Geology topics

Research about Grand Canyon National Park

Source-linked reports with geographic coverage including Grand Canyon National Park.

At least 19 recordsLinked to original sources

USGS2025

Sampling dragonflies for mercury analysis in Grand Canyon National Park, 2018–2024: A contribution of the Dragonfly Mercury Project

The Dragonfly Mercury Project is a collaborative initiative that utilizes dragonfly larvae as biosentinels to monitor mercury concentrations across 180 national parks and other protected lands, including Grand Canyon National Park (GRCA). These indicators serve as surrogates for environmental risk and can indicate where fish consumption could pose health risks through exposure to mercury. From 2018–2024, citizen scientists and staff from the National Park Service and U.S. Geological Survey helped collect close to 400 larvae from 25 GRCA sites across nearly 300 river miles, revealing mercury concentrations ranging 3.0–1337 ng/g (parts per billion) dry weight. Results were available for 20 sites. Upon comparing mercury concentrations to an impairment index, most sites were classified as low or no risk for ecological impairment, though 10% (2 sites) exceeded moderate or severe risk benchmarks (Pete’s Pocket and Buck Farm Canyon, respectively). Sources of mercury to GRCA likely stem from a combination of atmospheric deposition, upstream discharge from Lake Powell, and other watershed contributions. In addition, food web dynamics, underlying water chemistry, and environmental disturbances (e.g., floods) contribute to mercury mobilization, production, and bioaccumulation. Report findings provide a baseline for connecting ongoing science in the Colorado River watershed, informing management actions, and enhancing public engagement through citizen science.

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USGS2024

Landscape-scale modeling to forecast fluvial-aeolian sediment connectivity in river valleys

Sedimentary landforms on Earth and other planetary bodies are built through scour, transport, and deposition of sediment. Sediment connectivity refers to the hypothesis that pathways of sediment transport do not occur in isolation, but rather are mechanistically linked. In dryland river systems, one such example of sediment connectivity is the transport of fluvially deposited sediment by wind. However, predictive tools that can forecast fluvial-aeolian sediment connectivity at meaningful scales are rare. Here we develop a suite of models for quantifying the availability of river-sourced sediment for aeolian transport as a function of river flow, wind regime, and land cover across 168 km of the Colorado River in Grand Canyon, USA. We compare and validate these models using topographic changes observed over 10 years in a coupled river sandbar-aeolian dunefield setting. The models provide a path forward for directly linking fluvial hydrology with the management and understanding of aeolian landscapes.

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USGS2024

Changes in sand storage in the Colorado River in Grand Canyon National Park from July 2017 through June 2020

Changes in the quantity of sand stored within river segments can affect aquatic and riparian habitat, archeological resources, and recreation. Since summer to fall of 2002, gaging stations on the Colorado River in Grand Canyon National Park and on its major tributaries and selected lesser tributaries have measured the mass of sand transported past each station, which allows for changes in the mass of sand stored between gaging stations to be calculated. Sand mass balances on six Colorado River segments are currently measured; the upstream two segments measure sand mass balance in Marble Canyon, the middle three segments measure sand mass balance within the majority of Grand Canyon, and the downstream-most segment—western Grand Canyon and the Lake Mead delta—measures the quantity of sand transported past Diamond Creek and ultimately deposited in Lake Mead. Between July 1, 2017, and June 30, 2020, the amount of sand stored in the Colorado River in Marble Canyon decreased, whereas the sand mass balance in Grand Canyon was indeterminate. Of the 3 years of study presented herein, sand was eroded from Marble Canyon during sediment year 2018 (July 1, 2017–June 30, 2018), a year with less than 40 percent of the 2003–2020 mean Paria River sand input, and sediment year 2020 (July 1, 2019–June 30, 2020), a year with negligible Paria River sand input. During sediment year 2018, when the Little Colorado River supplied negligible sand, sand was also eroded from Grand Canyon. The sand mass balance was indeterminate for Grand Canyon during sediment year 2020. During sediment year 2019 (July 1, 2018–June 30, 2019) sand accumulated in both Marble Canyon and Grand Canyon. This sediment year had sand inputs from both the Paria River and the Little Colorado River of more than 170 percent the 2003–2020 mean, coupled with below post-1964 mean discharge from Glen Canyon Dam.

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USGS2023

Utilizing anthropogenic compounds and geochemical tracers to identify preferential structurally controlled groundwater pathways influencing springs in Grand Canyon National Park, Arizona, USA

Study region: This study focuses on the Colorado River watershed in the area along the South Rim of the Grand Canyon. Study focus: This study utilizes anthropogenic chemical tracers to investigate the fate of treated wastewater effluent discharged within Grand Canyon National Park. Anthropogenic chemical tracers were used to discern preferential structurally controlled pathways in a complex regional network of faults and fractures in which some are conduits and others barriers to flow. New hydrological insights for the region : Previous investigations on water resources of Grand Canyon have suggested two different discharge locations (Garden Springs versus Monument Spring) for the treated wastewater discharged on the South Rim of Grand Canyon yet the presence of wastewater at the springs remained unstudied for decades. The treated wastewater from Grand Canyon Village is released into Bright Angel Wash that flows along the surface expression of the Bright Angel Fault and past the inferred intersection with the perpendicular Monument Fault. Multiple anthropogenic compounds (pharmaceuticals, per- and polyfluoroalkyl substances (PFAS), and elevated nitrate) were found in Bright Angel Wash and Monument Spring. Stable isotopic measurements at Monument Spring show depletion over time also suggesting contribution from a depleted stable isotopic source found in the treated wastewater. The anthropogenic tracers utilized in this study provide good insight to which geologic structures are conduits versus barriers to flow and can be useful in other fracture flow and karst settings.

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USGS2023

Archaeological sites in Grand Canyon National Park along the Colorado River are eroding owing to six decades of Glen Canyon Dam operations

The archaeological record documenting human history in deserts is commonly concentrated along rivers in terraces or other landforms built by river sediment deposits. Today that record is at risk in many river valleys owing to human resource and infrastructure development activities, including the construction and operation of dams. We assessed the effects of the operations of Glen Canyon Dam – which, since its closure in 1963, has imposed drastic changes to flow, sediment supply and distribution, and riparian vegetation – on a population of 362 archaeological sites in the Colorado River corridor through Grand Canyon National Park, Arizona, USA. We leverage 50 years of evidence from aerial photographs and more than 30 years of field observations and measurements of archaeological-site topography and wind patterns to evaluate changes in the physical integrity of archaeological sites using two geomorphology-based site classification systems. We find that most archaeological sites are eroding; moreover, most are at increased risk of continuing to erode, due to six decades of operations of Glen Canyon Dam. Results show that the wind-driven (aeolian) supply of river-sourced sand, essential for covering archaeological sites and protecting them from erosion, has decreased for most sites since 1973 owing to effects of long-term dam operations on river sediment supply and riparian vegetation expansion on sandbars. Results show that the proportion of sites affected by erosion from gullies controlled by the local base-level of the Colorado River has increased since 2000. These changes to landscape processes affecting archaeological site integrity limit the ability of the National Park Service and Grand Canyon-affiliated Native American Tribes to achieve environmental management goals to maintain or improve site integrity in situ . We identify three environmental management opportunities that could be used to a greater extent to decrease the risk of erosion and increase the potential for in-situ preservation of archaeological sites. Environmental management opportunities are: 1) sediment-rich controlled river floods to increase the aeolian supply of river-sourced sand, 2) extended periods of low river flow to increase the aeolian supply of river-sourced sand, 3) the removal of riparian vegetation barriers to the aeolian transport of river-sourced sand.

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USGS2022

Exploring metapopulation-scale suppression alternatives for a global invader in a river network experiencing climate change

Invasive species can dramatically alter ecosystems, but eradication is difficult, and suppression is expensive once they are established. Uncertainties in the potential for expansion and impacts by an invader can lead to delayed and inadequate suppression, allowing for establishment. Metapopulation viability models can aid in planning strategies to improve responses to invaders and lessen invasive species’ impacts, which may be particularly important under climate change. We used a spatially explicit metapopulation viability model to explore suppression strategies for ecologically damaging invasive brown trout ( Salmo trutta ), established in the Colorado River and a tributary in Grand Canyon National Park. Our goals were to estimate the effectiveness of strategies targeting different life stages and subpopulations within a metapopulation; quantify the effectiveness of a rapid response to a new invasion relative to delaying action until establishment; and estimate whether future hydrology and temperature regimes related to climate change and reservoir management affect metapopulation viability and alter the optimal management response. Our models included scenarios targeting different life stages with spatially varying intensities of electrofishing, redd destruction, incentivized angler harvest, piscicides, and a weir. Quasi-extinction (QE) was obtainable only with metapopulation-wide suppression targeting multiple life stages. Brown trout population growth rates were most sensitive to changes in age 0 and large adult mortality. The duration of suppression needed to reach QE for a large established subpopulation was 12 years compared with 4 with a rapid response to a new invasion. Isolated subpopulations were vulnerable to suppression; however, connected tributary subpopulations enhanced metapopulation persistence by serving as climate refuges. Water shortages driving changes in reservoir storage and subsequent warming would cause brown trout declines, but metapopulation QE was achieved only through refocusing and increasing suppression. Our modeling approach improves understanding of invasive brown trout metapopulation dynamics, which could lead to more focused and effective invasive species suppression strategies and, ultimately, maintenance of populations of endemic fishes.

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USGS2022

Terrestrial lidar monitoring of the effects of Glen Canyon Dam operations on the geomorphic condition of archaeological sites in Grand Canyon National Park, 2010–2020

The U.S. Geological Survey’s Grand Canyon Monitoring and Research Center, in coordination with the Glen Canyon Dam Adaptive Management Program, has monitored the geomorphic condition of select archaeological sites along the Colorado River in Grand Canyon using high-resolution terrestrial light detection and ranging (lidar) topographic surveys. Many of these sites are vulnerable to degradation by natural erosional processes. Regulation of the Colorado River by some operations of Glen Canyon Dam has been shown to affect archaeological resources by directly or indirectly causing degradation of site condition. Conversely, some specific operations of Glen Canyon Dam, such as controlled flood releases (termed high flow experiments), can potentially be used to slow or stop erosion at some degraded archaeological sites. Results of monitoring conducted with terrestrial lidar surveys from 2006 to 2010 have been synthesized in previous reports and publications. Here, we present and summarize results of monitoring conducted at 30 archaeological sites within 23 monitoring locations from 2010 to 2020. This report presents a sample of a much larger population of Colorado River archaeological sites in Grand Canyon that are being qualitatively monitored by the National Park Service (NPS). To ensure relevance to the NPS monitoring program, the quantitative high-resolution topographic monitoring presented in this report focused on sites binned by geomorphic context, using two previously published geomorphic classification frameworks to identify important changes in geomorphic condition within archaeological sites that can be related to operations of Glen Canyon Dam. We found that 22 archaeological sites changed within one or both of the previously determined geomorphic classifications, and changes at 21 of those 22 sites were interpreted as a transition to a more degraded geomorphic condition. The monitoring records contained within this report represent the foundation for future monitoring of these and other archaeological sites with high-resolution topographic surveys and change detection. These monitoring results provide benchmarks for managers of cultural resources along the Colorado River in Grand Canyon to assess significant changes to cultural resource integrity, aid in future risk management at these locations, and illustrate methods relevant for assessing geomorphic condition changes within other river valleys.

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USGS2022

The influence of drying on the aeolian transport of river-sourced sand

Transgression and regression of water levels (stages) have impacted the evolution of aeolian landforms and sedimentary deposits throughout geologic history. We studied this phenomenon over a five-day period of reduced flow on the Colorado River in Grand Canyon National Park, AZ, USA, in March 2021. These transient low flows exposed river-channel sand deposits to the air, causing progressive desiccation (drying) and thereby making these deposits susceptible to aeolian transport. We measured aeolian threshold friction velocities ( u *t ) for sand saltation and PM10 dust emissions, as well as other characteristics, on a subaerially exposed sandbar and downwind aeolian dunefield during each day of the low river flow. The sandbar transitioned from supply-limited to transport-limited aeolian sediment transport conditions during the regression in river water stage. A possible tipping point between the two transport conditions occurred approximately 48 hours after the drop in river flow. The empirically measured u *t decreased as the sandbar sediment dried with increased subaerial exposure time. Theoretical estimates and empirical measurements of u *t corresponded closely on the aeolian dunefield and on the sandbar when it was drier during the third and fourth day of the experiment. Eighty-seven percent of the variability in u *t was explained by empirical models that provide practical estimates of aeolian transport potential of subaerial river sediment deposits using monitoring data that are commonly available in this and other river systems. The work provides theoretical insight into the response of aeolian processes to sediment supply changes driven by periods of anthropogenic activity, drought, and climate change.

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USGS2022

Life and death in a dynamic environment: Invasive trout, floods, and intraspecific drivers of translocated populations

Understanding the relative strengths of intrinsic and extrinsic factors regulating populations is a long-standing focus of ecology and critical to advancing conservation programs for imperiled species. Conservation could benefit from an increased understanding of factors influencing vital rates (somatic growth, recruitment, survival) in small, translocated populations, which is lacking owing to difficulties in long-term monitoring of rare species. Translocations, here defined as the transfer of wild-captured individuals from source populations to new habitats, are widely used for species conservation, but outcomes are often minimally monitored, and translocations that are monitored often fail. To improve our understanding of how translocated populations respond to environmental variation, we developed and tested hypotheses related to intrinsic (density dependent) and extrinsic (introduced rainbow trout Oncorhynchus mykiss , stream flow and temperature regime) causes of vital rate variation in endangered humpback chub ( Gila cypha ) populations translocated to Colorado River tributaries in the Grand Canyon (GC), USA. Using biannual recapture data from translocated populations over 10 years, we tested hypotheses related to seasonal somatic growth, and recruitment and population growth rates with linear mixed-effects models and temporal symmetry mark–recapture models. We combined data from recaptures and resights of dispersed fish (both physical captures and continuously recorded antenna detections) from throughout GC to test survival hypotheses, while accounting for site fidelity, using joint live-recapture/live-resight models. While recruitment only occurred in one site, which also drove population growth (relative to survival), evidence supported hypotheses related to density dependence in growth, survival, and recruitment, and somatic growth and recruitment were further limited by introduced trout. Mixed-effects models explained between 67% and 86% of the variation in somatic growth, which showed increased growth rates with greater flood-pulse frequency during monsoon season. Monthly survival was 0.56–0.99 and 0.80–0.99 in the two populations, with lower survival during periods of higher intraspecific abundance and low flood frequency. Our results suggest translocations can contribute toward the recovery of large-river fishes, but continued suppression of invasive fishes to enhance recruitment may be required to ensure population resilience. Furthermore, we demonstrate the importance of flooding to population demographics in food-depauperate, dynamic, invaded systems.

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USGS2021

Strandlines from large floods on the Colorado River in Grand Canyon National Park, Arizona

Strandlines of peak-stage indicators (such as driftwood logs, woody debris, and trash) provide valuable data for understanding the maximum stage and extent of inundation during floods. A series of seven strandlines have been preserved along the Colorado River in Grand Canyon National Park, Arizona, USA. A survey and analysis of these strandlines was completed from the Colorado River at Lees Ferry, Ariz., gaging station to the Colorado River near Grand Canyon, Ariz., gaging station. Owing to the longitudinally discontinuous nature of the strandlines, several lines of evidence were used to determine the year of the flood associated with each strandline segment. This evidence included strandline relative vertical position, degree of peak-stage indicator weathering, datable trash drift, and map-view location. The seven distinct strandlines identified were deposited during floods with the following peak discharges (in cubic feet per second [ft 3 /s]) at the Colorado River at Lees Ferry, Ariz., gaging station (year of flood in parentheses): 210,000 ft 3 /s (1884), 170,000 ft 3 /s (1921), 125,000 ft 3 /s (1957), 108,000 ft 3 /s (1958), 97,000 ft 3 /s (1983), 52,500 ft 3 /s (1986), and 45,000 ft 3 /s (multiple events between 1996 and 2012). Stage-discharge relations were developed in areas where all, or most of the strandlines were present, and were compared to predicted stage-discharge relations from a one-dimensional flow model. River width exerted a strong control on these relations, with much greater stage change occurring for a given discharge change in narrower bedrock-dominated reaches than in wider reaches with more extensive channel-margin alluvium. This comprehensive dataset allows for the verification of model-predicted flood stage along the Colorado River in Grand Canyon National Park.

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USGS2021

Comparison of aerial thermal infrared imagery and helicopter surveys of bison (Bison bison) in Grand Canyon National Park, USA

Aerial thermal infrared (TIR) surveys are an attractive option for estimating abundances of large mammals inhabiting extensive and heterogenous terrain. Compared to standard helicopter or fixed-wing aerial surveys, TIR flights can be conducted at higher altitudes translating into greater spatial coverage and increased observer safety; however, monetary costs are much greater. Further, there is no consensus on whether TIR surveys offer improved detection. Consequently, we per-formed a study to compare results of a TIR and helicopter survey of bison (Bison bison) on the Powell Plateau in Grand Canyon National Park, USA. We also compared results of both surveys to esti-mates obtained using a larger dataset of bison helicopter detections along the entire North Rim of the Grand Canyon. Observers in the TIR survey counted fewer individual bison than helicopter ob-servers (101 to 127) and the TIR survey cost was 367% higher. Additionally, the TIR estimate was 18.8% lower than the estimate obtained using a larger dataset, while the comparative helicopter survey was 9.3% lower. Given the higher raw count, ostensibly more accurate estimates, and lower cost, we propose that helicopter surveys are currently the best choice for estimation and monitoring of bison abundance in Grand Canyon National Park.

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USGS2021

Monitoring Tamarix changes using WorldView-2 satellite imagery in Grand Canyon National Park, Arizona

Remote sensing methods are commonly used to monitor the invasive riparian shrub tamarisk ( Tamarix spp. ) and its response to the northern tamarisk beetle ( D. carinulata ), a specialized herbivore introduced as a biocontrol agent to control tamarisk in the Southwest USA in 2001. We use a Spectral Angle Mapper (SAM) supervised classification method with WorldView-2 (2 m spatial resolution) multispectral images from May and August of 2019 to map healthy tamarisk, canopy dieback, and defoliated tamarisk over a 48 km segment of the Colorado River in the topographically complex Grand Canyon National Park, where coarse-resolution satellite images are of limited use. The classifications in May and August produced overall accuracies of 80.0% and 83.1%, respectively. Seasonal change detection between May and August 2019 indicated that 47.5% of the healthy tamarisk detected in May 2019 had been defoliated by August 2019 within the WorldView-2 image extent. When compared to a previously published tamarisk map from 2009, derived from multispectral aerial imagery, we found that 29.5% of healthy tamarisk canopy declined between 2009 and 2019. This implies that tamarisk beetle impacts are continuing to accumulate even though land managers have noted the presence of the beetles in this reach of the river for 7 years since 2012.

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USGS2020

Estimating the contribution of tributary sand inputs to controlled flood deposits for sandbar restoration using elemental tracers, Colorado River, Grand Canyon National Park, Arizona

Completion of Glen Canyon Dam in 1963 resulted in complete elimination of sediment delivery from the upstream Colorado River basin to Grand Canyon and nearly complete control of spring snowmelt floods responsible for creating channel and bar morphology. Management of the river ecosystem in Grand Canyon National Park now relies on dam-release floods to redistribute tributary-derived sediment accumulated on the channel bed to higher-elevation sandbars. Here, we used multivariate mixing analysis of sediment elemental compositions to evaluate the extent to which flood deposits derive from tributary-supplied sand compared to reworked, relict predam sediment. The concentrations of seven major and trace elements (Fe, Ca, K, Ti, Rb, Sr, and Zr) were measured in very fine−, fine-, and medium-grained sand from flood deposits using X-ray fluorescence and interpreted using a Bayesian mixing model to characterize the proportion of sand originating from the Paria River, the only major tributary within the study reach. Flood deposits from the 2013 and 2014 controlled floods contained 69% ± 16% and 84% ± 20% Paria River−derived material, respectively, with substantial variation among sites. Based on a sand mass balance, we calculated that under decreasing storage conditions since 1963, ∼77%−83% of the annual Paria River sand flux needs to be retained within the mass of active sand stored in Marble Canyon each year to reach the observed concentration of Paria River sand at sample locations. This finding suggests that the use of controlled floods may continue to be effective for sandbar maintenance, provided sand inputs from the Paria River do not decline.

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USGS2019

U.S. Geological research at Grand Canyon National Park: A century of collaboration

(Fairley) When historians describe the decades preceding designation of Grand Canyon National Park (GCNP), they typically focus attention on early scientific studies conducted by John Wesley Powell, Clarence Dutton, and Charles Walcott. All three of these pioneering scientists were employed by the U.S. Geological Survey (USGS), a small Federal agency first established in 1879. Yet rarely do historians mention later contributions of USGS scientists to the subsequent development and interpretation of GCNP. This article attempts to fill this gap. When GCNP was officially designated on February 26, 1919, Grand Canyon was already a popular, internationally renowned tourist destination. Its reputation derived in no small measure from books and articles written by USGS geologists, which included some of the earliest illustrations and photographs of Grand Canyon. In addition to Powell, Dutton, and Walcott , other noteworthy USGS scientists who contributed to Grand Canyon’s early fame included Francois Matthes who, along with topographers John Stewart and Richard Evans, mapped the Canyon’s topography in painstaking detail during the first decade of the 20th century ; Levi Noble, who mapped the Precambrian geology in the Shinumo area in 1909 , and Nelson Darton, who produced the first popular guidebook about Grand Canyon’s geology for distribution by the Santa Fe Railroad . Thus, by the time Grand Canyon was designated as the Nation’s 15th national park, USGS scientists had laid a solid foundation of basic geological knowledge about this remarkable landscape upon which the National Park Service (NPS) could build. But what about the century that followed? In what respects did USGS personnel contribute to the park’s subsequent development and interpretation? The intent of this article is not to recount every scientific study undertaken by USGS scientists in Grand Canyon during the past century. Instead, this article attempts to document the various roles played by USGS professionals, working in collaboration with NPS personnel, to shape the future development and interpretation of the Park.

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USGS2018

Quantifying geomorphic and vegetation change at sandbar campsites in response to flow regulation and controlled floods, Grand Canyon National Park, Arizona

Sandbars along the Colorado River in Grand Canyon National Park, USA, are an important recreational resource used as campsites by over 25,000 river runners and hikers annually. The number and size of campsites decreased following the completion of Glen Canyon Dam in 1963 due to reductions of sediment that replenish sandbars and increases in vegetation cover caused by flow regulation. Campsite area continues to decrease despite the use of controlled floods to rebuild sandbars. We quantify the relative magnitude of factors that contribute to changes in campsite size, such as fluvial deposition and erosion, gullying, and vegetation expansion with analysis of four‐band aerial imagery and digital elevation models. Campsite area declined by 37% between 2002 and 2016 (an average of 161 m 2 per site at long‐term monitoring sites). Two drivers contributed to campsite area change: (a) short‐term gains and losses associated with controlled floods and flood‐deposit erosion and (b) long‐term one‐directional loss of campsite area caused by vegetation encroachment. There was more erosion and slope change at sites in critical reaches—sections of river where campsites are infrequent or in high demand—than in noncritical reaches. Vegetation continues to expand at campsites under flow regulation, particularly in noncritical reaches. Although controlled floods have contributed to short‐term increases in sandbar size, long‐term increases in campsite area have not occurred because of sandbar erosion between controlled floods and vegetation expansion. Manual vegetation removal may need to be considered in future management strategies.

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USGS2016

Relations between rainfall–runoff-induced erosion and aeolian deposition at archaeological sites in a semi-arid dam-controlled river corridor

Process dynamics in fluvial-based dryland environments are highly complex with fluvial, aeolian, and alluvial processes all contributing to landscape change. When anthropogenic activities such as dam-building affect fluvial processes, the complexity in local response can be further increased by flood- and sediment-limiting flows. Understanding these complexities is key to predicting landscape behavior in drylands and has important scientific and management implications, including for studies related to paleoclimatology, landscape ecology evolution, and archaeological site context and preservation. Here we use multi-temporal LiDAR surveys, local weather data, and geomorphological observations to identify trends in site change throughout the 446-km-long semi-arid Colorado River corridor in Grand Canyon, Arizona, USA, where archaeological site degradation related to the effects of upstream dam operation is a concern. Using several site case studies, we show the range of landscape responses that might be expected from concomitant occurrence of dam-controlled fluvial sand bar deposition, aeolian sand transport, and rainfall-induced erosion. Empirical rainfall-erosion threshold analyses coupled with a numerical rainfall–runoff–soil erosion model indicate that infiltration-excess overland flow and gullying govern large-scale (centimeter- to decimeter-scale) landscape changes, but that aeolian deposition can in some cases mitigate gully erosion. Whereas threshold analyses identify the normalized rainfall intensity (defined as the ratio of rainfall intensity to hydraulic conductivity) as the primary factor governing hydrologic-driven erosion, assessment of false positives and false negatives in the dataset highlight topographic slope as the next most important parameter governing site response. Analysis of 4+ years of high resolution (four-minute) weather data and 75+ years of low resolution (daily) climate records indicates that dryland erosion is dependent on short-term, storm-driven rainfall intensity rather than cumulative rainfall, and that erosion can occur outside of wet seasons and even wet years. These results can apply to other similar semi-arid landscapes where process complexity may not be fully understood.

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USGS2014

Gully monitoring at two locations in the Grand Canyon National Park, Arizona, 1996-2010, with emphasis on documenting effects of the March 2008 high-flow experiment

Many archeological sites in the Grand Canyon are being impacted by gully incision. In March 2008, a high-flow experiment (2008 HFE) was conducted with the intention of redistributing fine sediment (sand, silt, and clay) from the bed of the Colorado River to higher elevations along the channel margin. Deposition of fine sediment in gully mouths has been hypothesized to slow gully erosion rates and lessen impacts to archeological sites. The effects of the 2008 HFE on gullies were evaluated by comparing the topographic changes of three gullies at two study sites before and after the 2008 HFE. Comparison results indicated that sediment was deposited in gully mouths during the 2008 HFE, and that the inundated areas nearest to the river can be extensively altered by mainstream flow during high-flow events. Additionally, the history of gully evolution at the two study sites was examined between 1996 and 2010 and indicated that gullies have been subjected to thalweg incision and gully widening processes over a decadal timescale. Although the small sample size precludes extrapolating the results to other gullies, the findings contribute to the understanding of gully erosion in archeologically significant areas and have implications for future monitoring of gully erosion and evaluating the effectiveness of check dams intended to mitigate that erosion at archaeological sites in the Grand Canyon National Park.

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USGS2013

An individual-based model for population viability analysis of humpback chub in Grand Canyon

We developed an individual-based population viability analysis model (females only) for evaluating risk to populations from catastrophic events or conservation and research actions. This model tracks attributes (size, weight, viability, etc.) for individual fish through time and then compiles this information to assess the extinction risk of the population across large numbers of simulation trials. Using a case history for the Little Colorado River population of Humpback Chub Gila cypha in Grand Canyon, Arizona, we assessed extinction risk and resiliency to a catastrophic event for this population and then assessed a series of conservation actions related to removing specific numbers of Humpback Chub at different sizes for conservation purposes, such as translocating individuals to establish other spawning populations or hatchery refuge development. Our results suggested that the Little Colorado River population is generally resilient to a single catastrophic event and also to removals of larvae and juveniles for conservation purposes, including translocations to establish new populations. Our results also suggested that translocation success is dependent on similar survival rates in receiving and donor streams and low emigration rates from recipient streams. In addition, translocating either large numbers of larvae or small numbers of large juveniles has generally an equal likelihood of successful population establishment at similar extinction risk levels to the Little Colorado River donor population. Our model created a transparent platform to consider extinction risk to populations from catastrophe or conservation actions and should prove useful to managers assessing these risks for endangered species such as Humpback Chub.

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