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At least 379 records · Page 21Linked to original sources
USGS2002

Borehole velocity measurements at five sites that recorded the Cape Mendocino, California earthquake of 25 April, 1992

The U.S. Geological Survey (USGS), as part of an ongoing program to acquire seismic velocity and geologic data at locations that recorded strong-ground motions during earthquakes, has investigated five sites in the Fortuna, California region (Figure 1). We selected drill sites at strong-motion stations that recorded high accelerations (Table 1) from the Cape Mendocino earthquake (M 7.0) of 25 April 1992 (Oppenheimer et al., 1993). The boreholes were drilled to a nominal depth of 95 meters (310 ft) and cased with schedule 80 pvc-casing grouted in place at each location. S-wave and P-wave data were acquired at each site using a surface source and a borehole three-component geophone. This report contains the velocity models interpreted from the borehole data and gives reference to locations and peak accelerations at the selected strong-motion stations.

California↗
USGS2008

Mapping "old" versus "young" piñon-juniper stands with a predictive topo-climatic model in north-central New Mexico, USA

Piñon pine and juniper woodlands in the southwestern United States are often represented as an expanding and even invasive vegetation type, a legacy of historic grazing, and culpable in the degradation of western rangelands. A long-standing emphasis on forage production, in combination with recent hazard fuel concerns, has prompted a new era of woodland management with stated restoration objectives. Yet the extent and dynamics of piñon–juniper communities that predate intensive Euro-American settlement activities are poorly known or understood, while the intrinsic ecological, aesthetic, and economic values of old-growth woodlands are often overlooked. Historical changes in piñon–juniper stands include two related, but poorly differentiated processes: recent tree expansion into grass- or shrub-dominated (i.e., non-woodland) vegetation and thickening or infilling of savanna or mosaic woodlands predating settlement. Our work addresses the expansion pattern, modeling the occurrence of “older” savanna and woodland stands extant prior to 1850 in contrast to “younger” piñon–juniper growth of more recent, postsettlement origin. We present criteria in the form of a diagnostic key for distinguishing “older,” pre-Euro-American settlement piñon–juniper from “younger” (post-1850) stands and report results of predictive modeling and mapping efforts within a north-central New Mexico study area. Selected models suggest a primary role for soil moisture in the current distribution of “old” vs. “young” piñon–juniper stands. Presettlement era woodlands are shown to occupy a discrete ecological space, defined by the interaction of effective (seasonal) moisture with landform setting and fine-scale (soil/water) depositional patterns. “Older” stands are generally found at higher elevations or on skeletal soils in upland settings, while “younger” stands (often dominated by one-seed juniper, Juniperus monosperma ) are most common at lower elevations or in productive, depositional settings. Modeling at broad regional scales can enhance our general understanding of piñon–juniper ecology, while predictive mapping of local areas has potential to provide products useful for land management. Areas of the southwestern United States with strong monsoonal (summer moisture) patterns appear to have been the most susceptible to historical woodland expansion, but even here the great majority of extant piñon–juniper has presettlement origins (although widely thickened and infilled historically), and old-growth structure is not uncommon in appropriate upland settings.

Ecological Applications↗
USGS2012

Conceptual and numerical models of the glacial aquifer system north of Aberdeen, South Dakota

This U.S. Geological Survey report documents a conceptual and numerical model of the glacial aquifer system north of Aberdeen, South Dakota, that can be used to evaluate and manage the city of Aberdeen's water resources. The glacial aquifer system in the model area includes the Elm, Middle James, and Deep James aquifers, with intervening confining units composed of glacial till. The Elm aquifer ranged in thickness from less than 1 to about 95 feet (ft), with an average thickness of about 24 ft; the Middle James aquifer ranged in thickness from less than 1 to 91 ft, with an average thickness of 13 ft; and the Deep James aquifer ranged in thickness from less than 1 to 165 ft, with an average thickness of 23 ft. The confining units between the aquifers consisted of glacial till and ranged in thickness from 0 to 280 ft. The general direction of groundwater flow in the Elm aquifer in the model area was from northwest to southeast following the topography. Groundwater flow in the Middle James aquifer was to the southeast. Sparse data indicated a fairly flat potentiometric surface for the Deep James aquifer. Horizontal hydraulic conductivity for the Elm aquifer determined from aquifer tests ranged from 97 to 418 feet per day (ft/d), and a confined storage coefficient was determined to be 2.4x10 -5 . Estimates of the vertical hydraulic conductivity of the sediments separating the Elm River from the Elm aquifer, determined from the analysis of temperature gradients, ranged from 0.14 to 2.48 ft/d. Average annual precipitation in the model area was 19.6 inches per year (in/yr), and agriculture was the primary land use. Recharge to the Elm aquifer was by infiltration of precipitation through overlying outwash, lake sediments, and glacial till. The annual recharge for the model area, calculated by using a soil-water-balance method for water year (WY) 1975-2009, ranged from 0.028 inch in WY 1980 to 4.52 inches in WY 1986, with a mean of 1.56 inches. The annual potential evapotranspiration, calculated in soil-water-balance analysis, ranged from 21.8 inches in WY 1983 to 27.0 inches in WY 1985, with a mean of 24.6 inches. Water use from the glacial aquifer system primarily was from the Elm aquifer for irrigation, municipal, and suburban water supplies, and the annual rate ranged from 1.0 to 2.4 cubic feet per second (ft 3 /s). The MODFLOW-2005 numerical model represented the Elm aquifer, the Middle James aquifer, and the Deep James aquifer with model layers 1-3 respectively separated by confining layers 1-2 respectively. Groundwater flow was simulated with 75 stress periods beginning October 1, 1974, and ending September 30, 2009. Model grid spacing was 200 by 200 ft and boundaries were represented by specified-head boundaries and no-flow boundaries. The model used parameter estimation that focused on minimizing the difference between 954 observed and simulated hydraulic heads for 135 wells. Calibrated mean horizontal hydraulic conductivity values for model layers 1-3 were 94, 41, and 30 ft/d respectively. Vertical hydraulic conductivity values for confining layers 1 and 2 were 0.0002 and 0.0003 ft/d, respectively. Calibrated specific yield for model layer 1was 0.1 and specific storage ranged from 0.0003 to 0.0005 per foot. Calibrated mean recharge rates ranged from 2.5 in/yr where glacial till thickness was less than 10 ft to 0.8 in/yr where glacial till thickness was greater than 30 ft. Calibrated mean annual evapotranspiration rate was 8.8 in/yr. Simulated net streamflow gain from model layer 1 was 3.1 ft 3 /s.

South Dakota↗
USGS2002

Simulation of a proposed emergency outlet from Devils Lake, North Dakota

From 1993 to 2001, Devils Lake rose more than 25 feet, flooding farmland, roads, and structures around the lake and causing more than $400 million in damages in the Devils Lake Basin. In July 2001, the level of Devils Lake was at 1,448.0 feet above sea level 1 , which was the highest lake level in more than 160 years. The lake could continue to rise to several feet above its natural spill elevation to the Sheyenne River (1,459 feet above sea level) in future years, causing extensive additional flooding in the basin and, in the event of an uncontrolled natural spill, downstream in the Red River of the North Basin as well. The outlet simulation model described in this report was developed to determine the potential effects of various outlet alternatives on the future lake levels and water quality of Devils Lake. Lake levels of Devils Lake are controlled largely by precipitation on the lake surface, evaporation from the lake surface, and surface inflow. For this study, a monthly water-balance model was developed to compute the change in total volume of Devils Lake, and a regression model was used to estimate monthly water-balance data on the basis of limited recorded data. Estimated coefficients for the regression model indicated fitted precipitation on the lake surface was greater than measured precipitation in most months, fitted evaporation from the lake surface was less than estimated evaporation in most months, and ungaged inflow was about 2 percent of gaged inflow in most months. Dissolved sulfate was considered to be the key water-quality constituent for evaluating the effects of a proposed outlet on downstream water quality. Because large differences in sulfate concentrations existed among the various bays of Devils Lake, monthly water-balance data were used to develop detailed water and sulfate mass-balance models to compute changes in sulfate load for each of six major storage compartments in response to precipitation, evaporation, inflow, and outflow from each compartment. The storage compartments--five for Devils Lake and one for Stump Lake--were connected by bridge openings, culverts, or natural channels that restricted mixing between compartments. A numerical algorithm was developed to calculate inflow and outflow from each compartment. Sulfate loads for the storage compartments first were calculated using the assumptions that no interaction occurred between the bottom sediments and the water column and no wind- or buoyancy-induced mixing occurred between compartments. However, because the fitted sulfate loads did not agree with the estimated sulfate loads, which were obtained from recorded sulfate concentrations, components were added to the sulfate mass-balance model to account for the flux of sulfate between bottom sediments and the lake and for mixing between storage compartments. Mixing between compartments can occur during periods of open water because of wind and during periods of ice cover because of water-density differences between compartments. Sulfate loads calculated using the sulfate mass-balance model with sediment interaction and mixing between compartments closely matched sulfate loads computed from historical concentrations. The water and sulfate mass-balance models were used to calculate potential future lake levels and sulfate concentrations for Devils Lake and Stump Lake given potential future values of monthly precipitation, evaporation, and inflow. Potential future inputs were generated using a scenario approach and a stochastic approach. In the scenario approach, historical values of precipitation, evaporation, and inflow were repeated in the future for a particular sequence of historical years. In the stochastic approach, a statistical time-series model was developed to randomly generate potential future inputs. The scenario approach was used to evaluate the effectiveness of various outlet alternatives, and the stochastic approach was used to evaluate the hydrologic and water-quality effects of the potential outlet alternatives that were selected on the basis of the scenario analysis. Given potential future lake levels and sulfate concentrations generated using either the scenario or stochastic approach and potential future ambient flows and sulfate concentrations for the Sheyenne River receiving waters, daily outlet discharges could be calculated for virtually any outlet alternative. For the scenario approach, future ambient flows and sulfate concentrations for the Sheyenne River were generated using the same sequence of years used for generating water-balance data for Devils Lake. For the stochastic approach, a procedure was developed for generating daily Sheyenne River flows and sulfate concentrations that were "in-phase" with the generated water-balance data for Devils Lake. Simulation results for the scenario approach indicated that neither of the West Bay outlet alternatives provided effective flood-damage reduction without exceeding downstream water-quality constraints. However, both Pelican Lake outlet alternatives provided significant flood-damage reduction with only minor downstream water-quality changes. The most effective alternative for controlling rising lake levels was a Pelican Lake outlet with a 480-cubic-foot-per-second pump capacity and a 250-milligram-per-liter downstream sulfate constraint. However, this plan is costly because of the high pump capacity and the requirement of a control structure on Highway 19 to control the level of Pelican Lake. A less costly, though less effective for flood-damage reduction, plan is a Pelican Lake outlet with a 300-cubic-foot-per-second pump capacity and a 250-milligram-per-liter downstream sulfate constraint. The plan is less costly because the pump capacity is smaller and because the control structure on Highway 19 is not required. The less costly Pelican Lake alternative with a 450-milligramper- liter downstream sulfate constraint rather than a 250-milligram-per-liter downstream sulfate constraint was identified by the U.S. Army Corps of Engineers as the preferred alternative for detailed design and engineering analysis. Simulation results for the stochastic approach indicated that the geologic history of lake-level fluctuations of Devils Lake for the past 2,500 years was consistent with a climatic history that consisted of two climate states--a wet state, similar to conditions during 1980-99, and a normal state, similar to conditions during 1950-78. The transition times between the wet and normal climatic periods occurred randomly. The average duration of the wet climatic periods was 20 years, and the average duration of the normal climatic periods was 120 years. The stochastic approach was used to generate 10,000 independent sequences of lake levels and sulfate concentrations for Devils Lake for water years 2001-50. Each trace began with the same starting conditions, and the duration of the current wet cycle was generated randomly for each trace. Each trace was generated for the baseline (natural) condition and for the Pelican Lake outlet with a 300-cubic-foot-per-second pump capacity and a 450-milligram-per-liter downstream sulfate constraint. The outlet significantly lowered the probabilities of future lake-level increases within the next 50 years and did not substantially increase the probabilities of reaching low lake levels or poor water-quality conditions during the same period.

Water-Resources Investigations Report↗
USGS2006

Evaluation of the ground-water flow model for northern Utah Valley, Utah, updated to conditions through 2002

This report evaluates the performance of a numerical model of the ground-water system in northern Utah Valley, Utah, that originally simulated ground-water conditions during 1947-1980 and was updated to include conditions estimated for 1981-2002. Estimates of annual recharge to the ground-water system and discharge from wells in the area were added to the original ground-water flow model of the area. The files used in the original transient-state model of the ground-water flow system in northern Utah Valley were imported into MODFLOW-96, an updated version of MODFLOW. The main model input files modified as part of this effort were the well and recharge files. Discharge from pumping wells in northern Utah Valley was estimated on an annual basis for 1981-2002. Although the amount of average annual withdrawals from wells has not changed much since the previous study, there have been changes in the distribution of well discharge in the area. Discharge estimates for flowing wells during 1981-2002 were assumed to be the same as those used in the last stress period of the original model because of a lack of new data. Variations in annual recharge were assumed to be proportional to changes in total surface-water inflow to northern Utah Valley. Recharge specified in the model during the additional stress periods varied from 255,000 acre-feet in 1986 to 137,000 acre-feet in 1992. The ability of the updated transient-state model to match hydrologic conditions determined for 1981-2002 was evaluated by comparing water-level changes measured in wells to those computed by the model. Water-level measurements made in February, March, or April were available for 39 wells in the modeled area during all or part of 1981-2003. In most cases, the magnitude and direction of annual water-level change from 1981 to 2002 simulated by the updated model reasonably matched the measured change. The greater-than-normal precipitation that occurred during 1982-84 resulted in period-of-record high water levels measured in many of the observation wells in March 1984. The model-computed water levels at the end of 1982-84 also are among the highest for the period. Both measured and computed water levels decreased during the period representing ground-water conditions from 1999 to 2002. Precipitation was less than normal during 1999-2002. The ability of the model to adequately simulate climatic extremes such as the wetter-than-normal conditions of 1982-84 and the drier-than-normal conditions of 1999-2002 indicates that the annual variation of recharge to the ground-water system based on streamflow entering the valley, which in turn is primarily dependent upon precipitation, is appropriate but can be improved. The updated transient-state model of the ground-water system in northern Utah Valley can be improved by making revisions on the basis of currently available data and information.

Utah↗
USGS2022

Simulation of heat flow in a synthetic watershed: Lags and dampening across multiple pathways under a climate-forcing scenario

Although there is widespread agreement that future climates tend toward warming, the response of aquatic ecosystems to that warming is not well understood. This work, a continuation of companion research, explores the role of distinct watershed pathways in lagging and dampening climate-change signals. It subjects a synthetic flow and transport model to a 30-year warming signal based on climate projections, quantifying the heat breakthrough on a monthly time step along connected pathways. The system corresponds to a temperate watershed roughly 27 km on a side and consists of (a) land-surface processes of overland flow, (b) infiltration through an unsaturated zone (UZ) above an unconfined sandy aquifer overlying impermeable bedrock, and (c) groundwater flow along shallow and deep pathlines that converge as discharge to a surface-water network. Numerical simulations show that about 40% of the warming applied to watershed infiltration arrives at the water table and that the UZ stores a large fraction of the upward-trending heat signal. Additionally, once groundwater reaches the surface-water network after traveling through the saturated zone, only about 10% of the original warm-up signal is returned to streams by discharge. However, increases in the simulated streamflow temperatures are of similar magnitude to increases at the water table, due to the addition of heat by storm runoff, which bypasses UZ and groundwater storage and counteracts subsurface dampening. The synthetic modeling method and tentative findings reported here provide a potential workflow for real-world applications of climate-change modeling at the full watershed scale.

Water↗
USGS2005

MODFLOW-2005 : the U.S. Geological Survey modular ground-water model--the ground-water flow process

This report presents MODFLOW-2005, which is a new version of the finite-difference ground-water model commonly called MODFLOW. Ground-water flow is simulated using a block-centered finite-difference approach. Layers can be simulated as confined or unconfined. Flow associated with external stresses, such as wells, areal recharge, evapotranspiration, drains, and rivers, also can be simulated. The report includes detailed explanations of physical and mathematical concepts on which the model is based, an explanation of how those concepts are incorporated in the modular structure of the computer program, instructions for using the model, and details of the computer code. The modular structure consists of a MAIN Program and a series of highly independent subroutines. The subroutines are grouped into 'packages.' Each package deals with a specific feature of the hydrologic system that is to be simulated, such as flow from rivers or flow into drains, or with a specific method of solving the set of simultaneous equations resulting from the finite-difference method. Several solution methods are incorporated, including the Preconditioned Conjugate-Gradient method. The division of the program into packages permits the user to examine specific hydrologic features of the model independently. This also facilitates development of additional capabilities because new packages can be added to the program without modifying the existing packages. The input and output systems of the computer program also are designed to permit maximum flexibility. The program is designed to allow other capabilities, such as transport and optimization, to be incorporated, but this report is limited to describing the ground-water flow capability. The program is written in Fortran 90 and will run without modification on most computers that have a Fortran 90 compiler.

Techniques and Methods↗
USGS1998

Application of nonlinear-regression methods to a ground-water flow model of the Albuquerque Basin, New Mexico

This report documents the application of nonlinear-regression methods to a numerical model of ground-water flow in the Albuquerque Basin, New Mexico. In the Albuquerque Basin, ground water is the primary source for most water uses. Ground-water withdrawal has steadily increased since the 1940's, resulting in large declines in water levels in the Albuquerque area. A ground-water flow model was developed in 1994 and revised and updated in 1995 for the purpose of managing basin ground- water resources. In the work presented here, nonlinear-regression methods were applied to a modified version of the previous flow model. Goals of this work were to use regression methods to calibrate the model with each of six different configurations of the basin subsurface and to assess and compare optimal parameter estimates, model fit, and model error among the resulting calibrations. The Albuquerque Basin is one in a series of north trending structural basins within the Rio Grande Rift, a region of Cenozoic crustal extension. Mountains, uplifts, and fault zones bound the basin, and rock units within the basin include pre-Santa Fe Group deposits, Tertiary Santa Fe Group basin fill, and post-Santa Fe Group volcanics and sediments. The Santa Fe Group is greater than 14,000 feet (ft) thick in the central part of the basin. During deposition of the Santa Fe Group, crustal extension resulted in development of north trending normal faults with vertical displacements of as much as 30,000 ft. Ground-water flow in the Albuquerque Basin occurs primarily in the Santa Fe Group and post-Santa Fe Group deposits. Water flows between the ground-water system and surface-water bodies in the inner valley of the basin, where the Rio Grande, a network of interconnected canals and drains, and Cochiti Reservoir are located. Recharge to the ground-water flow system occurs as infiltration of precipitation along mountain fronts and infiltration of stream water along tributaries to the Rio Grande; subsurface flow from adjacent regions; irrigation and septic field seepage; and leakage through the Rio Grande, canal, and Cochiti Reservoir beds. Ground water is discharged from the basin by withdrawal; evapotranspiration; subsurface flow; and flow to the Rio Grande, canals, and drains. The transient, three-dimensional numerical model of ground-water flow to which nonlinear-regression methods were applied simulates flow in the Albuquerque Basin from 1900 to March 1995. Six different basin subsurface configurations are considered in the model. These configurations are designed to test the effects of (1) varying the simulated basin thickness, (2) including a hypothesized hydrogeologic unit with large hydraulic conductivity in the western part of the basin (the west basin high-K zone), and (3) substantially lowering the simulated hydraulic conductivity of a fault in the western part of the basin (the low-K fault zone). The model with each of the subsurface configurations was calibrated using a nonlinear least- squares regression technique. The calibration data set includes 802 hydraulic-head measurements that provide broad spatial and temporal coverage of basin conditions, and one measurement of net flow from the Rio Grande and drains to the ground-water system in the Albuquerque area. Data are weighted on the basis of estimates of the standard deviations of measurement errors. The 10 to 12 parameters to which the calibration data as a whole are generally most sensitive were estimated by nonlinear regression, whereas the remaining model parameter values were specified. Results of model calibration indicate that the optimal parameter estimates as a whole are most reasonable in calibrations of the model with with configurations 3 (which contains 1,600-ft-thick basin deposits and the west basin high-K zone), 4 (which contains 5,000-ft-thick basin de

New Mexico↗
USGS2011

Adjustment of pesticide concentrations for temporal changes in analytical recovery, 1992–2010

Recovery is the proportion of a target analyte that is quantified by an analytical method and is a primary indicator of the analytical bias of a measurement. Recovery is measured by analysis of quality-control (QC) water samples that have known amounts of target analytes added ("spiked" QC samples). For pesticides, recovery is the measured amount of pesticide in the spiked QC sample expressed as a percentage of the amount spiked, ideally 100 percent. Temporal changes in recovery have the potential to adversely affect time-trend analysis of pesticide concentrations by introducing trends in apparent environmental concentrations that are caused by trends in performance of the analytical method rather than by trends in pesticide use or other environmental conditions. This report presents data and models related to the recovery of 44 pesticides and 8 pesticide degradates (hereafter referred to as "pesticides") that were selected for a national analysis of time trends in pesticide concentrations in streams. Water samples were analyzed for these pesticides from 1992 through 2010 by gas chromatography/mass spectrometry. Recovery was measured by analysis of pesticide-spiked QC water samples. Models of recovery, based on robust, locally weighted scatterplot smooths (lowess smooths) of matrix spikes, were developed separately for groundwater and stream-water samples. The models of recovery can be used to adjust concentrations of pesticides measured in groundwater or stream-water samples to 100 percent recovery to compensate for temporal changes in the performance (bias) of the analytical method.

Data Series↗
USGS2008

Simulations of Ground-Water Flow, Transport, Age, and Particle Tracking near York, Nebraska, for a Study of Transport of Anthropogenic and Natural Contaminants (TANC) to Public-Supply Wells

Contamination of public-supply wells has resulted in public-health threats and negative economic effects for communities that must treat contaminated water or find alternative water supplies. To investigate factors controlling vulnerability of public-supply wells to anthropogenic and natural contaminants using consistent and systematic data collected in a variety of principal aquifer settings in the United States, a study of Transport of Anthropogenic and Natural Contaminants to public-supply wells was begun in 2001 as part of the U.S. Geological Survey National Water-Quality Assessment Program. The area simulated by the ground-water flow model described in this report was selected for a study of processes influencing contaminant distribution and transport along the direction of ground-water flow towards a public-supply well in southeastern York, Nebraska. Ground-water flow is simulated for a 60-year period from September 1, 1944, to August 31, 2004. Steady-state conditions are simulated prior to September 1, 1944, and represent conditions prior to use of ground water for irrigation. Irrigation, municipal, and industrial wells were simulated using the Multi-Node Well package of the modular three-dimensional ground-water flow model code, MODFLOW-2000, which allows simulation of flow and solutes through wells that are simulated in multiple nodes or layers. Ground-water flow, age, and transport of selected tracers were simulated using the Ground-Water Transport process of MODFLOW-2000. Simulated ground-water age was compared to interpreted ground-water age in six monitoring wells in the unconfined aquifer. The tracer chlorofluorocarbon-11 was simulated directly using Ground-Water Transport for comparison with concentrations measured in six monitoring wells and one public supply well screened in the upper confined aquifer. Three alternative model simulations indicate that simulation results are highly sensitive to the distribution of multilayer well bores where leakage can occur and that the calibrated model resulted in smaller differences than the alternative models between simulated and interpreted ages and measured tracer concentrations in most, but not all, wells. Results of the first alternative model indicate that the distribution of young water in the upper confined aquifer is substantially different when well-bore leakage at known abandoned wells and test holes is removed from the model. In the second alternative model, simulated age near the bottom of the unconfined aquifer was younger than interpreted ages and simulated chlorofluorocarbon-11 concentrations in the upper confined aquifer were zero in five out of six wells because the conventional Well Package fails to account for flow between model layers though well bores. The third alternative model produced differences between simulated and interpreted ground-water ages and measured chlorofluorocarbon-11 concentrations that were comparable to the calibrated model. However, simulated hydraulic heads deviated from measured hydraulic heads by a greater amount than for the calibrated model. Even so, because the third alternative model simulates steady-state flow, additional analysis was possible using steady-state particle tracking to assess the contributing recharge area to a public supply well selected for analysis of factors contributing to well vulnerability. Results from particle-tracking software (MODPATH) using the third alternative model indicates that the contributing recharge area of the study public-supply well is a composite of elongated, seemingly isolated areas associated with wells that are screened in multiple aquifers. The simulated age distribution of particles at the study public-supply well indicates that all water younger than 58 years travels through well bores of wells screened in multiple aquifers. The age distribution from the steady-state model using MODPATH estimates the youngest 7 percent of the water to have a flow-weighted mean age

Scientific Investigations Report↗
USGS1983

Calculation of amorphous silica solubilities at 25° to 300°C and apparent cation hydration numbers in aqueous salt solutions using the concept of effective density of water

The solubility of amorphous silica in aqueous salt solutions at 25° to 300°C can be calculated using information on its solubility in pure water and a model in which the activity of water in the salt solution is defined to equal the effective density. p e , of “free” water in that solution. At temperatures of 100°C and above, p e closely equals the product of the density of the solution times the weight fraction of water in the solution. At 25°C, a correction parameter must be applied to p e that incorporates a term called the apparent cation hydration number, h . Because of the many assumptions and other uncertainties involved in determining values of h , by the model used here, the reported numbers are not necessarily real hydration numbers even though they do agree with some published values determined by activity and diffusion methods. Whether or not h is a real hydration number, it would appear to be useful in its inclusion within a more extensive activity coefficient term that describes the departure of silica solubilities in concentrated salt solutions from expected behavior according to the model presented here. Values of h can be calculated from measured amorphous silica solubilities in salt solutions at 25°C provided there is no complexing of dissolved silica with the dissolved salt, or if the degree of complexing is known. The previously postulated aqueous silica-sulfate complexing in aqueous Na 2 SO 4 solutions is supported by results of the present effective density of water model

Geochimica et Cosmochimica Acta↗
USGS2007

United States‐Mexican border watershed assessment: Modeling nonpoint source pollution in Ambos Nogales

Ecological considerations need to be interwoven with economic policy and planning along the United States‐Mexican border. Non‐point source pollution can have significant implications for the availability of potable water and the continued health of borderland ecosystems in arid lands. However, environmental assessments in this region present a host of unique issues and problems. A common obstacle to the solution of these problems is the integration of data with different resolutions, naming conventions, and quality to create a consistent database across the binational study area. This report presents a simple modeling approach to predict nonpoint source pollution that can be used for border watersheds. The modeling approach links a hillslopescale erosion‐prediction model and a spatially derived sediment‐delivery model within a geographic information system to estimate erosion, sediment yield, and sediment deposition across the Ambos Nogales watershed in Sonora, Mexico, and Arizona. This paper discusses the procedures used for creating a watershed database to apply the models and presents an example of the modeling approach applied to a conservation‐planning problem.

Arizona, Sonoma↗
USGS2007

New estimates for Io eruption temperatures: Implications for the interior

The initial interpretation of Galileo data from Jupiter's moon, Io, suggested eruption temperatures ≥1600°C. Tidal heating models have difficulties explaining Io's prodigious heat flow if the mantle is >1300°C, although we suggest that temperatures up to ~1450°C may be possible. In general, Io eruption temperatures have been overestimated because the incorrect thermal model has been applied. Much of the thermal emission from high-temperature hot spots comes from lava fountains but lava flow models were utilized. We apply a new lava fountain model to the highest reported eruption temperature, the SSI observation of the 1997 eruption at Pillan. This resets the lower temperature limit for the eruption from ~1600 to ~1340°C . Additionally, viscous heating of the magma may have increased eruption temperature by ~50-100°C as a result of the strong compressive stresses in the ionian lithosphere. While further work is needed, it appears that the discrepancy between observations and interior models is largely resolved.

Icarus↗
USGS2008

Empirical models to predict the volumes of debris flows generated by recently burned basins in the western U.S.

Recently burned basins frequently produce debris flows in response to moderate-to-severe rainfall. Post-fire hazard assessments of debris flows are most useful when they predict the volume of material that may flow out of a burned basin. This study develops a set of empirically-based models that predict potential volumes of wildfire-related debris flows in different regions and geologic settings. The models were developed using data from 53 recently burned basins in Colorado, Utah and California. The volumes of debris flows in these basins were determined by either measuring the volume of material eroded from the channels, or by estimating the amount of material removed from debris retention basins. For each basin, independent variables thought to affect the volume of the debris flow were determined. These variables include measures of basin morphology, basin areas burned at different severities, soil material properties, rock type, and rainfall amounts and intensities for storms triggering debris flows. Using these data, multiple regression analyses were used to create separate predictive models for volumes of debris flows generated by burned basins in six separate regions or settings, including the western U.S., southern California, the Rocky Mountain region, and basins underlain by sedimentary, metamorphic and granitic rocks. An evaluation of these models indicated that the best model (the Western U.S. model) explains 83% of the variability in the volumes of the debris flows, and includes variables that describe the basin area with slopes greater than or equal to 30%, the basin area burned at moderate and high severity, and total storm rainfall. This model was independently validated by comparing volumes of debris flows reported in the literature, to volumes estimated using the model. Eighty-seven percent of the reported volumes were within two residual standard errors of the volumes predicted using the model. This model is an improvement over previous models in that it includes a measure of burn severity and an estimate of modeling errors. The application of this model, in conjunction with models for the probability of debris flows, will enable more complete and rapid assessments of debris flow hazards following wildfire.

Geomorphology↗
USGS2004

Summary of studies supporting cumulative effects analysis of upper Yellowstone River channel modifications

During the last several decades, portions of the upper Yellowstone River have been modified for flood control and erosion prevention. The U.S. Army Corps of Engineers is responsible for administration of a permit program for evaluating construction activities affecting rivers, streams, and wetlands. The Corps regulates activities under the authority of Section 10 of the Rivers and Harbors Act and Section 404 of the Clean Water Act. Since assumption of jurisdiction in the mid-1970’s, the Corps has processed a total of 156 permit actions for the upper Yellowstone River. Over two-thirds of the permit actions occurred during or after two consecutive large floods during 1996 and 1997. In response to concern regarding the potential environmental and ecological consequences of channel modification, the Corps, in conjunction with State and local government agencies, initiated a series of scientific studies to better understand the effects of channel modification in the upper Yellowstone River (Figure 1). These included preparation of wetland and riparian inventory maps (Bon, 2001); hydraulic modeling and flood-plain delineation; watershed land-cover assessment (Pick and Potter, 2003); historic bottomland use analysis (Brelsford and others, 2003); analysis of channel modification effects on fish habitat (Bowen and others, 2003); comparison of juvenile salmonid use of modified and unmodified habitats (Zale and Rider, 2003); analysis of riparian vegetation and flood-plain turnover (Merigliano and Polzin, 2003); study of the relations between riparian habitat and bird communities (Hansen and others, 2003); analyses of geomorphology and historical channel changes (Dalby and Robinson, 2003); socioeconomic assessment (BBC Research and Consulting, 2002); and sediment transport investigations and modeling (Holnbeck, 2003). This report is a summary of results from the individual scientific studies as they bear on future programmatic cumulative effects analyses of channel modification of the upper Yellowstone River. We do not attempt a formal, cumulative impact assessment in the sense of evaluating alternatives or future scenarios. The first section presents major findings of the resource studies in terms of temporal comparisons, spatial comparisons, and causal relations. In this section, we present a series of conceptual models or flow diagrams of the major causal pathways of cumulative impacts from channel modification. These represent major pathways of potential impact based on knowledge from other rivers, concerns expressed about the upper Yellowstone, and results from the scientific studies. These diagrams serve to focus interpretation of study results as either supporting or not supporting the importance and magnitude of particular causal relations and to identify key linking variables appearing in multiple causal pathways. These key variables that connect channel modification actions to multiple, valued environmental attributes can serve as the foundation for both projecting and monitoring future responses of the system. A section on analytical realities outlines some of the limitations of projecting cumulative impacts from channel modification of the upper Yellowstone River on meaningful spatial and temporal scales and some of the difficulties of interpreting results from studies conducted shortly after two extreme floods and substantial increases in channel modification. A section on classification describes the two primary geomorphic classification systems of the upper Yellowstone River used in the various individual resource studies. Each of these systems has been valuable in supporting field sampling and expressing results concerning patterns of variation. Their integration or revision into a classification system to achieve some new purpose, such as a regulatory program or monitoring system, will depend on a crisp articulation of riverine management or regulatory objectives. A section on key variables identifies those that are central to the causal pathways connecting channel modification to impacts and provides a rationale for key variables as an alternative to other tools such as Proper Functioning Condition (Barrett and others, 1993), Index of Biotic Integrity (Karr, 1981), or the Synoptic Approach (Liebowitz and others, 1992). This section also explains relations among key variable to Hydrogeomorphic (HGM) assessment procedures (Hauer and Smith, 1998; Hauer and others, 2001) and outlines how these 2 variables might be monitored to track cumulative impacts. Examples of how selected key variables can be quantified using Geographic Information System data sets developed from the resource studies are presented for one reach. The largest portion of the document is an Appendix that summarizes each of the individual scientific studies in terms of scope and methods, findings, principal variables, and metrics used in the study or suggested by the study results, and important needs for further study.

Montana↗
USGS2005

Summary of dimensionless Texas hyetographs and distribution of storm depth developed for Texas Department of Transportation research project 0–4194

Hyetographs and storm depth distributions are important elements of hydraulic design by Texas Department of Transportation engineers. Design hyetographs are used in conjunction with unit hydrographs to obtain peak discharge and hydrograph shape for hydraulic design. Storm-depth distributions can be used to assess the probability of a total rainfall depth for a storm. A research project from 2000–2004 has been conducted to (1) determine if existing Natural Resources Conservation Service (NRCS) dimensionless hyetographs are representative of storms in Texas, (2) provide new procedures for dimensionless hyetograph estimation if the NRCS hyetographs are not representative, and (3) provide a procedure to estimate the distribution of storm depth for Texas. This report summarizes the research activities and results of the research project. The report documents several functional models of dimensionless hyetographs and provides curves and tabulated ordinates of empirical (nonfunctional) dimensionless hyetographs for a database of runoff-producing storms in Texas. The dimensionless hyetographs are compared to the NRCS dimensionless hyetographs. The distribution of storm depth is documented for seven values of minimum interevent time through dimensionless frequency curves and tables of mean storm depth for each county in Texas. Conclusions regarding application of the research results are included in the report.

Report↗
USGS2012

Hydrogeology and simulation of groundwater flow and land-surface subsidence in the northern part of the Gulf Coast aquifer system, Texas, 1891-2009

In cooperation with the Harris–Galveston Subsidence District, Fort Bend Subsidence District, and Lone Star Groundwater Conservation District, the U.S. Geological Survey developed and calibrated the Houston Area Groundwater Model (HAGM), which simulates groundwater flow and land-surface subsidence in the northern part of the Gulf Coast aquifer system in Texas from predevelopment (before 1891) through 2009. Withdrawal of groundwater since development of the aquifer system has resulted in potentiometric surface (hydraulic head, or head) declines in the Gulf Coast aquifer system and land-surface subsidence (primarily in the Houston area) from depressurization and compaction of clay layers interbedded in the aquifer sediments. The MODFLOW-2000 groundwater flow model described in this report comprises four layers, one for each of the hydrogeologic units of the aquifer system except the Catahoula confining system, the assumed no-flow base of the system. The HAGM is composed of 137 rows and 245 columns of 1-square-mile grid cells with lateral no-flow boundaries at the extent of each hydrogeologic unit to the northwest, at groundwater divides associated with large rivers to the southwest and northeast, and at the downdip limit of freshwater to the southeast. The model was calibrated within the specified criteria by using trial-and-error adjustment of selected model-input data in a series of transient simulations until the model output (potentiometric surfaces, land-surface subsidence, and selected water-budget components) acceptably reproduced field measured (or estimated) aquifer responses including water level and subsidence. The HAGM-simulated subsidence generally compared well to 26 Predictions Relating Effective Stress to Subsidence (PRESS) models in Harris, Galveston, and Fort Bend Counties. Simulated HAGM results indicate that as much as 10 feet (ft) of subsidence has occurred in southeastern Harris County. Measured subsidence and model results indicate that a larger geographic area encompassing this area of maximum subsidence and much of central to southeastern Harris County has subsided at least 6 ft. For the western part of the study area, the HAGM simulated as much as 3 ft of subsidence in Wharton, Jackson, and Matagorda Counties. For the eastern part of the study area, the HAGM simulated as much as 3 ft of subsidence at the boundary of Hardin and Jasper Counties. Additionally, in the southeastern part of the study area in Orange County, the HAGM simulated as much as 3 ft of subsidence. Measured subsidence for these areas in the western and eastern parts of the HAGM has not been documented.

Texas↗
USGS1986

Three-dimensional model simulation of steady-state ground-water flow in the Albuquerque-Belen Basin, New Mexico

As part of the Southwest Alluvial Basins study, model was constructed to simulate the alluvial aquifer system underlying the Albuquerque-Belen Basin. The model was used to simulate the steady-state flow condition assumed to have existed prior to 1960. Until this time there apparently were no long-term groundwater level changes of a significant magnitude outside the immediate vicinity of Albuquerque. Therefore, the construction of a steady-state flow model of the aquifer system based on reported hydrologic data predating 1960 was justified. During construction of the steady-state model, simulated hydraulic conductivity values were adjusted, within acceptable physical limits, until a best fit between measured or reported and computed heads at 34 control wells was achieved. The modeled area was divided into six sub-areas, or zones, within each of which hydraulic conductivity was assumed to be uniform. The model consisted of six layers for each of which simulated transmissivity was proportional to the layer thickness. Adjustments to simulated hydraulic conductivity values in the different zones resulted in final values that ranged from a low of 0.25 ft/day in the west to 50 ft/day in the eastern part of the basin. The error of the simulation, defined as the absolute difference between the computed and the measured or reported water level at the corresponding point in the physical system being modeled, ranged from 0.6 ft to 36 ft, with an average of 14.6 ft for the 34 control wells. (Author 's abstract)

Water-Resources Investigations Report↗