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SFEWS provides credible scientific information on California's complex water issues, linking new science to policy with great effect. SFEWS retains a regional focus on the San Francisco Bay and the Sacramento–San Joaquin Delta, also known as the Bay–Delta watershed. At the heart of open access from the California Digital Library, SFEWS's scholarly output ranks #1 for the UC Davis Institute  of the Environment and ranks #3 campus wide.

Volume 15, Issue 4, 2017

Issue cover

Research Article

21st Century California Water Storage Strategies

The goal of this paper is to analyze storage projects constructed and planned in California since 1980, in contrast with storage constructed before that date. As a result of California’s highly variable climate, storage is an essential tool for agricultural and urban water users. Today, the state regulates approximately 1,250 reservoirs, with a combined storage of 42 million acre-feet. Federal agencies regulate approximately 200 additional reservoirs. The vast majority of this surface storage was constructed before 1978, when New Melones Dam, the last large on-stream water supply reservoir in California, was completed. The role of storage in meeting future needs remains a high-profile issue in the California water debate. For example, funding for new storage was the largest item in Proposition 1, the most recent water bond voters approved. This analysis included a review of existing literature, such as the California Department of Water Resources Division of Dam Safety database, California Water Commission documents about new storage proposals, water agency documents, and interviews with water agency staff and others. Water managers face dramatically different conditions today, in comparison to conditions before 1980. These conditions have led to new approaches to water storage that represent a dramatic departure from past storage projects. During the past 37 years, a wide range of new water storage strategies have been planned and implemented. These facilities have created a combined new storage capacity greater than that of Lake Shasta, California’s largest reservoir. These new storage strategies suggest the need to revisit the fundamental definition of water storage. With limited potential for new storage drawing from the state’s rivers, California must choose storage projects wisely. By learning from successful strategies in recent decades, decision-makers can make better storage investment decisions to help reverse declines in ecosystem health and improve water supply reliability.

  • 2 supplemental PDFs

Simulation of Subsidence Mitigation Effects on Island Drain Flow, Seepage, and Organic Carbon Loads on Subsided Islands Sacramento–San Joaquin Delta

In light of desired implementation of subsidence mitigation practices on Delta islands and the need for evaluation tools, we developed groundwater-flow and solute-transport models and attempted to answer the following questions.

1. How do the groundwater-flow and drainage systems interact to influence island drainage volumes and drain dissolved organic carbon (DOC) concentrations and loads?

2. How will future subsidence affect drainage volumes, DOC loads, and seepage onto islands?

3. How will land-use changes to mitigate subsidence affect seepage, drain flow, and DOC loads?

4. How can seepage and water-quality effects from drainage, restoration, and rice cultivation on Delta islands be minimized?

We used hydrologic and geochemical data and modeling to answer these questions. Subsurface processes dominate subsided Delta island hydrology. Seepage and siphoned irrigation water recharge groundwater, which flows to drains. Drainage water that contains DOC derived from oxidation of organic soils is discharged to adjacent channels. We analyzed the effects of subsidence mitigation by simulating mosaics of rice and palustrine wetlands with varying hydrologic management on a representative subsided island (Twitchell Island). These alternative land uses reduce seepage onto islands and thus contribute to increased levee stability. However, most scenarios resulted in increased drain flow and DOC loads. Reducing drain flow is essential to reducing DOC loads relative to the business-as-usual scenario and can be accomplished through hydrologic controls that reduce drain flow on the islands.


  • 3 supplemental PDFs

A Covered Cod-End and Tow-Path Evaluation of Midwater Trawl Gear Efficiency for Catching Delta Smelt (Hypomesus transpacificus)

For nearly 50 years, the California Department of Fish and Wildlife has used a midwater trawl to intensively monitor fish populations in the San Francisco Estuary during the fall, sampling over 100 locations each month. The data collected have been useful for calculating indices of fish abundance and for detecting and documenting the decline of the endangered fish species delta smelt (Hypomesus transpacificus). However, efforts to calculate estimates of absolute abundance have been hampered by the lack of information on gear efficiency, in particular questions about contact selectivity and the effect of tow method on catches. To answer these questions we conducted a study that used a covered cod end on a net towed either near the surface, referred to as a surface tow, or throughout the water column, referred to as an oblique tow. A contact selectivity model was fit to estimate the probability that a delta smelt that has come into contact with the net is retained in the cod end of the net conditional on its body length. Full retention of delta smelt was found to occur around 60 mm fork length. Delta smelt catch densities for the surface tows were an order of magnitude greater than densities in the oblique tows, suggesting a surface orientation at the sub-adult life stage. These results represent an important step in being able to calculate absolute abundance estimates of the delta smelt population size using decades’ worth of monitoring data.

  • 2 supplemental PDFs

Evaluating the Aquatic Habitat Potential of Flooded Polders in the Sacramento-San Joaquin Delta

Large tracts of land in the Sacramento-San Joaquin Delta are subsided due to agricultural practices, creating polders up to 10 m below sea level that are vulnerable to flooding. As protective dikes breach, these become shallow, open water habitats that will not resemble any historical state. I investigated physical and biotic drivers of novel flooded polder habitat, using a Native Species Benefit Index (NSBI) to predict the nature of future Delta ecosystems. Results suggest that flooded polders in the north Delta will have the ecology and fish community composition of a tidal river plain, those in the Cache-Lindsey Complex will have that of a tidal backwater, those in the confluence of the Sacramento and San Joaquin Rivers a brackish estuary, and those in the south Delta a fresh water lake. Flooded east-side Delta polders will likely be a transitional zone between south Delta lake-like ecosystems and north Delta tidal river plains. I compared each regional zone with the limited available literature and data on local fish assemblies to find support for NSBI predictions. Because flood probabilities and repair prioritization analyses suggest that polders in the south Delta are most likely to flood and be abandoned, without extensive intervention, much of the Delta will become a freshwater lake ecosystem, dominated by alien species. Proactive management of flooded tracts will nearly always hedge risks, save money and offer more functional habitats in the future; however, without proper immediate incentives, it will be difficult to encourage strong management practices.

Policy and Program Analysis

Invasive Aquatic Vegetation Management in the Sacramento–San Joaquin River Delta: Status and Recommendations

Widespread growth of invasive aquatic vegetation is a major stressor to the Sacramento-San Joaquin River Delta, a region of significant recreational, economic, and ecological importance. Total invaded area in the Delta is increasing, with the risk of new invasions a continual threat. However, invasive aquatic vegetation in the Delta remains an elusive ecosystem management challenge despite decades of directed scientific research and prioritized policy recognition. In this paper, we summarize the current state of knowledge of the history, status, and potential future directions for coordinated research, management actions, and policy based on topics discussed at symposium head on invasive aquatic vegetation on September 15, 2015. Remote sensing technology, mechanical, chemical, and biological control, as well as community science networks have all been shown to be effective management tools, but overall effectiveness has been hindered by complex regulatory structure, the lack of a consistent monitoring program, regulations that restrict treatments in space and time, and funding cuts. In addition, new management options depend on continued research and development of new active ingredients for chemical control and testing of biological control agents. The ongoing development and implementation of new strategies for adaptive, integrated management of aquatic weeds, using currently-available management tools, new knowledge derived from remote sensing and plant growth models, and an area-wide, ecosystem-based approach, is showing promise to achieve improved management outcomes and enhance protection of the Delta’s water resources.