Sinking Land Crushes California Groundwater Storage Capacity

Feb 27, 2017 at 1:00pm

Brett Walton, Circle of Blue

The study, which provides the first estimate of the permanent loss of groundwater storage space that occurred during a drought from 2007 to 2010, also shows that California lost natural water storage capacity equal to a medium-sized reservoir. The losses occurred just as the state prepares to spend billions of dollars to build reservoirs to retain water, either above ground or below.

The study, accepted on February 23 for publication in the journal Water Resources Research, also comes as a series of winter storms have filled reservoirs to the point that managers are frantically dumping water to make room for more rain and spring snowmelt. So much water poured into Lake Oroville in northern California that it damaged the reservoir’s two spillways. All of the state’s big reservoirs are above their historical averages and several are lapping at the brim.

California officials will soon decide how to spend taxpayer money on projects to retain some of those big flows. The application window for $US 2.7 billion in state bond funding for storage projects will open in mid-March. Voters approved the bond measure in 2014. Both surface reservoirs and groundwater storage are eligible to apply. There is significant pressure to build Sites Reservoir, which would inundate a magnificent grassy basin in Colusa County, northwest of Sacramento.

The Stanford study focuses on the San Joaquin Valley, where groundwater plays an outsized role in the economy, culture, and politics. With seemingly endless rows of almond trees, orchards, and vineyards, the valley is a cornerstone of California’s $US 47 billion farm industry. It is home to thousands of families whose wells went dry during the recent five-year drought. And the valley is where large sections of land have sunk several feet in the last two years because of soil compaction linked to groundwater pumping. Water officials indicated earlier this month that this land subsidence is causing sections of water canals to buckle and reducing the effectiveness of the California’s extensive water transport network.

Think of the San Joaquin Valley aquifer as a sponge made of layers of sand, gravel, and clay. Other studies of the valley’s groundwater have looked at subsidence, which corresponds to a fall in land elevation. The Stanford study considers the sponge’s ability to refill with water. In effect, soil compaction, particularly of the clay layers, shrinks the sponge. It cannot hold as much water as it used to.

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