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At least 307 records · Page 17Linked to original sources

USGS1994

Crustal velocity structure of the northern Yukon-Tanana upland, central Alaska: Results from TACT refraction/wide-angle reflection data

The Fairbanks North seismic refraction/ wide-angle reflection profile, collected by the U.S. Geological Survey Trans-Alaska Crustal Transect (TACT) project in 1987, crosses the complex region between the Yukon-Tanana and Ruby terranes in interior Alaska. This region is occupied by numerous small terranes elongated in a northeast-southwest direction. These seismic data reveal a crustal velocity structure that is divided into three upper-crustal and at least two middle- to lower-crustal domains. The upper-crustal domains are delineated by two steeply dipping low-velocity anomalies that are interpreted as signatures of the Victoria Creek fault, and the Beaver Creek fault or a fault buried by the Beaver Creek fault. This tripartite upper crust extends to 8-10 km depth where a subhorizontal interface undercuts the northern and central domains. Beneath the northern domain, this interface is interpreted as the southeastwardly dipping boundary between the Tozina and Ruby terranes. The continuation of this interface beneath the central domain suggests that it may represent the detachment or basal thrust for thin-skinned tectonic amalgamation of the terranes caught between the Yukon-Tanana and Ruby terranes. The lower crust and Moho reflection exhibit differences from north to south that define at least two lower-crustal domains, interpreted as the Yukon-Tanana and Ruby terranes. Finally, the crustal thickness along the profile is nearly uniform and ranges from 31 to 34 km. Our data suggest that after initial thin-skinned amalgamation of the various terranes, this region experienced thick-skinned tectonic reorganization via strike-slip faulting. This interpretation supports a model in which at least one strand of the Tintina fault exists in this important region of Alaska.

Alaska↗

USGS2021

Subducting oceanic basement roughness impacts on upper plate tectonic structure and a backstop splay fault zone activated in the southern Kodiak aftershock region of the Mw 9.2, 1964 megathrust rupture, Alaska

In 1964, the Alaska margin ruptured in a giant Mw 9.2 megathrust earthquake, the 2nd largest during worldwide instrumental recording. The coseismic slip and aftershock region offshore Kodiak Island was surveyed in 1977 – 1981 to understand the region’s tectonics. We re-processed multichannel seismic (MCS) field data using current standard Kirchhoff depth migration and/or MCS traveltime tomography. Further surveys in 1994 added P-wave velocity structure from wide-angle seismic lines and multibeam bathymetry. Published regional gravity, backscatter, and earthquake compilations also became available at this time. Beneath the trench, rough oceanic crust is covered by ~3 to 5 km thick sediment. Sediment on the subducting plate modulates the plate interface relief. The accreted prism’s imbricate thrust faults have a complex P-wave velocity structure. Landward, an accelerated increase in P-wave velocities is marked by a backstop splay fault zone (BSFZ) that marks a transition from the prism to the higher rigidity rock beneath the middle and upper slope. Structures associated with this feature may indicate fluid flow. Further upslope, another fault extends >100 km along-strike across the middle slope. Erosion from subducting seamounts leaves embayments in the frontal prism. Plate interface roughness varies along the subduction zone. Beneath the lower and middle slope, 2.5 D plate interface images show modest relief whereas the oceanic basement image is rougher. The 1964 earthquake slip maximum coincides with the leading/landward flank of a subducting seamount and the BSFZ. The BSFZ is a potentially active structure and should be considered in tsunami hazard assessments.

Alaska↗

USGS2024

Comparing subduction ground-motion models to observations for Cascadia

We evaluate Cascadia subduction ground-motion models (GMMs), considered for the 2023 US National Seismic Hazard Model (NSHM) update, by comparing observations to model predictions. The observations comprise regional recordings from intraslab earthquakes, including contributions from 2021 and 2022 events in southern Cascadia and global records from interface earthquakes. Since the 2018 NSHM update, new GMMs for Cascadia have been published by the Next Generation Attenuation (NGA)-Subduction Project that require independent evaluation. In the regional intraslab comparisons, we highlight a characteristic frequency dependence for Cascadia data, with short periods having lower ground motions and longer periods being comparable to other subduction zones. We evaluate differences in northern and southern Cascadia and find that the NGA-Subduction GMMs developed using southern Cascadia data perform better in this region than the model that did not consider these data. We compare ground-motion variability in Cascadia with the NGA-Subduction model predictions and find differences at short periods ( T = 0.1 s) due to the use of global versus regional data in the development of these models. Moreover, the within-event component of aleatory variability from the GMMs overpredicts the standard deviation of Cascadia recordings at very short periods ( T < 0.05 s). Using global interface earthquakes as a proxy to evaluate the Cascadia GMMs, we find long-period overprediction from a simulation-based GMM and some of the empirical GMMs. When comparing recent observations, we find a similar misfit to GMMs and the 2010 and 2022 Ferndale earthquakes. Finally, we observe different basin amplification factors arising in different subsets of the data, which indicate that differences in basin factors between empirical GMMs could arise from the data selection choices by the developers. As part of evaluating the regional basin terms, we apply basin amplification factors from the magnitude 9 Cascadia earthquake simulations to the empirical GMMs for interface earthquakes. The comparisons presented in this study indicate that the NGA-Subduction GMMs for Cascadia perform well relative to observations and older subduction GMMs.

British Columbia, California, Oregon, Washington↗

USGS2006

Seismoelectric numerical modeling on a grid

Our finite-difference algorithm provides a new method for simulating how seismic waves in arbitrarily heterogeneous porous media generate electric fields through an electrokinetic mechanism called seismoelectric coupling. As the first step in our simulations, we calculate relative pore-fluid/grain-matrix displacement by using existing poroelastic theory. We then calculate the electric current resulting from the grain/fluid displacement by using seismoelectric coupling theory. This electrofiltration current acts as a source term in Poisson's equation, which then allows us to calculate the electric potential distribution. We can safely neglect induction effects in our simulations because the model area is within the electrostatic near field for the depth of investigation (tens to hundreds of meters) and the frequency ranges (10 Hz to 1 kHz) of interest for shallow seismoelectric surveys.We can independently calculate the electric-potential distribution for each time step in the poroelastic simulation without loss of accuracy because electro-osmotic feedback (fluid flow that is perturbed by generated electric fields) is at least 105 times smaller than flow that is driven by fluid-pressure gradients and matrix acceleration, and is therefore negligible. Our simulations demonstrate that, distinct from seismic reflections, the seismoelectric interface response from a thin layer (at least as thin as one-twentieth of the seismic wavelength) is considerably stronger than the response from a single interface. We find that the interface response amplitude decreases as the lateral extent of a layer decreases below the width of the first Fresnel zone. We conclude, on the basis of our modeling results and of field results published elsewhere, that downhole and/or crosswell survey geometries and time-lapse applications are particularly well suited to the seismoelectric method. ?? 2006 Society of Exploration Geophysicists.

Geophysics↗

USGS2007

Generalization of von Neumann analysis for a model of two discrete half-spaces: The acoustic case

Evaluating the performance of finite-difference algorithms typically uses a technique known as von Neumann analysis. For a given algorithm, application of the technique yields both a dispersion relation valid for the discrete time-space grid and a mathematical condition for stability. In practice, a major shortcoming of conventional von Neumann analysis is that it can be applied only to an idealized numerical model - that of an infinite, homogeneous whole space. Experience has shown that numerical instabilities often arise in finite-difference simulations of wave propagation at interfaces with strong material contrasts. These interface instabilities occur even though the conventional von Neumann stability criterion may be satisfied at each point of the numerical model. To address this issue, I generalize von Neumann analysis for a model of two half-spaces. I perform the analysis for the case of acoustic wave propagation using a standard staggered-grid finite-difference numerical scheme. By deriving expressions for the discrete reflection and transmission coefficients, I study under what conditions the discrete reflection and transmission coefficients become unbounded. I find that instabilities encountered in numerical modeling near interfaces with strong material contrasts are linked to these cases and develop a modified stability criterion that takes into account the resulting instabilities. I test and verify the stability criterion by executing a finite-difference algorithm under conditions predicted to be stable and unstable. ?? 2007 Society of Exploration Geophysicists.

Geophysics↗

USGS2003

Empirical ground-motion relations for subduction-zone earthquakes and their application to Cascadia and other regions

Ground-motion relations for earthquakes that occur in subduction zones are an important input to seismic-hazard analyses in many parts of the world. In the Cascadia region (Washington, Oregon, northern California, and British Columbia), for example, there is a significant hazard from megathrust earthquakes along the subduction interface and from large events within the subducting slab. These hazards are in addition to the hazard from shallow earthquakes in the overlying crust. We have compiled a response spectra database from thousands of strong-motion recordings from events of moment magnitude ( M ) 5-8.3 occurring in subduction zones around the world, including both interface and in-slab events. The 2001 M 6.8 Nisqually and 1999 M 5.9 Satsop earthquakes are included in the database, as are many records from subduction zones in Japan (Kyoshin-Net data), Mexico (Guerrero data), and Central America. The size of the database is four times larger than that available for previous empirical regressions to determine ground-motion relations for subduction-zone earthquakes. The large dataset enables improved determination of attenuation parameters and magnitude scaling, for both interface and in-slab events. Soil response parameters are also better determined by the data.

British Columbia, California, Oregon, Washington↗

USGS2015

Pathogen exposure varies widely among sympatric populations of wild and domestic felids across the United States

Understanding how landscape, host, and pathogen traits contribute to disease exposure requires systematic evaluations of pathogens within and among host species and geographic regions. The relative importance of these attributes is critical for management of wildlife and mitigating domestic animal and human disease, particularly given rapid ecological changes, such as urbanization. We screened >1,000 samples from sympatric populations of puma (Puma concolor), bobcat (Lynx rufus) and domestic cat (Felis catus) across urban gradients in six sites, representing three regions, in North America for exposure to a representative suite of bacterial, protozoal and viral pathogens (Bartonella sp., Toxoplasma gondii, feline herpesvirus-1, feline panleukopenea virus, feline calicivirus, feline immunodeficiency virus). We evaluated prevalence within each species, and examined host trait and land cover determinants of exposure-providing an unprecedented analysis of factors relating to potential for infections in domesticated and wild felids. Prevalence differed among host species (highest for puma and lowest for domestic cat) and was greater for indirectly transmitted pathogens. Sex was inconsistently predictive of exposure to directly transmitted pathogens only, and age infrequently predictive of both direct and indirectly transmitted pathogens. Determinants of pathogen exposure were widely divergent between the wild felid species. For puma, suburban landuse predicted increased exposure to Bartonella sp. in southern California, and FHV-1 exposure increased near urban edges in Florida. This may suggest inter-specific transmission with domestic cats via flea vectors (California) and direct contact (Florida) around urban boundaries. Bobcats captured near urban areas had increased exposure to T. gondii in Florida, suggesting an urban source of prey. Bobcats captured near urban areas in Colorado and Florida had higher FIV exposure, possibly suggesting increased intra-specific interactions through pile-up of home ranges. Beyond these regional and pathogen specific relationships, proximity to the wildland urban interface did not generally increase the probability of disease exposure in wild or domestic felids, emphasizing the importance of local ecological determinants. Indeed, pathogen exposure was often negatively associated with the wildland urban interface for all felids. Our analyses suggest cross-species pathogen transmission events around this interface may be infrequent, but followed by self-sustaining propagation within the new host species.

California, Colorado,Florida↗

USGS1970

Similarities, differences, and some genetic problems of the Wyoming and Colorado plateau types of uranium deposits in sandstone

Uranium deposits of the Wyoming roll type and the Colorado Plateau peneconcordant type are the principal domestic resources of uranium. Both types occur in lenticular sandstone beds of continental origin, have a similar suite of elements and minerals, are associated with mildly altered rock, and are thought to have formed by reduction precipitation from ground waters before significant regional deformation. They differ in several respects. The Wyoming deposits are in unlithified sandstone that is highly arkosic, whereas the Colorado Plateau deposits are in lithified sandstone that is only slightly to moderately arkosic. Uranium is the only ore metal in the Wyoming deposits, whereas vanadium or copper is more abundant than uranium in some of the Plateau deposits. The Wyoming deposits are elongate crescent-shaped bodies that extend vertically through, or partly through, a sandstone unit and which are scattered, like widely spaced beads on a string, along miles-long interfaces between oxidized (altered) and unoxidized sandstone, whereas the Plateau deposits are thin tabular layers that are nearly concordant to bedding and which occur as discrete bodies, like raisins in raisin bread, enveloped in rock altered by reduction. The Wyoming ore rolls and interfaces were dynamic, having been pushed downdip by downward-moving oxygen-bearing water that passed through the interfaces and deposited the ore minerals on the reducing side, whereas the Plateau deposits seemingly formed as static bodies, localized by intensive reducing "patches" in a mildly reducing environment. These differences focus attention on genetic problems relating to the Eh of the ore-bearing and altering solutions, the shape and localization of deposits, and the source of the uranium.

Arizona, Colorado, New Mexico, South Dakota, Utah,↗

USGS2008

Modeling soil moisture processes and recharge under a melting snowpack

Recharge into granitic bedrock under a melting snowpack is being investigated as part of a study designed to understand hydrologic processes involving snow at Yosemite National Park in the Sierra Nevada Mountains of California. Snowpack measurements, accompanied by water content and matric potential measurements of the soil under the snowpack, allowed for estimates of infiltration into the soil during snowmelt and percolation into the bedrock. During portions of the snowmelt period, infiltration rates into the soil exceeded the permeability of the bedrock and caused ponding to be sustained at the soil-bedrock interface. During a 5-d period with little measured snowmelt, drainage of the ponded water into the underlying fractured granitic bedrock was estimated to be 1.6 cm d?1, which is used as an estimate of bedrock permeability. The numerical simulator TOUGH2 was used to reproduce the field data and evaluate the potential for vertical flow into the fractured bedrock or lateral flow at the bedrock-soil interface. During most of the snowmelt season, the snowmelt rates were near or below the bedrock permeability. The field data and model results support the notion that snowmelt on the shallow soil overlying low permeability bedrock becomes direct infiltration unless the snowmelt rate greatly exceeds the bedrock permeability. Late in the season, melt rates are double that of the bedrock permeability (although only for a few days) and may tend to move laterally at the soil-bedrock interface downgradient and contribute directly to streamflow. ?? Soil Science Society of America.

Conference Paper↗

USGS2007

Surface-source downhole seismic analysis in R

This report discusses a method for interpreting a layered slowness or velocity model from surface-source downhole seismic data originally presented by Boore (2003). I have implemented this method in the statistical computing language R (R Development Core Team, 2007), so that it is freely and easily available to researchers and practitioners that may find it useful. I originally applied an early version of these routines to seismic cone penetration test data (SCPT) to analyze the horizontal variability of shear-wave velocity within the sediments in the San Francisco Bay area (Thompson et al., 2006). A more recent version of these codes was used to analyze the influence of interface-selection and model assumptions on velocity/slowness estimates and the resulting differences in site amplification (Boore and Thompson, 2007). The R environment has many benefits for scientific and statistical computation; I have chosen R to disseminate these routines because it is versatile enough to program specialized routines, is highly interactive which aids in the analysis of data, and is freely and conveniently available to install on a wide variety of computer platforms. These scripts are useful for the interpretation of layered velocity models from surface-source downhole seismic data such as deep boreholes and SCPT data. The inputs are the travel-time data and the offset of the source at the surface. The travel-time arrivals for the P- and S-waves must already be picked from the original data. An option in the inversion is to include estimates of the standard deviation of the travel-time picks for a weighted inversion of the velocity profile. The standard deviation of each travel-time pick is defined relative to the standard deviation of the best pick in a profile and is based on the accuracy with which the travel-time measurement could be determined from the seismogram. The analysis of the travel-time data consists of two parts: the identification of layer-interfaces, and the inversion for the velocity of each layer. The analyst usually picks layer-interfaces by visual inspection of the travel-time data. I have also developed an algorithm that automatically finds boundaries which can save a significant amount of the time when analyzing a large number of sites. The results of the automatic routines should be reviewed to check that they are reasonable. The interactivity of these scripts allows the user to add and to remove layers quickly, thus allowing rapid feedback on how the residuals are affected by each additional parameter in the inversion. In addition, the script allows many models to be compared at the same time.

Open-File Report↗

USGS2014

Continuous resistivity profiling and seismic-reflection data collected in April 2010 from Indian River Bay, Delaware

A geophysical survey to delineate the fresh-saline groundwater interface and associated sub-bottom sedimentary structures beneath Indian River Bay, Delaware, was carried out in April 2010. This included surveying at higher spatial resolution in the vicinity of a study site at Holts Landing, where intensive onshore and offshore studies were subsequently completed. The total length of continuous resistivity profiling (CRP) survey lines was 145 kilometers (km), with 36 km of chirp seismic lines surveyed around the perimeter of the bay. Medium-resolution CRP surveying was performed using a 50-meter streamer in a baywide grid. Results of the surveying and data inversion showed the presence of many buried paleochannels beneath Indian River Bay that generally extended perpendicular from the shoreline in areas of modern tributaries, tidal creeks, and marshes. An especially wide and deep paleochannel system was imaged in the southeastern part of the bay near White Creek. Many paleochannels also had high-resistivity anomalies corresponding to low-salinity groundwater plumes associated with them, likely due to the presence of fine-grained estuarine mud and peats in the channel fills that act as submarine confining units. Where present, these units allow plumes of low-salinity groundwater that was recharged onshore to move beyond the shoreline, creating a complex fresh-saline groundwater interface in the subsurface. The properties of this interface are important considerations in construction of accurate coastal groundwater flow models. These models are required to help predict how nutrient-rich groundwater, recharged in agricultural watersheds such as this one, makes its way into coastal bays and impacts surface-water quality and estuarine ecosystems.

Delaware↗

USGS2011

Physical and chemical characteristics including total and geochemical forms of phosphorus in sediment from the top 30 centimeters of cores collected in October 2006 at 26 sites in Upper Klamath Lake, Oregon

μThis study of phosphorus (P) cycling in eutrophic Upper Klamath Lake (UKL), Oregon, was conducted by the U.S. Geological Survey in cooperation with the U.S. Bureau of Reclamation. Lakebed sediments from the upper 30 centimeters (cm) of cores collected from 26 sites were characterized. Cores were sampled at 0.5, 1.5, 2.5, 3.5, 4.5, 10, 15, 20, 25, and 30 cm. Prior to freezing, water content and sediment pH were determined. After being freeze-dried, all samples were separated into greater than 63-micron (μm) particle-size (coarse) and less than 63-μm particle-size (fine) fractions. In the surface samples (0.5 to 4.5 cm below the sediment water interface), approximately three-fourths of the particles were larger than 63-μm. The ratios of the coarse particle-size fraction (>63 μm) and the fine particle-size fraction (<63 μm) were approximately equal in samples at depths greater than 10 cm below the sediment water interface. Chemical analyses included both size fractions of freeze-dried samples. Chemical analyses included determination of total concentrations of aluminum (Al), calcium (Ca), carbon (C), iron (Fe), poorly crystalline Fe, nitrogen (N), P, and titanium (Ti). Total Fe concentrations were the largest in sediment from the northern portion of UKL, Howard Bay, and the southern portion of the lake. Concentrations of total Al, Ca, and Ti were largest in sediment from the northern, central, and southernmost portions of the lake and in sediment from Howard Bay. Concentrations of total C and N were largest in sediment from the embayments and in sediment from the northern arm and southern portion of the lake in the general region of Buck Island. Concentrations of total C were larger in the greater than 63-μm particle-size fraction than in the less than 63-μm particle-size fraction. Sediments were sequentially extracted to determine concentrations of inorganic forms of P, including loosely sorbed P, P associated with poorly crystalline Fe oxides, and P associated with mineral phases. The difference between the concentration of total P and sum of the concentrations of inorganic forms of P is referred to as residual P. Residual P was the largest fraction of P in all of the sediment samples. In UKL, the correlation between concentrations of total P and total Fe in sediment is poor (R2<0.1). The correlation between the concentrations of total P and P associated with poorly crystalline Fe oxides is good (R2=0.43) in surface sediment (0.5-4.5 cm below the sediment water interface) but poor (R2<0.1) in sediments at depths between 10 cm and 30 cm. Phosphorus associated with poorly crystalline Fe oxides is considered bioavailable because it is released when sediment conditions change from oxidizing to reducing, which causes dissolution of Fe oxides.

Oregon↗

USGS2012

Preliminary investigation of the effects of sea-level rise on groundwater levels in New Haven, Connecticut

Global sea level rose about 0.56 feet (ft) (170 millimeters (mm)) during the 20th century. Since the 1960s, sea level has risen at Bridgeport, Connecticut, about 0.38 ft (115 mm), at a rate of 0.008 ft (2.56 mm + or - 0.58 mm) per year. With regional subsidence, and with predicted global climate change, sea level is expected to continue to rise along the northeast coast of the United States through the 21st century. Increasing sea levels will cause groundwater levels in coastal areas to rise in order to adjust to the new conditions. Some regional climate models predict wetter climate in the northeastern United States under some scenarios. Scenarios for the resulting higher groundwater levels have the potential to inundate underground infrastructure in lowlying coastal cities. New Haven is a coastal city in Connecticut surrounded and bisected by tidally affected waters. Monitoring of water levels in wells in New Haven from August 2009 to July 2010 indicates the complex effects of urban influence on groundwater levels. The response of groundwater levels to recharge and season varied considerably from well to well. Groundwater temperatures varied seasonally, but were warmer than what was typical for Connecticut, and they seem to reflect the influence of the urban setting, including the effects of conduits for underground utilities. Specific conductance was elevated in many of the wells, indicating the influence of urban activities or seawater in Long Island Sound. A preliminary steady-state model of groundwater flow for part of New Haven was constructed using MODFLOW to simulate current groundwater levels (2009-2010) and future groundwater levels based on scenarios with a rise of 3 ft (0.91 meters (m)) in sea level, which is predicted for the end of the 21st century. An additional simulation was run assuming a 3-ft rise in sea level combined with a 12-percent increase in groundwater recharge. The model was constructed from existing hydrogeologic information for the New Haven area and from new information on groundwater levels collected during October 2009-June 2010. For the scenario with a 3-ft rise in sea level and no increase in recharge, simulated groundwater levels near the coast rose 3 ft; this increased water level tapered off toward a discharge area at the only nontidal stream in the study area. Simulated stream discharge increased at the nontidal stream because of the increased gradient. Although groundwater levels rose, the simulated difference between the groundwater levels in the aquifer and the increased sea level declined, indicating that the depth to the interface between freshwater and saltwater may possibly decline. Simulated water levels were affected by rise in sea level even in areas where the water table was at 17-24 ft (5.2-7.3 m) above current (2011) sea level. For the scenario with increased recharge, simulated groundwater levels were as much as an additional foot higher at some locations in the study area. The results of this preliminary investigation indicate that groundwater levels in coastal areas can be expected to rise and may rise higher if groundwater recharge also increases. This finding has implications for the disposal of stormwater through infiltration, a low-impact development practice designed to improve water quality and reduce overland peak discharge. Other implications include increased risk of basement flooding and increased groundwater seepage into underground sewer pipes and utility corridors in some areas. These implications will present engineering challenges to New Haven and Yale University. The preliminary model developed for this study can be the starting point for further simulation of future alternative scenarios for sea-level rise and recharge. Further simulations could identify those areas of New Haven where infrastructure may be at greatest risk from rising levels of groundwater. The simulations described in this report have limitations due to the preliminary scope of the work. Approaches to improve simulations include but are not limited to incorporating: * The variable density of seawater into the model in order to understand the current and future location of the interface between freshwater and saltwater; * Collection of additional data in order to better resolve temporal and spatial patterns in water levels in the aquifer; * Improved estimates of recharge through direct and indirect measurements of freshwater discharge from the study area; and * Transient simulations for greater understanding of the amount of time required for water levels and the position of the interface between freshwater and saltwater to adjust to changes in sea level and recharge.

Connecticut↗

USGS2012

Groundwater flow and water budget in the surficial and Floridan aquifer systems in east-central Florida

A numerical transient model of the surficial and Floridan aquifer systems in east-central Florida was developed to (1) increase the understanding of water exchanges between the surficial and the Floridan aquifer systems, (2) assess the recharge rates to the surficial aquifer system from infiltration through the unsaturated zone and (3) obtain a simulation tool that could be used by water-resource managers to assess the impact of changes in groundwater withdrawals on spring flows and on the potentiometric surfaces of the hydrogeologic units composing the Floridan aquifer system. The hydrogeology of east-central Florida was evaluated and used to develop and calibrate the groundwater flow model, which simulates the regional fresh groundwater flow system. The U.S. Geological Survey three-dimensional groundwater flow model, MODFLOW-2005, was used to simulate transient groundwater flow in the surficial, intermediate, and Floridan aquifer systems from 1995 to 2006. The east-central Florida transient model encompasses an actively simulated area of about 9,000 square miles. Although the model includes surficial processes-rainfall, irrigation, evapotranspiration, runoff, infiltration, lake water levels, and stream water levels and flows-its primary purpose is to characterize and refine the understanding of groundwater flow in the Floridan aquifer system. Model-independent estimates of the partitioning of rainfall into evapotranspiration, streamflow, and aquifer recharge are provided from a water-budget analysis of the surficial aquifer system. The interaction of the groundwater flow system with the surface environment was simulated using the Green-Ampt infiltration method and the MODFLOW-2005 Unsaturated-Zone Flow, Lake, and Streamflow-Routing Packages. The model is intended to simulate the part of the groundwater system that contains freshwater. The bottom and lateral boundaries of the model were established at the estimated depths where the chloride concentration is 5,000 milligrams per liter in the Floridan aquifer system. Potential flow across the interface represented by this chloride concentration is simulated by the General Head Boundary Package. During 1995 through 2006, there were no major groundwater withdrawals near the freshwater and saline-water interface, making the general head boundary a suitable feature to estimate flow through the interface. The east-central Florida transient model was calibrated using the inverse parameter estimation code, PEST. Steady-state models for 1999 and 2003 were developed to estimate hydraulic conductivity (K) using average annual heads and spring flows as observations. The spatial variation of K was represented using zones of constant values in some layers, and pilot points in other layers. Estimated K values were within one order of magnitude of aquifer performance test data. A simulation of the final two years (2005-2006) of the 12-year model, with the K estimates from the steady-state calibration, was used to guide the estimation of specific yield and specific storage values. The final model yielded head and spring-flow residuals that met the calibration criteria for the 12-year transient simulation. The overall mean residual for heads, defining residual as simulated minus measured value, was -0.04 foot. The overall root-mean square residual for heads was less than 3.6 feet for each year in the 1995 to 2006 simulation period. The overall mean residual for spring flows was -0.3 cubic foot per second. The spatial distribution of head residuals was generally random, with some minor indications of bias. Simulated average evapotranspiration (ET) over the 1995 to 2006 period was 34.5 inches per year, compared to the calculated average ET rate of 36.6 inches per year from the model-independent water-budget analysis. Simulated average net recharge to the surficial aquifer system was 3.6 inches per year, compared with the calculated average of 3.2 inches per year from the model-independent waterbudget analysis. Groundwater withdrawals from the Floridan aquifer system averaged about 800 million gallons per day, which is equivalent to about 2 inches per year over the model area and slightly more than half of the simulated average net recharge to the surficial aquifer system over the same period. Annual net simulated recharge rates to the surficial aquifer system were less than the total groundwater withdrawals from the Floridan aquifer system only during the below-average rainfall years of 2000 and 2006.

Florida↗

USGS2013

Web-based flood database for Colorado, water years 1867 through 2011

In order to provide a centralized repository of flood information for the State of Colorado, the U.S. Geological Survey, in cooperation with the Colorado Department of Transportation, created a Web-based geodatabase for flood information from water years 1867 through 2011 and data for paleofloods occurring in the past 5,000 to 10,000 years. The geodatabase was created using the Environmental Systems Research Institute ArcGIS JavaScript Application Programing Interface 3.2. The database can be accessed at http://cwscpublic2.cr.usgs.gov/projects/coflood/COFloodMap.html. Data on 6,767 flood events at 1,597 individual sites throughout Colorado were compiled to generate the flood database. The data sources of flood information are indirect discharge measurements that were stored in U.S. Geological Survey offices (water years 1867–2011), flood data from indirect discharge measurements referenced in U.S. Geological Survey reports (water years 1884–2011), paleoflood studies from six peer-reviewed journal articles (data on events occurring in the past 5,000 to 10,000 years), and the U.S. Geological Survey National Water Information System peak-discharge database (water years 1883–2010). A number of tests were performed on the flood database to ensure the quality of the data. The Web interface was programmed using the Environmental Systems Research Institute ArcGIS JavaScript Application Programing Interface 3.2, which allows for display, query, georeference, and export of the data in the flood database. The data fields in the flood database used to search and filter the database include hydrologic unit code, U.S. Geological Survey station number, site name, county, drainage area, elevation, data source, date of flood, peak discharge, and field method used to determine discharge. Additional data fields can be viewed and exported, but the data fields described above are the only ones that can be used for queries.

Colorado↗

USGS2013

The Shoreline Management Tool—An ArcMap tool for analyzing water depth, inundated area, volume, and selected habitats, with an example for the lower Wood River Valley, Oregon

The Shoreline Management Tool is a geographic information system (GIS) based program developed to assist water- and land-resource managers in assessing the benefits and effects of changes in surface-water stage on water depth, inundated area, and water volume. Additionally, the Shoreline Management Tool can be used to identify aquatic or terrestrial habitat areas where conditions may be suitable for specific plants or animals as defined by user-specified criteria including water depth, land-surface slope, and land-surface aspect. The tool can also be used to delineate areas for use in determining a variety of hydrologic budget components such as surface-water storage, precipitation, runoff, or evapotranspiration. The Shoreline Management Tool consists of two parts, a graphical user interface for use with Esri™ ArcMap™ GIS software to interact with the user to define scenarios and map results, and a spreadsheet in Microsoft® Excel® developed to display tables and graphs of the results. The graphical user interface allows the user to define a scenario consisting of an inundation level (stage), land areas (parcels), and habitats (areas meeting user-specified conditions) based on water depth, slope, and aspect criteria. The tool uses data consisting of land-surface elevation, tables of stage/volume and stage/area, and delineated parcel boundaries to produce maps (data layers) of inundated areas and areas that meet the habitat criteria. The tool can be run in a Single-Time Scenario mode or in a Time-Series Scenario mode, which uses an input file of dates and associated stages. The spreadsheet part of the tool uses a macro to process the results from the graphical user interface to create tables and graphs of inundated water volume, inundated area, dry area, and mean water depth for each land parcel based on the user-specified stage. The macro also creates tables and graphs of the area, perimeter, and number of polygons comprising the user-specified habitat areas within each parcel. The Shoreline Management Tool is highly transferable, using easily generated or readily available data. The capabilities of the tool are demonstrated using data from the lower Wood River Valley adjacent to Upper Klamath and Agency Lakes in southern Oregon.

Oregon↗

USGS2014

User's manual for the upper Delaware River riverine environmental flow decision support system (REFDSS), Version 1.1.2

Between 2002 and 2006, the Fort Collins Science Center (FORT) at the U.S. Geological Survey (USGS) conducted field surveys, organized workshops, and performed analysis of habitat for trout and shad in the Upper Delaware River Basin. This work culminated in the development of decision support system software (the Delaware River DSS–DRDSS, Bovee and others, 2007) that works in conjunction with the Delaware River Basin Commission’s reservoir operations model, OASIS, to facilitate comparison of the habitat and water-delivery effects of alternative operating scenarios for the Basin. This original DRDSS application was developed in Microsoft Excel and is available to all interested parties through the FORT web site ( http://www.fort.usgs.gov/Products/Software/DRDSS/ ). Initial user feedback on the original Excel-based DSS highlighted the need for a more user-friendly and powerful interface to effectively deliver the complex data and analyses encapsulated in the DSS. In order to meet this need, the USGS FORT and Northern Appalachian Research Branch (NARB) developed an entirely new graphical user interface (GUI) application. Support for this research was through the DOI WaterSmart program ( http://www.doi.gov/watersmart/html/index.php ) of which the USGS component is the National Water Census ( http://water.usgs.gov/watercensus/WaterSMART.html ). The content and methodology of the new GUI interface emulates those of the original DSS with a few exceptions listed below. Refer to Bovee and others (2007) for the original information. Significant alterations to the original DSS include: • We moved from Excel-based data storage and processing to a more powerful database back end powered by SQLite. The most notable effect of this is that the previous maximum temporal extent of 10 years has been replaced by a dynamic extent that can now cover the entire period of record for which we have data (1928–2000). • We incorporated interactive geographic information system (GIS) visualization and dynamic data processing. Previous habitat maps were generated outside of the DSS in an ad hoc process that the end user could not update or investigate. • The original bathymetric data collected in 2005 at the three main stem reaches was augmented with a higher resolution dataset collected in 2010. This new dataset was collected in order to conduct higher resolution (finer pixel size) two-dimensional (2D) hydrodynamic modeling for evaluating dwarf wedgemussel (DWM, Alasmidonta heterodon ) habitat. • Results charts are now substantially more interactive, dynamic, and accessible, which allows users to more easily focus on their particular topics of interest as well as drill down to the source data used to calculate given results.

Open-File Report↗

USGS2018

Analysis of groundwater response to tidal fluctuations, Operable Unit 2, Area 8, Naval Base Kitsap, Keyport, Washington

Operable Unit 2, Area 8, at Naval Base Kitsap, Keyport is the site of a former chrome-plating facility that released metals (primarily chromium and cadmium), chlorinated volatile organic compounds, and petroleum compounds into the local environment. To ensure long-term protectiveness, as stipulated in the Fourth Five-Year Review for the site, Naval Facilities Engineering Command Northwest collaborated with the U.S. Environmental Protection Agency, the Washington State Department of Ecology, and the Suquamish Tribe, to collect data to monitor the contamination left in place and to ensure the site does not pose a risk to human health or the environment. To support these efforts, refined information was needed on the interaction of fresh groundwater with seawater in response to the up-to 13-ft tidal fluctuations at this nearshore site adjacent to Port Orchard Bay. The information was analyzed to meet the primary objective of this investigation, which was to determine the optimal time during the semi-diurnal and the neap-spring tidal cycles to sample groundwater for freshwater contaminants in Area 8 monitoring wells. Groundwater levels and specific conductance in five monitoring wells, along with marine water-levels (tidal levels) in Port Orchard Bay, were monitored every 15 minutes during a 3-week duration to determine how nearshore groundwater responds to tidal forcing. Time series data were collected from October 24, 2017, to November 16, 2017, a period that included neap and spring tides. Vertical profiles of specific conductance were also measured once in the screened interval of each well prior to instrument deployment to determine if a freshwater/saltwater interface was present in the well during that particular time. The vertical profiles of specific conductance were measured only one time during an ebbing tide at approximately the top, middle, and bottom of the saturated thickness within the screened interval of each well. The landward-most well, MW8-8, was completely freshwater, while one of the most seaward wells, MW8-9, was completely saline. A distinct saltwater interface was measured in the three other shallow wells (MW8-11, MW8-12, and MW8-14), with the topmost groundwater occurring fresh underlain by higher conductivity water. Lag times between minimum spring-tide level and minimum groundwater levels in wells ranged from about 2 to 4.5 hours in the less-than 20-ft deep wells screened across the water table, and was about 7 hours for the single 48-ft deep well screened below the water table. Those lag times were surprisingly long considering the wells are all located within 200-ft of the shoreline and the local geology is largely coarse-grained glacial outwash deposits. Various manmade subsurface features, such as slurry walls and backfilled excavations, likely influence and confuse the connectivity between seawater and groundwater. The specific-conductance time-series data showed clear evidence of substantial saltwater intrusion into the screened intervals of most shallow wells. Unexpectedly, the intrusion was associated with the neap part of the tidal cycle around November 13–16, when relatively low barometric pressure and high southerly winds led to the highest high and low tides measured during the monitoring period. The data consistently indicated that the groundwater had the lowest specific conductance (was least mixed with seawater) during the prior neap tides around October 30, the same period when the shallow groundwater levels were lowest. Although the specific conductance response is somewhat different between wells, the data do suggest that it is the heights of the actual high-high and low-low tides, regardless of whether or not they occur during the neap or spring part of the cycle, that allows seawater intrusion into the nearshore aquifer at Area 8. With all the data taken into consideration, the optimal time for sampling the shallow monitoring wells at Area 8 would be centered on a 2–5-hour period following the predicted low-low tide during neap tide, with due consideration of local atmospheric pressure and wind conditions that have the potential to generate tides that can be substantially higher than those predicted from lunar-solar tidal forces. The optimal time for sampling the deeper monitoring wells at Area 8 would be during the 6–8-hour period following a predicted low-low tide, also during the neap tide part of the tidal cycle. The specific time window to sample each well following a low tide can be found in table 5. Those periods are when groundwater in the wells is most fresh and least diluted by seawater intrusion. In addition to timing, consideration should be given to collecting undisturbed samples from the top of the screened interval (or top of the water table if below the top of the interval) to best characterize contaminant concentrations in freshwater. A downhole conductivity probe could be used to identify the saltwater interface, above which would be the ideal depth for sampling.

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