Drought

Land Subsides in California

A canal that delivers vital water supplies from Northern California to Southern California is sinking in places. On farms, well casings pop up like mushrooms as the ground around them drops.

Four years of drought and heavy reliance on pumping of groundwater have made the land sink faster than ever up and down the Central Valley, requiring repairs to infrastructure that experts say are costing billions of dollars.

This slow-motion land subsidence — more than one foot a year in some places — is not expected to stop anytime soon, experts say, nor will the expensive repairs. Land subsidence is largely the result of pumping water from the ground. As aquifers are depleted, the ground sags.

The most severe examples today are in San Joaquin Valley, where the U.S. Geological Survey in 1975 said half of the land is prone to sinking. USGS researchers later called it one of the "single largest alterations of the land surface attributed to humankind."

A sparse mountain snowpack in California's driest four-year span on record has forced farmers in the Central Valley, the nation's most productive agricultural region, to rely on groundwater to irrigate their crops.

Drought has spawned a well-drilling boom with some tapping ancient aquifers 3,000 feet down.

In wet years, groundwater provides about 40 percent of water used in California, but in times of drought, groundwater can amount to 65 percent of the state's water supply.

Decades of over-pumping have destroyed thousands of well casings and buckled canal linings. To keep water flowing through low spots, irrigation districts raise the sides of sagging canals so they can increase the water level and maintain a gravitational flow.

Parts of the California Aqueduct, a massive canal that delivers water 400 miles to Southern California, also sank by nearly 13 inches.