Flows of the Columbia River, although modified substantially during the twentieth century, still vary considerably between seasons and between years. Lowest flows tend to occur during summer months when demand for irrigation water is at its highest and when water temperatures are greatest. These periods of low flows, high demand, and high temperature are critical periods for juvenile salmon migrating downstream through the Columbia River hydropower system.
Although impacts on salmon of any individual water withdrawal may be small, the cumulative effects of numerous withdrawals will affect Columbia River flows and would pose increased risks to salmon survival. The body of scientific knowledge explaining salmon migratory behavior and physiology is substantial, but imperfect, and decision makers should acknowledge this and be willing to take action in the face of uncertainties.
In order to provide a more comprehensive water permitting process, the State of Washington, Canada, other basin states, and tribal groups should establish a basin-wide forum to consider future water withdrawal application permits. If the State of Washington issues additional permits for water withdrawals from the Columbia River, those permits should contain provisions that allow withdrawals to be curtailed during critical high-demand periods.
MANAGING THE COLUMBIA RIVER
INSTREAM FLOWS, WATER WITHDRAWALS, AND SALMON SURVIVALNATIONAL ACADEMIES PRESS
Copyright © 2004 National Academy of Sciences
All right reserved.ISBN: 978-0-309-09155-8Contents
EXECUTIVE SUMMARY.................................................................................11 INTRODUCTION...................................................................................15Columbia River Salmon.............................................................................15Study Background, Process, and Organization.......................................................232 DEVELOPMENT AND CHANGES IN THE COLUMBIA RIVER BASIN............................................27Settlement and Development of the Columbia Basin..................................................28Federal Columbia River Hydropower System..........................................................36Summary...........................................................................................393 HYDROLOGY AND WATER MANAGEMENT.................................................................42Columbia River Flows..............................................................................46Water Withdrawals.................................................................................52Return Flows and Water Quality....................................................................60Water Temperature.................................................................................63Climate Variability and Change....................................................................65Summary...........................................................................................694 ENVIRONMENTAL INFLUENCES ON SALMON.............................................................71Columbia River Salmon.............................................................................72Status of Salmon and Steelhead Stocks.............................................................76Research, Modelling, and Alternative Hypotheses...................................................83Water Temperature and Flow Management.............................................................96Summary...........................................................................................1045 WATER LAWS AND INSTITUTIONS....................................................................107Introduction......................................................................................107International Obligations.........................................................................108Interstate Compacts...............................................................................111Interstate Apportionment..........................................................................114Native American Water and Fisheries Rights........................................................116Federal Rights and Obligations....................................................................129State Laws and Institutions.......................................................................133Summary...........................................................................................1446 BETTER MANAGEMENT OF EXISTING WATER SUPPLIES...................................................146The Economic Value of Water.......................................................................146Water Markets and Water Banks.....................................................................158Summary...........................................................................................1727 WATER RESOURCES MANAGEMENT, RISKS, AND UNCERTAINTIES...........................................175Risk and Water Management.........................................................................175Columbia River Management Decisions...............................................................182The Management Scenarios..........................................................................188Summary...........................................................................................1948 EPILOGUE.......................................................................................199REFERENCES........................................................................................203APPENDIXESA Columbia River Initiative Draft Management Scenarios, July 7, 2003.............................223B Resources Group................................................................................229C Calculations on Annual Discharges of Water From the Columbia Basin Project.....................230D Climate Change and Hydrologic Impacts..........................................................235E Committee Biographical Information.............................................................238F National Research Council Board Membership and Staff...........................................244
Chapter One
Executive Summary
BACKGROUND
For thousands of years, North America's Columbia River salmon runs were the most abundant on Earth. The salmon evolved in a setting of many long- and short-term environmental changes and disruptions. With the introduction of an industrial-based economy to the region in the late nineteenth century, the scale and rate of environmental variability in the basin changed. The creation of impoundments on the Columbia River and its tributaries, dam operations, commercial fishing, logging, diversions for irrigated agriculture, and human population growth have altered the Columbia's presettlement flow regime and have reduced the quality of salmon habitat across the river basin. There have been attendant declines-including some extinctions-in the populations of all resident salmon species. Many of these salmon are currently listed as threatened and endangered pursuant to the federal Endangered Species Act. Annual salmon and steelhead returns to the Columbia River estuary are estimated to have been as high as 16 million fish per year during the late 1800s. The returns have dwindled over time, dropping to near 1 million fish per year in the 1990s. These numbers rebounded in the late 1990s and early 2000s, largely because that time frame coincided with a period of favorable ocean conditions for salmon. The majority of returns today consist of hatchery-reared fish.
The Columbia River makes up part of a large (basin size of roughly 250,000 square miles) ecological system with many features that vary naturally on several different timescales. In addition to natural ecological variability, salmon are affected by human- induced changes such as water diversions and water control structures. Furthermore, Columbia River salmon spend most of their lives in the highly dynamic Pacific Ocean. The combination of these and other factors presents a setting of extraordinary variability and uncertainty for Columbia River salmon. The life cycles of Columbia River salmon (there are several different species and subspecies) have been intensively studied. In fact, Columbia River salmon are among the world's most carefully studied fish species, and this research has yielded an excellent understanding of salmon physiology and migratory behavior.
The Washington State Department of Ecology issues water use permits for the portion of the Columbia River that flows through the state. Water withdrawal permit decisions must be balanced with the state's obligation to protect and enhance the quality of the natural environment, including salmon habitat. The department considers scientific knowledge of salmon and environmental variables in making permitting decisions. That body of knowledge, as extensive and thorough as it may be, is imperfect and contains competing theories, models, and perspectives.
This is the context in which the department requested that the National Research Council (NRC) provide advice regarding salmon and water management decisions. In response to this request, the NRC reviewed and evaluated existing scientific data and analyses related to fish species listed under the Endangered Species Act in the Columbia River basin and reviewed and evaluated environmental parameters critical to the survival and recovery of listed fish species. The cumulative effects and the risks to survival of listed fish species of potential future water withdrawals of between approximately 250,000 acre-feet and 1.3 million acre-feet per year were also evaluated. There are currently many pending water withdrawal permit applications along the Columbia River in the State of Washington. The total volume of water represented by these applications falls within this 250,000 to 1.3 million acre-feet per year range. In addition, the effects of proposed management criteria, specific diversion quantities, and specific features of potential water management alternatives provided by the state were also considered. To conduct the study, the NRC appointed the ad hoc Committee on Water Resources Management, Instream Flows, and Salmon Survival in the Columbia River. This report's Preface contains additional information about the study process, and Chapter 1 includes verbatim the committee's Statement of Task.
SALMON AND ENVIRONMENTAL PARAMETERS
There are competing scientific hypotheses and models regarding the effects of environmental forces on Columbia River salmon. River velocity and water temperature are of particular interest to fisheries scientists, water managers, and interest groups, as these factors influence the migratory behavior of salmonids. Several computer models have been used to simulate the effects of river flows (especially water velocity) and temperature on the migratory speed and survival of smolt (young salmon ready to migrate from fresh water to the sea). These models ascribe different levels of importance to river discharge and temperature and their effects on migratory conditions for juvenile salmonids. Selecting the "best" model of salmon-environmental relationships was neither part of this study nor was it critical to its completion. Several scientists presented analyses and models in open public meetings for consideration in this study. These presentations were used as background information for considering the degree to which proposed future water extractions may pose increased risks to the survival of endangered fish species. This information, along with the body of scientific evaluations of Columbia River salmon and their habitat, portrays a complex system of interacting environmental variables that influence the rates of salmon smolt survival on their downstream journey through the Columbia River hydrosystem. Within the body of scientific literature reviewed as part of this study, the relative importance of various environmental variables on smolt survival is not clearly established. When river flows become critically low or water temperatures excessively high, however, pronounced changes in salmon migratory behavior and lower survival rates are expected.
COLUMBIA RIVER FLOWS AND WITHDRAWALS
Changes to the Annual Hydrograph
The annual flow patterns of the Columbia River underwent a substantial transformation during the twentieth century. At the beginning of the century, the river's flows exhibited great seasonality, with roughly 75 percent of the annual flows occurring during summer months (April-September) and roughly 25 percent of annual flows occurring during winter months (October-March). The river's long-term average discharge is roughly 139 million acre-feet per year. The pattern of annual flows changed in response to the construction of numerous mainstem and tributary impoundments and the subsequent operations of this water control system. The system is known as the Federal Columbia River Power System (FCRPS), and the principal original purposes underlying its construction were to provide hydroelectricity, irrigation, and flood control benefits. Construction of some of the system's large mainstem projects, such as Grand Coulee and Bonneville dams, began in the 1930s. The post-World War II period saw a burst in project authorization and construction of additional large projects. Other projects were built in connection with the Canada-U.S. Columbia River Treaty signed in 1961. The hydrological implications of the system's construction were tremendous. As the system's water control projects came on line, annual flows of the Columbia became and less and less seasonal, as the differences between summer and winter flows were reduced in order to provide reliable year-round hydropower generation and distribution. In the late 1970s, the Columbia's annual flows had been modified such that they were divided roughly evenly between summer and winter, as compared to the 75:25 ratio that had existed at the beginning of the twentieth century. In addition to this "flattening" of the annual Columbia River hydrograph, other key impacts of the construction and operations of the hydropower system were a decrease in water velocities, a change in the size and orientation of the river's plume (a physical zone in the Pacific Ocean that extends from the Columbia's mouth into marine waters), and major changes to limnology and nutritional pathways in the river's estuary and food web. All these changes have likely had significant effects on the early ocean survival of juvenile fish leaving the Columbia River. Passage of such legislation as the National Environmental Policy Act (1969) and the Endangered Species Act (1973) resulted in changes in operational patterns and priorities. "Flow targets" have been established by federal and state agencies in an effort to sustain and recover salmon habitat and populations that had declined over time. The FCRPS today is operated primarily to provide benefits of flood control, hydropower, and instream flows.
This study's focus was on the implications of potential additional water withdrawals (which would be primarily for irrigated agriculture) from the mainstem Columbia River for salmon survival. The study charge did not call for an examination of the hydrological impacts of consumptive withdrawals in comparison with other actions, such as the creation of impoundments, dam operations, or changes in land cover. Knowledge of these historical changes to Columbia River hydrology, however, provided important context for the consideration of the specific issues within this study's Statement of Task.
Prospective Additional Water Withdrawals
Of special interest in this study was consideration of the effects and risks to salmonid survival of a specific range of possible additional water withdrawals, ranging from 250,000 acre-feet per year to 1.3 million acre-feet per year. The latter figure represents roughly 28 percent of the total volume of water permits that have been issued to the present by the State of Washington for surface water withdrawals from the Columbia River and groundwater withdrawals from the zone within 1 mile of the river. The effects of these proposed withdrawals and their attendant risks for the survival of a specific species will vary considerably depending on river flow levels. Despite construction and operations of the hydropower system, the river still exhibits considerable flow variations on daily, seasonal, and annual time scales. Under current conditions, less than 1 percent of total annual withdrawals are made during January. By contrast, during July-the month of highest withdrawals-about 18 percent of annual withdrawals from the Columbia River in the State of Washington are made. The seasonality of water withdrawals is of utmost importance when considering how the river's water withdrawals affect salmon survival rates.
Many calculations and speculations could be made with regard to the range of prospective additional withdrawals considered in this study. Assuming that the monthly pattern of withdrawals from the mainstem Columbia River continues essentially unchanged and that the maximum amount of prospective withdrawals in the range considered in this study (maximum of 1.3 million acre-feet per year) is diverted, additional withdrawals of roughly 2,600 acre-feet in January and roughly 234,000 acre-feet in July would result. The effects of these prospective additional January withdrawals would result in additional withdrawals of less than 1 percent of mean January Columbia River flow. The effects of these prospective additional withdrawals in July, when river flows are lower, would increase July withdrawals from their current value of roughly 6.8 percent of mean flows to roughly 8.6 percent of mean flows. Under minimum July flow conditions, the effects would be even greater: the upper end of the proposed range of diversions would increase current July withdrawals from roughly 16.6 percent to roughly 21 percent of Columbia River minimum flows. Water temperature is also a concern to salmon survival. Columbia River water temperatures have been increasing for decades, and those temperatures are at their highest during summer months (when demand for extractions is also at or near its peak). Water quality is also an issue, as return flows from irrigated agriculture and urban activities are of degraded quality and could affect fish already stressed from higher water temperatures and longer travel times.
The scale of the Columbia River basin and current limits of scientific understanding of salmon and their habitat inhibit reliable, precisely quantified predictions of how additional water withdrawals will affect risks to salmon survival. Nevertheless, further reductions in river flows during low-flow periods will increase those risks, especially since most of those withdrawals would occur during a critical period for those salmon species that are migrating through the mainstem river. There are differences in the migration patterns and timing of the Columbia River's listed salmon species and subspecies. Accordingly, only those salmon populations that migrate (downstream or upstream) through the river corridor during critical low-flow periods or years will be exposed to the greater risks entailed by additional withdrawals and reductions in discharge. Examples of these populations include subyearling ocean-type Chinook from the Snake and Columbia rivers, adult Snake and Columbia River summer Chinook, adult Snake and Columbia River steelhead, and adult sockeye salmon.
Columbia River salmon today are at a critical point. The basin's salmon populations have been in steady decline over the past century, and scientific evidence demonstrates that environmental and biological thresholds important to salmon-such as water temperature-are being reached or in some cases exceeded. Salmon are more likely to be imperiled during late summer on the Columbia River, as they experience pronounced changes in migratory behavior and survival rates when river flow becomes critically low or water temperature becomes too high. Further decreases in flows or increases in water temperature are likely to reduce survival rates. Trends such as human population growth in the region and prospective regional climate warming further increase risks regarding salmon survival.
Decisions regarding the issue of additional water withdrawal permits are matters of public policy, but if additional permits are issued, they should include specific conditions that allow withdrawals to be discontinued during critical periods. Allowing for additional withdrawals during the critical periods of high demand, low flows, and comparatively high water temperatures identified in this report would increase risks of survivability to listed salmon stocks and would reduce management flexibility during these periods.
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