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  California Water Science Center

North Delta Regional Salmon Outmigration Study

Location of flow station sites in the Delta Area of California

Location of flow station sites in the Delta Area of California

The interaction between seasonal timescale variations in upstream hydrology and strong tidal forcing within the Delta's complex network of channels has made it difficult to clearly identify the effects of water management actions on survival and recovery of endangered juvenile salmon populations.

The need to understand the effects of current and proposed water project operations on survival of endangered salmon populations is vital and time critical. While salmon runs have been on the rise in recent years, the 2008 returns of fall run Chinook at Sacramento and San Joaquin River hatcheries are at all time lows. Thus, it is important to conduct process level studies on salmon now, before their numbers are reduced to levels which further constrain water supplies and make scientific inquiries difficult (as is currently the case with delta smelt). This information is needed to better understand how existing operations (reservoir releases and DCC gate operations) effect fish populations to determine if current operations can be improved to enhance the overall survival of outmigrants as they move through the delta. Beyond this immediate need, information on salmon outmigration is needed to assess the efficacy of ongoing and planed large scale restoration efforts throughout the Central Valley and within the Delta that are designed to improve habitats for salmonids and increase their populations. Moreover, this information is needed to design, and determine operational criteria for, proposed structural changes in the Delta, such as those proposed in the Bay-Delta Conservation Plan (BDCP), the Through Delta Facility (TDF), and barriers/gates at Threemile Slough and False River, among others. The results from this effort will provide information that is essential for ongoing management actions and future political processes such as Governor Schwarzenegger's Blue Ribbon Delta Vision task force, and agency planning processes such as DWR's Delta Risk Management Strategy (DRMS), and CALFED's Bay-Delta Conservation Plan (BDCP) and Delta Regional Ecosystem Restoration Implementation Plan (DRERIP). Finally, these results should provide valuable information needed to manage the salmon fishery in the face of possible changes associated with global warming, such as changes in the quantity and timing of fresh water entering the Delta, and sea level rise and temperature increases.

Unfortunately, with our current level of understanding of salmon outmigration and survival we cannot predict, with any degree of certainty, the impacts of proposed significant physical and operational changes on the survival of juvenile salmon in the Delta. This lack of understanding could significantly delay/constrain the implementation of proposed changes in the system. Or, worse yet, this lack of understanding could lead to significant after-the-fact negative unintended consequences caused by ill-informed structural or operational changes. Proposed management actions include changes in geometry, such as modification of channel alignments at junctions, barriers/gates in Franks Tract and elsewhere, as well as changes in operations, such as changes in reservoir releases, export rates, DCC re-operations, and the Through Delta Facility (TDF). Moreover, predictive tools will be needed to manage the salmon fishery in the face of possible changes associated with climate change; such as changes in hydrology (timing and quantity of surface water to the delta), sea level rise and temperature increases.

This study is motivated by the following question: How do we manage the bay/delta system to maintain, or improve, the survival of Sacramento River salmon outmigrants within the Delta, using changes in water project operations (changes in geometry and plumbing - barriers, tide gates, canals), or through restoration efforts, in the face of potentially dramatic changes, such as global climate change?

The overarching objective of this salmon outmigration study is to: Develop a management model to predict the impacts of management actions on salmon survival.

We propose to characterize the impacts of proposed management actions through the linkage of a series of statistical and mechanistic sub-models representing key processes, such as salmon migration timing, route selection, and survival using the following methods.

A combination of field experiments and numerical modeling will be used in this investigation. Both the field work and modeling will be investigated at two principal scales: (1) at the scale of the junction, where mechanisms critical to route selection will be studied, and (2) at the scale of the channel network, where reach-specific survival will be studied.

The field experiments, and the way in which information is exchanged from more complex models to progressively simpler models, is based on separating the overall process of salmon outmigration into route selection at junctions and survival within reaches. Ultimately, we hope to develop relations for route selection and survival that depend on physical variables, such as flow splits and transit times, respectively; variables that are well predicted by existing numerical models. Thus, the field experiments will provide the data necessary to inform the development of a hierarchy of models, beginning with state of the art high resolution numerical 3D models, which will inform, in a natural progression, simplified models appropriate for use in a management setting.

The proposed investigation is unique in that it involves concurrent measurements of hydrodynamic processes and salmon movements at a variety of spatial and temporal scales that are specifically intended to develop and calibrate a hierarchy of interconnected statistical and deterministic models. The complex interactions between fish behavior, hydrodynamics and water management actions occur at fine temporal and spatial scales which, when integrated over space and time, determine the population distribution throughout the delta and overall survival rates that occur over the duration of the juvenile salmonid migration season. Thus, it is our intention to develop simplified management tools for predicting the impacts of various actions on the out-migration population, based on a hierarchy of detailed models that explicitly encompass appropriate temporal and spatial averages of behavioral responses of salmon outmigrants to the salient hydrodynamic processes.

Therefore, this study is designed to: (1) understand the fundamental mechanisms that govern how salmon move through, and survive within the existing system and (2) use field data to develop mechanistic models that predict how salmon will move through the system under substantially changed conditions, such as a Delta that includes a various BDCP options or through delta facility.

None of the physical and biological models proposed in this investigation will be developed in the absence of data collected at the appropriate scale. For example, at the scale of the junction, surface current maps and transects of secondary circulation will be made at the junction of the Sacramento River and the DCC as well as the junction of the Sacramento River and Georgiana Slough. Concurrently, acoustically-tagged salmon will be monitored at these junctions so that behavioral responses to the hydrodynamic environment can be deduced. The combination of physical and biological data will be used to: (1) calibrate and validate high resolution 3D numerical model simulations of these processes at these junctions, (2) provide the 3D current structure for understanding the role of bathymetric variations in the entrainment of juvenile salmon at junctions. The field data and detailed 3D numerical model simulations will hopefully lead to mechanistically based entrainment relations at these and other junctions in the Delta.

At the scale of the Delta, flow stations operated by the USGS will collect hydrodynamic information that will (1) provide the boundary condition data for the detailed 3D hydrodynamic calculations, (2) provide the data needed for the calibration and validation of 2D numerical hydrodynamic model (RMA) and (3) provide measures of the hydrodynamic conditions at many of the acoustic telemetry receiver locations. Most of the acoustic tag listening stations will be placed at the flow station locations so that correlations between current speed and the movements of acoustic tag salmon can be made. The acoustic tag listening stations will allow us to develop statistical models based on well known mark-recapture models. The mark-recapture models will provide route selection and survival probabilities for the balance of the model development, and so on. To our knowledge this is the first time the field data, in terms of both the physical and biological measurements, and the statistical and deterministic modeling efforts have been so tightly integrated, with the specific aim of developing simplified management tools.

The field experiment proposed for the winter of 2008-2009 will involve detailed investigations at two junctions (e.g. DCC and Georgiana Slough), the so-called "junction experiments", where the mechanisms that control route selection will be studied in detail, and a large network of acoustic tag listening stations, where route selection probabilities will be computed for numerous other junctions, and survival probabilities will be estimated throughout the Delta.

Project Chief: Jon Burau
Phone: 916-371-2582
Email: jrburau@usgs.gov

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