A recent study by the US Geological Survey (USGS) shows that the aquifer under California's Central Valley is changing. The over 400 mile long Central Valley is home to California's agriculture industry. Under the valley is the nation's largest groundwater basin which contains one-fifth (20%) of all the groundwater pumped in the nation.
Several sources of data were used for the study: water well driller logs going back to the early 1900''s, ground water data from 1962 to 2003 and surface water data from 1962 to 2003.
The USGS study shows the strains California's growing population is putting on the underground aquifer:
- Groundwater levels are declining in the Tulare Basin portion of the southern San Joaquin Valley. More water is being pumped out than is being put into the basin. The geology of the southern San Joaquin valley, coarse-grained soils and alluvial-fan sediments, make the basin a potential candidate for becoming a groundwater recharge basin.
- Groundwater levels in the Sacramento Valley and the northern portion of the San Joaquin Valley are generally stable.
- Drilling for water, which is driven by the continuing below-average precipitation, is causing groundwater levels to drop.
As part of the study, the USGS has developed an enhanced computer model, the Central Valley Hydrological Model, of water flows below ground. The model shows how water flows under ground, in the groundwater basins, and how the flows connect with rivers and other bodies of water on the surface. The Central Valley Hydrological Model provides a new scientific tool to track changes in surface and groundwater availability and make more informed water management decisions.
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