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USGS2024

Precision of four calcified structures for age estimation of Black Carp

Objective Black Carp Mylopharyngodon piceus is an emerging invasive species in North America with an expanding population in the Mississippi River basin. Current aging methods use a suite of structures for age estimation, and a single structure is needed to minimize processing time, to maximize consistency of age and growth measurements, and to allow for back-calculation of individual fish length at age. Methods In total, 236 Black Carp were collected throughout the year from 2017 to 2019 through incidental captures by commercial fishers and biologists. In a subsample, 119 Black Carp from 429 to 1268 mm total length were compared for the precision of annuli counts by two experienced readers for the two anterior pectoral fin rays, the anterior dorsal fin ray, sectioned vertebrae, and lapilli otoliths based on percent exact agreement (PA), percent agreement within 1 year (PA ± 1), coefficient of variation (CV), and bubble plots. Consensus annuli counts were compared by PA and CV between structures. We applied annuli counts, as opposed to age, as fish were collected during all seasons and structures were examined independently by readers without knowledge of capture date. Result Vertebrae and dorsal rays had the highest PA between readers. Dorsal ray had the lowest CV and higher PA ± 1. Pectoral rays and lapilli otoliths had the lowest PA. Between-structure consensus annuli counts indicated that pectoral rays and the dorsal ray annuli counts were the most similar (PA >70% and CV <12) and lapilli otoliths were the most dissimilar (PA >35% and CV >24). Reader-reported confidence was highest for vertebrae, then in decreasing order, dorsal ray, pectoral rays, and lapilli otoliths. Lumens were present in all fin rays with only minor effects observed on annuli counts, aside from the anterior-most pectoral fin ray, in which lumens obscured the presence of one or more potential annuli in 61% of structures. Conclusion The dorsal ray had the highest agreement between readers, with agreement with ±1 year at 98%; the structure can be efficiently extracted and processed, and the structure's morphology and growth pattern are conducive to aging older fish. Vertebrae had high agreement between readers, but a systematic pattern of double bands in vertebrae increased the between-reader variation in older fish as the interannual growth pattern compressed the viewable area; this was identified by readers based on aging criteria and highlights the need for training novice readers. Validation of annual growth in the tested suite of structures is still needed.

Mississippi River↗

USGS2005

Parallel structure among environmental gradients and three trophic levels in a subarctic estuary

We assessed spatial and temporal variability in the physical environment of a subarctic estuary, and examined concurrent patterns of chlorophyll α abundance (fluorescence), and zooplankton and forage fish community structure. Surveys were conducted in lower Cook Inlet, Alaska, during late July and early August from 1997 through 1999. Principle components analysis (PCA) revealed that spatial heterogeneity in the physical oceanographic environment of lower Cook Inlet could be modeled as three marine-estuarine gradients characterized by temperature, salinity, bottom depth, and turbidity. The gradients persisted from 1997 through 1999, and PCA explained 68% to 92% of the variance in physical oceanography for each gradient-year combination. Correlations between chlorophyll α abundance and distribution and the PCA axes were weak. Chlorophyll was reduced by turbidity, and low levels occurred in areas with high levels of suspended sediments. Detrended correspondence analysis (DCA) was used to order the sample sites based on species composition and to order the zooplankton and forage fish taxa based on similarities among sample sites for each gradient-year. Correlations between the structure of the physical environment (PCA axis 1) and zooplankton community structure (DCA axis 1) were strong (r = 0.43-0.86) in all years for the three marine-estuarine gradients, suggesting that zooplankton community composition was structured by the physical environment. The physical environment (PCA) and forage fish community structure (DCA) were weakly correlated in all years along Gradient 2, defined by halocline intensity and surface temperature and salinity, even though these physical variables were more important for defining zooplankton habitats. However, the physical environment (PCA) and forage fish community structure (DCA) were strongly correlated along the primary marine-estuarine gradient (#1) in 1997 (r = 0.87) and 1998 (r = 0.82). The correlation was poor (r = 0.32) in 1999, when fish community structure changed markedly in lower Cook Inlet. Capelin (Mallotus villosus), walleye pollock ( Theragra chalcogramma ), and arrowtooth flounder ( Atheresthes stomias ) were caught farther north than in previous years. Waters were significantly colder and more saline in 1999, a La Nina year, than in other years of the study. Interannual fluctuations in environmental conditions in lower Cook Inlet did not have substantial effects on zooplankton community structure, although abundance of individual taxa varied significantly. The abundance and distribution of chlorophyll α, zooplankton and forage fish were affected much more by spatial variability in physical oceanography than by interannual variability. Our examination of physical-biological linkages in lower Cook Inlet supports the concept of "bottom-up control," i.e., that variability in the physical environment structures higher trophic-level communities by influencing their distribution and abundance across space.

Progress in Oceanography↗

USGS2018

Investigation into the effect of heteroatom content on kerogen structure using advanced 13C solid-state nuclear magnetic resonance spectroscopy

To elucidate how different extreme heteroatom concentrations in oil shale kerogen may present and contribute to various structural features, three shale samples, containing kerogen with high oxygen content, low heteroatom content, and high sulfur content, were analyzed using advanced 13 C solid-state nuclear magnetic resonance (NMR) techniques, including multiple cross-polarization/magic angle spinning (multiCP/MAS), dipolar dephasing (multiCP/DD), and 2D 1 H– 13 C heteronuclear correlation (2D HETCOR). We found that oxygen in Estonian kukersite was present mostly in aromatic C–O structures and that nonprotonated aromatic carbons bonded to oxygen and alkyl chains led to more diverse aromatic signal distributions and structures in the kukersite organic matter than were observed in the other shales. The low-heteroatom kerogen present in Australian Glen Davis torbanite had the simplest structural pattern and the lowest aromaticity, despite having a lower atomic H/C ratio than the kerogens present in the other shales. The organic sulfur-rich Ghareb marinite from Jordan contained the highest aromaticity and most diverse alkyl structures among the three shales. 2D HETCOR with 1 H spin diffusion showed that the structural heterogeneity of the Glen Davis kerogen was <1 nm, indicating the preservation of structures present in precursor organic matter. Like previous NMR studies of shales and kerogens, this analysis of organic matter in whole shale samples with unusual heteroatom content demonstrates that structural characteristics in organic matter are not necessarily captured by kerogen typing based solely on elemental ratios (H/C, O/C) or programmed pyrolysis parameters and that NMR provides deeper insights into kerogen structure.

Energy & Fuels↗

USGS2001

Upper crustal structure in Puget Lowland, Washington: Results from the 1998 Seismic Hazards Investigation in Puget Sound

A new three-dimensional (3-D) model shows seismic velocities beneath the Puget Lowland to a depth of 11 km. The model is based on a tomographic inversion of nearly one million first-arrival travel times recorded during the 1998 Seismic Hazards Investigation in Puget Sound (SHIPS), allowing higher-resolution mapping of subsurface structures than previously possible. The model allows us to refine the subsurface geometry of previously proposed faults (e.g., Seattle, Hood Canal, southern Whidbey Island, and Devils Mountain fault zones) as well as to identify structures (Tacoma, Lofall, and Sequim fault zones) that warrant additional study. The largest and most important of these newly identified structures lies along the northern boundary of the Tacoma basin; we informally refer to this structure here as the Tacoma fault zone. Although tomography cannot provide information on the recency of motion on any structure, Holocene earthquake activity on the Tacoma fault zone is suggested by seismicity along it and paleoseismic evidence for abrupt uplift of tidal marsh deposits to its north. The tomography reveals four large, west to northwest trending low-velocity basins (Tacoma, Seattle, Everett, and Port Townsend) separated by regions of higher velocity ridges that are coincident with fault-bounded uplifts of Eocene Crescent Formation basalt and pre-Tertiary basement. The shapes of the basins and uplifts are similar to those observed in gravity data; gravity anomalies calculated from the 3-D tomography model are in close agreement with the observed anomalies. In velocity cross sections the Tacoma and Seattle basins are asymmetric: the basin floor dips gently toward a steep boundary with the adjacent high-velocity uplift, locally with a velocity "overhang" that suggests a basin vergent thrust fault boundary. Crustal fault zones grow from minor folds into much larger structures along strike. Inferred structural relief across the Tacoma fault zone increases by several kilometers westward along the fault zone to Lynch Cove, where we interpret it as a zone of south vergent faulting overthrusting Tacoma basin. In contrast, structural relief along the Seattle fault zone decreases west of Seattle, which we interpret as evidence that the N-S directed compression is being accommodated by slip transfer between the Seattle and Tacoma fault zones. Together, the Tacoma and Seattle fault zones raise the Seattle uplift, one of a series of east-west trending, pop-up structures underlying Puget Lowland from the Black Hills to the San Juan Islands.

Washington↗

USGS2010

The evolution of forearc structures along an oblique convergent margin, central Aleutian Arc

Multichannel seismic reflection data were used to determine the evolutionary history of the forearc region of the central Aleutian Ridge. Since at least late Miocene time this sector of the ridge has been obliquely underthrust 30° west of orthogonal convergence by the northwestward converging Pacific plate at a rate of 80–90 km/m.y. Our data indicate that prior to late Eocene time the forearc region was composed of rocks of the arc massif thinly mantled by slope deposits; the forearc region probably lacked both major depositional basins and a tectonically attached accretionary prism of offscraped oceanic deposits. Beginning in latest Miocene or earliest Pliocene time, a zone of outer-arc structural highs and a forearc basin began to form. Formation of these companion intraarc structures may be linked to the late Neogene growth of an accretionary wedge that formed as the result of the deposition of a thick turbidite wedge in the Aleutian Trench. Initial structures of the zone of outer-arc highs formed as the thickening wedge underran, compressively deformed, and uplifted the seaward edge of the arc massif above a landward dipping backstop thrust. Forearc basin strata ponded arcward of the elevating zone of outer-arc highs. However, most younger structures of the zone of outer-arc highs cannot be ascribed simply to the orthogonal effects of an underrunning wedge. Oblique convergence created a major right-lateral shear zone (the Hawley Ridge shear zone) that longitudinally disrupted the zone of outer-arc highs, truncating the seaward flank of the forearc basin and shearing the southern limb of Hawley Ridge, an exceptionally large antiformal outer-arc high structure. Slivers of forearc basement rocks and overlying strata have been transported along the shear zone that is flanked by differentially elevated structures attributed to localized transpressive and transtensional processes. Uplift of Hawley Ridge may be related to the thickening of the arc massif by westward directed basement duplexes. In addition, the forearc is disrupted by structures transverse to the margin that occur where unusually high-stress accumulations have resulted in the rupture of repeated great earthquakes. It is likely that many ancient active margins evolved in tectonic and depositional settings similar to those of the central Aleutian Ridge. Great structural complexity, including the close juxtaposition of coeval structures recording compression, extension, differential vertical movements, and strike-slip displacement, should be expected, even within areas of generally kindred tectonostratigraphic terranes.

Alaska↗

USGS2001

Tomographic inversion of P-wave velocity and Q structures beneath the Kirishima volcanic complex, Southern Japan, based on finite difference calculations of complex traveltimes

We estimate the P-wave velocity and attenuation structures beneath the Kirishima volcanic complex, southern Japan, by inverting the complex traveltimes (arrival times and pulse widths) of waveform data obtained during an active seismic experiment conducted in 1994. In this experiment, six 200-250 kg shots were recorded at 163 temporary seismic stations deployed on the volcanic complex. We use first-arrival times for the shots, which were hand-measured interactively. The waveform data are Fourier transformed into the frequency domain and analysed using a new method based on autoregressive modelling of complex decaying oscillations in the frequency domain to determine pulse widths for the first-arrival phases. A non-linear inversion method is used to invert 893 first-arrival times and 325 pulse widths to estimate the velocity and attenuation structures of the volcanic complex. Wavefronts for the inversion are calculated with a finite difference method based on the Eikonal equation, which is well suited to estimating the complex traveltimes for the structures of the Kirishima volcano complex, where large structural heterogeneities are expected. The attenuation structure is derived using ray paths derived from the velocity structure. We obtain 3-D velocity and attenuation structures down to 1.5 and 0.5 km below sea level, respectively. High-velocity pipe-like structures with correspondingly low attenuation are found under the summit craters. These pipe-like structures are interpreted as remnant conduits of solidified magma. No evidence of a shallow magma chamber is visible in the tomographic images.

Geophysical Journal International↗

USGS2020

Panmixia in a sea ice-associated marine mammal: evaluating genetic structure of the Pacific walrus (Odobenus rosmarus divergens) at multiple spatial scales

The kin structure of a species at relatively fine spatial scales impacts broad-scale patterns in genetic structure at the population level. However, kin structure rarely has been elucidated for migratory marine mammals. The Pacific walrus ( Odobenus rosmarus divergens ) exhibits migratory behavior linked to seasonal patterns in sea ice dynamics. Consequently, information on the spatial genetic structure of the subspecies, including kin structure, could aid wildlife managers in designing future studies to evaluate the impacts of sea ice loss on the subspecies. We sampled 8,303 individual walruses over a 5-year period and used 114 single-nucleotide polymorphisms to examine both broad-scale patterns in genetic structure and fine-scale patterns in relatedness. We did not detect any evidence of genetic structure at broad spatial scales, with low F ST values (≤ 0.001) across all pairs of putative aggregations. To evaluate kin structure at fine spatial scales, we defined a walrus group as a cluster of resting individuals that were less than one walrus body length apart. We found weak evidence of kin structure at fine spatial scales, with 3.72% of groups exhibiting mean relatedness values greater than expected by chance, and a significantly higher overall observed mean value of relatedness within groups than expected by chance. Thus, the high spatiotemporal variation in the distribution of resources in the Pacific Arctic environment likely has favored a gregarious social system in Pacific walruses, with unrelated animals forming temporary associations.

Bering Sea↗

USGS2015

Landscape structure affects specialists but not generalists in naturally fragmented grasslands

Understanding how biotic communities respond to landscape spatial structure is critically important for conservation management as natural landscapes become increasingly fragmented. However, empirical studies of the effects of spatial structure on plant species richness have found inconsistent results, suggesting that more comprehensive approaches are needed. In this study, we asked how landscape structure affects total plant species richness and the richness of a guild of specialized plants in a multivariate context. We sampled herbaceous plant communities at 56 dolomite glades (insular, fire-adapted grasslands) across the Missouri Ozarks, and used structural equation modeling (SEM) to analyze the relative importance of landscape structure, soil resource availability, and fire history for plant communities. We found that landscape spatial structure-defined as the area-weighted proximity of glade habitat surrounding study sites (proximity index)-had a significant effect on total plant species richness, but only after we controlled for environmental covariates. Richness of specialist species, but not generalists, was positively related to landscape spatial structure. Our results highlight that local environmental filters must be considered to understand the influence of landscape structure on communities, and that unique species guilds may respond differently to landscape structure than the community as a whole. These findings suggest that both local environment and landscape context should be considered when developing management strategies for species of conservation concern in fragmented habitats.

Ecology↗

USGS2000

The Beaver River structure: A cross-strike discontinuity of possible crustal dimensions in the southern Mackenzie Fold Belt, Yukon and Northwest territories, Canada

A significant cross-strike structural discontinuity, the Beaver River Structure, has been recognized near the boundary between the north-central part of the Mackenzie Fold Belt and its southern part, the Liard Plateau. The Beaver River Structure is the northeast continuation of the Beaver Fault toward the confluence of the South Nahanni and Liard rivers and into the Interior Platform. It is oriented sub-parallel with the Liard Line farther south. Cumulative Laramide-aged dextral movement of 10 to 20 kilometres is inferred to have occurred along the Beaver River Structure. Small dextral offsets occur along the Beaver Fault, a possible surface manifestation of the Beaver River Structure and large, dominantly north-south oriented Laramide-aged folds and faults, such as the Kotaneelee and Liard synclines and the Nahanni Thrust Fault appear to have been locally rotated in a manner consistent with dextral strike-slip of at least 10 to 20 kilometres. The absence of Permian and Triassic strata in the Mackenzie Fold Belt north of the Beaver River Structure may indicate that uplift and erosion occurred north of the Beaver River Structure during the Early Cretaceous Columbian Orogeny. It is likely that the Beaver River Structure is an ancient, possibly Precambrian, structure that has been reactivated several times throughout Phanerozoic time.

British Columbia, Northwest Territories, Yukon↗

USGS2004

Structure of the Red Dog District, western Brooks Range, Alaska

The Red Dog district of the western Brooks Range of northern Alaska, which includes the sediment-hosted Zn-Pb-Ag ± Ba deposits at Red Dog, Su-Lik, and Anarraaq, contains one of the world's largest reserves of zinc. This paper presents a new model for the structural development of the area and shows that understanding the structure is crucial for future exploration efforts and new mineral discoveries in the district. In the Red Dog district, a telescoped Late Devonian through Jurassic continental passive margin is exposed in a series of subhorizontally stacked, internally imbricated, and regionally folded thrust sheets. These sheets were emplaced during the Middle Jurassic to Late Cretaceous Brookian orogeny and subsequently were uplifted by late tectonic activity in the Tertiary. The thrust sheet stack comprises seven tectonostratigraphically distinct allochthonous sheets, three of which have been subject to regional and detailed structural analysis. The lowermost of these is the Endicott Mountains allochthon, which is overlain by the structurally higher Picnic Creek and Kelly River allochthons. Each individual allochthon is itself internally imbricated into a series of tectonostratigraphically coherent and distinct thrust plates and subplates. This structural style gives rise to duplex development and imbrication at a range of scales, from a few meters to tens of kilometers. The variable mechanical properties of the lithologic units of the ancient passive margin resulted in changes in structural styles and scales of structures across allochthon boundaries. Structural mapping and analysis of the district indicate a dominant northwest to west-northwest direction of regional tectonic transport. Local north to north-northeast transport of thrust sheets is interpreted to reflect the influence of underlying lateral and/or oblique ramps, which may have been controlled by inherited basin margin structures. Some thrust-sheet stacking patterns suggest out-of-sequence thrusting. The west-northwest-east-southeast-trending Wrench Creek and Sivukat Mountain faults were previously interpreted to be strike-slip faults, but this study shows that they are Tertiary (Eocene?) late extensional faults with little or no lateral displacement.

Alaska↗

USGS1988

Structure contour map of the greater Green River basin, Wyoming, Colorado, and Utah

The Greater Green River basin of Wyoming, Colorado, and Utah contains five basins and associated major uplifts (fig. 1). Published structure maps of the region have commonly used the top of the Lower Cretaceous Dakota Sandstone as a structural datum (Petroleum Ownership Map Company (POMCO), 1984; Rocky Mountain Association of Geologists, 1972). However, because relatively few wells in this area penetrate the Dakota, the Dakota structural datum has to be constructed by projecting down from shallower wells. Extrapolating in this manner may produce errors in the map. The primary purpose of this report is to present a more reliable structure contour map of the Greater Green River basin based on datums that are penetrated by many wells. The final map shows the large- to small-scale structures present in the Greater Green River basin. The availability of subsurface control and the map scale determined whether or not a structural feature was included on the map. In general, large structures such as the Moxa arch, Pinedale anticline, and other large folds were placed on the map based solely on the structure contours. In comparison, smaller folds and some faults were placed on the map based on structure contours and other reports (Bader 1987; Bradley 1961; Love and Christiansen, 1985; McDonald, 1975; Roehler, 1979; Wyoming Geological Association Oil and Gas Symposium Committee, 1979). State geologic maps and other reports were used to position basin margin faults (Bryant, 1985; Gries, 1983a, b; Hansen 1986; Hintze, 1980; Love and Christiansen, 1985; Tweto, 1979, 1983). In addition, an interpreted east-west-trending regional seismic line by Garing and Tainter (1985), which shows the basin configuration in cross-section, was helpful in locating buried faults, such as the high-angle reverse or thrust fault along the west flank of the Rock Springs uplift.

Colorado, Utah, Wyoming↗

USGS2001

Use of structural geology in exploration for and mining of sedimentary rock-hosted Au deposits

Structural geology is an important component in regional-, district- and orebody-scale exploration and development of sedimentary rock-hosted Au deposits. Identification of timing of important structural events in an ore district allows analysis and classification of fluid conduits and construction of genetic models for ore formation. The most practical uses of structural geology deal with measurement and definition of various elements that comprise orebodies, which can then be directly applied to ore-reserve estimation, ground control, grade control, safety issues, and mine planning. District- and regional-scale structural studies are directly applicable to long-term strategic planning, economic analysis, and land ownership. Orebodies in sedimentary rock-hosted Au deposits are discrete, hypogene, epigenetic masses usually hosted in a fault zone, breccia mass, or lithologic bed or unit. These attributes allow structural geology to be directly applied to the mining and exploration of sedimentary rock-hosted Au deposits. Internal constituents in orebodies reflect unique episodes relating to ore formation. The main internal constituents in orebodies are ore minerals, gangue, and alteration minerals that usually are mixed with one another in complex patterns, the relations among which may be used to interpret the processes of orebody formation and control. Controls of orebody location and shape usually are due to structural dilatant zones caused by changes in attitude, splays, lithologic contacts, and intersections of the host conduit or unit. In addition, conceptual parameters such as district fabric, predictable distances, and stacking also are used to understand the geometry of orebodies. Controls in ore districts and location and geometry of orebodies in ore districts can be predicted to various degrees by using a number of qualitative concepts such as internal and external orebody plunges, district plunge, district stacking, conduit classification, geochemical, geobarometric and geothermal gradients, and tectonic warps. These concepts have practical and empirical application in most mining districts where they are of use in the exploration for ore, but are of such broad and general application that they may not represent known or inferred ore formation processes. Close spatial relation among some sedimentary rock- hosted Au deposits and their host structures suggests that the structures and the orebodies are genetically linked because they may have shared the same developmental history. Examples of probable syn-deformational genesis and structural control of sedimentary rock-hosted Au deposits are in the large Betze deposit in the Carlin trend, Nevada and in the Lannigou, Jinlongshan, and Maanqiao Au deposits, China.

Open-File Report↗

USGS1950

Structural geology of the Terlingua quicksilver district, Texas

Geologic mapping, supplemented by detailed investigations at the mines, has revealed new information about the geologic structure of the Terlingua quicksilver district, Texas. Attention is focused on the nature and origin of domes, grabens, and breccia pipes, structures that are unusually well developed in the area. The sedimentary rocks, of Cretaceous age, are overlain and intruded by igneous rocks of Tertiary age. Much of the structural deformation was an accompaniment of igneous intrusion. The Terlingua uplift, an irregular dome with a structural relief of several thousand feet, covers about half of the district. The southern boundary of the uplift is a steep monocline. Smaller domes, found throughout the district, were formed by igneous uplift. Evidence for this origin includes exposures of the igneous rock, the occurrence of baked rock on the domes, and theoretical consideration of the forces necessary to form a dome. Almost all the major faults are normal faults bounding depressed tracts, or grabens. Most of the major faults trend northwest; the strike varies markedly, with both sinuous curves and angular turns. The vertical displacement of the grabens below adjacent blocks varies, up to approximately 2,000 feet. Minor faults belong to two sets; one set trends northwest, parallel to the major faults, and the other northeast. Masses of breccia with a pipelike or chimneylike shape have been designated descriptively as breccia-filled pipes, or simply breccia pipes. A total of 76 breccia pipes was mapped, and four typical breccia pipes are described in detail. They range from 75 feet to 500 feet in diameter, and one has been explored vertically for more than 800 feet. The top of one breccia pipe has been found, in the Chisos mine, but the bottom of none has been found. The displacement of the fragments is downward, commonly several hundred feet, and in one instance more than 1,000 feet. The nature of the breccia and its walls indicates collapse due to undermining as the origin of the Terlingua pipes. Features, common to all the pipes, that point to this origin are the downward displacement of the fragments, the absence of drag or thrust structures, the presence of slump structures along the walls, and the vertical cylindrical form. The general structural problems of the district include the age relations, the origin of the uplift, the origin of the domes, and the origin of the grabens. The earliest structural movement involving the Cretaceous rocks was the beginning of rise of the Terlingua uplift. Before this rise ceased, the graben faulting probably began. Volcanism and widespread hypabyssal intrusion, which was accompanied by doming, was partly contemporaneous with graben faulting. The breccia pipes were formed after the beginning, and before the end, of igneous activity. Minor faulting, accompanied by mineralization, continued later than other structural movements, The Terlingua uplift was probably caused primarily by laccolithic igneous intrusion but was influenced by horizontal compression. A basic intrusion, rather than a silicic intrusion, is required to explain the exposed igneous rocks. The geometry of the large grabens indicates that they are relatively superficial accompaniments of horizontal extension. It is suggested that horizontal extension of the upper part of the earth's crust occurred during the formation of the Terlingua uplift and was accompanied by graben faulting.

Texas↗

USGS1987

Gravity profiles across the Uyaijah Ring structure, Kingdom of Saudi Arabia

Three detailed gravity profiles across parts of the Uyaijah ring structure have been completed using an average station spacing of 260 M (giving a total of 217 gravity stations) and level surveys for elevation control. When combined with regional gravity-anomaly data, the profiles are adequate for construction of a structural model of the ring complex based on gravity models. The resulting structural model, based on profile fits to gravity responses of three-dimensional models and excess-mass calculations, gives a depth estimate to the base of the complex of 4.75 km. The contacts of the complex are inferred to be steeply dipping inward along the southwest margin of the structure. To the north and east, however, the basal contact of the complex dips more gently inward (about 30 degrees). The ring structure appears to be composed of three laccolith-shaped plutons; two are granitic in composition and make up about 85 percent of the volume of the complex, and one is granodioritic and comprises the remaining 15 percent. The source area for the plutons appears to be in the southwest quadrant of the Uyaijah ring structure. A northwest-trending shear zone cuts the northern half of the structure and contains mafic dikes that have a small but identifiable gravity-anomaly response. The structural model agrees with models derived from geological interpretation except that the estimated depth to which the structure extends is decreased considerably by the gravity results.

Open-File Report↗

USGS2009

Control-Structure Ratings on the Fox River at McHenry and Algonquin, Illinois

The Illinois Department of Natural Resources-Office of Water Resources operates control structures on a reach of the Fox River in northeastern Illinois between McHenry and Algonquin. The structures maintain water levels in the river for flood-control and recreational purposes. This report documents flow ratings for hinged-crest gates, a broad-crested weir, sluice gates, and an ogee spillway on the control structures at McHenry and Algonquin. The ratings were determined by measuring headwater and tailwater stage along with streamflow at a wide range of flows at different gate openings. Standard control-structure rating techniques were used to rate each control structure. The control structures at McHenry consist of a 221-feet(ft)-long broad-crested weir, a 4-ft-wide fish ladder, a 50-ft-wide hinged-crest gate, five 13.75-ft-wide sluice gates, and a navigational lock. Sixty measurements were used to rate the McHenry structures. The control structures at Algonquin consist of a 242-ft-long ogee spillway and a 50-ft-wide hinged-crest gate. Forty-one measurements were used to rate the Algonquin control structures.

Scientific Investigations Report↗

USGS2012

Simulating potential structural and operational changes for Detroit Dam on the North Santiam River, Oregon, for downstream temperature management

Detroit Dam was constructed in 1953 on the North Santiam River in western Oregon and resulted in the formation of Detroit Lake. With a full-pool storage volume of 455,100 acre-feet and a dam height of 463 feet, Detroit Lake is one of the largest and most important reservoirs in the Willamette River basin in terms of power generation, recreation, and water storage and releases. The U.S. Army Corps of Engineers operates Detroit Dam as part of a system of 13 reservoirs in the Willamette Project to meet multiple goals, which include flood-damage protection, power generation, downstream navigation, recreation, and irrigation. A distinct cycle in water temperature occurs in Detroit Lake as spring and summer heating through solar radiation creates a warm layer of water near the surface and isolates cold water below. Controlling the temperature of releases from Detroit Dam, therefore, is highly dependent on the location, characteristics, and usage of the dam's outlet structures. Prior to operational changes in 2007, Detroit Dam had a well-documented effect on downstream water temperature that was problematic for endangered salmonid fish species, releasing water that was too cold in midsummer and too warm in autumn. This unnatural seasonal temperature pattern caused problems in the timing of fish migration, spawning, and emergence. In this study, an existing calibrated 2-dimensional hydrodynamic water-quality model [CE-QUAL-W2] of Detroit Lake was used to determine how changes in dam operation or changes to the structural release points of Detroit Dam might affect downstream water temperatures under a range of historical hydrologic and meteorological conditions. The results from a subset of the Detroit Lake model scenarios then were used as forcing conditions for downstream CE-QUAL-W2 models of Big Cliff Reservoir (the small reregulating reservoir just downstream of Detroit Dam) and the North Santiam and Santiam Rivers. Many combinations of environmental, operational, and structural options were explored with the model scenarios. Multiple downstream temperature targets were used along with three sets of environmental forcing conditions representing cool/wet, normal, and hot/dry conditions. Five structural options at Detroit Dam were modeled, including the use of existing outlets, one hypothetical variable-elevation outlet such as a sliding gate, a hypothetical combination of a floating outlet and a fixed-elevation outlet, and a hypothetical combination of a floating outlet and a sliding gate. Finally, 14 sets of operational guidelines for Detroit Dam were explored to gain an understanding of the effects of imposing different downstream minimum streamflows, imposing minimum outflow rules to specific outlets, and managing the level of the lake with different timelines through the year. Selected subsets of these combinations of operational and structural scenarios were run through the downstream models of Big Cliff Reservoir and the North Santiam and Santiam Rivers to explore how hypothetical changes at Detroit Dam might provide improved temperatures for endangered salmonids downstream of the Detroit-Big Cliff Dam complex. Conclusions that can be drawn from these model scenarios include: *The water-temperature targets set by the U.S. Army Corps of Engineers for releases from Detroit Dam can be met through a combination of new dam outlets or a delayed drawdown of the lake in autumn. *Spring and summer dam operations greatly affect the available release temperatures and operational flexibility later in the autumn. Releasing warm water during midsummer tends to keep more cool water available for release in autumn. *The ability to meet downstream temperature targets during spring depends on the characteristics of the available outlets. Under existing conditions, although warm water sometimes is present at the lake surface in spring and early summer, such water may not be available for release if the lake level is either well below or well above the spillway crest. *Managing lake releases to meet downstream temperature targets depends on having outlet structures that can access both (warm) lake surface water and (cold) deeper lake water throughout the year. The existing outlets at Detroit Dam do not allow near-surface waters to be released during times when the lake surface level is below the spillway (spring and autumn). *Using the existing outlets at Detroit Dam, lake level management is important to the water temperature of releases because it controls the availability and depth of water at the spillway. When lake level is lowered below the spillway crest in late summer, the loss of access to warm water at the lake surface can result in abrupt changes to release temperatures. *Because the power-generation intakes (penstocks) are 166 feet below the full-pool lake level, imposing minimum power production requirements at Detroit Dam limits the amount of warm surface water that can be expelled from the lake in midsummer, thereby postponing and amplifying warm outflows from Detroit Lake into the autumn spawning season. *Likewise, imposing minimum power production requirements at Detroit Dam in autumn can limit the amount of cool hypolimnetic water that is released from the lake, thereby limiting cool outflows from Detroit Lake during the autumn spawning season. *Model simulations indicate that a delayed drawdown of Detroit Lake in autumn would result in better control over release temperatures in the immediate downstream vicinity of Big Cliff Dam, but the reduced outflows necessary to retain more water in the lake in late summer are more susceptible to rapid heating downstream. *Compared to the existing outlets at Detroit Dam, floating or sliding-gate outlet structures can provide greater control over release temperatures because they provide better access to warm water at the lake surface and cooler water at depth. These conclusions can be grouped into several common themes. First, optimal and flexible management and achievement of downstream temperature goals requires that releases of warm water near the surface of the lake and cold water below the thermocline are both possible with the available dam outlets during spring, summer, and autumn. This constraint can be met to some extent with existing outlets, but only if access to the spillway is extended into autumn by keeping the lake level higher than called for by the current rule curve (the typical target water-surface elevation throughout the year). If new outlets are considered, a variable-elevation outlet such as a sliding gate structure, or a floating outlet in combination with a fixed-elevation outlet at sufficient depth to access cold water, is likely to work well in terms of accessing a range of water temperatures and achieving downstream temperature targets. Furthermore, model results indicate that it is important to release warm water from near the lake surface during midsummer. If not released downstream, the warm water will build up at the top of the lake as a result of solar energy inputs and the thermocline will deepen, potentially causing warm water to reach the depth of deeper fixed-elevation outlets in autumn, particularly when the lake level is drawn down to make room for flood storage. Delaying the drawdown in autumn can help to keep the thermocline above such outlets and preserve access to cold water. Although it is important to generate hydropower at Detroit Dam, minimum power-production requirements limit the ability of dam operators to meet downstream temperature targets with existing outlet structures. The location of the power penstocks below the thermocline in spring and most of summer causes the release of more cool water during summer than is optimal. Reducing the power-production constraint allows the temperature target to be met more frequently, but at the cost of less power generation. Finally, running the Detroit Dam, Big Cliff Dam, and North Santiam and Santiam River models in series allows dam operators to evaluate how different operational strategies or combinations of new dam outlets might affect downstream temperatures for many miles of critical endangered salmonid habitat. Temperatures can change quickly in these downstream reaches as the river exchanges heat with its surroundings, and heating or cooling of 6 degrees Celsius is not unusual in the 40–50 miles downstream of Big Cliff Dam. The results published in this report supersede preliminary results published in U.S. Geological Survey Open-File Report 2011-1268 (Buccola and Rounds, 2011). Those preliminary results are still valid, but the results in this report are more current and comprehensive.

Oregon↗

USGS1997

Full equations utilities (FEQUTL) model for the approximation of hydraulic characteristics of open channels and control structures during unsteady flow

The Full EQuations UTiLities (FEQUTL) model is a computer program for computation of tables that list the hydraulic characteristics of open channels and control structures as a function of upstream and downstream depths; these tables facilitate the simulation of unsteady flow in a stream system with the Full Equations (FEQ) model. Simulation of unsteady flow requires many iterations for each time period computed. Thus, computation of hydraulic characteristics during the simulations is impractical, and preparation of function tables and application of table look-up procedures facilitates simulation of unsteady flow. Three general types of function tables are computed: one-dimensional tables that relate hydraulic characteristics to upstream flow depth, two-dimensional tables that relate flow through control structures to upstream and downstream flow depth, and three-dimensional tables that relate flow through gated structures to upstream and downstream flow depth and gate setting. For open-channel reaches, six types of one-dimensional function tables contain different combinations of the top width of flow, area, first moment of area with respect to the water surface, conveyance, flux coefficients, and correction coefficients for channel curvilinearity. For hydraulic control structures, one type of one-dimensional function table contains relations between flow and upstream depth, and two types of two-dimensional function tables contain relations among flow and upstream and downstream flow depths. For hydraulic control structures with gates, a three-dimensional function table lists the system of two-dimensional tables that contain the relations among flow and upstream and downstream flow depths that correspond to different gate openings. Hydraulic control structures for which function tables containing flow relations are prepared in FEQUTL include expansions, contractions, bridges, culverts, embankments, weirs, closed conduits (circular, rectangular, and pipe-arch shapes), dam failures, floodways, and underflow gates (sluice and tainter gates). The theory for computation of the hydraulic characteristics is presented for open channels and for each hydraulic control structure. For the hydraulic control structures, the theory is developed from the results of experimental tests of flow through the structure for different upstream and downstream flow depths. These tests were done to describe flow hydraulics for a single, steady-flow design condition and, thus, do not provide complete information on flow transitions (for example, between free- and submerged-weir flow) that may result in simulation of unsteady flow. Therefore, new procedures are developed to approximate the hydraulics of flow transitions for culverts, embankments, weirs, and underflow gates.

Water-Resources Investigations Report↗

USGS1993

General implicit representation of hydraulic structures in numerical flow models

Effects of hydraulic structures (such as culverts, bridge openings, or gates) can be simulated in numerical surface-water-flow models. Generally the scale and dimension of the numerical model is insufficient to model flow through the structure directly. However, if for a particular hydraulic structure a unique relation exists among headwater elevation, tailwater elevation, and discharge through the structure, the effect of the structure can be introduced by enforcing the unique three-parameter relation among three dependent model variables: water-surface elevations immediately upstream and downstream of the structure and discharge through the structure. The three-parameter relation might be implemented through an equation or sets of equations specific to each particular structure. The technique described is more general, viewing the locus of points satisfying any unique three-parameter relation as a surface. The surface is described by a set of points with coordinates corresponding to the three parameters. Values and gradients required for implicit implementation of the unique three-parameter relation in a numerical flow model are interpolated from the surface. The technique described provides a general interface between numerical flow models and effects of any hydraulic structure characterized by a unique three-parameter relation.

Conference Paper↗