Extravagant pumping of groundwater at thousands of wells in California's San Joaquin Valley has brought land in sections of the valley to subside or sink, by as much as 28 feet (8.5 meters) since the 1920s. This subsidence worsened during droughts when farmers over rely on groundwater to sustain one of the most productive agricultural regions in the nation.

According to Jet Propulsion Laboratory's report, long-term subsidence is a daunting concern for California's water managers, risking state and federal aqueducts, levees, bridges and roads to a certain level of damage. As of now, this issue has damaged thousands of public and private groundwater wells throughout the San Joaquin Valley.

"Furthermore, the subsidence can permanently reduce the storage capacity of underground aquifers, threatening future water supplies. It's also expensive. While there is no comprehensive estimate of damage costs associated with subsidence, state and federal water agencies have spent an estimated $100 million on subsidence-related repairs since the 1960s." the report added.

Though the rains are helping, it may take a longer time to refill these reservoirs as the state has been running on a groundwater deficit for some time. Interestingly, the report also pointed out that small amount of land subsidence had been identified in the Sacramento Valley near Davis and Arbuckle. On top of that, a small area shows about 6 inches (15 centimeters) of subsidence in Sierra Valley, north of Lake Tahoe for the first time.

Though there has not been an exact calculation of the comprehensive estimate of damage costs caused by the subsidence, Daily Mail said state and federal water agencies have spent an estimated $100 million on related repairs since the 1960s.

The California Aqueduct, the main artery of the State Water Project supplies 25 million Californians and nearly a million acres of farmland. It is a system of canals, pipelines, and tunnels that carry water 444 miles (715 kilometers) from the Sierra Nevada and Northern/Central California valleys to Southern California.