Skip to main content

Recently Published Research


 To see a complete list of white paper from the Future of the Colorado River Project, click here.


From AGU Advances
Water Temperature Controls for Regulated Canyon‐Bound Rivers

by Bryce A. Mihalevich, Bethany T. Neilson, Caleb A. Buahin, Charles B. Yackulic, and John C. Schmidt

Read the article

Summary

Many canyon‐bound rivers have been dammed and downstream flow and water temperatures modified. In some regions, climate change is expected to cause lower storage in reservoirs and warmer release temperatures, which may further alter downstream flow and thermal regimes. To anticipate potential future changes, we first need to understand the dominant heat transfer mechanisms in canyon‐bound river systems. Toward this end, we adapt a dynamic process‐based river routing and temperature model to account for complex shading and radiation characteristics found in canyon‐bound rivers. We apply the model to a 362 km segment of the Colorado River in Grand Canyon National Park, USA to simulate temperature over an 18‐year period. Extensive temperature and flow data sets from within the canyon were used to assess model performance. At the most downstream gaging location, root mean square errors of hourly flow routing and temperature predictions were 11.5 m3/s and 0.93°C, respectively. We found that heat fluxes controlling temperatures were highly variable over space and time, primarily due to shortwave radiation dynamics and hydropeaking flow conditions. Additionally, the large differences between air and water temperature during summer periods resulted in high sensible and latent heat fluxes. Sensitivity analyses indicate that reservoir release temperatures are most influential above the RM88 gage (141 km below Glen Canyon Dam), while a combination of discharge, shortwave radiation, and air temperature become more important farther downstream. This study illustrates the importance of understanding the spatial and temporal variability of topographic shading when predicting water temperatures in canyon‐bound rivers.


From Geomorphology
The roles of flood magnitude and duration in controlling channel width and complexity on the Green River in Canyonlands, Utah, USA

by Author links open overlay panel  Author links open overlay panelPaul E. Grams, David J. Dean, Alexander E.Walker, Alan Kasprak and John C. Schmidt

Read the article

Summary

Predictions of river channel adjustment to changes in streamflow regime based on relations between mean channel characteristics and mean flood magnitude can be useful to evaluate average channel response. However, because these relations assume equilibrium sediment transport, their applicability to cases where streamflow and sediment transport are decoupled may be limited. These general relations also lack the specificity that is required to connect specific characteristics of the streamflow and sediment regime with the dynamics of channel morphological change that create channel complexity, which is often of ecological interest. We integrate historical records of channel change, observations of scour and fill during a snowmelt flood, measurements of sediment transport, and predictions from a two-dimensional streamflow model to describe how annual peak flow magnitude and peak-flow duration interact with the upstream sediment supply to control channel form for a 15-km study reach on the regulated Green River in Canyonlands National Park, Utah. Two major decadal-scale episodes of channel narrowing have occurred within the study area. For each of these episodes, the reduction in average channel width was consistent with the change predicted by hydraulic geometry relations as a function of average flood magnitude. However, channel narrowing occurred during periods of exceptionally low annual floods. The most recent episode of channel narrowing occurred between 1988 and 2009, during low-flow cycles when the 5-yr mean peak flow was less than 60% of the long-term (1959–2016) mean peak flow. These findings, together with findings from previous studies, demonstrate that decreases in peak-flow magnitude caused by streamflow regulation, climate change, or a combination of those factors have driven episodes of channel narrowing on the Green River. Observations of streamflow, sediment-transport, and morphologic change coupled with predictions from a two-dimensional streamflow model indicate that peak flow magnitudes of at least 75% of the long-term mean peak flow are required to transport bed-material sand in suspension in all regions of the multi-thread channel and that the ~2-month duration of the snowmelt flood played an important role in creating conditions necessary to maintain channel conveyance. These results indicate that detailed characterizations of channel response such as these are needed to predict how river channels will respond to changes in streamflow regime that affect annual peak flow magnitude and duration.


 From AGU Advances
Does Channel Narrowing by Floodplain Growth Necessarily Indicate Sediment Surplus? Lessons From Sediment Transport Analyses in the Green and Colorado Rivers, Canyonlands, Utah

by Author links open overlay panel  David J. Dean, David J. Topping, Paul E. Grams, Alexander E. Walker, and John C. Schmidt

Read the article

Summary

Analyses of suspended sediment transport provide valuable insight into the role that sediment supply plays in causing geomorphic change. The sediment supply within a river system evolves depending on the discharge, flood frequency and duration, changes in sediment input, and ecohydraulic conditions that modify sediment transport processes. Changes in supply can be evaluated through analyses of coupled changes in suspended sediment concentration and grain size. The concentration of sand in transport in the Green and Colorado Rivers is most strongly controlled by discharge and the bed sand grain size distribution. Since the 1950s, sand loads have decreased in response to declines in peak discharge in the Green River and coarsening of the bed sand in the Colorado River. However, changes in the bed sand grain size distribution are associated with large changes in suspended sand concentration in both rivers; concentration varies by a factor of ~3 in the Green River and a factor of ~8 in the Colorado River, depending on the bed sand grain size distribution. Analyses of hysteresis in suspended sediment measurements show that sediment depletion during annual floods is most strongly controlled by flood duration, with peak discharge being nearly equally important in the Green River. Despite channel narrowing in both rivers, periods of bed sand coarsening and sediment depletion during annual floods indicate that these rivers are not necessarily in sediment surplus. Channel narrowing appears to be strongly controlled by short‐term declines in flood magnitude and the ecohydraulic effects of vegetation and may not be indicative of the long‐term sediment budget.


From The Geological Society of America

From The Geological Society of America
Channel narrowing by inset floodplain formation of the lower Green River in the Canyonlands region, Utah

by Author links open overlay panel  Alexander E. Walker, Johnnie N. Moore, Paul E. Grams, David J. Dean, and John C. Schmidt

Read the article

Summary

The lower Green River episodically narrowed between the mid-1930s and present day through deposition of new floodplains within a wider channel that had been established and/or maintained during the early twentieth century pluvial period. Comparison of air photos spanning a 74-yr period (1940–2014) and covering a 61 km study area shows that the channel narrowed by 12% from 138 ± 3.4 m to 122 ± 2.1 m. Stratigraphic and sedimentologic analysis and tree ring dating of a floodplain trench corroborates the air photo analysis and suggests that the initial phase of floodplain formation began by the mid-1930s, approximately the same time that the flow regime decreased in total annual and peak annual flow. Tamarisk, a nonnative shrub, began to establish in the 1930s as well. Narrowing from the 1940s to the mid-1980s was insignificant, because floodplain formation was approximately matched by bank erosion. Air photo analysis demonstrates that the most significant episode of narrowing was underway by the late 1980s, and analysis of the trench shows that floodplain formation had begun in the mid-1980s during a multi-year period of low peak annual flow. Air photo analysis shows that mean channel width decreased by ∼7% between 1993 and 2009. A new phase of narrowing may have begun in 2003, based on evidence in the trench. Comparison of field surveys made in 1998 and 2015 in an 8.5 km reach near Fort Bottom suggests that narrowing continues and demonstrates that new floodplain formation has been a very small proportion of the total annual fine sediment flux of the Green River. Vertical accretion of new floodplains near Fort Bottom averaged 2.4 m between 1998 and 2015 but only accounted for ∼1.5% of the estimated fine sediment flux during that period. Flood control by Flaming Gorge Dam after 1962 significantly influenced flow regime, reducing the magnitude of the annual snowmelt flood and increasing the magnitude of base flows. Though narrowing was initiated by changes in flow regime, native and nonnative riparian vegetation promoted floodplain formation and channel narrowing especially through establishment on channel bars and incipient floodplains during years of small annual floods.


From Geomorphology
The roles of flood magnitude and duration in controlling channel width and complexity on the Green River in Canyonlands, Utah, USA

by Author links open overlay panel  Paul E.GramsDavid J.DeanAlexander E.WalkerAlan Kasprak, and John C.Schmidt

Read the article

Summary

Predictions of river channel adjustment to changes in streamflow regime based on relations between mean channel characteristics and mean flood magnitude can be useful to evaluate average channel response. However, because these relations assume equilibrium sediment transport, their applicability to cases where streamflow and sediment transport are decoupled may be limited. These general relations also lack the specificity that is required to connect specific characteristics of the streamflow and sediment regime with the dynamics of channel morphological change that create channel complexity, which is often of ecological interest. We integrate historical records of channel change, observations of scour and fill during a snowmelt flood, measurements of sediment transport, and predictions from a two-dimensional streamflow model to describe how annual peak flow magnitude and peak-flow duration interact with the upstream sediment supply to control channel form for a 15-km study reach on the regulated Green River in Canyonlands National Park, Utah.


From Earth Surface Process and Landforms
Measuring channel planform change from image time series: A generalizable, spatially distributed, probabilistic method for quantifying uncertainty

by Christina M. Leonard, Carl J. Legleiter, Devin M. Lea, and John C. Schmidt

Read the article

Summary

River channels change in response to natural and human-caused fluctuations in streamflow and sediment supply. Predicting how the channel might change from alterations in streamflow and sediment supply is an important and challenging part of managing a river system, especially as water resource development and climate change continue to alter the amount of sediment and flow to the world’s rivers. Case studies of channel change—how much, at what rate, and why changes are occurring—are the primary means of understanding the trajectory of channel adjustment after a disturbance. In many cases, historic aerial images, dating back to the 1930s, are the only record of the pre-disturbed channel.   They provide a window to the channel’s pre-disturbed condition which can be compared to the current condition to measure how the channel has changed. 

But there is uncertainty in measurements of channel change from before-and-after aerial images.  For instance, slight misalignments in overlaying the images on top of one another might give the false impression of a channel change, or it may be difficult to decipher the precise location of the channel boundary on the aerial image, and one must demonstrate that the changes measured were greater than these uncertainties. The importance of deciphering real channel change from uncertainty has led to the development and use of numerous techniques to quantify uncertainty in an aerial photo comparison. However, these methods are not standard, and vary in rigor and complexity, meaning that channel change deemed as ‘real’ using one method might be characterized as error using a different method. Moreover, these uncertainty methods are not generalizable—methods to measure uncertainty developed for one study might not be transferrable to another study. Until now, a generalizable, robust methodology to quantify the uncertainty in measurements of channel change from aerial images has been missing.

In this research, the authors introduce a generalizable method for quantifying the uncertainty associated with measurements of channel change from repeat aerial images—called the Spatially Distributed Probabilistic (SDP) method. The SDP method can be applied to all metrics of channel change, and can reduce the magnitude of uncertainty by 83-87%, as compared to two other commonly used methods. By reducing the amount of uncertainty, the authors were able to detect more nuanced changes in river systems. More importantly, the SDP method allowed them to measure changes in aerial photos that, up to now, had been categorized as too uncertain to even undergo analysis.


From the Geological Society of America
Channel narrowing by inset floodplain formation of the lower Green River in the Canyonlands region, Utah

by Alexander E. Walker, Johnnie N. Moore, Paul E. Grams, David J. Dean, and John C. Schmidt

Read the article

Abstract

The lower Green River episodically narrowed between the mid-1930s and present day through deposition of new floodplains within a wider channel that had been established and/or maintained during the early twentieth century pluvial period. Comparison of air photos spanning a 74-yr period (1940–2014) and covering a 61 km study area shows that the channel narrowed by 12% from 138 ± 3.4 m to 122 ± 2.1 m. Stratigraphic and sedimentologic analysis and tree ring dating of a floodplain trench corroborates the air photo analysis and suggests that the initial phase of floodplain formation began by the mid-1930s, approximately the same time that the flow regime decreased in total annual and peak annual flow. Tamarisk, a nonnative shrub, began to establish in the 1930s as well.

Narrowing from the 1940s to the mid-1980s was insignificant, because floodplain formation was approximately matched by bank erosion. Air photo analysis demonstrates that the most significant episode of narrowing was underway by the late 1980s, and analysis of the trench shows that floodplain formation had begun in the mid-1980s during a multi-year period of low peak annual flow. Air photo analysis shows that mean channel width decreased by ∼7% between 1993 and 2009. A new phase of narrowing may have begun in 2003, based on evidence in the trench. Comparison of field surveys made in 1998 and 2015 in an 8.5 km reach near Fort Bottom suggests that narrowing continues and demonstrates that new floodplain formation has been a very small proportion of the total annual fine sediment flux of the Green River. Vertical accretion of new floodplains near Fort Bottom averaged 2.4 m between 1998 and 2015 but only accounted for ∼1.5% of the estimated fine sediment flux during that period. Flood control by Flaming Gorge Dam after 1962 significantly influenced flow regime, reducing the magnitude of the annual snowmelt flood and increasing the magnitude of base flows. Though narrowing was initiated by changes in flow regime, native and nonnative riparian vegetation promoted floodplain formation and channel narrowing especially through establishment on channel bars and incipient floodplains during years of small annual floods.


Research Briefing
Sedimentation of Lake Powell Tributary Canyons, 1959-2017

by Alan Kasprak and John C. Schmidt

Read the brief

Abstract

Understanding the volume of accumulated sediment present in the inundated mouths of tributary canyons of Lake Powell is an essential first step for estimation of whether, and over what time period, sediment deposits may be evacuated. We analyzed topographic and bathymetric data from 1959 (prior to the construction of Glen Canyon Dam), 1986, and 2017 to estimate the total thickness and annual accumulation rate of sediment in 27 selected tributary canyons of Lake Powell. Sedimentation rates in these tributary canyons varied widely, from no measurable sediment accumulation, to more than 2 feet per year of sediment deposition over the 58 year analysis period.

We additionally computed unit stream power, a proxy for sediment transport potential, for 23 selected tributary canyons to estimate relative sediment remobilization timescales. We hypothesize that Aztec Canyon, and other canyons with little accumulated sediment and high unit stream power, have the potential to quickly evacuate sediment in the event of sustained reservoir drawdown. Future work will focus on developing a physical framework for understanding why sedimentation rates vary notably between individual tributary canyons, along with integrating soon-to-be-published airborne lidar data to extend sediment accumulation rate estimates to areas currently above the water surface of Lake Powell.


In EOS: Earth & Space Science News
Green and Grand: John Wesley Powell and the West That Wasn’t

by 

Read the article

Abstract:

The American West, while steeped in mythology, is also a region that depends heavily on science for its long-term livability—and perhaps no one was quicker to realize that than John Wesley Powell. A Civil War veteran and an indefatigable explorer, Powell landed on the national stage in 1869, after an expedition he led became the first to navigate the Colorado River’s path through the Grand Canyon. In the decades that followed, Powell would argue that careful, democratic management of water resources in the West must be a crucial component of its development and that a pattern of settlement and land cultivation based on the 19th century status quo would prove unsustainable.

“One thing that he didn’t anticipate [was] the degree to which we would accumulate western society in big, urban complexes,” says Jack Schmidt, the Janet Quinney Lawson Chair in Colorado River Studies at Utah State University and former chief of the U.S. Geological Survey’s (USGS) Grand Canyon Monitoring and Research Center. Powell, Schmidt says, might not have imagined that these urban complexes “would have these tentacles that extended way out into the distant landscape [or] the degree to which these big urban centers would be maintained by these really long canals…these really complicated electricity transmission systems that bring in power from distant coal-fired and nuclear and hydroelectric dam facilities.”


In Environmental Sustainability
Incorporating social-ecological considerations into basin-wide responses to climate change in the Colorado River Basin

by Lucas Bair, Charles Yackulic, John C Schmidt and others

Read the article

AbstractDuring the last 50 years, construction of dams in the western United States declined. This is partly because of increasing recognition of diverse and unintended social-ecological consequences of dams. Today, resource managers are recognizing the wide array of tradeoffs and are including a more diverse group of stakeholders in decision making for individual dams. Yet decisions at the regional scale maintain a focus on a limited number of resources and objectives, leading to inefficient and inequitable outcomes. Social- ecological changes compounded by climate change challenge this management paradigm. Increasing water demands for humans and the environment and renewed interest in hydropower present opportunities for operations that include climate change mitigation and adaptation strategies while considering tradeoffs and equitable responses at the regional scale.


In AGU Publications
Estimating the Natural Flow Regime of Rivers with Long-Standing Development: The Northern Branch of the Rio Grande

by Todd L. Blythe and John C. Schmidt

Download data from this research
Read the article

AbstractAn estimate of a river’s natural flow regime is useful for water resource planning and ecosystem rehabilitation by providing insight into the predisturbance form and function of a river. The natural flow regime of most rivers has been perturbed by development during the 20th century and in some cases, before stream gaging began. The temporal resolution of natural flows estimated using traditional methods is typically not sufficient to evaluate cues that drive native ecosystem function. Additionally, these traditional methods are watershed specific and require large amounts of data to produce accurate results. We present a mass balance method that estimates natural flows at daily time step resolution for the northern branch of the Rio Grande, upstream from the Rio Conchos, that relies only on easily obtained streamflow data. Using an analytical change point method, we identified periods of the measured flow regime during the 20th century for comparison with the estimated natural flows. Our results highlight the significant deviation from natural conditions that occurred during the 20th century. The total annual flow of the northern branch is 95% lower than it would be in the absence of human use. The current 2 year flood has decreased by more than 60%, is shorter in duration, and peaks later in the year. When compared to unregulated flows estimated using traditional mass balance accounting methods, our approach provides similar results. 


CCRS White Paper
Fill Mead First: a technical assessement

by John C. Schmidt

Read the executive summary
Read the complete white paper

AbstractThe Fill Mead First (FMF) plan would establish Lake Mead reservoir as the primary water storage facility of the main-stem Colorado River and would relegate Lake Powell reservoir to a secondary water storage facility to be used only when Lake Mead is full. The objectives of the FMF plan are to re-expose some of Glen Canyon’s sandstone walls that are now inundated, begin the process of re-creating a riverine ecosystem in Glen Canyon, restore a more natural stream-flow, temperature, and sediment-supply regime of the Colorado River in the Grand Canyon ecosystem, and reduce system-wide water losses caused by evaporation and movement of reservoir water into ground-water storage. The FMF plan would be implemented in three phases. Phase I would involve lowering Lake Powell to the minimum elevation at which hydroelectricity can still be produced (called minimum power pool elevation): 3490 ft asl (feet above sea level). At this elevation, the water surface area of Lake Powell is approximately 77 mi2, which is 31% of the surface area when the reservoir is full. Phase II of the FMF plan would involve lowering Lake Powell to dead pool elevation (3370 ft asl), abandoning hydroelectricity generation, and releasing water only through the river outlets. The water surface area of Lake Powell at dead pool is approximately 32 mi2 and is 13% of the reservoir surface area when it is full. Implementation of Phase III would necessitate drilling new diversion tunnels around Glen Canyon Dam in order to eliminate all water storage at Lake Powell. In this paper, we summarize the FMF plan and identify critical details about the plan’s implementation that are presently unknown. We estimate changes in evaporation losses and ground-water storage that would occur if the FMF plan was implemented, based on review of existing data and published reports. We also discuss significant river-ecosystem issues that would arise if the plan was implemented.


In Geomorphology
The role of feedback mechanisms in historic channel changes of the lower Rio Grande in the Big Bend region

by David J. Dean and John C. Schmidt 

AbstractOver the last century, large-scale water development of the upper Rio Grande in the US and Mexico, and of the Rio Conchos in Mexico, has resulted in progressive channel narrowing of the lower Rio Grande in the Big Bend region. We used methods operating at multiple spatial and temporal scales to analyze the rate, magnitude, and processes responsible for channel narrowing. These methods included: hydrologic analysis of historic stream gage data, analysis of notes of measured discharges, historic oblique and aerial photograph analysis, and stratigraphic and dendrogeomorphic analysis of inset floodplain deposits. Our analyses indicate that frequent large floods between 1900 and the mid-1940s acted as a negative feedback mechanism and maintained a wide, sandy, multi-threaded river. Declines in mean and peak flow in the mid-1940s resulted in progressive channel …


In Geomorphology
The geomorphic effectiveness of a large flood on the Rio Grande in the Big Bend region: Insights on geomorphic controls and post-flood geomorphic response

by David J. Dean and John C. Schmidt 

AbstractAbstract Since the 1940s, the Rio Grande in the Big Bend region has undergone long periods of channel narrowing, which have been occasionally interrupted by rare, large floods that widen the channel (termed a channel reset). The most recent channel reset occurred in 2008 following a 17-year period of extremely low stream flow and rapid channel narrowing. Flooding was caused by precipitation associated with the remnants of tropical depression Lowell in the Rio Conchos watershed, the largest tributary to the Rio Grande. Floodwaters approached 1500 m 3/s (between a 13 and 15 year recurrence interval) and breached levees, inundated communities, and flooded the alluvial valley of the Rio Grande; the wetted width exceeding 2.5 km in some locations. The 2008 flood had the 7th largest magnitude of record, however, conveyed the largest volume of water than any other flood …


In GSA Bulletin
Stratigraphic, sedimentologic, and dendrogeomorphic analyses of rapid floodplain formation along the Rio Grande in Big Bend National Park, Texas

by David J. Dean, M. Scott, Patrick Shaffroth and John C. Schmidt 

AbstractThe channel of the lower Rio Grande in the Big Bend region rapidly narrows during years of low mean and peak flow. We conducted stratigraphic, sedimentologic, and dendrogeomorphic analyses within two long floodplain trenches to precisely reconstruct the timing and processes of recent floodplain formation. We show that the channel of the Rio Grande narrowed through the oblique and vertical accretion of inset floodplains following channel-widening floods in 1978 and 1990–1991. Vertical accretion occurred at high rates, ranging from 16 to 35 cm/yr.


In Journal of Geophysical Research
Sediment supply versus local hydraulic controls on sediment transport and storage in a river with large sediment loads

by David J. Dean, John J. Topping, John C. Schmidt, Ronald E. Griffiths and Thomas A. Sabol

AbstractThe Rio Grande in the Big Bend region of Texas, USA, and Chihuahua and Coahuila, Mexico, undergoes rapid geomorphic changes as a result of its large sediment supply and variable hydrology; thus, it is a useful natural laboratory to investigate the relative importance of flow strength and sediment supply in controlling alluvial channel change. We analyzed a suite of sediment transport and geomorphic data to determine the cumulative influence of different flood types on changing channel form. In this study, physically based analyses suggest that channel change in the Rio Grande is controlled by both changes in flow strength and sediment supply over different spatial and temporal scales. Channel narrowing is primarily caused by substantial deposition of sediment supplied to the Rio Grande during tributary-sourced flash floods.