Storing Water for the Environment: Operating Reservoirs to Improve California’s Freshwater Ecosystems

Public Policy Institute of California (PPIC) | August 23rd, 2022

Large reservoirs like those that rim the Central Valley are essential for managing water in California’s highly variable climate. They provide multiple benefits includi

Large reservoirs like those that rim the Central Valley are essential for managing water in California’s highly variable climate. They provide multiple benefits including water supply, hydropower, flood management, and recreation. However, construction and operation of these reservoirs have also imposed significant environmental costs, including native fishes’ loss of access to high-quality habitat above dams and degradation of freshwater ecosystems below them. Moreover, regulatory uncertainty for water users is rising as these ecosystems decline. California needs a new approach for managing environmental water in its large reservoirs, particularly as the climate warms and droughts become more intense.

Suisun Marsh Monitoring Program Annual Data Summary Water Year 1999

California Department of Water Resources (DWR) | July 31st, 2001

This report summarizes data collected in the Suisun Marsh during Water Year 1999 (October 1, 1998 through September 30, 1999) pursuant to the following agreements, perm

This report summarizes data collected in the Suisun Marsh during Water Year 1999 (October 1, 1998 through September 30, 1999) pursuant to the following agreements, permits, and water rights decisions: • State Water Resources Control Board Decision 1485, August 1978 (SWRCB 1978); • State Water Resources Control Board Order WR 95-6, 1995 (SWRCB 1995a); • Suisun Marsh Preservation Agreement, 1987 (USBR and others 1987); • Suisun Marsh Monitoring Agreement, 1987 (DWR and others 1987); • San Francisco Bay Conservation and Development Commission Permit No. 35-78 (M) Amendment 7, 1997 (for construction of the initial facilities, namely the Roaring River Distribution System, Morrow Island Distribution System, and Goodyear Slough Outfall) (BCDC 1997); • San Francisco Bay Conservation and Development Commission Permit No. 4-84 (M) Amendment 4, 1991 (for construction of the Suisun Marsh Salinity Control Gates) (1991); and, • U.S. Army Corps of Engineers Permit No. 16223E58 (for construction of the Suisun Marsh Salinity Control Gates), Special Condition 1, 1986 (USACE 1986). This report fulfills a portion of the annual reporting requirements of the above-listed, agreements, permits, and water rights decisions as detailed in Table 1. Remaining reporting requirements will be fulfilled in other Department of Water Resources (DWR) and/or University of California Davis reports. DWR and the California Department of Fish and Game (DFG) primarily collected data summarized in this report. The data include • general hydrologic data; • continuous channel water specific conductance and tidal height measurements; • marsh-wide vegetation survey update; • waterfowl abundance; and • salt marsh harvest mouse occurrence.

Summary of NMFS BiOp RPA Actions for Water Year 2014

Delta Stewardship Council (Delta Council) | October 30th, 2014

Summary Report on the Transactions of the Smelt Working Group in Water Year 2014

Delta Stewardship Council (Delta Council) | August 29th, 2014

The Bay‐Delta Fish and Wildlife Office (BDFWO) has prepared this report to summarize the implementation the U.S. Fish and Wildlife Service’s (Service) biological opi

The Bay‐Delta Fish and Wildlife Office (BDFWO) has prepared this report to summarize the implementation the U.S. Fish and Wildlife Service’s (Service) biological opinion on the Central Valley Project (CVP) and State Water Project (SWP) Long‐term Operations (BiOp) in Water Year (WY) 2014. In addition to background information pertinent to implementation of the BiOp , this report provides a summary of the transactions of the Smelt Working Group (SWG), as well as water operations and during WY 2014. The SWG is a technical team that evaluates biological and technical issues regarding Delta Smelt (Hypomesus transpacificus) and develops recommendations for consideration by the Service during implementation of the BiOp’s Reasonable and Prudent Alternative (RPA) actions. During WY 2014 the SWG made no recommendations for more restrictive water operations and the Service issued no determinations to reduce water exports.

Summary Report on the Transactions of the Smelt Working Group in Water Year 2018

Delta Stewardship Council (Delta Council) | November 1st, 2018

Supplement to the 2007 Colorado River Interim Guidelines for Lower Basin Shortages and the Coordinated Operations for Lake Powell and Lake Mead

U.S. Bureau of Reclamation (USBR) | May 6th, 2024

This ROD revises the 2007 Interim Guidelines for the near-term operation of Glen Canyon and Hoover Dams to address the potential for continued low-runoff conditions in th

This ROD revises the 2007 Interim Guidelines for the near-term operation of Glen Canyon and Hoover Dams to address the potential for continued low-runoff conditions in the Basin. Reclamation has concluded that the potential impacts of low-runoff conditions pose unacceptable risks to routine operations of Glen Canyon and Hoover Dams during the remainder of the interim period (through the end of the 2026 operating year) and that modified operating guidelines need to be expeditiously developed.

Synergies between climate anomalies and hydrological modifications facilitate estuarine biotic invasions

Ecology Letters (Wiley) | June 6th, 2011

Environmental perturbation, climate change and international commerce are important drivers for biological invasions. Climate anomalies can further increase levels of hab

Environmental perturbation, climate change and international commerce are important drivers for biological invasions. Climate anomalies can further increase levels of habitat disturbance and act synergistically to elevate invasion risk. Herein, we use a historical data set from the upper San Francisco Estuary to provide the first empirical evidence for facilitation of invasions by climate extremes. Invasive zooplankton species did not become established in this estuary until the 1970s when increasing propagule pressure from Asia coincided with extended drought periods. Hydrological management exacerbated the effects of post‐1960 droughts and reduced freshwater inflow even further, increasing drought severity and allowing unusually extreme salinity intrusions. Native zooplankton experienced unprecedented conditions of high salinity and intensified benthic grazing, and life history attributes of invasive zooplankton were advantageous enough during droughts to outcompete native species and colonise the system. Extreme climatic events can therefore act synergistically with environmental perturbation to facilitate the establishment of invasive species.

Synthesis of data and studies relating to Delta Smelt biology in the San Francisco Estuary, emphasizing water year 2017

Interagency Ecological Program (IEP) | November 1st, 2021

In the San Francisco Estuary (SFE), the effects of freshwater flow on the aquatic ecosystem have been studied extensively over the years and remains a contentious managem

In the San Francisco Estuary (SFE), the effects of freshwater flow on the aquatic ecosystem have been studied extensively over the years and remains a contentious management issue. It is especially contentious with regards to the Delta Smelt (Hypomesus transpacificus), a species endemic to the SFE that has been listed as threatened under the Federal Endangered Species Act and endangered by the State of California. Early studies of Delta Smelt distribution within the SFE suggested that Delta Smelt habitat is determined largely by freshwater flow; however, the exact mechanisms and processes producing such benefits remained unclear. In the summer of 2017, the Flow Alteration Management, Analysis, and Synthesis Team (FLOAT-MAST) was established to analyze, synthesize, and summarize the data collected from the various flow-related monitoring and special studies occurring in 2017(see Table Intro 4). This report will focus on the 2017 summer-fall status of Delta Smelt and its habitat following a record wet year. There has been a long-term decline in the abundance of Delta Smelt associated with a decline in other pelagic fishes. Investigators concluded that the decline has likely been caused by the interactive effects of several causes, including changes in both physical and biotic habitats, many of which are tied to amount and timing of freshwater flow. For this report, we formulated a number of basic predictions about the likely effects of high flows in 2017 on Delta Smelt and their habitat (Table 3). We use a qualitative weight of evidence approach to evaluate whether these predictions were supported by available data. Data sources included a variety of long-term monitoring surveys conducted by Interagency Ecological Program (IEP) agencies, as well as model outputs. Delta Smelt population, health, and life history metrics rarely responded as predicted. Water temperature appears to have a stronger effect on Delta Smelt growth rate and some metrics of life history diversity than outflow or X2 position. Other life history diversity attributes varied but did not appear to be driven by outflow or temperature. Health status was difficult to interpret. Low prevalence of lesions and improved nutritional condition during the drought was contradicted by declining overall population levels. Because of the sparse catches of Delta Smelt in the post-POD years, we consider the data insufficient to reach firm conclusions about the predictions concerning range and distribution of Delta Smelt, especially in the fall. The prediction of high survival was not supported. The 2017 Delta Smelt year class began with poor recruitment in spring of 2017 and below average survival for spring to summer and summer to fall. Thus, low production and low survival led to low abundance of all life stages. During the fall to winter period survival improved, yet the resulting adults were low in number. Foraging success of the fish captured, as measured by stomach fullness, was high for juveniles and adults in 2017 relative to recent years associated with the higher densities of common zooplankton prey that occurred in 2017.

Synthesizing Relationships Between Winter-Run Chinook Salmon Out-Migration Survival and Water Operations in the Sacramento–San Joaquin Delta

University of California, Davis (UC Davis) | December 19th, 2025

Sacramento River winter-run Chinook Salmon (Oncorhynchus tshawytscha) are an endangered population that faces numerous challenges across its life cycle, including juvenil

Sacramento River winter-run Chinook Salmon (Oncorhynchus tshawytscha) are an endangered population that faces numerous challenges across its life cycle, including juvenile out-migration through the heavily anthropogenically modified Sacramento–San Joaquin Delta, or Delta. Water exports from pumping facilities in the Delta can alter local hydrology and influence movement of out-migrating juveniles, some of which are observed in or near pumping facilities. Monitoring and regulations, intended to protect out-migrating fish through restrictions on pumping, are predicated on assumed relationships among fish observations, water operations, and through-Delta migratory survival. In this study, we use a new conceptual model to review the current state of science for winter-run Chinook Salmon out-migration survival in the Delta, and use simulation modeling to address pertinent knowledge gaps. Results of this study highlight varying support for the influence of Sacramento River flow, temperature, and water exports on routing and survival in different regions of the Delta. The contributions of specific routing pathways to the interior Delta (e.g., through Threemile Slough) to survival, and the relationship between fish entrainment at pumping facilities and overall migratory survival, remain uncertain. Recommended future work includes continued fine-scale acoustic telemetry studies throughout the Delta, novel integrated modeling of monitoring data, and contextualizing the relevance of Delta-based survival to population viability by incorporating explicit uncertainties about survival into existing life-cycle models.

System Reoperation (Resource Management Strategy)

California Department of Water Resources (DWR) | July 29th, 2016

System reoperation in the context of water resources means changing existing operation and management procedures for a water resources system consisting of supply and con

System reoperation in the context of water resources means changing existing operation and management procedures for a water resources system consisting of supply and conveyance facilities and end user demands with the goal of increasing desired benefits from the system. System reoperation may seek to improve existing water facilities to meet existing system needs more efficiently and reliably, or it may seek to prioritize one system need over another. Although reoperation of existing facilities is generally regarded as the preferred alternative to constructing major new facilities, minor physical modifications to existing facilities may be necessary to eliminate constraints to reoperation and to meet operational goals. Changes to the water rights or regulatory framework for allocating water — for example, modifying existing water rights or creating new supply exchange agreements — may also be required. Some systems may be very simple and include only a single surface water reservoir or groundwater basin. Other water systems may be much more complex, consisting of many facilities that form a combination of local, interregional, and interstate water sources and delivery destinations. The concept “system reoperation” applies to the system at all scales, thus reoperation can be implemented at different scales within a system, ranging from individual facilities to several integrated components.