Delta Watermaster previews CalWaters transition, Open ET measurement work and flags federal data cuts

The State Water Board’s Delta Watermaster told the board on July 16 that the agency’s new CalWaters reporting system is entering a soft launch and that open‑satellite evapotranspiration methods (Open ET) and local measurement projects are giving an increasingly detailed picture of consumptive use within the legal Delta.

Jay Ziegler said the CalWaters team delivered the system on time and on budget and that it will be used for the water‑year 2025 reporting period, with further refinements expected as users enroll. He added that in the legal Delta the project and regional data currently describe about 2,800 water‑right filings and roughly 1,000 unique owners; staff reported in‑Delta diversions at about 1,400,000 acre‑feet and project operations diverting about 4,200,000 acre‑feet (staff caveated the numbers as part of ongoing reconciliation work).

Why it matters: CalWaters is the State Water Board’s consolidated reporting database; its success depends on accurate point‑of‑diversion/location shape files, quality control and training for the agents who file on behalf of multiple users. The Watermaster said the new platform and Open ET together should make clearer how diversions relate to in‑channel flows, and that a subset of large users account for a substantial share of in‑Delta diversions.

Measurement and research work: Ziegler and staff described the Delta Measurement Experimental Consortium (DMEC), an interagency and academic partnership that is testing Open ET and island water‑balance approaches using satellite ET, eddy‑covariance towers, and metered diversion data. Staff emphasized that consumptive use estimated by Open ET can be combined with measured diversion data, seepage and return flows to create island water budgets and better understand the relationship between diversions and in‑channel net flow.

Pilot measurements under development include full metering of diversions on several Delta islands (Metropolitan Water District of Southern California), drainage monitoring (The Nature Conservancy on Staten Island) and finer‑scale eddy‑covariance transects by UC Davis. Staff said top 10 owners represent about one‑third of in‑Delta diversions and that roughly two‑thirds of reported consumptive use in the Delta currently comes through Open ET reporting under the Delta alternative compliance platform.

Sediment management and local projects: Ziegler said the department and stakeholders are advancing an MOU to accelerate sediment management in the South Delta and that state work is identifying pilot maintenance dredging and sediment projects. He also mentioned proposals such as Diablo Water Agency’s approach to acquiring Jersey Island and collaborating with state partners to integrate restoration, levee durability and sustainable agriculture as a climate‑resilient project — noting that any water‑right changes would require future board action.

Federal monitoring and science cuts: Ziegler told the board he is tracking a series of proposed federal budget reductions and program changes that could affect Delta data. He cited proposed or enacted cuts that include a reduction in some Bureau of Reclamation field staff, a reported 23% cut at U.S. EPA in a recent House budget measure, proposed reductions to Pacific Salmon Restoration Fund grants and proposed reductions to the WaterSMART program. He warned that contracting out an existing 55‑station stage/gauge network in the Delta could risk continuity and QA/QC that agencies and users rely on for compliance and operations decisions.

Board members and staff said they will continue to press for stable, reliable monitoring and to work with partners to maintain data quality and continuity as CalWaters is rolled out and Open ET reporting expands.

Ending: Ziegler closed by asking the board to note the value of integrated, continuous monitoring for near‑real‑time understanding of diversions and in‑channel conditions and invited further discussion as CalWaters moves into full use.