Delta diversions

Sources. California Department of Water Resources, Dayflow (CNRA open data; water years 1930 through 2025, vintage loaded before 2026-09-18, with water year 2024 added 2026-09-18 from the CNRA resource). State Water Resources Control Board, Water Right Decision 1641, Table 3 minimum net Delta outflow. Sacramento Valley water-year type: CDEC water-year classification (Bulletin 120 and WSIHIST), served by the Water Supply Live set on this site. Allocations: U.S. Bureau of Reclamation news releases (CVP, 2011 onward) and DWR Historical Table A Allocations (SWP, 1996 onward). Binding reason: the Delta Export Constraints dataset on this site (Layer 3 rule).

Method. Volumes are Dayflow daily flows summed at 1.9835 acre-feet per cfs-day. Exports are Dayflow EXPORTS from water year 1997 and the CVP plus SWP columns before that. The floor is the D-1641 monthly minimum for the year type, applied to every year as a reference; outflow above the floor is the surplus measure. In-Delta use is Dayflow’s net channel depletion (column CD, gross channel depletion less precipitation on the Delta) plus its miscellaneous diversions (MISDV), loaded for every day of the record on 2026-09-18; the four terms close the Dayflow balance (outflow equals inflow less exports, in-Delta use, and miscellaneous diversions) to within rounding from water year 1997. Before water year 1997 the small gap is the Contra Costa and North Bay diversions, which the CVP plus SWP columns do not carry. Dayflow restates prior years annually; the series here is the vintage named above. Full rules: definitions .

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