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At least 667 records · Page 37Linked to original sources
USGS2019

Morphodynamic modelling of the wilderness breach, Fire Island, New York. Part I: Model set-up and validation

On October 29, 2012, storm surge and large waves produced by Hurricane 13 Sandy resulted in the formation of a breach in eastern Fire Island, NY. The goals of this study 14 are to gain a better understanding of the physical processes that govern breach behavior and 15 to assess whether process-based models can be used to forecast the evolution of future 16 breaches. The Wilderness Breach grew rapidly in size during the first winter following 17 formation. Growth of the breach was accompanied by the formation of a complex of flood 18 shoals inside Great South Bay, a primary channel that flowed through the eastern part of the 19 flood shoals, and an ebb shoal on the ocean side of the breach. From the summer of 2013 20 through late 2015, the breach continued to change and evolve, albeit at a much slower pace 21 than in the first year after formation. A hybrid combination of Delft3D and XBeach models is 22 used to hindcast the morphodynamic evolution of the Wilderness Breach over the first three 23 years after formation. The formation of the breach during Hurricane Sandy is not part of the 24 simulations. Model simulations are initiated with a post-storm topography in which the 25 breach is already present. The models are capable of hindcasting the main morphodynamic 26 changes of the Wilderness Breach. The spatial patterns, as well as the bulk statistics, such as 27 2 breach geometry and sediment volume changes, are reasonably 28 well reproduced by the model. 29 The model sheds light on previously unknown processes of breach evolution, especially 30 regarding sediment transport and flow regimes within the breach complex.

New York↗
USGS1987

Simulation of tidal flow and circulation patterns in the Loxahatchee River Estuary, southeastern Florida

Results of a two-dimensional, vertically averaged, computer simulation model of the Loxahatchee River estuary show that under typical low freshwater inflow and vertically well mixed conditions, water circulation is dominated by freshwater inflow rather than by tidal influence. The model can simulate tidal flow and circulation in the Loxahatchee River estuary under typical low freshwater inflow and vertically well mixed conditions, but is limited, however, to low-flow and well mixed conditions. Computed patterns of residual water transport show a consistent seaward flow from the northwest fork through the central embayment and out Jupiter Inlet to the Atlantic Ocean. A large residual seaward flow was computed from the North Intracoastal Waterway to the inlet channel. Although the tide produces large flood and ebb flows in the estuary, tide-induced residual transport rates are low in comparison with freshwater-induced residual transport. Model investigations of partly mixed or stratified conditions in the estuary need to await development of systems capable of simulating three-dimensional flow patterns. (Author 's abstract)

Florida↗
USGS2016

Observations of nearshore groundwater discharge: Kahekili Beach Park submarine springs, Maui, Hawaii

Study region The study region encompasses the nearshore, coastal waters off west Maui, Hawaii. Here abundant groundwater—that carries with it a strong land-based fingerprint—discharges into the coastal waters and over a coral reef. Study focus Coastal groundwater discharge is a ubiquitous hydrologic feature that has been shown to impact nearshore ecosystems and material budgets. A unique combined geochemical tracer and oceanographic time-series study addressed rates and oceanic forcings of submarine groundwater discharge at a submarine spring site off west Maui, Hawaii. New hydrological insights for the region Estimates of submarine groundwater discharge were derived for a primary vent site and surrounding coastal waters off west Maui, Hawaii using an excess 222 Rn ( t 1/2 = 3.8 d) mass balance model. Such estimates were complemented with a novel thoron ( 220 Rn, t 1/2 = 56 s) groundwater discharge tracer application, as well as oceanographic time series and thermal infrared imagery analyses. In combination, this suite of techniques provides new insight into the connectivity of the coastal aquifer with the near-shore ocean and examines the physical drivers of submarine groundwater discharge. Lastly, submarine groundwater discharge derived constituent concentrations were tabulated and compared to surrounding seawater concentrations. Such work has implications for the management of coastal aquifers and downstream nearshore ecosystems that respond to sustained constituent loadings via this submarine route.

Hawaii↗
USGS2020

Probabilistic application of an integrated catchment-estuary-coastal system model to assess the evolution of inlet-interrupted coasts over the 21st century

Inlet-interrupted sandy coasts are dynamic and complex coastal systems with continuously evolving geomorphological behaviors under the influences of both climate change and human activities. These coastal systems are of great importance to society (e.g., providing habitats, navigation, and recreational activities) and are affected by both oceanic and terrestrial processes. Therefore, the evolution of these inlet-interrupted coasts is better assessed by considering the entirety of the Catchment-Estuary-Coastal (CEC) systems, under plausible future scenarios for climate change and increasing pressures due to population growth and human activities. Such a holistic assessment of the long-term evolution of CEC systems can be achieved via reduced-complexity modeling techniques, which are also ably quantifying the uncertainties associated with the projections due to their lower simulation times. Here, we develop a novel probabilistic modeling framework to quantify the input-driven uncertainties associated with the evolution of CEC systems over the 21 st century. In this new approach, probabilistic assessment of the evolution of inlet-interrupted coasts is achieved by (1) probabilistically computing the exchange sediment volume between the inlet-estuary system and its adjacent coast, and (2) distributing the computed sediment volumes along the inlet-interrupted coast. The model is applied at three case study sites: Alsea estuary (United States), Dyfi estuary (United Kingdom), and Kalutara inlet (Sri Lanka). Model results indicate that there are significant uncertainties in projected volume exchange at all the CEC systems (min-max range of 2.0 million cubic meters in 2100 for RCP 8.5), and the uncertainties in these projected volumes illustrate the need for probabilistic modeling approaches to evaluate the long-term evolution of CEC systems. A comparison of 50 th percentile probabilistic projections with deterministic estimates shows that the deterministic approach overestimates the sediment volume exchange in 2100 by 15–30% at Alsea and Kalutara estuary systems. Projections of coastline change obtained for the case study sites show that accounting for all key processes governing coastline change along inlet-interrupted coasts in computing coastline change results in projections that are between 20 and 134% greater than the projections that would be obtained if only the Bruun effect were taken into account, underlining the inaccuracies associated with using the Bruun rule at inlet-interrupted coasts.

Frontiers in Applied Mathematics and Statistics↗
USGS2024

Modeling the potential spread of the non-native regal demoiselle, Neopomacentrus cyanomos, in the western Atlantic

Predicting the potential distribution of a non-native species can assist management efforts to mitigate impacts on recipient ecosystems. However, such predictions are lacking for marine species, such as the non-native regal demoiselle, Neopomacentrus cyanomos , that is currently expanding its distribution in the western Atlantic. We used correlative species distribution models with three common algorithms to predict suitable habitat for N. cyanomos in the region. We compared models developed using native, non-native, and global occurrences to differentiate drivers across separate ranges using a suite of 12 environmental characteristics. While final models included an ensemble of variables, the majority ranked the combined effect of temperature variables as a key predictor correlated with the distribution of N. cyanomos. Habitat suitability increased as water temperatures increased beyond 16 °C and where annual thermal ranges were greater than 10 °C at the shallowest depth with substrate within a study cell (~ 9.2 km 2 resolution). Habitat suitability also increased where maximum surface temperatures were greater than 27 °C. In the non-native range, the proportion of reef available in each cell was another important variable increasing the suitable habitat for N. cyanomos . Our models predicted high habitat suitability for N. cyanomos throughout the Greater Caribbean, in higher latitudes along North and South American Atlantic coasts, in the eastern Pacific Ocean, and highlights key areas where managers can monitor and target potential removal efforts. The distribution of this non-native species is likely to continue expanding throughout the region with little known about potential implications on native communities.

Coral Reefs↗
USGS1987

Origins of seawater intrusion in a coastal aquifer - A case study of the Pajaro Valley, California

Seawater may enter and contaminate stratified coastal aquifers through a number of different pathways. These pathways and their relative contribution are examined in the Pajaro Valley, California, a coastal area with extensive groundwater development. This study considers three pathways of possible intrusion of the primary confined aquifer: (1) onshore leakage from brackish sources, the estuary and sloughs, through the confining layer; (2) near-shore leakage from the ocean through the confining layer; and (3) offshore flow from the ocean through the submarine canyon outcrop of the aquifer. Groundwater flow and seawater intrusion are simulated using an areal, two-dimensional solute-transport computer model. This analysis indicates that leakage through confining layers is the principal mechanism of recharge to the aquifer. Although lateral flow through the offshore outcrop contaminates the aquifer, as a whole, at a higher rate, vertical leakage through the sea floor initially is the main pathway of seawater intrusion to the onshore portion of the aquifer. It is likely that leakage generally is the dominant mechanism of recharge and initial cause of seawater intrusion for poorly-confined, stratified coastal aquifers. This analysis suggests that a significant time interval follows the initial observation of seawater intrusion, during which remedial action can be taken to control lateral flow through the offshore outcrop, which ultimately will be the largest component of future intrusion in these aquifers.

California↗
USGS2019

Isotopic ratios of Saturn's rings and satellites: Implications for the origin of water and Phoebe

Isotopic ratios have long been used to learn about physical processes acting over a wide range of geological environments, and in constraining the origin and/or evolution of planetary bodies. We report the spectroscopic detection of deuterium in Saturn's rings and satellites, and use these measurements to determine the (D/H) ratios in their near-surface regions. Saturn's moons, Phoebe and Iapetus, show a strong signature of CO2 and the 13C component of this molecule is detected and quantified. Large averages of spectra obtained by the Cassini Visual and Infrared Mapping Spectrometer, VIMS, were computed for the rings and icy satellites. The observed intensities of the infrared absorptions in H2O and CO2 and their isotopes were calibrated using laboratory data and radiative transfer models to derive the D/H and 13C/12C ratios. We find that the D/H in Saturn's rings and satellites is close to the Vienna Standard Mean Ocean Water (VSMOW) and bulk Earth (4% lower than VSMOW) value except for Phoebe, which is 8.3 times the VSMOW value. This is the highest value for any Solar-System surface yet measured, and suggests that Phoebe formed from material with a different D/H ratio than the other satellites in the Saturn system. Phoebe’s 13C/12C ratio is also unusual: 4.7 times greater than terrestrial, and greater than values measured for the interstellar medium and the galactic center. The high 13C abundance in the CO2 suggests that Phoebe was never warm enough for the large D/H ratio in its surface to have originated by evaporative fractionation of its waterice (e.g., from heating in the inner Solar System before its eventual capture by Saturn). We also report the detection of a probable O-D stretch absorption due to OD in minerals on Phoebe at 3.62 μm. This absorption is not detected on other Saturnian satellites. Stronger signatures of bound water absorptions are found in the dark material of Iapetus and we report a new detection of bound water at 1.9 μm. The position of this absorption matches that seen in spectra of hydrated iron oxides but does not match absorptions seen in spectra of tholins. Despite the strong bound water signature in the Iapetus dark material, no 3.62-μm OD absorption is seen in the spectra, further indicating the high deuterium level on Phoebe is unusual. As such, it is likely that Phoebe originated in a colder part of the outer Solar System, relative to the prevailing temperatures at Saturn’s distance from the Sun.

Icarus↗
USGS2006

Composition of Titan's surface from Cassini VIMS

Titan's bulk density along with Solar System formation models indicates considerable water as well as silicates as its major constituents. This satellite's dense atmosphere of nitrogen with methane is unique. Deposits or even oceans of organic compounds have been suggested to exist on Titan's solid surface due to UV-induced photochemistry in the atmosphere. Thus, the composition of the surface is a major piece of evidence needed to determine Titan's history. However, studies of the surface are hindered by the thick, absorbing, hazy and in some places cloudy atmosphere. Ground-based telescope investigations of the integral disk of Titan attempted to observe the surface albedo in spectral windows between methane absorptions by calculating and removing the haze effects. Their results were reported to be consistent with water ice on the surface that is contaminated with a small amount of dark material, perhaps organic material like tholin. We analyze here the recent Cassini Mission's visual and infrared mapping spectrometer (VIMS) observations that resolve regions on Titan. VIMS is able to see surface features and shows that there are spectral and therefore likely compositional units. By several methods, spectral albedo estimates within methane absorption windows between 0.75 and 5 ??m were obtained for different surface units using VIMS image cubes from the Cassini-Huygens Titan Ta encounter. Of the spots studied, there appears to be two compositional classes present that are associated with the lower albedo and the higher albedo materials, with some variety among the brighter regions. These were compared with spectra of several different candidate materials. Our results show that the spectrum of water ice contaminated with a darker material matches the reflectance of the lower albedo Titan regions if the spectral slope from 2.71 to 2.79 ??m in the poorly understood 2.8-??m methane window is ignored. The spectra for brighter regions are not matched by the spectrum of water ice or unoxidized tholin, in pure form or in mixtures with sufficient ice or tholin present to allow the water ice or tholin spectral features to be discerned. We find that the 2.8-??m methane absorption window is complex and seems to consist of two weak subwindows at 2.7 and 2.8 ??m that have unknown opacities. A ratio image at these two wavelengths reveals an anomalous region on Titan that has a reflectance unlike any material so far identified, but it is unclear how much the reflectances in these two subwindows pertain to the surface. ?? 2006 Elsevier Ltd. All rights reserved.

Planetary and Space Science↗
USGS2003

Density of the continental roots: Compositional and thermal contributions

The origin and evolution of cratonic roots has been debated for many years. Precambrian cratons are underlain by cold lithospheric roots that are chemically depleted. Thermal and petrologic data indicate that Archean roots are colder and more chemically depleted than Proterozoic roots. This observation has led to the hypothesis that the degree of depletion in a lithospheric root depends mostly on its age. Here we test this hypothesis using gravity, thermal, petrologic, and seismic data to quantify differences in the density of cratonic roots globally. In the first step in our analysis we use a global crustal model to remove the crustal contribution to the observed gravity. The result is the mantle gravity anomaly field, which varies over cratonic areas from -100 to +100 mGal. Positive mantle gravity anomalies are observed for cratons in the northern hemisphere: the Baltic shield, East European Platform, and the Siberian Platform. Negative anomalies are observed over cratons in the southern hemisphere: Western Australia, South America, the Indian shield, and Southern Africa. This indicates that there are significant differences in the density of cratonic roots, even for those of similar age. Root density depends on temperature and chemical depletion. In order to separate these effects we apply a lithospheric temperature correction using thermal estimates from a combination of geothermal modeling and global seismic tomography models. Gravity anomalies induced by temperature variations in the uppermost mantle range from -200 to +300 mGal, with the strongest negative anomalies associated with mid-ocean ridges and the strongest positive anomalies associated with cratons. After correcting for thermal effects, we obtain a map of density variations due to lithospheric compositional variations. These maps indicate that the average density decrease due to the chemical depletion within cratonic roots varies from 1.1% to 1.5%, assuming the chemical boundary layer has the same thickness as the thermal boundary layer. The maximal values of the density drop are in the range 1.7-2.5%, and correspond to the Archean portion of each craton. Temperatures within cratonic roots vary strongly, and our analysis indicates that density variations in the roots due to temperature are larger than the variations due to chemical differences.

Earth and Planetary Science Letters↗
USGS2014

Pb-Sr-Nd-O isotopic characterization of Mesozoic rocks throughout the northern end of the Peninsular Ranges batholith: Isotopic evidence for the magmatic evolution of oceanic arc–continental margin accretion during the Late Cretaceous of southern California

Within the duration of the U.S. Geological Survey (USGS)–based Southern California Areal Mapping Project (SCAMP), many samples from the northern Peninsular Ranges batholith were studied for their whole-rock radioisotopic systematics (rubidium-strontium [Rb-Sr], uranium-thorium-lead [U-Th-Pb], and samarium-neodymium [Sm-Nd]), as well as oxygen (O), a stable isotope. The results of three main studies are presented separately, but here we combine them (>400 analyses) to produce a very complete Pb-Sr-Nd-O isotopic profile of an arc-continent collisional zone—perhaps the most complete in the world. In addition, because many of these samples have U-Pb zircon as well as argon mineral age determinations, we have good control of the timing for Pb-Sr-Nd-O isotopic variations. The ages and isotopic variations help to delineate at least four zones across the batholith from west to east—an older western zone (126–108 Ma), a transitional zone (111–93 Ma), an eastern zone (94–91 Ma), and a much younger allochthonous thrust sheet (ca. 84 Ma), which is the upper plate of the Eastern Peninsular Ranges mylonite zone. Average initial 87 Sr/ 86 Sr (Sr i ), initial 206 Pb/ 204 Pb ( 206 Pb i ), initial 208 Pb/ 204 Pb (average 208 Pb i ), initial epsilon Nd (average ε Ndi ), and δ 18 O signatures range from 0.704, 18.787, 38.445, +3.1, and 4.0‰–9.0‰, respectively, in the westernmost zone, to 0.7071, 19.199, 38.777, −5, and 9‰–12‰, respectively, in the easternmost zone. The older western zone is therefore the more chemically and isotopically juvenile, characterized mostly by values that are slightly displaced from a mantle array at ca. 115 Ma, and similar to some modern island-arc signatures. In contrast, the isotopic signatures in the eastern zones indicate significant amounts of crustal involvement in the magmatic plumbing of those plutons. These isotopic signatures confirm previously published results that interpreted the Peninsular Ranges batholith as a progressively contaminated magmatic arc. The Peninsular Ranges batholith magmatic arc was initially an oceanic arc built on Panthalassan lithosphere that eventually evolved into a continental margin magmatic arc collision zone, eventually overriding North American cratonic lithosphere. Our Pb-Sr-Nd data further suggest that the western arc rocks represent a nearshore or inboard oceanic arc, as they exhibit isotopic signatures that are more enriched than typical mid-ocean-ridge basalt (MORB). Isotopic signatures from the central zone are transitional and indicate that enriched crustal magma sources were becoming involved in the northern Peninsular Ranges batholith magmatic plumbing. As the oceanic arc–continental margin collision progressed, a mixture of oceanic mantle and continental magmatic sources transpired. Magmatic production in the northern Peninsular Ranges batholith moved eastward and continued to tap enriched crustal magmatic sources. Similar modeling has been previously proposed for two other western margin magmatic arcs, the Sierra Nevada batholith of central California and the Idaho batholith. Calculated initial Nd signatures at ca. 100 Ma for Permian–Jurassic and Proterozoic basement rocks from the nearby San Gabriel Mountains and possible source areas along the southwestern Laurentian margin of southern California, southwestern Arizona, and northern Sonora strongly suggest their involvement with deep crustal magma mixing beneath the eastern zones of the Peninsular Ranges batholith, as well as farther east in continental lithospheric zones. Last, several samples from the allochthonous, easternmost upper-plate zone, which are considerably younger (ca. 84 Ma) than any of the rocks from the northern Peninsular Ranges batholith proper, have even more enriched average Sr i , 206 Pb i , 208 Pb i , and ε Ndi signatures of 0.7079, 19.344, 38.881, and −6.6, respectively, indicative of the most-evolved magma sources in the northern Peninsular Ranges batholith and similar to radioisotopic values for rocks from the nearby Transverse Ranges, suggesting a genetic connection between the two.

Book chapter↗
USGS2005

Advanced Very High Resolution Radiometer Normalized Difference Vegetation Index Composites

The Advanced Very High Resolution Radiometer (AVHRR) is a broad-band scanner with four to six bands, depending on the model. The AVHRR senses in the visible, near-, middle-, and thermal- infrared portions of the electromagnetic spectrum. This sensor is carried on a series of National Oceanic and Atmospheric Administration (NOAA) Polar Orbiting Environmental Satellites (POES), beginning with the Television InfraRed Observation Satellite (TIROS-N) in 1978. Since 1989, the United States Geological Survey (USGS) Center for Earth Resources Observation and Science (EROS) has been mapping the vegetation condition of the United States and Alaska using satellite information from the AVHRR sensor. The vegetation condition composites, more commonly called greenness maps, are produced every week using the latest information on the growth and condition of the vegetation. One of the most important aspects of USGS greenness mapping is the historical archive of information dating back to 1989. This historical stretch of information has allowed the USGS to determine a 'normal' vegetation condition. As a result, it is possible to compare the current week's vegetation condition with normal vegetation conditions. An above normal condition could indicate wetter or warmer than normal conditions, while a below normal condition could indicate colder or dryer than normal conditions. The interpretation of departure from normal will depend on the season and geography of a region.

Fact Sheet↗
USGS2000

Modeling surface trapped river plumes: A sensitivity study

To better understand the requirements for realistic regional simulation of river plumes in the Gulf of Maine, we test the sensitivity of the Blumberg-Mellor hydrodynamic model to choice of advection scheme, grid resolution, and wind, using idealized geometry and forcing. The test case discharges 1500 m3/s of fresh water into a uniform 32 psu ocean along a straight shelf at 43?? north. The water depth is 15 m at the coast and increases linearly to 190 m at a distance 100 km offshore. Constant discharge runs are conducted in the presence of ambient alongshore current and with and without periodic alongshore wind forcing. Advection methods tested are CENTRAL, UPWIND, the standard Smolarkiewicz MPDATA and a recursive MPDATA scheme. For the no-wind runs, the UPWIND advection scheme performs poorly for grid resolutions typically used in regional simulations (grid spacing of 1-2 km, comparable to or slightly less than the internal Rossby radius, and vertical resolution of 10% of the water column), damping out much of the plume structure. The CENTRAL difference scheme also has problems when wind forcing is neglected, and generates too much structure, shedding eddies of numerical origin. When a weak 5 cm/s ambient current is present in the no-wind case, both the CENTRAL and standard MPDATA schemes produce a false fresh- and dense-water source just upstream of the river inflow due to a standing two-grid length oscillation in the salinity field. The recursive MPDATA scheme completely eliminates the false dense water source, and produces results closest to the grid-converged solution. The results are shown to be very sensitive to vertical grid resolution, and the presence of wind forcing dramatically changes the nature of the plume simulations. The implication of these idealized tests for realistic simulations is discussed, as well as ramifications on previous studies of idealized plume models.

Maine↗
USGS2003

Source depth dependence of micro-tsunamis recorded with ocean-bottom pressure gauges: The January 28, 2000 Mw 6.8 earthquake off Nemuro Peninsula, Japan

Micro-tsunami waves with a maximum amplitude of 4-6 mm were detected with the ocean-bottom pressure gauges on a cabled deep seafloor observatory south of Hokkaido, Japan, following the January 28, 2000 earthquake (M w 6.8) in the southern Kuril subduction zone. We model the observed micro-tsunami and estimate the focal depth and other source parameters such as fault length and amount of slip using grid searching with the least-squares method. The source depth and stress drop for the January 2000 earthquake are estimated to be 50 km and 7 MPa, respectively, with possible ranges of 45-55 km and 4-13 MPa. Focal depth of typical inter-plate earthquakes in this region ranges from 10 to 20 km and stress drop of inter-plate earthquakes generally is around 3 MPa. The source depth and stress drop estimates suggest that the earthquake was an intra-slab event in the subducting Pacific plate, rather than an inter-plate event. In addition, for a prescribed fault width of 30 km, the fault length is estimated to be 15 km, with possible ranges of 10-20 km, which is the same as the previously determined aftershock distribution. The corresponding estimate for seismic moment is 2.7x10 19 Nm with possible ranges of 2.3x10 19 -3.2x10 19 Nm. Standard tide gauges along the nearby coast did not record any tsunami signal. High-precision ocean-bottom pressure measurements offshore thus make it possible to determine fault parameters of moderate-sized earthquakes in subduction zones using open-ocean tsunami waveforms. Published by Elsevier Science B. V.

Earth and Planetary Science Letters↗
USGS2014

An enhanced model of land water and energy for global hydrologic and earth-system studies

LM3 is a new model of terrestrial water, energy, and carbon, intended for use in global hydrologic analyses and as a component of earth-system and physical-climate models. It is designed to improve upon the performance and to extend the scope of the predecessor Land Dynamics (LaD) and LM3V models by better quantifying the physical controls of climate and biogeochemistry and by relating more directly to components of the global water system that touch human concerns. LM3 includes multilayer representations of temperature, liquid water content, and ice content of both snowpack and macroporous soil–bedrock; topography-based description of saturated area and groundwater discharge; and transport of runoff to the ocean via a global river and lake network. Sensible heat transport by water mass is accounted throughout for a complete energy balance. Carbon and vegetation dynamics and biophysics are represented as in LM3V. In numerical experiments, LM3 avoids some of the limitations of the LaD model and provides qualitatively (though not always quantitatively) reasonable estimates, from a global perspective, of observed spatial and/or temporal variations of vegetation density, albedo, streamflow, water-table depth, permafrost, and lake levels. Amplitude and phase of annual cycle of total water storage are simulated well. Realism of modeled lake levels varies widely. The water table tends to be consistently too shallow in humid regions. Biophysical properties have an artificial stepwise spatial structure, and equilibrium vegetation is sensitive to initial conditions. Explicit resolution of thick (>100 m) unsaturated zones and permafrost is possible, but only at the cost of long (≫300 yr) model spinup times.

Journal of Hydrometeorology↗
USGS1996

Hydrogeology of structurally extended terrain in the eastern Great Basin of Nevada, Utah, and adjacent states, from geologic and geophysical models

The Great Basin of the western United States encompasses most of Nevada and western Utah (fig. 1). The climate of the region is semiarid to arid, with most precipitation falling as winter Show. The region is characterized by internal drainage (generally no hydrologic outlet to the ocean). Water resources in the region are limited and nearly all reliable surface-water sources have been allocated for use. The most commonly used aquifers arc sand-and-gravel basin-fill deposits in structural basins of the region. In many basins, pumpage from the basin-fill aquifers is as much as (or more than) the safe yield. Consequently, aquifers other than basin fill are being assessed in the eastern Great Basin to determine where and how much additional ground water is present and what might be the effects of development. This study was part of the Nevada Carbonate Aquifers Program, in cooperation with the State of Nevada, Las Vegas Valley Water District, City of North Las Vegas, and the Bureau of Reclamation. This atlas presents a conceptual model of the geologic and hydrologic features of structurally extended terrains in the eastern Great Basin. First, the model is described and major structural features are compared with regional groundwater flow patterns. Second, the validity of the conceptual hydrogeologic model is evaluated using geophysical data and geologic models derived from geophysical profiles.

Nevada;Utah↗
USGS1998

Geohydrology of Storage Unit III and a combined flow model of the Santa Barbara and foothill ground-water basins, Santa Barbara County, California

The city of Santa Barbara pumps most of its ground water from the Santa Barbara and Foothill ground-water basins. The Santa Barbara basin is subdivided into two storage units: Storage Unit I and Storage Unit III. The Foothill basin and Storage Unit I of the Santa Barbara basin have been studied extensively and ground-water flow models have been developed for them. In this report, the geohydrology of the Santa Barbara ground- water basin is described with a special emphasis on Storage Unit III in the southwestern part of the basin. The purposes of this study were to summarize and evaluate the geohydrology of Storage Unit III and to develop an areawide model of the Santa Barbara and Foothill basins that includes the previously unmodeled Storage Unit III. Storage Unit III is in the southwestern part of the city of Santa Barbara. It is approximately 3.5 miles long and varies in width from about 2,000 feet in the southeast to 4,000 feet in the north-west. Storage Unit III is composed of the Santa Barbara Formation and overlying alluvium. The Santa Barbara Formation (the principal aquifer) consists of Pleistocene and Pliocene(?) unconsolidated marine sand, silt, and clay, and it has a maximum saturated thickness of about 160 feet. The alluvium that overlies the Santa Barbara Formation has a maximum saturated thickness of about 140 feet. The storage unit is bounded areally by faults and low-permeability deposits and is underlain by rocks of Tertiary age. The main sources of recharge to Storage Unit III are seepage from Arroyo Burro and infiltration of precipitation. Most of the recharge occurs in the northwest part of the storage unit, and ground water flows toward the southeast along the unit's long axis. Lesser amounts of recharge may occur as subsurface flow from the Hope Ranch subbasin and as upwelling from the underlying Tertiary rocks. Discharge from Storage Unit III occurs as pumpage, flow to underground drains, underflow through alluvium in the vicinity of Arroyo Burro across the Lavigia Fault, evapotranspiration, and underflow to the Pacific Ocean. The faults that bound Storage Unit III generally are considered to be effective barriers to the flow of ground water. Interbasin ground-water flow occurs where deposits of younger alluvium along stream channels cross faults. Ground-water quality in Storage Unit III deposits varies with location and depth. Upward leakage of poor-quality water from the underlying Tertiary rocks occurs in the storage unit, and such leakage can be influenced by poor well construction or by heavy localized pumping. The highest dissolved-solids concentration (4,710 milligrams per liter) in ground water resulting from this upward leakage is found in the coastal part of the storage unit. The ground-water system was modeled as two horizontal layers. In the Foothill basin and Storage Unit I the layers are separated by a confining bed. The upper layer represents the upper producing zone and the shallow zone near the coast. The lower layer represents the lower producing zone. In general, the faults in the study area were assumed to be no-flow boundaries, except for the offshore fault that forms the southeast boundary; the southeast boundary was simulated as a general-head boundary. The Storage Unit III model was combined with the preexisting Storage Unit I and Foothill basin models, using horizontal flow barriers, to form an areawide model. The areawide model was calibrated by simulating steady-state predevelopment conditions and transient conditions for 1978-92. The nonpumping steady- state simulation was used to verify that the calibrated model yielded physically reasonable results for predevelopment conditions. The calibrated areawide model calculates water levels in Storage Unit III that are within 10 feet of measured water levels at all sites of comparison. In addition, the model adequately simulates water levels in the Storage Unit I and Foothill basin areas. A total of 33,430 acre-feet of water was pumped from the study area during the simulation period. Model results indicate that 2,833 acre-feet came from storage and 5, 332 acre-feet crossed the general-head boundary from the ocean, thus indicating that seawater intrusion could occur. A sensitivity analysis indicates that, in general, the model is most sensitive to changes in transmissivity and total recharge.

California↗
USGS2010

Preliminary slope-stability analysis of Augustine Volcano: Chapter 14 in The 2006 eruption of Augustine Volcano, Alaska

Augustine Volcano has been a prolific producer of large debris avalanches during the Holocene. Originating as landslides from the steep upper edifice, these avalanches typically slide into the surrounding ocean. At least one debris avalanche that occurred in 1883 during an eruption initiated a far-traveled tsunami. The possible occurrence of another edifice collapse and ensuing tsunami was a concern during the 2006 eruption of Augustine. To aid in hazard assessments, we have evaluated the slope stability of Augustine's edifice, using a quasi-three-dimensional, geotechnically based slope-stability model implemented in the computer program SCOOPS. We analyzed the effects of topography, variations in rock strength, and earthquake-induced strong ground motion on the relative stability of millions of potential large (>0.1 km 3 volume) slope failures throughout the edifice. Preliminary results from pre-2006 topography provide three insights. First, the predicted stability of all parts of the upper edifice is approximately the same, suggesting an equal likelihood of slope failure, in agreement with geologic observations that debris avalanches have swept all sectors of the volcano. Second, the least stable (by a small amount) sector is on the east flank where a debris avalanche would flow into deeper ocean water and a resulting tsunami would be directed toward the southwestern part of the Kenai Peninsula. Third, most model scenarios predict stable edifice slopes, and only scenarios assuming extensive weak rocks and moderate to strong ground shaking predict potential large collapses. Because other transient triggering mechanisms, such as shallow magma intrusion, may be needed to instigate slope instability, monitoring ground deformation and seismicity could

Alaska↗
USGS2015

Documentation of a restart option for the U.S. Geological Survey coupled Groundwater and Surface-Water Flow (GSFLOW) model

A new option to write and read antecedent conditions (also referred to as initial conditions) has been developed for the U.S. Geological Survey (USGS) Groundwater and Surface-Water Flow (GSFLOW) numerical, hydrologic simulation code. GSFLOW is an integration of the USGS Precipitation-Runoff Modeling System (PRMS) and USGS Modular Groundwater-Flow Model (MODFLOW), and provides three simulation modes: MODFLOW-only, PRMS-only, and GSFLOW (or coupled). The new capability, referred to as the restart option, can be used for all three simulation modes, such that the results from a pair (or set) of spin-up and restart simulations are nearly identical to results produced from a continuous simulation for the same time period. The restart option writes all results to files at the end of a spin-up simulation that are required to initialize a subsequent restart simulation. Previous versions of GSFLOW have had some capability to save model results for use as antecedent condiitions in subsequent simulations; however, the existing capabilities were not comprehensive or easy to use. The new restart option supersedes the previous methods. The restart option was developed in collaboration with the National Oceanic and Atmospheric Administration, National Weather Service as part of the Integrated Water Resources Science and Services Partnership. The primary focus for the development of the restart option was to support medium-range (7- to 14-day) forecasts of low streamflow conditions made by the National Weather Service for critical water-supply basins in which groundwater plays an important role. The spin-up simulation should be run for a sufficient length of time necessary to establish antecedent conditions throughout a model domain. Each GSFLOW application can require different lengths of time to account for the hydrologic stresses to propagate through a coupled groundwater and surface-water system. Typically, groundwater hydrologic processes require many years to come into equilibrium with dynamic climate and other forcing (or stress) data, such as precipitation and well pumping, whereas runoff-dominated surface-water processes respond relatively quickly. Use of a spin-up simulation can substantially reduce execution-time requirements for applications where the time period of interest is small compared to the time for hydrologic memory; thus, use of the restart option can be an efficient strategy for forecast and calibration simulations that require multiple simulations starting from the same day.

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