Groundwater Level Declines

Chronic declines in groundwater levels occur when groundwater extraction exceeds recharge on an long-term basis. Chronic groundwater level declines may serve as an indicator or proxy for other undesirable results such as subsidence, compaction, and concentration of pollutants.

Groundwater level measurements are the principal source of information about changes in groundwater storage and flow in a basin. Thus it is important that GSAs monitor groundwater levels to ensure sufficient understanding of the aquifer systems in their basin and their response to changes in groundwater pumping, recharge and other variables.

FOR MORE INFORMATION: USGS webpage for groundwater level declines

Key information

Lowering groundwater levelsBMP 1: Monitoring Protocols Standards and SitesBMP 2: Monitoring Networks and Indentification of Data Gaps

Lowering groundwater levels

This fact sheet was prepared by the California Farm Bureau Federation.

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SGMA-Insert-1-Lowering of Groundwater Levels

BMP 1: Monitoring Protocols Standards and Sites

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BMP 1 Monitoring Protocols Standards and Sites_ay_19
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​ BMP 2 Monitoring Networks and Identification of Data Gaps_ay_19
Case Studies

Mojave water level studies​  Since 1992, the USGS, in cooperation with the Mojave Water Agency, has ​developed a series of regional water-table maps for intermittent years ​used to monitor groundwater conditions in the Mojave River and Morongo groundwater basins.

Water availability in the Cuyama Valley ​ Groundwater is the only source for domestic, agricultural and municipal water use in the Cuyama Valley groundwater basin. The USGS, in cooperation with the Santa Barbara County Water Agency, have developed tools to facilitate the sustainable use of groundwater resources in the region.

San Bernardino Optimal Basin Management website  ​The USGS San Bernardino Optimal Basin Management website provides all of the data associated with seven multi-depth monitoring well installations, including site description, lithologic and geophysical logs, data from core samples, and links to the water-level and water-quality data.

Central Valley One in five wells run dry according to a UC Santa Barbara mapping study published in February 2020 by the American Geophysical Union.

Paso Robles Subbasin Groundwater Sustainability Plan observed more than 80′ of groundwater decline in some areas in a study of groundwater levels between 1997 and 2017.

Satellite-monitoring of the Central Valley’s southern Tulare hydrologic region, as reported in November 2019 in the journal Nature Scientific Reports, is now able to spot aquifer reduction around specific wells … from space.