Basin-wide surveys are conducted during the fall of each year to monitor annual changes in groundwater levels and the corresponding changes in the quantity of groundwater in storage. Static water level measurements are conducted from early November to late December, a time coinciding with the end of the irrigation season and before seasonal recharge by winter rains has begun raising water levels. Fall groundwater levels record year to year changes in storage, which reflect net recharge and withdrawals of groundwater.

Approximately 450 wells are included in the Fall Monitoring Program. Each validated water level measurement is compared to the previous year’s measurement. These one-year differences in water levels are then averaged by Township and Range quadrant, yielding an informative general geographic distribution of storage change over the most recent year. Finally, quadrant averages are combined into hydrologic subarea-wide weighted averages. Numerical results of these analyses for the 2023 Fall Measurement Program are summarized in the tables below.

A PDF version of the Cumulative Change Chart can be accessed here.

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Subarea average groundwater levels are used to update the Agency’s chart of Annual Groundwater Level Changes by Subarea, a cumulative graphical summary of groundwater storage changes and trends since 1944. As illustrated in the 2019 graph above, water levels rise and fall in each of the subareas throughout the period in response to natural and operational hydrologic variations related to climate-driven precipitation and land use-driven water demands.