the Trinity River basin with an inflow to Trinity Lake of 1,780,800 acre-feet, according to a water year summary from the Trinity River Restoration Program.

The water year runs from October through September. Inflow to the reservoir was the highest it’s been since the extremely wet year of 2006 when inflow was 2,396,500 acre-feet. Average yearly inflow is 1,254,000 acre-feet.

Of the 1,780,800 inflow in 2011, 721,800 acre-feet of water was released to the Trinity River for fisheries and 10,800 acre-feet was released for tribal ceremonial purposes. Another 473,100 acre-feet of water was diverted for Central Valley Project use.

Typically in a wet year more water is diverted south for CVP use, but the last couple of years diversions have been limited by work on power plants, said Larry Ball, operations supervisor for the U.S. Bureau of Reclamation in the North State.

Under the Trinity River Record of Decision signed in 2000, about half of the inflow to Trinity Lake is released to the Trinity River. In wet years a lower percentage of the inflow goes down the river, and in dry years a higher percentage is released to the river with the remainder available for CVP use.

Ball noted that amount being diverted to the tunnels now -- 1,587 cubic feet per second on Monday -- is higher than usual. Trinity Lake is very high for this time of year, and a “comfort zone” is needed for the winter months, he said.

It’s not a bad problem to have. “Some years you don’t have enough water,” Ball noted.

Long term, from 2000 to 2011, 45 percent of the average inflow has been released to the river for fisheries while 6 percent has been released to the river for other reasons, primarily the safety of dam releases when Trinity Lake rises too quickly during a very wet winter. During that same time period, 57 percent of the average inflow was diverted to the Sacramento River. The combined release was 107 percent of average annual inflow.

The five-year average for 2007 through 2011 water years was 47 percent of average inflow for the release to the Trinity River for restoration purposes and 39 percent diverted to the Sacramento River, for a combined total release of 86 percent.

The percentages above or below 100 percent are possible due to changes in reservoir storage across water years.


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