Weather Watch

Drought drastically shrinks reservoirs that feed 'salad bowl of the world'

Special to The TribuneJanuary 25, 2014 

Water flowing from Lake Nacimiento will make its way to the Salina River.

JOHN LINDSEY — Courtesy photo

Since the gold rush era of 1849 when rain records started in San Francisco, even the driest of years in Northern and Central California had at least a few significant precipitation events; enough rain to turn the hills to emerald green and snow to whiten the mountains.

However, so far, this rain season — which runs from July 1, 2013, through June 30, 2014 — has seen the smallest amount of precipitation on record.

The Paso Robles airport has only recorded about a half-inch of rain, while Cal Poly (home of climatology for San Luis Obispo) has logged an inch of rain. The last time the rain gauge at Diablo Canyon Power Plant recorded more than an inch of rain in a 24-hour period was Dec. 22, 2012. In fact, Cal Poly has seen 49 dry days in a row.

Not only has it been abnormally dry this rain season, but the last three seasons have experienced well below average precipitation.

John Neil of the Atascadero Mutual Water company told me that the “three-year running rainfall totals” this decade, compared with the drought years of 1976 and 1990, are considerably drier.

“They’re nothing compared to what’s going on presently,” he said.

These dry conditions have ominously reduced the amount of water stored in our lakes and reservoirs. As of Friday, Lake San Antonio was at 5 percent of capacity, with its water elevation at 656 feet, the lowest on record. The dead pool elevation of the lake is 645 feet. When the lake is at that level, water cannot be released via gravity flow. The previous all-time-low water elevation at the lake occurred in February 1991, when the level dropped to 657 feet.

Currently, 10 cubic feet of water per second (cfs) is being released from this lake into the San Antonio River for environmental compliance. This water eventually flows into the Salinas River.

On the other hand, Nacimiento Lake is currently at 22 percent of capacity with its water elevation at 726 feet. The dead pool elevation at this lake is 670 feet. At this time, Nacimiento Lake has 83,360 acre feet of storage. When full, the lake holds 377,900 acre feet of storage.

An agreement between Monterey County and San Luis Obispo County sets the minimum pool level at 688 feet or 22,300 acre feet to insure that a highly reliable source of water — 12,000 acre feet — is reserved for San Luis Obispo County. Currently, 60 cfs of water is being released from the lake into the Nacimiento River which also makes it way to the Salinas River.

These lakes were built by Monterey County to provide flood control by storing the large impulses of runoff from winter storms, then releasing that water over the spring and summer to recharge the groundwater basin when pumping is at its maximum.

The lakes, when coupled with other agency projects, help combat seawater intrusion into the Salinas Valley —the “Salad Bowl of the World.” If significant additional rainfall doesn't materialize over the Lake San Antonio and Lake Nacimento watersheds, there will not be enough water to deliver to the Salinas River Diversion Facility (near Marina, Calif.) during the peak produce-growing season from April through October.

Farmers will either be forced to reduce crops, find alternative source water or pump fresh water from the aquifers below, which could increase the threat of saltwater intrusion into the northern Salinas Valley. If this was to ever to occur, prices for produce would skyrocket.

According to data from SLOCountyWater.org, here are the other San Luis Obispo County lake and reservoir percent of capacity figures as of Friday: Lopez Lake in Arroyo Grande at 56 percent; Salinas Reservoir in Santa Margarita at 39 percent; Whale Rock Reservoir in Cayucos at 56 percent.

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John Lindsey’s column is special to The Tribune. He is a media relations representative for PG&E and a longtime local meteorologist. He is president of the Point San Luis Lighthouse Keepers. If you have a question, send him an email at pgeweather@pge.com.

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