Groundwater depletion and salt-impaired lands in the San Joaquin Valley

The Groundwater Resources Association of California and the University of California Water Security and Sustainability Research Initiative have proposed large increases in future diversions from the Sacramento River and the Sacramento-San Joaquin Delta to provide recharge of overdrafted groundwater basins in the San Joaquin Valley.

Their white paper states:

What Are the Legal and Regulatory Bottlenecks, and How Can They Be Eliminated or Reduced?

3.a The current, temporary and standard permitting processes should be reviewed and evaluated to determine whether it is sufficiently effective to support large increases in future diversions. The legislature’s AB 2649, as amended on April 25, 2018, was an important step in the right direction.

There are lower impact solutions to groundwater depletion than large increases in future diversions from the Sacramento River and the Delta. These include retirement of salt-impaired land and agricultural water efficiency measures.  Both are also needed to reduce the rate of degradation of land in the San Joaquin Valley.

There has been a long-standing problem that soils on the west side of the San Joaquin Valley are washed down from the east side of the Coast Range, which was formerly seabed.  As a result, the soils have naturally occurring salt, boron, selenium, molybdenum and other trace minerals.  When the soils are irrigated, the salt and boron wash into shallow groundwater and eventually impair the growth of crops.

The map below  (from Water and the Future of the San Joaquin Valley)  shows salinity in shallow groundwater in the San Joaquin Valley, and how it impairs crop production.

The Rainbow Report, a comprehensive study in 1990 estimated that 1,000,000 acres of land on the west side of the San Joaquin Valley would be salt-impaired by 2000.  A 2017 study of remote sensing data by the US Salinity Laboratory confirmed that 955,000 acres on the west side is now moderately to extremely saline, with another 349,000 acres slightly saline.

The map below, from Technical Appendix E of Water and the Future of the San Joaquin Valley, shows that some of the areas of largest overdraft during the 2012-2016 drought were in areas with salt and drainage-impaired lands on the west side.

This is a picture of a salt evaporation pan from salinity-impaired lands in the Tulare Lake Basin.  The soils in the western part of the Tulare Lake basin have enormous amounts of salt, and the land is going out of production.

It is not cost-effective to prop up agricultural production on degraded land in the San Joaquin Valley.  As Laurence McKenney said at the California Water Policy Conference,

Though the problem with salt accumulation was identified a long time ago, and it has been the doom of several past civilizations, we still lack effective financially viable management solutions..

Therefore using increases in diversions from the Sacramento River and the Sacramento-San Joaquin Delta to recharge groundwater on salt-impaired lands is a losing proposition. The following solutions should be implemented instead:

1. The State Department of Land Conservation reported that 276,000 acres of land have been fallowed in the San Joaquin Valley between 2006 and 2012 (net change.)  Funding should be provided to regularly update maps of salt-impaired and fallowed land in the western San Joaquin Valley.
2. The legislature should implement a program to incentivize retirement of the most salt-impaired lands, and to mitigate local impacts.
3. According to the 1990 Rainbow Report, over-irrigation of drainage impaired lands increases the rate of deep percolation and soil salinization.  The legislature should provide incentives to rotate away from high water use crops in saline-sodic soils on the west side of the San Joaquin Valley.
4. Both the state and federal governments should prioritize funding for rapid implementation of irrigation management measures in saline-sodic soils on the west side of the San Joaquin Valley to reduce the rate of deep percolation and soil salinization.

The most salt-impaired lands on the San Joaquin Valley floor grow salt-tolerant field crops such as cotton, wheat, barley, and canola. The crops generally require sprinkler or flood irrigation, as well as leaching.  But the most salt-impaired lands on the San Joaquin Valley floor are also the lands that are being converted to non-irrigated uses such as grazing.  As the lands are retired, the irrigation water will no longer be needed.

The PPIC estimates crop fallowing with water trading using the SWAP model in Technical Appendix C of Water and the Future of the San Joaquin Valley.  The following graph is from that appendix:

The SWAP model estimates of economic costs do not take into account the lands that are going out of production due to drainage and salinity issues.  The 300,000-350,000 acres of “other field crops and grains” that will be idled would be expected to include such lands.

This post was updated on January 18, 2020.