Putting Back What We've Taken Out

Central Valley sinkhole (Ecowatch)

The problem: "voracious" groundwater pumping during the multiyear drought has caused the ground to sink alarmingly [bold added]:

Certain hotspots are shrinking at an astonishing rate — regions of the Tulare Basin, which includes Fresno, sank 13 inches (33 cm) in just eight months...The Sacramento Valley is sinking about 0.5 inches (1.3 cm) per month.

Subsidence isn't just an aesthetic problem; bridges and highways can sink and crack in dangerous ways, and flood-control structures can be compromised. In the San Joaquin Valley, the sinking Earth has destroyed the outer shell around thousands of privately drilled wells.

Recharge pond in Fresno County (Chron photo)

A possible solution: while the welcome El Niño storms are recharging the aquifers, water districts are trying to hurry along this natural process through geological engineering:

The Consolidated Irrigation District, which serves parts of Fresno, Tulare and Kings counties in the Central Valley....lets the precious liquid soak in at percolation sites so it stores in the ground. The agency introduced these “recharge ponds” to the region in the 1920s, and today is leading a popular charge.

According to the Chronicle four new dams and reservoirs will cost $10 billion and increase the State's water storage by 9%. By some estimates replenishing the aquifer would make available five times the water volume of the new-dam project for about the same cost (where recharge ponds are not feasible, expensive injection wells have to be built).

IMHO, California should do both---build new above-ground capacity while refilling below-ground storage---but while we're arguing about the former we can at least do the latter.