Recent rains have dramatically increased the volume of water flowing into major central Sierra lakes and reservoirs that are vital to San Joaquin Valley farmers and communities.
But the storms so far this winter, including the ones that drenched the Valley and dumped snow in the mountains over the last week, aren’t adding up to enough to end the region’s four-year drought.
Behind Pine Flat Dam on the Kings River east of Fresno, water was flowing into Pine Flat Lake at a rate of about 2,140 cubic feet per second (or 16,038 gallons per second), and the lake held about 329,354 acre-feet as of Monday afternoon. That’s 41 percent, about 96,000 acre-feet, more water than a month ago. And while it’s more storage than any March since 2013, it is painfully short of the lake’s capacity of 1 million acre-feet.
Millerton Lake, behind Friant Dam on the San Joaquin River northeast of Fresno, has experienced a similar surge. Inflow to the lake a month ago was about 569 cfs, compared to more than 2,760 cfs this week. The volume of water stored in the reservoir grew from 230,960 acre-feet on Feb. 14 to 330,057 acre-feet on Sunday – a difference of about 43 percent over the past month. Millerton Lake has a capacity of 520,500 acre-feet.
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An acre-foot of water is about 326,000 gallons – the amount of water it would take to cover one acre of land with one foot of water.
“We’re below where we typically would be at this time of year” in storage at Pine Flat, said Steve Haugen, watermaster for the Kings River Water Association. Storage can fluctuate greatly based on a number of factors, including carryover from the previous year, or how much precipitation in the watershed upstream is falling as rain flowing immediately into the lake, or snow that will melt through the spring and summer months.
It’s the snowmelt and the gradual runoff that water officials covet because it helps feed the reservoirs – and meet the demands of water users – on a more gradual basis.
Think of it like this: Rainfall filling a reservoir now is like cash burning a hole in your pocket, while snow is what’s in your piggy bank that you can’t get to right away. In particularly wet years, if reservoirs fill up early with rainfall, a rapid spring snowmelt can create a situation where water managers have to release more water for flood control than can be used downstream – water that essentially goes to waste.
“As of last week, the forecast for anticipated runoff was 83 percent,” Haugen said. “That assumes normal precipitation from today through July 30. To sustain that mid-80-percent forecast, we would have to keep getting some good storm activity in the coming months.”
But, Haugen added, “we’re getting toward the tail end of the really productive part of the season. On average, April precipitation is about half of March, and May is about half of April. And in June or July – well, if we get a thunderstorm, I’ll take it.”
Complicating matters this year is that the upstream watershed – the mountains and the meadows where snow piles up before it melts – are thirsty for water and soaking up more of what normally would flow downstream in an average water year.
“If you look at the watershed above Pine Flat, that area has suffered four years of really dry conditions,” Haugen said. “That watershed is going to need a good, heavy year to rebuild its groundwater. We’re losing some of our runoff because the watershed is holding more water in the soil itself.”
For the southern Sierra Nevada, a much-ballyhooed El Niño cycle – a warmup of water temperatures in the eastern equatorial Pacific Ocean – that some expected to be the salvation to the region’s drought brought its share of moisture to the region. But this year’s El Niño, which was reported as one of the strongest over the last 50 years, has thus far fallen short of prospects to be a drought-buster for the Valley.
“It’s less than I hoped for, but is it less than I expected? Not necessarily,” Haugen said. “If you look at historic El Niño events, it generally indicates above-average precipitation,” but it doesn’t guarantee anything. “What people don’t consider is that El Niño isn’t rain; it’s sea surface temperatures in the ocean, and in a very specific part of the ocean. … There are a lot of other things that influence precipitation that we don’t really understand.”
Northern California reservoirs
Four straight days of rain have replenished key reservoirs elsewhere in California, particularly in the northern part of the state.
Authorities reported that Shasta and Oroville lakes haven’t been this full since 2013, delighting a state in its fifth year of drought but falling short of ending concerns about the drought.
Lake Shasta, the state’s largest reservoir, was at 79 percent capacity on Monday and at 103 percent of its historical average for this time of year.
The 21-mile long reservoir north of Redding now holds 3.6 million acre-feet of water, enough to supply 3 million to 6 million households for a year. The federal reservoir is critical to farms and cities throughout the agriculture-rich Central Valley.
“It’s definitely welcome news, but it’s kind of a mixed bag for us,” said Shane Hunt, a spokesman for the U.S. Bureau of Reclamation. “We still don’t have water in all the right places to meet demand going into peak season.”
For example, man-made Lake Melones in the central Sierra Nevada foothills remains at just 22 percent of capacity and well below the historical average.
The state’s second-largest reservoir, Lake Oroville, was at 70 percent of capacity and 97 percent of its historical average. Folsom Lake, 25 miles northeast of Sacramento, was at 69 percent of capacity.
Heavy snow fell throughout the weekend in the Sierra Nevada, and up to 3 feet was expected in the higher elevations through Monday. That snowpack normally stores about 30 percent of California’s water supply.
Behind Valley dams
Recent storms have increased the amount of water stored behind local dams, but lake levels remain short of their capacity.
Pine Flat Dam / Pine Flat Lake
Storage (Capacity 1 million acre-feet)
230,960 acre-feet (23 percent full)
1,091 cubic feet per second
301,441 acre feet (30 percent full)
3,424 cubic feet per second
329,354 acre-feet (33 percent full)
2,144 cubic feet per second
Friant Dam / Millerton Lake
Storage (Capacity 520,500 acre-feet)
230,960 acre-feet (44 percent full)
569 cubic feet per second
298,861 acre feet (57 percent full)
3,978 cubic feet per second
330,057 acre-feet (63 percent full)
2,764 cubic feet per second
Sources: California Department of Water Resources, U.S. Bureau of Reclamation