The next drought could end up with two domestic wells going dry in the water basin that most of San Joaquin County and parts of surrounding counties rely on.
Compare that to Kern County in the southern San Joaquin Valley where many wells go as deep as 1,200 to 1,600 feet.
Water experts anticipate 200 wells will go dry in Kern County when the next drought rolls around.
That extreme outlook elsewhere underscores what looks like sound decisions made over 100 years ago to develop surface water and more recent decisions to shift the cities of Tracy, Manteca, and Lathrop to partial dependence on surface water.
The Eastern San Joaquin County Groundwater Basin is likely the only one among some 515 groundwater basins and subbasins throughout California that already is — or almost at the point — of being on task to meet a 2042 state mandate that no more water can be taken from a groundwater basin than is recharged in any given year.
That’s according to Brandon Nakagawa, the water resources coordinator for the South San Joaquin Irrigation District.
Nakagawa recently provided an update on the progress made since the mandate was adopted in 2014.
He is currently helping coordinate the effort of 17 agencies — cities, irrigation districts, and water districts within the basin — to meet the state mandate.
Given groundwater doesn’t “respect” manmade political jurisdictions above ground, the answer to achieving basin sustainability will require all the jurisdictions to work in unison. At the same time, each jurisdiction is seeking to protect their share of the water “pie.”
Nakagawa noted SSJID’s adjudicated water rights on the Stanislaus River watershed coupled with the Tri-Dam Project that has allowed 50,000 acres of farmland within its boundaries to rely primarily on surface water has worked to the district’s advantage under the state mandate.
A decision more than 100 years ago to locate Woodward Reservoir for district storage on land that likely wouldn’t have happened in modern times due to the relatively porous condition of the soil, has helped to effectively recharge the basin.
So has the flood irrigation of a number of orchards within the district.
Other areas of the state are now looking at deliberate flooding of farmland with releases of excess storage from irrigation reservoirs during the rainy season to help recharge groundwater.
Nakagawa noted other basins seeking to obtain sustainability will likely need to make massive investments in infrastructure for surface storage and recharge basins.
The Sustainable Groundwater Management Act of 2014 was designed to put a break on the depletion of groundwater supplies that provide 41 percent of California’s water supplies.
The depletion of groundwater has also led to subsidence issues that — monitored since the 1920s — shows some areas in the southern San Joaquin Valley where the ground level has dropped between 20 and 40 feet.
Subsidence, based on monitoring points in Stockton, for years was thought to fluctuate in millimeters between rainy seasons and heavy summer use.
The local 800,000 acre water basin, though, might have a more serious subsidence issue.
Nakagawa noted satellite images used by the state shows areas in the eastern county around Linden northeast of Manteca may have dropped as much as six inches since 2015.
He said the local groundwater authority is in the process of collecting ground monitoring data to verify the six-inch drop.
The state wants local basin authorities to rely on satellite imagery as the basic means to monitor subsidence.
But as Nagasawa pointed out, satellite images don’t take things such as whether the ground is level, the height of grass and such into consideration.
Actual monitoring stations on the ground that can detect whether land is dropping due to subsidence are more accurate.
