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Summary report to assist development of ecosystem flow recommendations for the Coast Fork and Middle Fork of the Willamette River, Oregon

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Title Summary report to assist development of ecosystem flow recommendations for the Coast Fork and Middle Fork of the Willamette River, Oregon
Names Gregory, Stanley V.
Ashkenas, Linda
Nygaard, Chris
Date Issued 2007-06-25 (iso8601)
Extent 9285923 bytes
Note Prepared for Sustainable Rivers Project of The Nature Conservancy and the
U.S. Army Corps of Engineers.
Abstract Introduction
The Willamette River Flow Project
The Nature Conservancy (TNC) and the U. S. Army Corps of Engineers (USACE) are
collaborating on a project to determine environmental flow requirements for the
Willamette River and its tributaries and to design and test alternative flow releases from
the dams that can meet these requirements. The project is part of the Sustainable
Rivers Project (SRP), a national effort by TNC and USACE to investigate opportunities
to change Corps Dam operations (“reoperate”) to achieve more ecologically sustainable
flows, while maintaining or enhancing project benefits. Through the SRP, TNC and
USACE have developed and tested a process for identifying and refining environmental
flow objectives (Richter et. al. 2006). The process utilizes a series of steps to define
environmental flow requirements, implement changes in operation of dams to meet
those flow objectives, monitor and model the effects of those changes on both the river
ecosystem and the operation of the dams, and refine over time.
The Willamette River Flow Project is being conducted in conjunction with the USACE
Willamette Floodplain Restoration Feasibility Study. This feasibility study is designed to
identify opportunities to restore natural floodplain function in the Willamette River basin
to provide ecosystem restoration, natural flood storage, and other benefits. The initial
study phase has focused on the Coast and Middle Forks of the Willamette River. These
subbasins contain 6 of the 13 dams in the Willamette system; their operation has
implications for the operation of the other dams in the system. To date, the Floodplain
Restoration Study has focused on two important aspects of the aquatic ecosystem: 1)
identifying habitat, flow and water quality requirements for a variety of aquatic and
floodplain species; and 2) describing and evaluating the current channel and floodplain
morphological characteristics, and their changes from historic condition. Partners in the
feasibility study include the Willamette Partnership, the Willamette Middle and Coast
Fork Watershed councils, the Oregon Department of Fish and Wildlife, and The Nature
Conservancy. There is also an inter-disciplinary expert and stakeholder group of
approximately 20 federal, state and local entities plus private landowners that informs
the process.
The Willamette River Flow Project will build upon the Floodplain Restoration study by
developing environmental flow requirements for the reaches downstream of the Corps
dams and linking those flows to opportunities for stream channel and floodplain
restoration, and to improvement in operation of the dams. Given the existing floodplain
restoration study, the initial SRP efforts will use the Coast and Middle Forks and the
mainstem Willamette immediately downstream of these tributaries as a pilot study that
can be replicated in the rest of the Willamette system. River flows from both subbasins
have been greatly affected by operation of the dams: 56% of the drainage area of the
Coast Fork and 87% of the Middle Fork drain into USACE reservoirs. General effects of
the reservoirs include reduced peak flows, lower spring flows, increased summer low
flows, and infrequent bankfull and out-of-bank flows. The Willamette Flow Project
partners anticipate the study will be expanded in the future to encompass the other
major tributaries controlled by USACE dams.
Genre Technical Report
Table Of Contents TABLE OF CONTENTS
Introduction
Willamette River Flow Project.............................................................................................1
Goals and Objectives .........................................................................................................2
Summary Report Purpose ..................................................................................................3
Background
Study Area Description.......................................................................................................5
Hydrologic Network and Discharge Regime .......................................................................6
Physical Processes and Conditions: Flow Requirements
Water Quality .....................................................................................................................9
Temperature..................................................................................................................9
Nutrients and Toxic Pollutants .......................................................................................11
Sediment and Turbidity..................................................................................................12
Geomorphology and Floodplain Inundation ........................................................................14
Biological/Ecological Conditions: Flow Requirements .....................................................20
Terrestrial Vegetation .........................................................................................................20
Cottonwood and Willow.................................................................................................22
Ash, maple and alder.....................................................................................................23
Invasives .......................................................................................................................24
Terrestrial Vertebrates: Birds and Mammals.......................................................................28
Aquatic Invertebrates .........................................................................................................31
Short-lived species ........................................................................................................32
Long-lived species.........................................................................................................32
Aquatic Vertebrates............................................................................................................34
Amphibians and Reptiles...............................................................................................34
Western pond turtles ..............................................................................................34
Red-legged frog......................................................................................................35
Bullfrog ...................................................................................................................35
Fish ...............................................................................................................................38
Spring Chinook.......................................................................................................39
Lamprey .................................................................................................................40
Coastal cutthroat trout ............................................................................................41
Oregon chub...........................................................................................................41
Large-scale sucker .................................................................................................42
Large- and smallmouth bass...................................................................................43
Summary...............................................................................................................................47
Bibliography ..........................................................................................................................48
Tables....................................................................................................................................58
Figures..................................................................................................................................100
Appendices...........................................................................................................................199
Topic Water quality
Identifier http://hdl.handle.net/1957/5965

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