Increase Delta outflows (65% unimpaired flow target) A management strategy in the COEQWAL scenario library
This strategy adapts USBR's “Alternative 3” or “Modified Natural Hydrograph” scenario configuration — increased Delta outflow requirements supported by upstream actions and limits on Delta exports — with the December–May outflow targets set to a combination of 65% of estimated unimpaired flow or a condition-dependent enhanced flow schedule, as in the original USBR studies. The 65% of unimpaired flow target is the highest level among the four Delta-outflow strategies in the library.
This brief describes a scenario that increases Delta outflows (up to 65% of unimpaired flow) for part of the year, one of 28 management strategies in the COEQWAL scenario library. Each strategy is simulated once under each of five hydroclimates; the references note at the end of this brief lists the model runs.
§2 What this strategy changes
USBR undertook an exploratory modeling exercise while developing scenarios for what became the 2024 Long-Term Operations consultation. One set of scenarios, informed by discussions with environmental and non-governmental organizations, included increased Delta outflows and upstream actions to conserve water for environmental and ecological purposes, attempting to balance flows in rivers and the Delta with reservoir storage in Shasta to support cold-water salmon habitat. USBR formalized these actions as its “Alt3” (modified natural hydrograph) scenario; a detailed description appears in Chapter 3 of the Final Environmental Impact Statement for the consultation, published in November 2024.
This member of the set applies the maximum Delta outflow requirement at 65% of estimated unimpaired flow, as was done in the original USBR studies. The companion strategies apply the same configuration at the 55%, 45%, and 35% levels.
The unimpaired-flow requirement applies only December through May and carries numerous overriding and off-ramping contingencies — simulated Delta outflow should not be expected to strictly match a 65%-of-unimpaired condition. Where unregulated flows are available (runoff on the valley floor during storms, for example), outflows can exceed the requirement level.
§3 The configuration in detail
The table compares the eight operational fields that define this strategy against current operations — the strategy that represents existing operational rules, recent (2020) land use, and TUCPs. Rows that match current operations are shown in light gray; rows that differ are highlighted.
| Aspect | Current operations | This strategy |
|---|---|---|
| TUCP actions | Active | Active |
| SGMA actions | None | None |
| Land use | 2020 LandIQ | 2020 LandIQ |
| Delta regulations | Standard | Modified Delta outflow (65% unimpaired); limits on exports |
| BiOps | 2019 / 2020 ITP | Modified versions of 2019 / 2020 ITP |
| Infrastructure | Standard | Standard |
| Flows | Standard | Delta outflow up to 65% unimpaired, supported by contributions from select tributaries |
| Allocation / priorities | Standard | Allows CVP Settlement allocations down to 0% |
§4 Lineage and source
This configuration was adapted from USBR's Alt3 scenario, made available after the Long-Term Operations consultation concluded in December 2024. The COEQWAL team replaced the hydrology with DWR's adjusted historical dataset and updated agricultural demands to the 2020 LandIQ-based land-use dataset; the 65% unimpaired and enhanced outflow targets are carried over from the original USBR studies. The CalSim model files for this strategy are referenced by the run IDs in the references note at the end of this brief.
§6 What this doesn't say
This brief describes a scenario representation in CalSim, not a real-world policy proposal or implementation plan. The strategy as modeled may not capture all details necessary to support direct translation to actual operations. The brief does not predict, evaluate, or recommend any outcome — it describes what the scenario changes about CalSim's representation of the system. For what the model produces under this strategy, see the result briefs referenced in §7.
§7 See results for this strategy
To see modeled outcomes under this strategy across all nine key outcomes at the reference hydroclimate, see the The Delta as a living place theme brief.
To see outcomes at a specific location of interest, see the relevant LOI briefs — particularly those for Delta locations and the tributaries that contribute to Delta outflow.
References — model runs
Each strategy is simulated once under each of five hydroclimates. The table lists the model run behind this strategy and the current-operations run it is compared against, for each hydroclimate, so any reader can trace this page to specific CalSim runs.
| Hydroclimate | This strategy | Current operations |
|---|---|---|
| Historical hydroclimate (adjusted) | s0039 | s0020 |
| Moderate climate stress (EC-Earth3-Veg) | s0150 | s0134 |
| Moderate-high climate stress (cc50) | s0078 | s0047 |
| High climate stress (cc95) | s0098 | s0056 |
| Extreme climate stress (TaiESM1) | s0124 | s0108 |