- Overall, groundwater levels are declining in the southern, Tulare Basin portion of the San Joaquin Valley as more water is pumped out than recharges naturally. But the southern valley also shows the most promise for large-scale artificial groundwater recharge, particularly along the eastern side with its coarse-grained soils from river and alluvial-fan sediments.
- By contrast, groundwater levels in the Sacramento Valley and the northern portion of the San Joaquin Valley are generally stable.
- As the state faces its third year of below-average precipitation, groundwater supplies are under increasing pressure, according to data gathered since 2003. Landowners are drilling more and deeper wells, and underground water levels are starting to drop once again – as they did during previous droughts in the 1970’s and 1980’s.
But unlike above ground reservoirs, once drawn down it takes more than single good winter's worth of precipitation to refill it. This story is being repeated all over the globe. If we don't get smarter about water management soon, we could end up in a situation that makes today look like the good old days of abundant water.
The Central Valley is more than 400 miles long, comprised of the water-rich Sacramento Valley in the north and the drier San Joaquin Valley in the south. One of the nation’s most productive agricultural regions, the Central Valley has the largest groundwater system in the state. The groundwater basin, or aquifer, contains one-fifth of all groundwater pumped in the nation.
It is, in effect, California’s largest reservoir.