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J. Rose Wallick

Publications and source records attributed to J. Rose Wallick.

At least 19 recordsLinked to original sources
USGS2026

Navigating uncertainty and competing objectives: Spring chinook salmon recovery in the upper Willamette river

Globally, anadromous fish populations are threatened with extinction due to multiple factors, including river impoundments that block migration, widespread alteration of physical habitat, temperature, and flow regimes, commercial and recreational harvest, changes in biological communities, and long-term climate trends. In this synthesis, we describe how physical and biological factors, policy and law, and public resource allocation affect management of spring-run Chinook Salmon ( Oncorhynchus tshawytscha ) in the Upper Willamette River (UWR), Oregon, USA. Efforts to restore salmon populations often involve trade-offs, for example, water management decisions must account for flood control, agricultural and municipal water use, and management of other species. UWR Chinook Salmon recovery efforts are also governed by multiple laws, policies, and action agencies that in some cases have incongruent objectives. Competing and conflicting objectives, combined with uncertainty regarding the outcomes of proposed management actions, create significant challenges for decision makers. Resource limitations, regulatory constraints, and incongruent objectives have created challenges for managers in the UWR, but opportunities exist for improved adaptive management and collaboration, which could build trust and engagement among stakeholders and ultimately support the successful implementation of decision tools. A suite of decision support tools that have been used in the Willamette River basin and elsewhere across the range of Pacific salmon have the potential to enhance decision processes. These tools can be effective when decision makers and stakeholders commit to long-term, collaborative utilization of the tools for decision making, and when available resources and regulatory environments are conducive to implementation and adaptive refinement of both the decision-support tools and management plans. The general biological and institutional principles discussed for UWR Chinook Salmon in this work apply more generally to populations of anadromous fishes across their range, especially to populations in highly regulated river systems.

Oregon↗
USGS2026

Quantifying Chinook Salmon habitat across flow regimes: High resolution modeling in Oregon’s Willamette River basin

The Santiam and McKenzie River basins of western Oregon provide critical habitat for federally listed Upper Willamette River Spring Chinook salmon ( Oncorhynchus tshawytscha ). Streamflows in each basin are regulated in part by high-head multi-purpose dams; however, quantitative linkages between regulated streamflows and downstream habitat for juvenile and adult Chinook salmon remain limited. This study integrates high-resolution topo-bathymetric lidar, two-dimensional hydraulic models, and novel detailed sediment distribution models to evaluate habitat across a range of flows for over 400 river km. Results suggest that habitat quantity for two juvenile life stages (fry and parr) differs in response to streamflow; fry habitat appears to be relatively insensitive to streamflow, except in the downstream-most reaches of each river, while parr habitat generally increases from low to moderate flows, yet decreases at higher flows. Spawning habitat is largely inversely related to streamflow and is primarily limited by suitable substrate availability, likely reflecting sediment retention effects of upstream dams. Additionally, streamflow thresholds were identified where redd desiccation risk increases significantly with declining streamflow. These findings provide managers with spatially explicit tools to evaluate flow management tradeoffs during critical rearing and spawning periods and provide insights into habitat dynamics in large, regulated rivers. This work demonstrates how high-resolution modeling can support quantification of habitat at the landscape level.

Oregon↗
USGS2024

Reservoir evolution, downstream sediment transport, downstream channel change, and synthesis of geomorphic responses of Fall Creek and Middle Fork Willamette River to water years 2012–18 streambed drawdowns at Fall Creek Lake, Oregon

Executive Summary Chapter A. Introduction Fall Creek Dam impounds Fall Creek Lake, a 10-kilometer-long reservoir in western Oregon and is operated by the U.S. Army Corps of Engineers (USACE) primarily for flood-risk management (or flood control) in late autumn through early spring months, as well as for water quality, irrigation, recreation, and habitat in late spring through early autumn. Since 2011 (water year [WY] 2012), Fall Creek Lake has been temporarily drawn down each year to facilitate downstream passage of juvenile spring Chinook salmon ( Oncorhynchus tshawytscha ) through the 55-meter (m) high dam. This annual dam operation is temporary, typically lasting about 1–2 weeks from WY 2012 through 2020 (drawdown operations in WY 2022–24 have increased to more than 6 weeks). Drawdown of the reservoir results in lake levels being lowered to the elevation near the historical, pre-dam streambed. The annual streambed drawdowns of WY 2012–18 have improved fish passage and led the USACE to formally adopt streambed drawdowns as part of annual operations at Fall Creek Dam. However, temporarily lowering the lake to streambed creates free-flowing conditions in the reservoir that result in the erosion and episodic export of predominantly sand and finer-grained sediments (less than 2 millimeters [mm]) to the lower gravel-bed reaches of Fall Creek and the Middle Fork Willamette River. The introduction of large volumes of sand and finer-grain sediment into the dam-regulated reaches downstream from Fall Creek Dam prompted questions about the geomorphic responses to annual streambed drawdowns within Fall Creek Lake and downstream reaches along Fall Creek and the Middle Fork Willamette River. The U.S. Geological Survey (USGS) in partnership with USACE initiated a comprehensive geomorphic and sediment transport investigation to assess the coupled processes of reservoir erosion, sediment evacuation from Fall Creek Lake, and patterns of sediment transport and deposition in reaches downstream from the Fall Creek Dam that have resulted from annual streambed drawdowns. The purpose of this report is to systematically describe the processes of sediment erosion, transport, and deposition at Fall Creek Lake and geomorphic interactions between reaches upstream and downstream from Fall Creek Dam that relate to dam operations. Specifically, this report focuses on evaluating geomorphic responses to streambed drawdowns from WY 2012 through 2018 and placing drawdown-induced geomorphic responses within the broader context of physiographic and historical conditions and dam operations of Fall Creek and Middle Fork Willamette Rivers. Key objectives for this study were to characterize changes in reservoir morphology and substrate at Fall Creek Lake, describe the character and temporal pattern of sediment transport downstream from Fall Creek Dam, characterize geomorphic changes in channel reaches downstream from the Fall Creek Dam, and relate these data to the annual streambed drawdowns of WY 2012–18. This study uses multiple independent monitoring and measurement approaches to assess site, reach, and river-scale geomorphic responses to drawdowns to inform dam and reservoir management. Patterns and processes of reservoir evolution were assessed with geomorphic mapping and volumetric analyses of topography through comparison of multiple digital surface models (DSMs). Just downstream from Fall Creek Dam, analyses of sediment export from the reservoir focused on suspended sediment but also incorporated bedload analyses to assess sediment sizes. Geomorphic assessments downstream from the dam used reach-scale and site-scale approaches to document changes in channel morphology and substrate, including site measurements of sand and finer-grained sediment deposition and in-channel bed-material, volumetric change analyses from comparison of digital elevation models (DEMs), and repeat geomorphic mapping. Findings from this study inform river management and dam operations by providing an understanding of (1) coupled upstream-downstream geomorphic responses to the Fall Creek Lake streambed drawdowns, (2) geomorphic responses of Fall Creek Lake streambed drawdowns in comparison to drawdowns at other large dams, (3) controls on reservoir erosion and downstream geomorphic responses, and (4) implications for future hydrogeomorphic changes that may result from continued drawdowns and monitoring activities to assess those changes. Chapter B. Reservoir Morphology and Evolution Related to Dam Operations at Fall Creek Lake To understand the volume and distribution of sediment accumulation in Fall Creek Lake since dam closure in 1965, decadal-scale sedimentation patterns (spanning approximately 1965–2016) are evaluated using a combination of storage curve analyses and geomorphic mapping. Short-term (drawdown event-scale) patterns of erosion, sedimentation, and sediment export downstream are evaluated using a combination of geomorphic mapping and change detection analyses that quantify the distribution and total volume of sediment erosion and deposition within Fall Creek Lake. Geomorphic mapping of reservoir topography and analyses of historical datasets reveals four categories of landforms and sediment processes within Fall Creek Lake related to lake level operations: lacustrine sedimentation expressed in the reservoir floor, fluvial erosion and deposition within historical stream channels during streambed drawdowns, channel-like features created by erosion within the reservoir floor during streambed drawdowns, and erosion on reservoir hillslopes. Where the reservoir floor is mapped for this study as pelagic (deep water), deposition up to 3 meters (m) thick by lacustrine processes and burial of pre-dam topography with deposits thinning toward the edges of the valley floor and upstream areas of reservoir are observed. Despite over 50 years of sediment accumulation since dam construction, the main stream channels of Fall and Winberry Creeks (or reservoir thalwegs) through the reservoir are well defined, though their distinct morphology is likely influenced by a long history of recurring historical drawdowns to or near streambed since dam construction. Unregulated streamflow and sediment transport through the reservoir primarily are confined to these channels during the streambed drawdown periods. Erosional channel-like features created by drawdowns are carved through underlying, unconsolidated reservoir floor sediments and are most prominent in the lower reservoir below minimum conservation pool (the low pool elevation during winter flood season); sediment generated from the formation of these drawdown channels is more likely to be transported through and out of the reservoir than sediment deposits along the reservoir hillslopes at the valley margins that are separated from main channels by areas of low-gradient reservoir floor. Morphologic changes in the lower reservoir topography between January 2012 and November 2016 indicate overall net erosion of about 129,500 cubic meters (m 3 ). The most prominent geomorphic changes occurred along the main channels of Fall and Winberry Creeks near the Fall Creek Dam where incision, lateral migration, and slumping banks resulted in vertical and lateral adjustments to channel position, whereas most changes fell below the detectable limit on higher-elevation reservoir floor surfaces except where erosion occurred along features mapped as drawdown channels. Chapter C. Sediment Delivery from Fall Creek Lake and Transport through Downstream Reaches USGS implemented a sediment monitoring program in WY 2013–18 to evaluate the quantity and character of reservoir sediment exported from Fall Creek Lake during streambed drawdowns. Turbidity and suspended sediments were monitored annually autumn through spring to span the WY 2013–18 streambed drawdowns; however, unequal monitoring timeframes each year reduced the ability to compare results and factors affecting sediment export from the reservoir difficult between years. These data were originally measured to develop regressions and compute suspended-sediment loads (SSL). Bedload sediment monitoring from a cableway at the Fall Creek streamgage was completed in the autumn-winter of WY 2013 and 2017. The limited number of samples and presumed variability in sediment supply from the reservoir precluded construction of streamflow and bedload discharge relations to compute more than instantaneous bedload. Sand and finer-grained silts and clays were transported from the reservoir in suspension, though some coarser grains (up to 32 mm) were also mobilized and transported downstream from the dam as bedload. Observations of increased sediment transport downstream from Fall Creek Dam coincided with lake levels approaching about 3 m (10 feet [ft] or elevation 690 ft) above the streambed regulating outlets. Suspended-sediment loads computed for the full monitoring periods WY 2013–18 at the Fall Creek streamgage, located 1.4 kilometers (km) downstream from Fall Creek Dam, range from 54,700 metric tons (t) in WY 2013 to 13,900 t in WY 2018. Although the total annual SSL varied from year to year, the overall seasonal patterns of suspended sediment transport throughout each year were similar during monitoring in WY 2013-18. Suspended-sediment loads were low prior to the drawdown, then increased rapidly as lake levels lowered and approached the streambed. In the weeks following the drawdown period, as pool levels were increased, SSL remained slightly elevated above pre-drawdown levels but generally declined through the following winter and spring except during streamflow-driven pulses of suspended-sediment transport. WY 2013 had the greatest total computed SSL for each streambed drawdown and partial-year monitoring period. SSL computed for the partial-year period have generally decreased since WY 2013 and have varied by about 6,800 t with the exception of WY 2014. WY 2014 SSL reflects anomalously low sediment export due to low streamflows and freezing conditions that stabilized reservoir floor deposits. Bedload measurements in the short 1.4-km reach between Fall Creek Dam and the Fall Creek streamgage showed an inverse correlation between bedload transport rates and discharge, which probably reflects diminishing supply of coarse-sized sediment. Sand was more abundant (60–100 percent) than gravel in bedload samples confirming sand and finer-grained sediment dominated sediment evacuated from the reservoir during streambed drawdowns at Fall Creek Lake. Chapter D. Geomorphic Responses to Fall Creek Lake Streambed Drawdowns Downstream from Fall Creek Dam In the days, weeks, and months following streambed drawdown operations at Fall Creek Dam through WY 2018, sites downstream from the dam displayed a variety of geomorphic responses to reservoir sediment delivery within the main channel and overbank areas. Evaluation of streambed elevations at two streamgages located 1.4 km downstream from the dam on Fall Creek and 16.3 km downstream from the dam on the Middle Fork Willamette River indicated the effects of drawdown sediment on bed elevations were modest and transient. Repeat particle size measurements (October 2015 and September 2016) at five sites along Fall Creek and the Middle Fork Willamette River showed similar grain-sized distributions that do not reveal substantial deposition of fine-grained sediment related to the WY 2016 streambed drawdown. Altogether, these findings indicate that transport capacity in the main, low-flow channels of Fall Creek and Middle Fork Willamette River during WY 2012–18 was sufficient to mobilize and evacuate reservoir sediments from streambed drawdowns or other bank material and tributary sources. However, other monitoring for this study indicate low-velocity zones in off-channel areas are prime locations for sand and finer-grain sediment deposition. Patterns of overbank sediment accumulation indicate that the magnitude and timing of overbank deposition on bars and low-elevation floodplain varies with proximity to the dam, geomorphic setting, streamflows, and other factors. Sand and finer-grained reservoir sediments carried as suspended-sediment load in the reaches downstream from Fall Creek Dam were deposited in overbank areas as observed with clay-horizon markers during WY 2016–17. Overbank deposition quantified with Geomorphic Change Detection (GCD) software evaluated landform-scale patterns of erosion and deposition using repeat light detection and ranging (lidar) surveys at two sites in the Upper Fall Creek reach and one site in the Jasper reach for 3 years (2012–15) and one site in the Clearwater reach for 6 years (2009–15). Deposition thickness and spatial patterns from the GCD analysis were variable; some sites had dispersed but measurable deposition while at others, deposition was highly localized and exceeded 1 m in depth. Patterns of overbank deposition illustrate interactions among bar morphology, local hydraulics, and suspended-sediment transport dynamics that can create patches of highly localized deposition. The measured deposition at the two Fall Creek GCD sites likely resulted from reservoir sediments released from Fall Creek Lake during streambed drawdowns in WY 2016 and 2017 because the limited sediment inputs from bank material (geomorphically laterally stable reach) or tributaries (no significant tributaries) provided few other sediment sources. On the Middle Fork Willamette River, observed patterns of overbank deposition could reflect sediment sourced from upstream tributaries, bank erosion, or Fall Creek Lake streambed drawdown operations. Despite the introduction of several thousand tons of reservoir sediment delivered from the Fall Creek Lake streambed drawdowns to below-dam river corridors, reach-scale mapping of channel features downstream from Fall Creek Dam shows minimal evidence of changes in channel planform or landforms that can be attributed to a drawdowns in WY 2012–16. On Upper Fall Creek reach, widespread increases in gravel bars or other in-channel sediment did not result from the five streambed drawdowns. The main changes attributable to sediment releases from Fall Creek Lake were localized increases in vegetated bar area, particularly on channel margin areas where sand and finer-grain sediment was deposited and rapidly colonized by vegetation. The area of mapped secondary water features decreased between 2005 and 2016, but that may be due to lower discharges depicted in the 2016 aerial photographs and less mapped area of inundation. Primary changes along the Lower Fall Creek reach include a 6.4 percent decrease in area of secondary water features between 2011 and 2016, and a nearly twofold increase in the area of unvegetated bars. Immediately downstream from the Fall Creek confluence, there were negligible changes in the location and areas of vegetated bars and the main wetted channel between 2005 and 2016, and local increases in bar area cannot be attributed solely to deposition of reservoir sediments from Fall Creek Lake because (1) areas along the Middle Fork Willamette River just upstream from the Fall Creek confluence display similar type and magnitude of changes and (2) some of the increases at the confluence area pre-date the drawdowns. The cumulative effect of sediment releases from Fall Creek Lake streambed drawdowns from WY 2012 to 2016 on downstream channel planform and landforms are modest compared to the river-scale transformations and planform changes that occurred in the decades following dam construction. Chapter E. Discussion of Geomorphic Responses of Fall Creek and Middle Fork Willamette River to Streambed Drawdowns at Fall Creek Lake Multiple aspects of Fall Creek Dam infrastructure and operations exert first-order controls on the magnitudes of reservoir erosion that occur during the streambed drawdowns and ultimately determine the sediment delivery to downstream reaches. Key aspects of the dam and its operations that are most relevant to assessing geomorphic responses to streambed drawdowns include the (1) dam infrastructure, including configuration and size of regulating outlets and their proximity to the streambed which dictates the capacity and competence of the river to deliver sediment to downstream reaches and mode of sediment transport as suspended-sediment load or bedload; (2) frequency of historical drawdowns and long-term, year-round dam operations and lake level management, which partly dictate reservoir morphology and locations and magnitudes of readily erodible materials; (3) dam operations and hydroclimatic conditions during the streambed drawdown (including length of the drawdown and streamflows entering the reservoir), which directly control the timing, duration and magnitude of reservoir erosion and sediment evacuation; and (4) dam operations following the streambed drawdown operation that regulate streamflows (and thereby sediment transport conditions) downstream of Fall Creek Dam which primarily reflect interactions between hydroclimatic conditions and flood control operations. Patterns of sediment erosion and evacuation observed in this study at Fall Creek Lake from WY 2012–18 suggest that reservoir erosion during annual streambed drawdowns may remain similar or decrease in future years assuming (1) annual streambed drawdown operations are implemented in similar manner as the WY 2012–18 drawdowns (in terms of duration, late autumn or early winter implementation, rate of pool-level lowering to reach streambed, and other factors), (2) streambed drawdowns coincide with similar conditions as were observed WY 2012–18 (similar sediment yield into reservoir, low reservoir inflows, limited precipitation, moderate air temperature), and (3) no major geomorphic changes in the main reservoir channels of Fall and Winberry Creeks occur (for example, channel avulsion). Under such conditions, it is hypothesized that the stream channel within the reservoir would achieve a quasi-equilibrium state with respect to annual influx and export of sediment and aided by the substantial amount of in-channel bedrock, will remain laterally stable without erosion across reservoir deposits. Patterns of sediment transport measured at the Fall Creek streamgage downstream from Fall Creek Dam provide insight into the potential effects of future streambed drawdowns at Fall Creek Lake. Analyses of suspended sediment measured in WY 2013–18 show a major reduction in suspended-sediment loads between WY 2013 and later years, indicating streamflows transporting sediment through the reservoir to downstream reaches during streambed drawdowns have become supply limited. The 6-year suspended-sediment monitoring and sampling program is insufficient to make predictions about future sediment transport conditions because of uneven monitoring periods and varying controls on reservoir sediment erosion. It is likely that future suspended-sediment loads will be variable but similar to those observed in WY 2015–18 if operational, climatic, and geomorphological factors remain similar to those monitored WY 2015–18. Suspended-sediment loads downstream from Fall Creek Lake will likely remain highest when regulating outlets are fully open and Fall Creek is free flowing with the reservoir fully drained with little to no residual pool. Over time, it is possible that the suspended-sediment loads would reflect mobilization of reservoir sediment deposited in the previous year rather than erosion of sediment deposited years or decades earlier. Bedload is likely to remain a small fraction of the total sediment load evacuated from the reservoir and is relatively modest compared with pre-dam bedload transport rates because most coarse sediment remains trapped by the dam. If sediment releases from Fall Creek Lake and ensuing streamflow conditions follow a similar pattern in the future as was assessed in this study spanning WY 2012–18, near-term geomorphic adjustments downstream of the dam are expected to be modest. Barring major operational, climatic, and geomorphological changes, local site-scale deposition on bars, overbank areas, or off-channel features that persists several months after the streambed drawdown will likely continue to be highly variable, ranging from negligible to several centimeters of deposition. At the landform-scale, low velocity areas nearest to Fall Creek Dam will likely continue to undergo rapid deposition immediately during and after a streambed drawdown event, similar to patterns observed for WY 2012–18. Some of the sediment entering these off-channel features and margin areas may be temporarily stored, then later remobilized and dispersed farther downstream. But if newly deposited sediment persists through the following spring, there is a greater likelihood that local vegetation will establish, reinforce deposited material, and trap sediment during later drawdowns. The reach-scale geomorphic changes may become more apparent if (1) streambed drawdowns continued for several decades, and geomorphic changes were measured at decadal scales or (2) the amount of sediment introduced to downstream reaches substantially increased and (or) sediment transport capacity decreased. The continued streamflow regulation of Fall Creek Dam after sediment releases provides an opportunity to strategically manage streamflows during and after the streambed drawdowns to minimize downstream sediment impacts and ensure other operational thresholds are satisfied. This study provides a comprehensive foundation of datasets and geomorphic analyses to inform dam operations at Fall Creek Lake, monitor sediment transport downstream, and consider operational schemes for future drawdowns. The datasets from this study also provide baselines of sediment transport and geomorphic conditions to assess future changes in reservoir and downstream environments. Future monitoring could be tailored to address specific questions regarding the long-term geomorphic effects of streambed drawdowns on fluvial habitats, flood hazards, cultural resources, or downstream water quality. Future monitoring activities could focus on the relevant geomorphic processes and spatial domains within the three categories used for this study: (1) reservoir erosion and net sediment evacuation, (2) sediment delivery to downstream reaches, including magnitude and temporal pattern of sediment transport, and (3) geomorphic responses of downstream reaches to sediment delivery. Specifically, high priority future monitoring activities could include: Repeat topographic or photographic surveys in the reservoir to characterize changes occurring within individual drawdowns, to quantify sediment export, to determine temporal changes in reservoir storage, and to identify locations of erosion and deposition. Continuous, year-round turbidity monitoring supplemented with suspended-sediment measurements at a streamflow-gaging station immediately downstream from the dam to quantify sediment export. Repeat geomorphic monitoring, mapping, or modeling in downstream reaches to track changes in channel and over bank features using a combination of site- and reach-scale monitoring approaches. This could support assessments of sediment deposition and ensuing vegetation encroachment on flood hazards and habitats and examine how sediment transport and depositional processes may be affected by different sediment supply, streamflow, or dam management scenarios.

Oregon↗
USGS2023

Historical changes to channel planform and bed elevations downstream from dams along Fall Creek and Middle Fork Willamette River, Oregon, 1926–2016

Operation of large, multipurpose dams within the Middle Fork Willamette River Basin, Oregon, including the Fall Creek sub-basin, have disrupted natural streamflow and sediment transport regimes and fish passage along the river corridors. Documenting channel morphology, including channel planform, landforms, vegetation cover, and river channel elevations at multiple points in time spanning the 20th and early 21st centuries, is useful for characterizing net changes occurring in response to construction and operation of these dams. The U.S. Geological Survey assessed historical channel changes that occurred within the past century in response to the construction and operation of flood-control dams by evaluating planimetric datasets (from 1926 plan and profile surveys and 1936 and 2016 aerial photographs) and elevation datasets (from 1926 plan and profile surveys and 2015 light detection and ranging [lidar]). This study specifically focuses on the lower 27.3 kilometers (km) of the Middle Fork Willamette River and the lower 11.5 km of Fall Creek, or the reaches downstream from the U.S. Army Corps of Engineers Dexter Dam and Fall Creek Dam, to the confluence with Coast Fork Willamette River. Altogether, compilation and evaluation of datasets for Fall Creek and the Middle Fork Willamette River downstream from the dams provide a foundation for understanding: channel morphology and patterns of geomorphic stability prior to dam construction in 1926 and 1936; channel morphology and patterns of lateral and vertical stability of the early 21st century that reflect present-day (post-dam) streamflow and sediment regimes as of 2015–16; and geomorphic transformations of the river corridors in the decades following dam construction, including changes in planform and bed elevation (determined from water-surface elevations). Findings from this study can be used to provide historical and geomorphic context for geomorphic responses to deep reservoir drawdowns on Fall Creek Lake that mobilize reservoir sediment downstream and informing other restoration and river-management activities; this report summarizes one component of a larger research effort to document the magnitude and spatial distribution of geomorphic responses to sediment releases from draining Fall Creek Lake. As of 2016, the modern Fall Creek flows through a narrow, semi-alluvial channel that efficiently conveys water and sediment at typical streamflows downstream from Fall Creek Dam. This channel planform, including the positions and distributions of bars and secondary water features (side channels, alcoves, and ponds), generally reflects pre-dam conditions in 1936, suggesting relatively modest morphological adjustments resulted from reductions in sediment supply and alterations to peak streamflow after dam construction. The most substantial morphologic change detected over this period was a reduction in unvegetated gravel bars. As of 2016, the modern Middle Fork Willamette River is a large, gravel-bed river that, despite substantial transformations in channel morphology and reduction in lateral dynamism following the construction of multiple upstream dams, remains a dominantly alluvial river. Prior to dam construction in 1926 and 1936, the reaches of the Middle Fork Willamette River downstream from Dexter Dam were laterally active with multi-thread and single-thread channels flanked by large, shifting gravel bars. Since streamflow regulation and other channel modifications in the mid-20th century, these reaches have become less laterally active and encompass a narrower floodplain corridor as abundant former gravel bars were converted to low-elevation floodplains colonized by young, dense forests. The Middle Fork Willamette River downstream from Dexter Dam has remained mostly vertically stable between 1926 and 2015, although localized segments possibly decreased in elevation as much as 2.3 meters.

Oregon↗
USGS2023

Assessment of habitat use by juvenile Chinook salmon (Oncorhynchus tshawytscha) in the Willamette River Basin, 2020–21

We conducted a field study during 2020–21 to describe habitat use patterns of juvenile Chinook salmon ( Oncorhynchus tshawytscha ) in the mainstem Willamette, McKenzie, and Santiam Rivers and to evaluate how habitat suitability criteria affected the predictive accuracy of a hydraulic habitat model. Two approaches were used to collect habitat use data: a stratified sampling design was used to ensure that a representative sample of available habitats was included in our sampling; and a targeted sampling design was used to collect additional data in habitat cells where juvenile Chinook salmon were observed. Habitat attributes and fish presence data were collected in habitat cells that were approximately 2 square meters during April, June, and July. A total of 632 cells were sampled during the study and included habitat located in the main channel (373 cells), side channels (228 cells), and in alcoves (31 cells). Juvenile Chinook salmon were observed in 42 percent of the cells located in the main channel, 38 percent of the cells located in side channels, and 7 percent of the cells located in alcoves. We used logistic regression to develop resource selection functions for April, June, and July, which produced probability-based predictions of habitat use for juvenile Chinook salmon based on water velocity and water depth. The resource selection functions revealed a habitat shift by juvenile Chinook salmon to locations with higher water velocities and greater water depths from April to July as juvenile Chinook salmon size increased. The resource selection functions that we developed are an important addition to habitat modeling in the Willamette River basin because they were developed from in-basin data, capture seasonal differences in habitat use, and facilitate probability-based estimates of habitat use for juvenile Chinook salmon. These advancements will improve habitat modeling efforts for juvenile Chinook salmon during spring and summer months within the Willamette River.

Oregon↗
USGS2023

Science to support conservation action in a large river system: The Willamette River, Oregon, USA

Management and conservation efforts that support the recovery and protection of large rivers are daunting, reflecting the complexity of the challenge and extent of effort (in terms of policy, economic investment, and spatial extent) needed to afford measurable change. These large systems have generally experienced intensive development and regulation, compromising their capacity to respond to disturbances such as climate change or wildfire. Functionally, large river and basin management require insights gained from social, ecological, geophysical, and hydrological sciences. This multi-disciplinary perspective can unveil the integrated relationship between a river network's biotic community and seasonally variable environmental conditions that are often influenced by human activities. Large rivers and their basins are constantly changing due to anthropogenic influences and as climate modifies patterns of temperature and precipitation. Because of these factors, the state of knowledge must advance to address changing conditions. The Willamette River, in western Oregon, USA, is a prime example of a basin that has experienced significant degradation and investment in rehabilitation in recent decades. Innovative science has facilitated development of fine-scale, spatially extensive datasets and models that can generate targeted conservation and rehabilitation actions that are prioritized across the entire river network. This prioritization allows investment decisions to be driven by site-specific conditions while simultaneously considering potentials for ecological improvement. Here, we review hydrologic, geomorphic, ecologic, and social conditions in the Willamette River basin through time—including pre-settlement, river development, and contemporary periods—and offer a future vision for consideration. Currently, detailed information about fish populations and habitat, hydrologic conditions, geomorphology, water quality, and land use can be leveraged to make informed decisions about protection, rehabilitation, and development. The time is ripe for strategic management and goal development for the entire Willamette River, and these efforts can be informed by comprehensive science realized through established institutions (e.g., public agencies, non-profit watershed groups, Tribes, and universities) focused on conservation and management. The approaches to science and social-network creation that were pioneered in the Willamette River basin offer insights into the development of comprehensive conservation-based planning that could be implemented in other large river systems globally.

Oregon↗
USGS2022

Monitoring framework to evaluate effectiveness of aquatic and floodplain habitat restoration activities for native fish along the Willamette River, northwestern Oregon

Since 2008, large-scale restoration programs have been implemented along the Willamette River, Oregon, to address historical losses of floodplain habitats caused by dam construction, bank protection, large wood removal, land conversion, and other anthropogenic influences. The Willamette Focused Investment Partnership (WFIP) restoration initiative brings together more than 16 organizations to improve floodplain habitats on more than 35,000 hectares upstream from Willamette Falls with the overarching goal to expand and enhance native fish habitats through the following restoration activities implemented along the floodplains and off-channel areas of the Willamette River: (A) modify floodplain topography and human-made barriers to inundation; (B) enhance gravel pits; (C) remove revetments; (D) construct off-channel features; (E) increase and enhance floodplain forest vegetation; and (F) treat aquatic invasive plant species (AIS). The WFIP Effectiveness Monitoring Program was initiated to inform future refinement of Willamette River restoration program goals and activities and has three goals: (1) evaluate the effectiveness of different restoration activities at increasing and enhancing native fish habitat, (2) improve overall understanding of the physical and ecological responses associated with different restoration activities undertaken by the WFIP, and (3) relate site-scale responses to restoration with broader patterns of fish communities, hydrogeomorphology, stream temperature, and vegetation across the Willamette River floodplain, so that the relative importance of restoration activities on habitat availability for native fish can be assessed. A monitoring framework was developed to evaluate effectiveness of floodplain restoration activities at increasing and enhancing habitat for native fish in the Willamette River corridor, northwestern Oregon. This framework describes monitoring indicators, metrics, and approaches for evaluating responses in native fish communities and physical habitat conditions to restoration activities and determining effectiveness of restoration activities at improving habitats for native fish. The monitoring indicators and approaches are grouped into five restoration monitoring categories that are useful for characterizing ecological and physical habitat responses to restoration activities: fish, hydrogeomorphology, floodplain forest vegetation, birds, and AIS. This monitoring framework provides a common science foundation to support collaborative decisions on future interdisciplinary effectiveness monitoring activities for Willamette River restoration programs. To evaluate restoration effectiveness, data must be evaluated according to metrics and thresholds that permit direct comparison between habitat conditions at the restoration site and restoration program goals; this framework provides examples of metrics and thresholds for evaluating data, recognizing that the precise evaluation criteria for a particular site or program will need to be tailored to meet program questions and available resources. Refining restoration goals and activities as part of an adaptively managed process requires addressing critical uncertainties between restoration goals, restoration activities, and outcomes for habitats used by native fish. Although the monitoring activities of this framework will generate important datasets useful for evaluating restoration effectiveness, additional research, syntheses, and reporting is ultimately necessary to provide a common science foundation to support adaptively managed restoration programs. This report is intended as a resource for restoration program managers, practitioners, scientists, and contractors as they develop detailed annual monitoring plans for data collection and identify the monitoring indicators, metrics, and approaches that are appropriate for evaluating effectiveness of different restoration activities.

Oregon↗
USGS2022

Assessment of habitat availability for juvenile Chinook salmon (Oncorhynchus tshawytscha) and steelhead (O. mykiss) in the Willamette River, Oregon

The Willamette River, Oregon, is home to two salmonid species listed as threatened under the Endangered Species Act, Upper WIllamette River spring Chinook salmon ( Oncorhynchus tshawytscha ) and Upper Willamette River winter steelhead ( O. mykiss ). Streamflow in the Willamette River is regulated by upstream dams, 13 of which are operated by the U.S. Army Corps of Engineers (USACE) as part of the Willamette Valley Project. In 2008, these dams were determined to have a deleterious effect on Endangered Species Act-listed salmonids, resulting in USACE taking actions to mitigate those effects. Mitigation actions included setting seasonal streamflow targets at various locations along the river to improve survival and migration of juvenile salmonids. Although these targets were established with the best available information at the time, recent data and models have advanced understanding of Willamette River bathymetric, hydraulic, and thermal conditions, allowing for a more robust analysis of the effect of streamflow on downstream habitat. This study integrates those recent advances to build high-resolution models of usable habitat for juvenile Chinook salmon and steelhead to assess variation in spatial and seasonal patterns of habitat availability. Specifically, this study develops detailed maps of habitat availability for juvenile Chinook salmon and steelhead for two size classes (fry and pre-smolt). Habitat availability is modeled in a three-step process whereby (1) two-dimensional hydraulic models are paired with literature-supplied data on habitat preferences to create spatially explicit maps of rearing habitats for a wide range of streamflows; (2) reach-specific relations between streamflow and habitat area are developed and paired with streamgage records to create habitat time series for 2011, 2015, and 2016, which reflect “cool and wet,” “hot and dry,” and “warm but average precipitation” conditions, respectively; (3) temperature models are coupled with literature-based thermal thresholds to determine time periods and locations along the river corridor when rearing habitat has optimal, harmful, or lethal temperature conditions; (4) finally, habitat availability is summarized at several spatial scales to characterize longitudinal and seasonal patterns. Findings show that modeled area of rearing habitat for Chinook salmon and steelhead responds non-uniformly to streamflow, where habitat in some reaches of the Willamette River consistently increase with additional streamflow, while in other reaches, habitat area decreases when streamflows increase from low to moderate flows. Modeled differences in flow-habitat relations are primarily explained by local geomorphology in each reach and resulting hydraulic conditions that arise with different streamflows. These are most pronounced when comparing laterally active, multi-channel reaches upstream from Corvallis with downstream reaches that are laterally stable with single-channel planforms. The reaches upstream from Corvallis generally have more habitat available per unit stream distance than downstream reaches, but all reaches display greatest amounts of habitat at the highest streamflows. Finally, results show that warm water temperature in summer greatly decreases the utility of habitat available to the focal species, particularly downstream from Corvallis. Together, these findings serve to inform flow management by characterizing spatial and seasonal patterns of habitat availability for juvenile spring Chinook salmon and winter steelhead and provide a quantitative assessment of the effects of streamflow on rearing habitat.

Oregon↗
USGS2022

Development of continuous bathymetry and two-dimensional hydraulic models for the Willamette River, Oregon

The Willamette River is home to at least 69 species of fish, 33 of which are native, including Chinook salmon ( Oncorhynchus tshawytscha ) and steelhead ( Oncorhynchus mykiss ). These fish need suitable hydraulic conditions, such as water depth and velocity, to fulfill various stages of their life. Hydraulic conditions are driven by interactions between channel morphology and streamflow, which throughout the Willamette River are strongly influenced by the operation of flood-control dams in upstream tributaries. To assess how streamflow management at these dams affects downstream fish habitat, the U.S. Geological Survey has developed high-resolution bathymetric datasets to support the development of two-dimensional hydraulic models. The datasets were created by combining data collected by airborne topo-bathymetric Light Detection and Ranging with boat-based sonar to create a seamless modeling surface over which a computational mesh with a resolution of roughly 5 by 5 meters was overlaid using the U.S. Army Corps of Engineers Hydraulic Engineering Center’s River Analysis System 5.0.7 hydraulic modeling software. Models were developed for about 200 river kilometers, separated into five modeling reaches, and hydraulic conditions were simulated at flows ranging from extremely low values to annual peak flows. Results of the simulations highlight distinct patterns of inundation extents, water depths, and velocities that vary longitudinally along the Willamette River. In the two farthest upstream model reaches, from Eugene to Corvallis, the river is slower, shallower, and inundates more area at similar seasonal flows than in reaches downstream from Corvallis, where the river generally is deeper and faster. These findings align with previous geomorphic analysis of the Willamette River showing the upper reaches of the river to be geomorphically more dynamic compared to the largely single-thread channel farther downstream. Results of simulations made with these hydraulic models can be used to drive fish-habitat models to further inform flow-management decisions.

Oregon↗
USGS2021

Synthesis of habitat availability and carrying capacity research to support water management decisions and enhance conditions for Pacific salmon in the Willamette River, Oregon

Flow management is complex in the Willamette River Basin where the U.S. Army Corps of Engineers owns and operates a system of 13 dams and reservoirs (hereinafter Willamette Project), which are spread throughout three large tributaries including the Middle Fork Willamette, McKenzie, and Santiam Rivers. The primary purpose of the Willamette Project is flood-risk management, which provides critical protection to the Willamette Valley, but flow managers must also consider factors such as power generation, water-quality improvement, irrigation, recreation, and protection for aquatic species such as U.S. Endangered Species Act-listed Chinook salmon ( Oncorhynchus tshawytscha ) and steelhead ( O. mykiss ). Flow-management decision-making in the basin can benefit from models that allow for flow-scenario comparisons and a wide range of modeling methods are available. For this study, we examined existing datasets and modeling efforts in the basin and provided an overview of available options. Most previous studies used Physical Habitat Simulation System, habitat data were collected from a series of transects within modeled reaches, and habitat suitability indices were obtained from the literature, or using expert opinion. These studies provide information for specific reaches of the Willamette River Basin, which limits their ability to provide broad-scale predictive capability. Recent efforts to develop a two-dimensional hydraulic model in the mainstem Willamette River, and in specific reaches of primary tributaries downstream from Project dams, have bolstered modeling capabilities in the basin. This work has developed spatially continuous water depth and velocity data in more than 250 kilometers (km) of river downstream from Project dams and has predictive capability throughout the year at flows up to normal peak levels. Additionally, other methods are described for estimating habitat availability, which include habitat suitability criteria, logistic regression, occupancy and abundance modeling, and energetic based approaches. There are strengths and weaknesses to each approach and selection of the preferred approach in the Willamette River Basin will depend on the desired metrics of interest and the risk tolerance of managers and stakeholders in the basin.

Oregon↗
USGS2021

Integrated tools for identifying optimal flow regimes and evaluating alternative minimum flows for recovering at-risk salmonids in a highly managed system

Water resource managers are faced with difficult decisions on how to satisfy human water needs while maintaining or restoring riverine ecosystems. Decision sciences have developed approaches and tools that can be used to break down difficult water management decisions into their component parts. An essential aspect of these approaches is the use of quantitative models to evaluate alternative management strategies. Here, we describe four integrated decision support models for evaluating the effect of flows on two life history stages of Chinook salmon ( Oncorhynchus tshawytscha ) and Steelhead ( O. mykiss ). We then use constrained nonlinear optimization to identify optimal flow regimes for the water year type with the least available water. These flow regimes were then used by managers to develop candidate minimum flow strategies that were evaluated using forward simulation and sensitivity analyses. We found that optimal flow regimes differed markedly from existing regulations and varied among species and life history stages. However, evaluation of tradeoffs among the four competing objectives indicated relatively minimal losses for most objectives when the optimal flows were based on equally weighting the objectives. Sensitivity analysis indicated that water temperature was the primary driver of estimated outcomes and suggested that managers consider alternative means of managing temperatures. Decision sciences have created multiple analytical tools and approaches that simplify complex problems, such as water resource management, and we believe that water resource management would benefit from their increased use.

Oregon↗
USGS2018

Monitoring framework for evaluating hydrogeomorphic and vegetation responses to environmental flows in the Middle Fork Willamette, McKenzie, and Santiam River Basins, Oregon

This report summarizes a framework for monitoring hydrogeomorphic and vegetation responses to environmental flows in support of the Willamette Sustainable Rivers Program (SRP). The SRP is a partnership between The Nature Conservancy (TNC) and U.S. Army Corps of Engineers (USACE) to provide ecologically sustainable flows downstream of dams while still meeting human needs and congressionally authorized purposes. TNC, USACE, and U.S. Geological Survey (USGS) developed this framework specifically for the spawning reaches and lower, alluvial reaches of the Middle Fork Willamette, McKenzie, North Santiam, South Santiam, and main-stem Santiam Rivers. This monitoring framework links stakeholder-defined ecological goals and environmental flow recommendations with measurable objectives and monitoring activities to assess whether those objectives are achieved. Monitoring activities are described for distinct spatial scales (reaches, zones, and sites), which are coupled with appropriate measurement frequency (monthly to decadal or following specific flow conditions). Initial monitoring efforts could focus on developing baseline datasets for tracking future changes and developing robust relationships between flow and hydrogeomorphic and vegetation processes. These relationships would support stakeholders in developing refined environmental flow recommendations that could be efficiently evaluated in the future using continuous discharge records and strategic field-based monitoring. Environmental flow recommendations were developed to achieve certain hydraulic targets (generally defined through water-surface elevation and inundation extent) to support critical habitats for native species at different times of the year. Additionally, flow recommendations were created to support geomorphic processes that create and sustain important riparian and aquatic habitats. The spatial extent, depth, timing, duration, and frequency of inundation extents can be monitored using a combination of water-level loggers, crest-stage gages, surveys, and mapping from aerial photographs or satellite images. Changes in channel morphology (such as increases in gravel bars, side channels or channel width) can be evaluated through repeat mapping of aerial photographs or lidar and carried, and repeat surveys of channel-bed elevations could document patterns of incision or aggradation. Changes in bed texture (such as fining or coarsening) could focus on spawning habitats for spring Chinook salmon ( Oncorhynchus tshawytscha ). Deposition of fine-grained sediment in floodplain channels could be evaluated with deposition pads, repeat surveys, or lidar. Environmental flow recommendations also were developed to promote various stages of floodplain forest succession, with a focus on black cottonwood ( Populus trichocarpa ) because its life history is tightly coupled with floodplain hydrology and disturbance processes. Monitoring approaches for vegetation include strategies for tracking all phases of stand recruitment, establishment, and succession for black cottonwood. Potential recruitment sites can be identified by mapping unvegetated gravel bars from aerial photographs or lidar. Reach-scale patterns of stand recruitment and early succession can be monitored at the reach scale by mapping seral stages of floodplain vegetation from aerial photographs and lidar at the decadal scale. These monitoring approaches also could identify areas of stand recruitment or floodplain recycling. Site-scale monitoring of black cottonwood recruitment and establishment could focus on vegetation plots situated along floodplain transects within laterally dynamic monitoring zones to track seedling establishment or stem exclusion and early seral succession. Reach-scale landcover mapping from aerial photographs and lidar would complement site-scale observations and aid in characterizing overall status and condition of floodplain forests, which could be related to streamflows and hydrogeomorphic processes.

Oregon↗
USGS2017

Geomorphic response of the North Fork Stillaguamish River to the State Route 530 landslide near Oso, Washington

On March 22, 2014, the State Route 530 Landslide near Oso, Washington mobilized 8 million cubic meters of unconsolidated Pleistocene material, creating a valley‑spanning deposit that fully impounded the North Fork Stillaguamish River. The river overtopped the 8-meter high debris impoundment within 25 hours and began steadily incising a new channel through the center of the deposit. Repeat topographic surveys, sediment transport measurements, bedload transport models, and observations of downstream channel change were used to document the establishment of that new channel through the landslide and assess the potential for downstream aggradation or channel change that might increase downstream flood hazards. Efficient erosion of the landslide deposit, associated with the steep knickzone formed by the downstream edge of the deposit, resulted in the re-establishment of a 20–40 meters wide, deeply inset channel through the entire deposit by May 2014, 2 months after the landslide. The mean water-surface elevation of the channel through the landslide decreased 7 meters during that 2-month period, and was about 1 meter above the pre-landslide profile in July 2014. The 2014–15 flood season, which included flows near the 0.5 annual exceedance probability discharge (2-year flood), widened the channel tens of meters, and further lowered the water-surface profile 0.5 meter. The planform position evolved slowly as a result of 5–20-meter high banks predominantly composed of clay-rich, cohesive lacustrine material. Erosion of the landslide deposit delivered a total of 820 thousand metric tons of sediment to the North Fork Stillaguamish River over the 18 months following the landslide. The sediment delivery from the deposit was predominantly fine grained: 77 percent (by mass) of the eroded material was silt or clay (less than 0.063 millimeter [mm]), 19 percent sand (0.063–2 mm), and 4 percent pebbles and cobbles (greater than 2 mm). Over the 18 months following the landslide, the bedload at a site 5 kilometers downstream of the landslide was estimated to be 310±65 thousand metric tons, and the suspended load at that same site was estimated to be 990±110 thousand metric tons. These loads represent the combined input from the landslide and ambient upstream sources; over the study interval, landslide sediment made up about 20–40 percent of the bedload, and 65–85 percent of the suspended-sediment load at this site. At a site 70 kilometers downstream of the landslide, near the mouth of the main‑stem Stillaguamish River, suspended sediment loads were estimated to be about 1,440 thousand metric tons, of which about 600 thousand metric tons, or 30 percent, likely was derived from the landslide. The mass of landslide sediment in suspension at the mouth of the river, and the timing of arrival of that sediment, indicates that about 70 percent of the landslide sediment eroded during the study period was quickly transported through the entire basin, exiting into Puget Sound within weeks of initial entrainment. Empirical bedload transport equations, in conjunction with surficial grain-size data and output from a one‑dimensional hydraulic model, were used to estimate spatial trends in bedload transport capacity, highlighting areas where reach-scale conditions would be most likely to promote deposition of coarse landslide sediment. Transport capacities decreased sharply over a reach about 5 kilometers downstream of the landslide and remained relatively low over the next 10 kilometers downstream. However, the magnitude of calculated transport capacities are large relative to the coarse sediment input from the landslide, suggesting that substantial deposition of landslide sediment was not likely to occur. These assessments were corroborated by observations of channel change, which indicated that the downstream channel response to the landslide was modest and short-lived. The most pronounced downstream effects included a wedge of aggradation just downstream of the landslide, about 1 meter high and extending a kilometer downstream, and a 0.3-meter pulse of aggradation observed 5 kilometers downstream of the landslide. In both locations, peak aggradation and channel response occurred within about a month of the landslide, and both sites had largely recovered to pre-landslide conditions by July 2014. No substantial channel change clearly linked to the landslide was observed after July 2014 except for a modest fining of surficial gravel size distributions and continued recovery and incision of the reach just downstream of the landslide. The muted downstream response of the North Fork Stillaguamish River to the State Route 530 Landslide primarily can be attributed to the cohesive, silt- and clay-rich material that bounded most of the new channel. Although the river efficiently incised a new channel through the deposit, subsequent rates of lateral erosion were slowed by the tall, cohesive banks, limiting the total volume of sediment delivery. Once entrained, however, most landslide material was rapidly transported downstream in suspension with little geomorphic effect. Landslide material coarse enough to travel as bedload was predominantly sand and fine gravel, and sediment transport models and observations of downstream change indicated that the rate of coarse sediment delivery from the landslide did not exceed the rivers ability to transport that material. The generally muted downstream response to sediment delivery from the State Route 530 Landslide, as well as the mechanics of that delivery and response, were generally consistent with observations made following the intentional removal of constructed dams. The rate and efficiency of erosion from the landslide decreased over the period of analysis, as the new channel approached a quasi-equilibrium form. In the absence of additional hillslope activity, rates of erosion from the landslide are likely to be small compared to those over the first 18 months after the landslide. The modest channel response to the highest rates of sediment delivery, and rapid recovery thereafter, indicate that the river should be able to convey the continued supply of landslide-derived sediment effectively with little effect on the downstream morphology and flood risks.

Washington↗
USGS2016

Summary of environmental flow monitoring for the Sustainable Rivers Project on the Middle Fork Willamette and McKenzie Rivers, western Oregon, 2014–15

This report presents the results of an ongoing environmental flow monitoring study by The Nature Conservancy (TNC), U.S. Army Corps of Engineers (USACE), and U.S. Geological Survey in support of the Sustainable Rivers Project (SRP) of TNC and USACE. The overarching goal of this study is to evaluate and characterize relations between streamflow, geomorphic processes, and black cottonwood ( Populus trichocarpa ) recruitment on the Middle Fork Willamette and McKenzie Rivers, western Oregon, that were hypothesized in earlier investigations. The SRP can use this information to plan future monitoring and scientific investigations, and to help mitigate the effects of dam operations on streamflow regimes, geomorphic processes, and biological communities, such as black cottonwood forests, in consultation with regional experts. The four tasks of this study were to: Compare the hydrograph from Water Year (WY) 2015 with hydrographs from WYs 2000–14 and the SRP flow recommendations, Assess short-term and system-wide changes in channel features and vegetation throughout the alluvial valley section of the Middle Fork Willamette River (2005–12), Examine changes in channel features and vegetation over two decades (1994–2014) for two short mapping zones on the Middle Fork Willamette and McKenzie Rivers, and Complete a field investigation of summer stage and the growth of black cottonwood and other vegetation on the Middle Fork Willamette and McKenzie Rivers in summer 2015.

Oregon↗
USGS2014

Geologic and physiographic controls on bed-material yield, transport, and channel morphology for alluvial and bedrock rivers, western Oregon

The rivers of western Oregon have diverse forms and characteristics, with channel substrates ranging from continuous alluvial gravel to bare bedrock. Analysis of several measurable morphologic attributes of 24 valley reaches on 17 rivers provides a basis for comparing nonalluvial and alluvial channels. Key differences are that alluvial reaches have greater bar area, greater migration rates, and show systematic correlation among variables relating grain size to bed-material transport capacity. We relate these differences between channel types to bed-material transport rates as derived from a coupled regional analysis of empirical sediment yield measurements and physical experiments of clast attrition during transport. This sediment supply analysis shows that overall bed-material transport rates for western Oregon are chiefly controlled by (1) lithology and basin slope, which are the key factors for bed-material supply into the stream network, and (2) lithologic control of bed-material attrition from in-transport abrasion and disintegration. This bed-material comminution strongly affects bed-material transport in the study area, reducing transport rates by 50%–90% along the length of the larger rivers in the study area. A comparison of the bed-material transport estimates with the morphologic analyses shows that alluvial gravel-bed channels have systematic and bounding relations between bed-material transport rate and attributes such as bar area and local transport capacity. By contrast, few such relations are evident for nonalluvial rivers with bedrock or mixed-bed substrates, which are apparently more influenced by local controls on channel geometry and sediment supply. At the scale of western Oregon, the physiographic and lithologic controls on the balance between bed-material supply and transport capacity exert far-reaching influence on the distribution of alluvial and nonalluvial channels and their consequently distinctive morphologies and behaviors—differences germane for understanding river response to tectonics and environmental perturbations, as well as for implementing effective restoration and monitoring strategies.

California, Nevada, Oregon, Washington↗
USGS2013

Geomorphic and vegetation processes of the Willamette River floodplain, Oregon: current understanding and unanswered science questions

This report summarizes the current understanding of floodplain processes and landforms for the Willamette River and its major tributaries. The area of focus encompasses the main stem Willamette River above Newberg and the portions of the Coast Fork Willamette, Middle Fork Willamette, McKenzie, and North, South and main stem Santiam Rivers downstream of U.S. Army Corps of Engineers dams. These reaches constitute a large portion of the alluvial, salmon-bearing rivers in the Willamette Basin. The geomorphic, or historical, floodplain of these rivers has two zones - the active channel where coarse sediment is mobilized and transported during annual flooding and overbank areas where fine sediment is deposited during higher magnitude floods. Historically, characteristics of the rivers and geomorphic floodplain (including longitudinal patterns in channel complexity and the abundance of side channels, islands and gravel bars) were controlled by the interactions between floods and the transport of coarse sediment and large wood. Local channel responses to these interactions were then shaped by geologic features like bedrock outcrops and variations in channel slope. Over the last 150 years, floods and the transport of coarse sediment and large wood have been substantially reduced in the basin. With dam regulation, nearly all peak flows are now confined to the main channels. Large floods (greater than 10-year recurrence interval prior to basinwide flow regulation) have been largely eliminated. Also, the magnitude and frequency of small floods (events that formerly recurred every 2–10 years) have decreased substantially. The large dams trap an estimated 50–60 percent of bed-material sediment—the building block of active channel habitats—that historically entered the Willamette River. They also trap more than 80 percent of the estimated bed material in the lower South Santiam River and Middle and Coast Forks of the Willamette River. Downstream, revetments further decrease bed-material supply by an unknown amount because they limit bank erosion and entrainment of stored sediment. The rivers, geomorphic floodplain, and vegetation within the study area have changed noticeably in response to the alterations in floods and coarse sediment and wood transport. Widespread decreases have occurred in the rates of meander migration and avulsions and the number and diversity of landforms such as gravel bars, islands, and side channels. Dynamic and, in some cases, multi-thread river segments have become stable, single-thread channels. Preliminary observations suggest that forest area has increased within the active channel, further reducing the area of unvegetated gravel bars. Alterations to floods and sediment transport and ongoing channel, floodplain, and vegetation responses result in a modern Willamette River Basin. Here, the floodplain influenced by the modern flow and sediment regimes, or the functional floodplain, is narrower and inset with the broader and older geomorphic floodplain. The functional floodplain is flanked by higher elevation relict floodplain features that are no longer inundated by modern floods. The corridor of present- day active channel surfaces is narrower, enabling riparian vegetation to establish on formerly active gravel bar surfaces. The modern Willamette River Basin with its fundamental changes in the flood, sediment transport, and large wood regimes has implications for future habitat conditions. System-wide future trends probably include narrower floodplains and a lower diversity of landforms and habitats along the Willamette River and its major tributaries compared to historical patterns and today. Furthermore, specific conditions and future trends will probably vary between geologically stable, anthropogenically stable, and dynamic reaches. The middle and lower segments of the Willamette River are geologically stable, whereas the South Santiam and Middle Fork Willamette Rivers were historically dynamic, but are now largely stable in response to flow regulation and revetment construction. The upper Willamette and North Santiam Rivers retain some dynamic characteristics, and provide the greatest diversity of aquatic and riparian habitats under the current flow and sediment regime. The McKenzie River has some areas that are more dynamic, whereas other sections are stable due to geology or revetments. Historical reductions in channel dynamism also have implications for ongoing and future recruitment and succession of floodplain forests. For instance, the succession of native plants like black cottonwood is currently limited by (1) fewer low-elevation gravel bars for stand initiation; (2) altered streamflow during seed release, germination, and stand initiation; (3) competition from introduced plant species; and (4) frequent erosion of young vegetation in some locations because scouring flows are concentrated within a narrow channel corridor. Despite past alterations, the Willamette River Basin has many of the physical and ecological building blocks necessary for highly functioning rivers. Management strategies, including environmental flow programs, river and floodplain restoration, revetment modifications, and reclamation of gravel mines, are underway to mitigate some historical changes. However, there are some substantial gaps in the scientific understanding of the modern Willamette basin that is needed to efficiently integrate these blocks and to establish realistic objectives for future conditions. Unanswered questions include: 1. What is the distribution and diversity of landforms and habitats along the Willamette River and its tributaries? 2. What is the extent of today’s functional floodplain—the part of the river corridor actively formed and modified by fluvial processes? 3. How are landforms and habitats in the Willamette River Basin created and sustained by present-day flow and sediment conditions? 4. How is the succession of native floodplain vegetation shaped by present-day flow and sediment conditions? Answering these questions will produce baseline data on the current distributions of landforms and habitats (question 1), the extent of the functional floodplain (question 2), and the effects of modern flow and sediment regimes on future floodplain landforms, habitats, and vegetation succession (questions 3 and 4). Addressing questions 1 and 2 is a logical next step because they underlie questions 3 and 4. Addressing these four questions would better characterize the modern Willamette Basin and help in implementing and setting realistic targets for ongoing management strategies, demonstrating their effectiveness at the site and basin scales, and anticipating future trends and conditions.

Oregon↗
USGS2012

Preliminary assessment of channel stability and bed-material transport in the Rogue River basin, southwestern Oregon

This report summarizes a preliminary assessment of bed-material transport, vertical and lateral channel changes, and existing datasets for the Rogue River basin, which encompasses 13,390 square kilometers (km 2 ) along the southwestern Oregon coast. This study, conducted to inform permitting decisions regarding instream gravel mining, revealed that: The Rogue River in its lowermost 178.5 kilometers (km) alternates between confined and unconfined segments, and is predominately alluvial along its lowermost 44 km. The study area on the mainstem Rogue River can be divided into five reaches based on topography, hydrology, and tidal influence. The largely confined, active channel flows over bedrock and coarse bed material composed chiefly of boulders and cobbles in the Grants Pass (river kilometers [RKM] 178.5–152.8), Merlin (RKM 152.8–132.7), and Galice Reaches (RKM 132.7–43.9). Within these confined reaches, the channel contains few bars and has stable planforms except for locally wider segments such as the Brushy Chutes area in the Merlin Reach. Conversely, the active channel flows over predominately alluvial material and contains nearly continuous gravel bars in the Lobster Creek Reach (RKM 43.9–6.7). The channel in the Tidal Reach (RKM 6.7–0) is also alluvial, but tidally affected and unconfined until RKM 2. The Lobster Creek and Tidal Reaches contain some of the most extensive bar deposits within the Rogue River study area. For the 56.6-km-long segment of the Applegate River included in this study, the river was divided into two reaches based on topography. In the Upper Applegate River Reach (RKM 56.6–41.6), the confined, active channel flows over alluvium and bedrock and has few bars. In the Lower Applegate River Reach (RKM 41.6–0), the active channel alternates between confined and unconfined segments, flows predominantly over alluvium, shifts laterally in unconfined sections, and contains more numerous and larger bars. The 6.5-km segment of the lower Illinois River included in this study was treated as one reach. This stretch of the Illinois River is fully alluvial, with nearly continuous gravel bars flanking the channel. The width of the active channel is confined by the narrow topography of the valley. The primary human activities that have likely influenced channel condition, bed-material transport, and the extent and area of bars are (1) historical gold mining throughout the basin, (2) historical and ongoing gravel mining from instream sites in the Tidal Reach and floodplain sites such as those in the Lower Applegate River Reach, (3) hydropower and flow control structures, (4) forest management and fires throughout the basin, and (5) dredging. These anthropogenic activities likely have varying effects on channel condition and the transport and deposition of sediment throughout the study area and over time. Several vertical (aspect) aerial photographs (including the complete coverages of the study area taken in 1995, 2000, 2005, and 2009 and the partial coverages taken in 1967, 1968, 1969, and 1990) are available for assessing long-term changes in attributes such as channel condition, bar area, and vegetation cover. A Light Detection And Ranging (LiDAR) survey performed in 2007–2008 provides 1-m resolution topographic data for sections of the Grants Pass (RKM 178.5–167.6) and Lobster Creek (RKM 17.8–12 and 10–6.7) Reaches and the entire Tidal Reach. Previous studies provide information for specific locations, including (1) an estimated average annual bed-material load of 76,000 m 3 at the former Savage Rapids Dam site (RKM 173.1, Grants Pass Reach), (2) over 490 m of channel shifting from 1965 to 1991 in the Brushy Chutes area (RKM 142–141, Merlin Reach), (3) active sediment transport and channel processes in the Lobster Creek Reach, (4) lateral channel migration in the Tidal Reach, and (5) up to 1.8 m of bar aggradation from the town of Agness (RKM 45.1) to the Rogue River mouth following the flood in water year 1997. Review of the repeat surveys conducted at the instream gravel-mining sites on Elephant and Wedderburn Bars tentatively indicated that these bars (1) experience some bed-material deposition in most years and more substantial deposition following high flows such as those in water years 1997 and 2006, and (2) are dynamic and subject to local scour and deposition. Results from the specific gage analyses completed for five long-term USGS streamflow-gaging stations showed that only the Grants Pass station on the Rogue River (RKM 164.4, Grants Pass Reach) experienced substantial changes in the stage–discharge relationship across a range of flows from 1938 to 2009. Observed changes indicate channel incision at this site. The Rogue and Applegate Rivers are dynamic and subject to channel shifting, aggradation, and incision, as indicated by channel cross sections surveyed during 2000–2010 on the Rogue River and 1933–2010 on the Applegate River. The elevation of the riverbed changed substantially (defined here as more than a net 0.5 m of incision or aggradation) at three locations on the Rogue River (near RKM 164.5, 139.2, and 1.3) and two on the Applegate River (near RKM 42 and 13.5). Systematic delineation of bar features from vertical photographs taken in 1967–69, 2005, and 2009 indicated that most of the repeat mapping sites had a net loss in bar area over the analysis period, ranging from 22 percent at the Oak Flat site (Illinois River Reach) to 69 percent at the Thompson Creek site (Upper Applegate River Reach). Bar area remained stable at the Williams Creek site (Lower Applegate River Reach), but increased 11 percent at the Elephant Rock site (Tidal Reach). The declines in bar area were associated primarily with the establishment of vegetation on upper bar surfaces lacking obvious vegetation in the 1960s. Some of the apparent changes in bar area may also owe to some differences in streamflow and tide levels between the vertical photographs. On the mainstem Rogue River, the median diameter of surface particles varied from 21 mm at the Wedderburn Bar in the Tidal Reach to more than 100 millimeters (mm) at some of the coarsest bars in the Galice Reach. Low armoring ratios tentatively indicated that sediment supply likely exceeds transport capacity at Orchard (Lobster Creek Reach) and Wedderburn (Tidal Reach) Bars. Conversely, relatively higher armoring ratios indicated that transport capacity likely is in balance with sediment supply at Roberston Bridge Bar (Merlin Reach) and exceeds sediment supply at Rogue River City (Grants Pass Reach), Solitude Riffle (Galice Reach), and Hooks Gulch (Galice Reach) Bars. Limited particle data were collected in the study areas on the Applegate and Illinois Rivers. Particle size measurements and armoring ratios tentatively show that sediment supply likely exceeds transport capacity at Bakery Bar in the Lower Applegate Reach. Also, the bed material exiting the Applegate River is likely finer than the bed material in the Rogue River, whereas bed material exiting the Illinois River is likely coarser than the bed material in the Rogue River. Together, these observations and findings indicate that (1) the size, area, and overall position of bars in the Rogue River study area are determined largely by valley physiography, such that unconfined alluvial sections have large channel-flanking bars, whereas confined sections have fewer and smaller bars, (2) segments within the Grants Pass, Merlin, Tidal, Upper Applegate River, and Lower Applegate River Reaches are prone to vertical and/or lateral channel adjustments, and (3) the balance between transport capacity and sediment supply varies throughout the study area. High winter flows and the steep, confined character of much of the Rogue River within the study area result in a river corridor with a high capacity to transport bed material. In the Grants Pass and Galice Reaches, the extensive in-channel bedrock as well as the sparse number and coarse texture of bars indicate that these reaches are likely supply-limited, meaning that the river’s transport capacity exceeds the supply of bed material. In contrast, the Lobster Creek and Tidal Reaches and perhaps portions of the Merlin Reach receive bed-material inputs that more closely balance or even exceed the river’s transport capacity. The lowermost reaches on the Illinois and Applegate Rivers are fully alluvial segments that are likely transport limited, meaning sediment supply likely exceeds the river's transport capacity. However, the steeper Upper Applegate River Reach is likely supply-limited as indicated by the sparse number and area of bars mapped in this reach and the intermittent bedrock outcrops in the channel. The sediment loads derived from these large tributaries draining the Klamath Mountains are probably important contributions to the overall transport of bed material in the Rogue River basin. Compared to the slightly smaller Umpqua River basin (drainage area 12,103 km 2 ) to the north, the Rogue River (13,390 km 2 ) likely transports more bed material. Although this conclusion of greater bed-material transport in the Rogue River is tentative in the absence of either actual transport measurements or transport capacity calculations, empirical evidence, including the much greater area and frequency of bars along most of the Rogue River as well as the much shorter tidal reach on the Rogue River (6.7 km) compared to the Umpqua River (40 km) supports this inference. More detailed investigations of bed-material transport rates and channel morphology would support assessments of channel condition, longitudinal trends in particle size, the relation between sediment supply and transport capacity, and the potential causes of bar area loss (such as vegetation establishment and potential changes in peak flow patterns). The reaches most practical for such assessments and relevant to several management and ecological issues are (1) the lower Rogue River basin, including the Lobster Creek and Tidal Reaches of the Rogue River as well as the Illinois River Reach and (2) the Lower Applegate River Reach.

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