The further adventures of a California reservoir. A year and a week ago -- late March 2013 -- Kate and I camped in the very nice Loafer Creek campground at Lake Oroville State Recreation Area. The lake, the main reservoir for the State Water Project and the second largest California reservoir after Lake Shasta, was about 85 percent full at the time. If you were following the vagaries of the state's water season, you might have been a little troubled by the fact the 2012-13 rains had virtually disappeared after the turn of the new year. What wasn't apparent during the first visit up there was that the rains wouldn't return in the fall, either, and that the lake would fall to just one-third full by January -- low in any season, but especially alarming in that the reservoir levels here and virtually everywhere else across the state continued to decline at a time when they'd usually be filling up with runoff from winter storms.
I drove up to Lake Oroville on January 18, which happened to mark the lake's low point during the current water year (July 1, 2013-June 30, 2014). The difference in the lake's appearance was dramatic -- see the slideshow below. But when seasonal rains finally returned in early February, the lake began to rise. One way of measuring lake level is the height of the lake surface above sea level. When full, Lake Oroville's surface is 900 feet above sea level. When Kate and I visited in March 2013, the surface level was 860 feet; when I went back in January, it stood at 701 feet according to the numbers from the state Department of Water Resources. The same source shows the lake at 759 feet now and rising.
Yesterday, Thom and I drove up to Oroville to take a look and take a new set of pictures to show the change since January (they're incorporated into the slideshow). My impressions:
I suppose this is a "glass half-full/half-empty" exercise on a grand scale, especially since the lake is at almost exactly 50 percent of its total capacity right now. On one hand the lake is up almost 60 feet from the last time I saw it and has added about 40 percent to its storage -- it's added about 500,000 acre-feet since January, enough water for about 1 million California households. More water is coming, too: Even though the forecast for the next couple of weeks and beyond looks pretty dry, and even though we're nearing the tail end of the rainy season, the snowpack will start too melt and run down the branches of the Feather River that flow into the lake.
The conventional wisdom is that half of the state's stored water is captured in the Sierra snows that wind up in streams, rivers and reservoirs. One slice of Lake Oroville history shows how dramatic an impact the snowpack can have:
A drier-than-normal water year in 2008-09 reduced the reservoir's storage to a shade more than 1 million acre-feet, less than 30 percent of capacity, and lowered the surface to 665 feet above sea level by early January 2009; that's about 20 percent less water and about 45 feet lower than the level we saw this past January. Then storms began arriving and began building the northern Sierra snowpack. The water content of the snow in the Feather River drainage reached about 130 percent of normal by early April 2010, and the lake had come up to virtually the same level as it is this weekend. The reservoir, which had reached its lowest point on January 11, kept rising through June 29, when it reached its high point of about 2.7 million acre-feet and elevation of 843 feet above sea level. That's a rise of 178 feet in less than six months.
So that's the glass half-full. It's normal for our reservoirs to rise and fall, often dramatically (and no, I'm not addressing here the impact of how the reservoirs are operated -- how much water is released, when, and why).
Here's the empty half of the glass for Lake Oroville: This year, the Department of Water Resources estimates that the water content in the thin layer of snow in the Feather River watershed's high country is just 13 percent of average for this time of year. Thirteen percent. So, we're not going to see any late season rise in the lake. More likely, we'll see a scenario more like the one that unfolded in 2007-08, when two drier-than-normal years left the lake at close to the same level we see today -- 753 feet. The watershed's snowpack was lower than normal, and although runoff gave the lake a boost, it topped out at just 760 feet and 50 percent capacity in late May. That dry rain year was followed by another, and in February 2009, the state declared a drought emergency.
None of this is meant to make a single reservoir, even a big one like Lake Oroville, seem more important than it really is. But reservoirs are important to making it possible for 38 million people to live, and for a rich agricultural industry to thrive,in a place where it typically doesn't rain much for six months of the year. And Lake Oroville's water storage happens to mirror what's happening with the state's water supply picture as a whole at the moment: The Department of Water Resources' daily summary of 44 key reservoirs shows them collectively at 64.4 percent of average for today's date. Lake Oroville is at 65 percent.
Here's the revised slideshow: