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At least 919 records · Page 51Linked to original sources
USGS2013

User’s guide and reference to Ash3d—A three-dimensional model for Eulerian atmospheric tephra transport and deposition

Ash3d is a three-dimensional Eulerian atmospheric model for tephra transport, dispersal, and deposition to study and forecast hazards of volcanic ash clouds and tephra fall. In this report, we explain how to set up simulations using a web interface, and how to view and interpret model output. We also summarize the architecture of the model and some of its properties.

Open-File Report↗
USGS1974

A program to compute aquifer-response coefficients

An alternating direction technique is used to solve finite difference equations approximating the flow of water in an aquifer. The solutions produce response coefficients relating pumping from wells to drawdowns within those wells. The product of the response coefficient with the pumping values produces a linear algebraic technological function that can be used for integrating hydrologic phenomena into planning and management models.

Open-File Report↗
USGS1996

Documentation of model input and output values for simulation of pumping effects in Paradise Valley, a basin tributary to the Humboldt River, Humboldt County, Nevada

Documentation is provided of model input and sample output used in a previous report for analysis of ground-water flow and simulated pumping scenarios in Paradise Valley, Humboldt County, Nevada.Documentation includes files containing input values and listings of sample output. The files, in American International Standard Code for Information Interchange (ASCII) or binary format, are compressed and put on a 3-1/2-inch diskette. The decompressed files require approximately 8.4 megabytes of disk space on an International Business Machine (IBM)- compatible microcomputer using the MicroSoft Disk Operating System (MS-DOS) operating system version 5.0 or greater.

Open-File Report↗
USGS2017

Streamflow distribution maps for the Cannon River drainage basin, southeast Minnesota, and the St. Louis River drainage basin, northeast Minnesota

Streamflow distribution maps for the Cannon River and St. Louis River drainage basins were developed by the U.S. Geological Survey, in cooperation with the Legislative-Citizen Commission on Minnesota Resources, to illustrate relative and cumulative streamflow distributions. The Cannon River was selected to provide baseline data to assess the effects of potential surficial sand mining, and the St. Louis River was selected to determine the effects of ongoing Mesabi Iron Range mining. Each drainage basin (Cannon, St. Louis) was subdivided into nested drainage basins: the Cannon River was subdivided into 152 nested drainage basins, and the St. Louis River was subdivided into 353 nested drainage basins. For each smaller drainage basin, the estimated volumes of groundwater discharge (as base flow) and surface runoff flowing into all surface-water features were displayed under the following conditions: (1) extreme low-flow conditions, comparable to an exceedance-probability quantile of 0.95; (2) low-flow conditions, comparable to an exceedance-probability quantile of 0.90; (3) a median condition, comparable to an exceedance-probability quantile of 0.50; and (4) a high-flow condition, comparable to an exceedance-probability quantile of 0.02. Streamflow distribution maps were developed using flow-duration curve exceedance-probability quantiles in conjunction with Soil-Water-Balance model outputs; both the flow-duration curve and Soil-Water-Balance models were built upon previously published U.S. Geological Survey reports. The selected streamflow distribution maps provide a proactive water management tool for State cooperators by illustrating flow rates during a range of hydraulic conditions. Furthermore, after the nested drainage basins are highlighted in terms of surface-water flows, the streamflows can be evaluated in the context of meeting specific ecological flows under different flow regimes and potentially assist with decisions regarding groundwater and surface-water appropriations. Presented streamflow distribution maps are foundational work intended to support the development of additional streamflow distribution maps that include statistical constraints on the selected flow conditions.

Minnesota↗
USGS2012

Development of a flood-warning system and flood-inundation mapping in Licking County, Ohio

Digital flood-inundation maps for selected reaches of South Fork Licking River, Raccoon Creek, North Fork Licking River, and the Licking River in Licking County, Ohio, were created by the U.S. Geological Survey (USGS), in cooperation with the Ohio Department of Transportation; U.S. Department of Transportation, Federal Highway Administration; Muskingum Watershed Conservancy District; U.S. Department of Agriculture, Natural Resources Conservation Service; and the City of Newark and Village of Granville, Ohio. The inundation maps depict estimates of the areal extent of flooding corresponding to water levels (stages) at the following USGS streamgages: South Fork Licking River at Heath, Ohio (03145173); Raccoon Creek below Wilson Street at Newark, Ohio (03145534); North Fork Licking River at East Main Street at Newark, Ohio (03146402); and Licking River near Newark, Ohio (03146500). The maps were provided to the National Weather Service (NWS) for incorporation into a Web-based flood-warning system that can be used in conjunction with NWS flood-forecast data to show areas of predicted flood inundation associated with forecasted flood-peak stages. As part of the flood-warning streamflow network, the USGS re-installed one streamgage on North Fork Licking River, and added three new streamgages, one each on North Fork Licking River, South Fork Licking River, and Raccoon Creek. Additionally, the USGS upgraded a lake-level gage on Buckeye Lake. Data from the streamgages and lake-level gage can be used by emergency-management personnel, in conjunction with the flood-inundation maps, to help determine a course of action when flooding is imminent. Flood profiles for selected reaches were prepared by calibrating steady-state step-backwater models to selected, established streamgage rating curves. The step-backwater models then were used to determine water-surface-elevation profiles for up to 10 flood stages at a streamgage with corresponding streamflows ranging from approximately the 50 to 0.2-percent chance annual-exceedance probabilities for each of the 4 streamgages that correspond to the flood-inundation maps. The computed flood profiles were used in combination with digital elevation data to delineate flood-inundation areas. Maps of Licking County showing flood-inundation areas overlain on digital orthophotographs are presented for the selected floods. The USGS also developed an unsteady-flow model for a reach of South Fork Licking River for use by the NWS to enhance their ability to provide advanced flood warning in the region north of Buckeye Lake, Ohio. The unsteady-flow model was calibrated based on data from four flooding events that occurred from June 2008 to December 2011. Model calibration was approximate due to the fact that there were unmeasured inflows to the river that were not able to be considered during the calibration. Information on unmeasured inflow derived from NWS hydrologic models and additional flood-event data could enable the NWS to further refine the unsteady-flow model.

Ohio↗
USGS2013

Two-dimensional simulation of the June 11, 2010, flood of the Little Missouri River at Albert Pike Recreational Area, Ouachita National Forest, Arkansas

In the early morning hours of June 11, 2010, substantial flooding occurred at Albert Pike Recreation Area in the Ouachita National Forest of west-central Arkansas, killing 20 campers. The U.S. Forest Service needed information concerning the extent and depth of flood inundation, the water velocity, and flow paths throughout Albert Pike Recreation Area for the flood and for streamflows corresponding to annual exceedence probabilities of 1 and 2 percent. The two-dimensional flow model Fst2DH, part of the Federal Highway Administration’s Finite Element Surface-water Modeling System, and the graphical user interface Surface-water Modeling System (SMS) were used to perform a steady-state simulation of the flood in a 1.5-mile reach of the Little Missouri River at Albert Pike Recreation Area. Peak streamflows of the Little Missouri River and tributary Brier Creek served as inputs to the simulation, which was calibrated to the surveyed elevations of high-water marks left by the flood and then used to predict flooding that would result from streamflows corresponding to annual exceedence probabilities of 1 and 2 percent. The simulated extent of the June 11, 2010, flood matched the observed extent of flooding at Albert Pike Recreation Area. The mean depth of inundation in the camp areas was 8.5 feet in Area D, 7.4 feet in Area C, 3.8 feet in Areas A, B, and the Day Use Area, and 12.5 feet in Lowry’s Camp Albert Pike. The mean water velocity was 7.2 feet per second in Area D, 7.6 feet per second in Area C, 7.2 feet per second in Areas A, B, and the Day Use Area, and 7.6 feet per second in Lowry’s Camp Albert Pike. A sensitivity analysis indicated that varying the streamflow of the Little Missouri River had the greatest effect on simulated water-surface elevation, while varying the streamflow of tributary Brier Creek had the least effect. Simulated water-surface elevations were lower than those modeled by the U.S. Forest Service using the standard-step method, but the comparison between the two was favorable with a mean absolute difference of 0.58 feet in Area C and 0.32 feet in Area D. Results of a HEC-RAS model of the Little Missouri River watershed upstream from the U.S. Geological Survey streamflow-gaging station near Langley showed no difference in mean depth in the areas in common between the models, and a difference in mean velocity of only 0.5 foot per second. Predictions of flooding that would result from streamflows corresponding to annual exceedence probabilities of 1 and 2 percent indicated that the extent of inundation of the June 11, 2010, flood exceeded that of the 1 percent flood, and that for both the 1 and 2 percent floods, all of Areas C and D, and parts of Areas A, B, and the Day Use Area were inundated. Predicted water-surface elevations for the 1 and 2 percent floods were approximately 1 foot lower than those predicted by the U.S. Forest Service using a standard-step model.

Arkansas↗
USGS2011

Hyperspectral remote sensing of vegetation and agricultural crops: Knowledge gain and knowledge gap after 40 years of research

The focus of this chapter was to summarize the advances made over last 40+ years, as reported in various chapters of this book, in understanding, modeling, and mapping terrestrial vegetation using hyperspectral remote sensing (or imaging spectroscopy) using sensors that are ground-based, truck-mounted, airborne, and spaceborne. As we have seen in various chapters of this book and synthesized in this chapter, the advances made include: (a) significantly improved characterization and modeling of a wide array of biophysical and biochemical properties of vegetation, (b) ability to discriminate plant species and vegetation types with high degree of accuracies (c) reducing uncertainties in determining net primary productivity or carbon assessments from terrestrial vegetation, (d) improved crop productivity and water productivity models, (b), (e) ability to access stress resulting from causes such as management practices, pests and disease, water deficit or excess; , and (f) establishing more sensitive wavebands and indices to detect plant water\moisture content. The advent of spaceborne hyperspectral sensors (e.g., NASA’s Hyperion, ESA’s PROBA, and upcoming NASA’s HyspIRI) and numerous methods and techniques espoused in this book to overcome Hughes phenomenon or data redundancy when handling large volumes of hyperspectral data have generated tremendous interest in advancing our hyperspectral applications knowledge base over larger spatial extent such as region, nation, continent, and globe.

Book chapter↗
USGS1990

The quantification of instream flow rights to water

Energy development of all types continues to grow in the Rocky Mountain Region of the western United States. Federal resource managers increasingly need to balance energy demands, their effects on the natural and human landscape, and public perceptions towards these issues. The Western Energy Citation Clearinghouse (WECC v.1.0), part of a suite of data and information management tools developed and managed by the Wyoming Landscape Conservation Initiative (WLCI), provides resource managers with a searchable online database of citations that covers a broad spectrum of energy and landscape related topics relevant to resource managers, such as energy sources, natural and human landscape effects, and new research, methods and models. Based on the 2011 USGS Open-file Report "Abbreviated bibliography on energy development" (Montag, et al. 2011), WECC is an extensive collection of energy-related citations, as well as categorized lists of additional online resources related to oil and gas development, best practices, energy companies and Federal agencies. WECC incorporates the powerful web services of Sciencebase 2.0, the enterprise data and information platform for USGS scientists and partners, to provide secure, role-based data management features. For example, public/unauthenticated WECC users have full search and read access to the entire energy citation collection, while authenticated WLCI data stewards can manage WECC's citation collection using Sciencebase data management forms.

Book↗
USGS2018

An interim harvest strategy for Taiga Bean geese

In 2016 the AEWA European Goose Management International Working Group (EGM IWG) adopted document AEWA/EGM IWG 1.8 (Johnson et al. 2016), which contained initial elements of an Adaptive Harvest Management programme for Taiga Bean Geese. This report addresses a number of limitations with the population model presented in that document, and provides up-to-date population projections for the Central Management Unit under a range of constant harvest rates. Based on simulations for the 2017-2025 timeframe, median population size was near the median goal of 70,000 in 2019, 2020, and 2021 for harvest rates of birds aged one year or more of 0.00, 0.02, and 0.04, respectively. Simulated population sizes generally increased over the timeframe, albeit with a lot of variation and with the degree of uncertainty increasing over time. With a harvest rate of 0.02, harvests averaged 1,848 (95% CI: 1,403 – 2,492) over the timeframe; a harvest rate of 0.04 produced an average harvest of 3,484 (95% CI: 2,617 – 4,884). Future work for the Central Management Unit will involve development of a dynamic harvest strategy by employing a Markov decision process, in which multiple, possibly competing, management objectives can be addressed.

Conference Paper↗
USGS2020

Geophysical surveys, hydrogeologic characterization, and groundwater flow model for the Truxton basin and Hualapai Plateau, northwestern Arizona

This is the third and final report in a series that describe the groundwater resources of the Hualapai Indian Reservation. These reports document the findings of a comprehensive groundwater study conducted on the reservation and adjacent areas from 2015 through 2018 by the U.S. Geological Survey in cooperation with the Bureau of Reclamation. The first report described the hydrologic framework and characterization of the Truxton aquifer on the Hualapai Indian Reservation (Bills and Macy, 2016). The second report described the hydrogeologic characterization of the Hualapai Plateau part of the reservation (Mason, Macy, and others, 2020). This report includes five chapters. Chapter A (Mason, Knight, and others, 2020) is a summary of this multichapter volume and briefly describes the study area. Chapter B (Mason, Bills, and Macy, 2020) describes the geology and hydrology of the Truxton basin and Hualapai Plateau. Chapter C (Kennedy, 2020) describes the results of a gravity geophysical survey of the Truxton basin. Chapter D (Ball, 2020) describes the findings of an airborne electromagnetic survey of the Truxton aquifer and Hualapai Plateau. Chapter E (Knight, 2020) describes the results of a transient groundwater model created for the entire Truxton aquifer both on and off the reservation. The groundwater-flow model is used to estimate projected groundwater levels based on future groundwater withdrawal scenarios.

Arizona↗
USGS2012

Spectral damping scaling factors for shallow crustal earthquakes in active tectonic regions

Ground motion prediction equations (GMPEs) for elastic response spectra, including the Next Generation Attenuation (NGA) models, are typically developed at a 5% viscous damping ratio. In reality, however, structural and non-structural systems can have damping ratios other than 5%, depending on various factors such as structural types, construction materials, level of ground motion excitations, among others. This report provides the findings of a comprehensive study to develop a new model for a Damping Scaling Factor (DSF) that can be used to adjust the 5% damped spectral ordinates predicted by a GMPE to spectral ordinates with damping ratios between 0.5 to 30%. Using the updated, 2011 version of the NGA database of ground motions recorded in worldwide shallow crustal earthquakes in active tectonic regions (i.e., the NGA-West2 database), dependencies of the DSF on variables including damping ratio, spectral period, moment magnitude, source-to-site distance, duration, and local site conditions are examined. The strong influence of duration is captured by inclusion of both magnitude and distance in the DSF model. Site conditions are found to have less significant influence on DSF and are not included in the model. The proposed model for DSF provides functional forms for the median value and the logarithmic standard deviation of DSF. This model is heteroscedastic, where the variance is a function of the damping ratio. Damping Scaling Factor models are developed for the “average” horizontal ground motion components, i.e., RotD50 and GMRotI50, as well as the vertical component of ground motion.

PEER Report↗
USGS1964

Discharge characteristics of embankment-shaped weirs

An embankment-shaped weir is an embankment overtopped by flood waters. Among the engineering problems frequently resulting from. this occurrence is the need to compute the peak discharge from postflood yield observations. The research described in this. report was concerned with the theoretical and experimental bases for the computation procedure. The research had two main objectives. One was to determine the relationship between embankment form and roughness and some of the more important discharge characteristics. The second was to define, theoretically and experimentally, the relationship between free-flow discharge and the boundary layer on the roadway. The first objective was accomplished with the experimental determination of coefficients of discharge and other significant flow characteristics for a variety of boundary and flow conditions. The second objective was accomplished with the development and experimental verification of a discharge equation which involved the boundary layer displacement thickness. This phase of the research included a general investigation of boundary layer growth on the roadway. It is included that both free- and submerged-flow discharge are virtually independent of the influence of embankment shape and relative height. The influence of boundary resistance is appreciable only for smaller heads. The most practical solution for discharge is one which is based on. the simple weir equation and experimentally determined coefficients. A completely analytical equation of discharge is impractical. The report contains the results of 936 experiments on the discharge characteristics of 17 different models; plus 106 boundary-layer velocity traverses on 4 different models. The data are summarized in both graphical and tabular form.

Water Supply Paper↗
USGS2018

Estimating metal concentrations with regression analysis and water-quality surrogates at nine sites on the Animas and San Juan Rivers, Colorado, New Mexico, and Utah

The purpose of this report is to evaluate the use of site-specific regression models to estimate metal concentrations at nine U.S. Geological Survey streamflow-gaging stations on the Animas and San Juan Rivers in Colorado, New Mexico, and Utah. Downstream users could use these regression models to determine if metal concentrations are elevated and pose a risk to water supplies, agriculture, and recreation. Multiple linear-regression models were developed by relating metal concentrations in discrete water-quality samples to continuously monitored streamflow and surrogate parameters (specific conductance, pH, turbidity, and water temperature) collected at the U.S. Geological Survey stations. Models were developed for dissolved and total concentrations of aluminum, arsenic, cadmium, copper, iron, lead, manganese, and zinc using water-quality samples collected from 2005 to 2017 by several Federal, State, Tribal, and local agencies using different collection methods and analytical laboratories. Model performance varied but, in general, models for dissolved metals did not perform as well as those for total metals. Dissolved metals generally were correlated to specific conductance or streamflow and total metals generally were better correlated with turbidity. Explanatory variables in the models reflected hydrologic and geochemical processes within the basin. A larger number of regression models were statistically significant for the most upstream sites, where metal concentrations were elevated by drainage from abandoned mines and mineralized bedrock. Models generally did not perform as well at downstream sites, especially for dissolved metals, which occurred at lower concentrations than at the upstream sites. In the lower reaches of the rivers, the input of more alkaline water from tributaries and groundwater reduced metal solubility and diluted metal concentrations. The number and distribution of samples in the calibration datasets also may have been a factor in model development. At some sites on the San Juan River, calibration datasets were more limited and did not represent the full range of observed hydrologic and water-quality conditions, especially during storm events in summer and fall. Recommendations for model use are given based on estimates of model precision, biases, and adequacy of the calibration datasets in terms of the number of samples and representativeness of the observed range of streamflow and water-quality conditions.

Colorado, New Mexico, Utah↗
USGS2016

Science information to support Missouri River Scaphirhynchus albus (pallid sturgeon) effects analysis

The Missouri River Pallid Sturgeon Effects Analysis (EA) was commissioned by the U.S. Army Corps of Engineers to develop a foundation of understanding of how pallid sturgeon ( Scaphirhynchus albus ) population dynamics are linked to management actions in the Missouri River. The EA consists of several steps: (1) development of comprehensive, conceptual ecological models illustrating pallid sturgeon population dynamics and links to management actions and other drivers; (2) compilation and assessment of available scientific literature, databases, and models; (3) development of predictive, quantitative models to explore the system dynamics and population responses to management actions; and (4) analysis and assessment of effects of system operations and actions on species’ habitats and populations. This report addresses the second objective, compilation and assessment of relevant information. Scientific information on pallid sturgeon and its environment has grown substantially during the last decade. Presently available (2015) information indicates that stocked sturgeon are surviving and growing, and that wild and hatchery sturgeon are spawning in the wild. However, natural recruitment to age-1 and older has not been detected since systematic sampling began in 2005. Population models indicate the sensitivity of population growth to certain demographic variables, in particular early-life stage survival and perhaps adult fecundity. This report documents the existing population models for the pallid sturgeon, and the substantial quantities of information developed through the Pallid Sturgeon Population Assessment Program (PSPAP), the Habitat Assessment and Monitoring Program (HAMP), the Comprehensive Sturgeon Research Project (CSRP), range-wide genetics databases, and related research studies. The reference database compiled for the EA consists of over 190 peer-reviewed documents specifically related to pallid sturgeon and over 12,000 references on the Missouri River system and related species. Notwithstanding the large quantity of information available, the EA faces challenges in synthesizing the information into useful, quantitative models. In particular, critical demographic parameters for population models remain uncertain and the functional relationships between the two main categories of physical management action—changes in flow regime and reengineering channel form—and pallid sturgeon survival responses are obscure. In addition, there is an overarching uncertainty about how physical management actions interact with propagation management actions in view of evolving understanding of genetic structuring of the pallid sturgeon population. Synthesis efforts are also challenged by the fragmentation of information sources among projects and agencies; one objective of this report is to facilitate future assessments by providing documentation of what information is available and where.

Iowa, Kansas, Missouri, Montana, Nebraska, North D↗
USGS2014

Hydrostratigraphic interpretation of test-hole and borehole geophysical data, Kimball, Cheyenne, and Deuel Counties, Nebraska, 2011-12

Recently (2004) adopted legislation in Nebraska requires a sustainable balance between long-term supplies and uses of surface-water and groundwater and requires Natural Resources Districts to understand the effect of groundwater use on surface-water systems when developing a groundwater-management plan. The South Platte Natural Resources District (SPNRD) is located in the southern Nebraska Panhandle and overlies the nationally important High Plains aquifer. Declines in water levels have been documented, and more stringent regulations have been enacted to ensure the supply of ground-water will be sufficient to meet the needs of future generations. Because an improved understanding of the hydrogeologic characteristics of this aquifer system is needed to ensure sustainability of groundwater withdrawals, the U.S. Geological Survey, in cooperation with the SPNRD, Conservation and Survey Division of the University of Nebraska-Lincoln, and the Nebraska Environmental Trust, began a hydrogeologic study of the SPNRD to describe the lithology and thickness of the High Plains aquifer. This report documents these characteristics at 29 new test holes, 28 of which were drilled to the base of the High Plains aquifer. Herein the High Plains aquifer is considered to include all hydrologically connected units of Tertiary and Quaternary age. The depth to the base of aquifer was interpreted to range from 37 to 610 feet in 28 of the 29 test holes. At some locations, particularly northern Kimball County, the base-of-aquifer surface was difficult to interpret from drill cutting samples and borehole geophysical logs. The depth to the base of aquifer determined for test holes drilled for this report was compared with the base-of-aquifer surface interpreted by previous researchers. In general, there were greater differences between the base-of-aquifer elevation reported herein and those in previous studies for areas north of Lodgepole Creek compared to areas south of Lodgepole Creek. The largest difference was at test hole 5-SP-11, where an Ogallala-filled paleovalley prevously had been interpreted based on relatively sparse test-hole data west of 5-SP-11. The base of aquifer near test hole 5-SP-11 reported herein is approximately 230 ft higher in elevation than previously interpreted. Among other test holes that are likely to have been drilled in Ogallala-filled paleovalleys, the greatest difference in the interpreted base of aquifer was for test hole 7-CC-11, northeast of Potter, Nebraska, where the base of aquifer is 180 feet deeper than previously interpreted. Interpretation of test-hole and borehole geophysical data for 29 additional test holes will improve resource managers’ understanding of the hydrogeologic characteristics, including aquifer thickness. Aquifer thickness, which is related to total water in storage, is not well quantified in the north and south tablelands. The additional hydrostratigraphic interpretations provided in this report will improve the hydrogeologic framework used in current (2014) and future groundwater models, which are the basis for many water-management decisions.

Nebraska↗
USGS2014

Age, chemistry, and correlations of Neoproterozoic–Devonian igneous rocks of the Arctic Alaska–Chukotka terrane: An overview with new U-Pb ages

The Arctic Alaska–Chukotka terrane is a microcontinent with an origin exotic to Laurentia. We used a sensitive high-resolution ion microprobe (SHRIMP) to date nine samples of Neoproterozoic rock and five samples of Devonian rock from the Brooks Range and Seward Peninsula of Alaska and from the Chukotka Peninsula of northeastern Russia. Felsic magmatism occurred at 968 Ma and 742 Ma in the Brooks Range and at 865 Ma and 670–666 Ma on Seward Peninsula. Felsic igneous rocks in Chukotka were dated at 656 Ma and 574 Ma. Devonian igneous rocks are found throughout the Arctic Alaska–Chukotka terrane, and we dated samples with ages of 391 Ma, 390 Ma, 385 Ma, 371 Ma, and 363 Ma. The felsic character of the Neoproterozoic rocks suggests formation at least in part through crustal melting. The age of the crustal source rocks that melted to form the Neoproterozoic rocks is inferred to be Mesoproterozoic based on Nd model ages ranging from 1.6 to 1.4 Ga. Rocks of this age range have been reported from the basement of Baltica but are rare in Laurentia. The 565 Ma orthogneisses on Seward Peninsula have ca. 1.1 Ga Nd model ages. Devonian igneous rocks have a wide range of model ages ranging from 1.6 to 0.8 Ga. The tectonic setting of the 968 Ma, 865 Ma, and 742 Ma rocks is unknown. The ca. 670 Ma magmatism on Seward Peninsula is interpreted to have occurred in an arc setting based on geochemistry and similarities in their ages to the Avalonian–Cadomian arc system peripheral to Gondwana. Latest Neoproterozoic magmatism is inferred to have occurred in a rift setting based on composition and the Paleozoic passive margin sequence that was deposited across the Arctic Alaska–Chukokta terrane. Devonian magmatism likely occurred in an arc and/or backarc rift setting. Significant uncertainties remain concerning the age of the Arctic Alaska–Chukotka terrane basement, particularly the age of the host rocks for Neoproterozoic intrusions.

Alaska↗
USGS1998

Implementation of the century ecosystem model for an eroding hillslope in Mississippi

The objective of this study was to parameterize and implement the Century ecosystem model for an eroding, cultivated site near Senatobia, in Panola County, Mississippi, in order to understand the loss and replacement of soil organic carbon on an eroding cropland. The sites chosen for this study are located on highly eroded loess soils where USDA has conducted studies on rates of soil erosion. We used USDA sediment data from the study site and historical erosion estimates from the nearby area as model input for soil loss; in addition, inputs for parametization include particle-size data, climate data, and rainfall/runoff data that were collected and reported in companion papers. A cropping scenario was implemented to simulate a research site at the USDA watershed 2 at the Nelson Farm. Model output was compiled for comparison with data collected and reported in companion reports; interpretive comparisons are reported in Harden et al, in press.

Open-File Report↗
USGS2004

Simulation of ground-water flow in glaciofluvial aquifers in the Grand Rapids area, Minnesota

A calibrated steady-state, finite-difference, ground-waterflow model was constructed to simulate ground-water flow in three glaciofluvial aquifers, defined in this report as the upper, middle, and lower aquifers, in an area of about 114 mi2 surrounding the city of Grand Rapids in north-central Minnesota. The calibrated model will be used by Minnesota Department of Health and communities in the Grand Rapids area in the development of wellhead protection plans for their water supplies. The model was calibrated through comparison of simulated ground-water levels to measured static water levels in 351 wells, and comparison of simulated base-flow rates to estimated base-flow rates for reaches of the Mississippi and Prairie Rivers. Model statistics indicate that the model tends to overestimate ground-water levels. The root mean square errors ranged from +12.83 ft in wells completed in the upper aquifer to +19.10 ft in wells completed in the middle aquifer. Mean absolute differences between simulated and measured water levels ranged from +4.43 ft for wells completed in the upper aquifer to +9.25 ft for wells completed in the middle aquifer. Mean algebraic differences ranged from +9.35 ft for wells completed in the upper aquifer to +14.44 ft for wells completed in the middle aquifer, with the positive differences indicating that the simulated water levels were higher than the measured water levels. Percentage errors between simulated and estimated base-flow rates for the three monitored reaches all were less than 10 percent, indicating good agreement. Simulated ground-water levels were most sensitive to changes in general-head boundary conductance, indicating that this characteristic is the predominant model input variable controlling steady-state water-level conditions. Simulated groundwater flow to stream reaches was most sensitive to changes in horizontal hydraulic conductivity, indicating that this characteristic is the predominant model input variable controlling steady-state flow conditions.

Minnesota↗