GSA committee reviews annual reports showing storage deficits, and recommends adopting Chachilla demand-management and subsidence measures

Committee members on April 7 received annual-report highlights for the Madera and Chachilla subbasins and recommended adoption of the Chachilla groundwater demand management and subsidence mitigation report.

John Davids of Davids Engineering walked the committee through groundwater contour and change maps and summarized storage outcomes for spring 2025. He reported a noted overdraft in the Madera subbasin upper aquifer of about 64,000 acre‑feet and an upper‑aquifer deficit of about 41,000 acre‑feet in the Chachilla subbasin. For lower aquifers, Davids reported roughly a 6,500 acre‑foot deficit in the Madera lower aquifer and just over 21,000 acre‑feet in the Chachilla lower aquifer. Davids described spring 2025 as a below‑normal year following several wetter years.

Davids also summarized surface‑water and extraction metrics. For Chachilla, total groundwater extraction was reported just under 306,000 acre‑feet, total surface water supplies about 152,000 acre‑feet and total recharge about 144,000 acre‑feet (with 48% from surface water). For the Madera subbasin, reported extractions were just under 568,000 acre‑feet, surface supplies about 389,000 acre‑feet, and total recharge about 264,000 acre‑feet (with 46% accounted for by surface water recharge).

Davids reviewed projects and management actions across the subbasins: Chachilla reported roughly 17–21 projects among multiple GSAs with an estimated benefit of nearly 61,000 acre‑feet for water year 2025; Madera reported about 35 projects across seven GSAs and at least 26,000 acre‑feet of documented benefit, though Davids noted some projects did not report a quantity and overall benefits may be understated.

On subsidence and demand‑management, Davids explained the program's purpose as a state‑requested "backstop" if projects and management actions fail to achieve intended benefits. He described triggers for potential additional mandatory measures tied to a 1‑foot cumulative subsidence threshold between 2025 and 2030, spatial targeting based on measured RMS wells, and an emphasis on voluntary measures before imposing mandatory actions. Davids said that water year 2025 falls within the program's "green" condition, meaning additional mandatory measures are not currently triggered.

The committee voted to recommend adoption of the Chachilla demand management and subsidence mitigation report to the full board; Chachilla Water District and Triangle T Water District had already approved similar measures earlier in March.

Why it matters: The annual reports quantify deficits and ongoing extraction that shape future allocations, project priorities, and potential demand‑management steps. The demand‑management report provides a framework for targeted, proportional action if subsidence thresholds are exceeded.

Next steps: The GDM report will be considered by the full GSA board next week; staff will continue annual monitoring and provide opportunities for public input and program refinement.