The Water Beneath Our Feet: New Study on California's Central Valley Groundwater Level Decline

Hello and welcome to this U.S. Geological Survey PodCast. I'm Laurel Rogers and today, I am speaking with Dr. Claudia Faunt, a USGS hydrologist who has just completed an extensive study of groundwater in California's Central Valley. Hello Claudia. Thank you for talking with us today.

Claudia: Thanks, it's nice to talk with you.

Laurel: What does this study tell us about California's groundwater. Can you sort of paint a picture for us about the state of California's groundwater now?

Claudia: Well, competition for water supplies are intensifying, there are urban populations, agriculture, and the environment all needing water. Despite all the conservation efforts that have taken place over the last few years, the competing needs coupled with drought conditions have limited the availability of water. When there are limited supplies of surface water, Californian's turn towards groundwater. Groundwater is not directly observable except at springs and wells, so groundwater could be considered CA's hidden resource and also an important source of water during drought.

Laurel: What are some of the results of this study?

Claudia: In the Central Valley, like in all of California, the conditions vary. There are general trends, and exceptions to these general trends. In general, the system responds to climatic variations and changes. In wetter periods, water goes into storage, while in drier periods, or droughts, water is removed from storage. Take the Sacramento Valley for example. It has a cooler and wetter climate and much more surface water than the southern San Joaquin Valley. The groundwater system there is less stressed in general and groundwater levels there remain relatively constant. In the southern and southwestern San Joaquin Valley, there has been intense irrigation from surface water and groundwater. Irrigation from surface and groundwater has increased recharge to, and discharge from the groundwater system by a factor of 6.

Laurel: How far have groundwater levels dropped?

Claudia: It varies; it depends on where you are. In the lower pumped zone, in the southwestern part of the San Joaquin Valley like we talked about before, the decline has been as much as 400 feet from predevelopment conditions. These predevelopment conditions are like, from the 1800's. In the 1970's the water levels rose, with less pumping associated with the surface-water deliveries. Groundwater quality has changed and subsidence has occurred. Recent drought conditions have caused groundwater pumping to increase, and groundwater levels to approach their historic lows.

Laurel: And, land subsidence can cause problems?

Claudia: Yes, historically land subsidence in the Central Valley has cost the state millions of dollars, the land subsidence has resulted in damage to buildings, aqueducts, well casings, bridges and highways, and often causes flooding.

Laurel: Now, associated with this study you developed an extensive groundwater model of the Central Valley. What is a groundwater model?

A groundwater model is a hard thing to define. Usually, is it referred to as, like, a computer program the c(computer) program based on mathematical equations, and is often called a mathematical, or numerical model. It's used to predict aquifer behavior in responses to changes. These changes can be things like irrigation developments or groundwater pumping.

Laurel: So, I understand that when you develop a model like this, it’s available to the public, and anyone, theoretically, could use it, but realistically, who would use this model and how would they take advantage of it?

Claudia: Yes, in theory anyone could use the model. However, like any tool for a particular trade, to use it effectively a person would need some training and background. Realistically, the model is probably most useful to hydrologists and water resource managers and those familiar with numerical codes for looking at hydrogeologic resources. The model is released with a report that has several parts. The first two sections are oriented toward the lay reader and lay person. They pull information from the literature and the model to document the status of the Central Valley groundwater system, and hydrologic system, and how it responds to changing conditions. The final section and the appendix are oriented more towards an experienced modeler. They document the model: how it was set up and constructed, details of the input data, and the results.

Laurel: Claudia, how can people learn more about this study?

Claudia: There are several ways. A four page fact sheet giving an overview of the study is available online. Also, a full report documenting the study in detail is available. Both should be available online through the publications warehouse.

Laurel: Thank you Claudia. Dr. Claudia Faunt, thank you very much for talking with us today, and thank you to our listeners for tuning in to the podcast. This podcast is a production of the U.S. Geological Survey, the Department of the Interior. Until next time, I'm Laurel Rogers and thanks for tuning in.