Large wood distribution,mobility, and recruitment in an inter‐dam river reach: A comparison with geomorphic process on the Garrison Reach of the Missouri River pre and post the historical 2011 flood          下载免费PDF全文

Edward R. Schenk  Adam J. Benthem  Mark D. Dixon  Melissa Mittelman  Katherine J. Skalak  Cliff R. Hupp  Joel M. Galloway  Rochelle A. Nustad 《地球表面变化过程与地形》2018,43(8):1677-1688

This study assessed the effect of the largest flood since dam regulation on geomorphic and large wood (LW) trends using LW distributions at three time periods on the 150 km long Garrison Reach of the Missouri River. In 2011, a flood exceeded 4390 m³/s for a two‐week period (705% above mean flow; 500 year flood). LW was measured using high resolution satellite imagery in summer 2010 and 2012. Ancillary data including forest character, vegetation cover, lateral bank retreat, and channel capacity. Lateral bank erosion removed approximately 7400 standing trees during the flood. Other mechanisms, that could account for the other two‐thirds of the measured in‐channel LW, include overland flow through floodplains and islands. LW transport was commonly near or over 100 km as indicated by longitudinal forest and bank loss and post‐flood LW distribution. LW concentrations shift at several locations along the river, both pre‐ and post‐flood, and correspond to geomorphic river regions created by the interaction of the Garrison Dam upstream and the Oahe Dam downstream. Areas near the upstream dam experienced proportionally higher rates of bank erosion and forest loss but in‐channel LW decreased, likely due to scouring. A large amount of LW moved during this flood, the chief anchoring mechanism was not bridges or narrow channel reaches but the channel complexity of the river delta created by the downstream reservoir. Areas near the downstream dam experienced bank accretion and large amounts of LW deposition. This study confirms the results of similar work in the Reach: despite a historic flood longitudinal LW and channel trends remain the same. Dam regulation has created a geomorphic and LW pattern that is largely uninterrupted by an unprecedented dam regulation era flood. River managers may require other tools than infrequent high intensity floods to restore geomorphic and LW patterns. Copyright © 2018 John Wiley & Sons, Ltd.  相似文献   

Spectral variation in the X-ray pulsar GX 1+4 during a low-flux episode     

D. K. Galloway  A. B. Giles  J. G. Greenhill  M. C. Storey 《Monthly notices of the Royal Astronomical Society》2000,311(4):755-761

The X-ray pulsar GX 1+4 was observed with the RXTE satellite for a total of 51 ks between 1996 July 19 and 21. During this period the flux decreased smoothly from an initial mean level of ≈6×10³⁶ erg s⁻¹ to a minimum of ≈4×10³⁵ erg s⁻¹ (2–60 keV, assuming a source distance of 10 kpc) before partially recovering towards the initial level at the end of the observation.
BATSE pulse timing measurements indicate that a torque reversal took place approximately 10 d after this observation. Both the mean pulse profile and the photon spectrum varied significantly. The observed variation in the source may provide important clues as to the mechanism of torque reversals.
The single best-fitting spectral model was based on a component originating from thermal photons with kT ₀≈1 keV Comptonized by a plasma of temperature kT ≈7 keV. Both the flux modulation with phase during the brightest interval and the evolution of the mean spectra over the course of the observation are consistent with variations in this model component; with, in addition, a doubling of the column density n _H contributing to the mean spectral change.
A strong flare of duration ≲50 s was observed during the interval of minimum flux, with the peak flux ≈20 times the mean level. Although beaming effects are likely to mask the true variation in M ˙ thought to give rise to the flare, the timing of a modest increase in flux prior to the flare is consistent with dual episodes of accretion resulting from successive orbits of a locally dense patch of matter in the accretion disc.  相似文献   

Biases for neutron star mass, radius and distance measurements from Eddington-limited X-ray bursts     

D. K. Galloway †  F. Özel ‡  D. Psaltis ‡ 《Monthly notices of the Royal Astronomical Society》2008,387(1):268-272

Eddington-limited X-ray bursts from neutron stars can be used in conjunction with other spectroscopic observations to measure neutron star masses, radii and distances. In order to quantify some of the uncertainties in the determination of the Eddington limit, we analysed a large sample of photospheric radius-expansion thermonuclear bursts observed with the Rossi X-ray Timing Explorer . We identified the instant at which the expanded photosphere 'touches down' back on to the surface of the neutron star and compared the corresponding touchdown flux to the peak flux of each burst. We found that for the majority of sources, the ratio of these fluxes is smaller than ≃1.6, which is the maximum value expected from the changing gravitational redshift during the radius expansion episodes (for a  2 M_⊙  neutron star). The only sources for which this ratio is larger than ≃1.6 are high-inclination sources that include dippers and Cyg X-2. We discuss two possible geometric interpretations of this effect and show that the inferred masses and radii of neutron stars are not affected by this bias. On the other hand, systematic uncertainties as large as ∼50 per cent may be introduced to the distance determination.  相似文献   

Review: Regional land subsidence accompanying groundwater extraction   总被引：9，自引：4，他引：5  

Devin L. Galloway  Thomas J. Burbey 《Hydrogeology Journal》2011,19(8):1459-1486

The extraction of groundwater can generate land subsidence by causing the compaction of susceptible aquifer systems, typically unconsolidated alluvial or basin-fill aquifer systems comprising aquifers and aquitards. Various ground-based and remotely sensed methods are used to measure and map subsidence. Many areas of subsidence caused by groundwater pumping have been identified and monitored, and corrective measures to slow or halt subsidence have been devised. Two principal means are used to mitigate subsidence caused by groundwater withdrawal??reduction of groundwater withdrawal, and artificial recharge. Analysis and simulation of aquifer-system compaction follow from the basic relations between head, stress, compressibility, and groundwater flow and are addressed primarily using two approaches??one based on conventional groundwater flow theory and one based on linear poroelasticity theory. Research and development to improve the assessment and analysis of aquifer-system compaction, the accompanying subsidence and potential ground ruptures are needed in the topic areas of the hydromechanical behavior of aquitards, the role of horizontal deformation, the application of differential synthetic aperture radar interferometry, and the regional-scale simulation of coupled groundwater flow and aquifer-system deformation to support resource management and hazard mitigation measures.  相似文献   

High field strength modified ABC and rotor dynamos     

Robert Cameron  David Galloway 《Monthly notices of the Royal Astronomical Society》2006,367(3):1163-1169

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Water quality of two streams near Yellowstone Park, Wyoming, following the 1988 Clover-Mist wildfire     

P. J. Gerla  J. M. Galloway 《Environmental Geology》1998,36(1-2):127-136

 In 1988, wildfire burned over 50% of the Jones Creek watershed near Yellowstone Park, Wyoming. Crow Creek, an adjacent watershed, was unburned. Water quality data collected from 1989–1993 may show the fire's effect on weathering and nutrient transport. Jones Creek had 25–75% larger concentrations of dissolved solids than Crow Creek during the sampling period. Both streams revealed molar ratios consistent with the stoichiometry of andesine and pyroxene hydrolysis in the trachyandesites that underlie the basins. During 1989, nitrate transported from the unburned Crow Creek basin peaked at 2 mmol ha^–1 s^–1. This was twice as much as Jones Creek, possibly indicating a source from ash fallout. By 1992 these rates diminished to 0.1 mmol ha^–1 s^–1 in Crow Creek and increased to 1.8 mmol ha^–1 s^–1 in Jones Creek, suggesting later nitrate mobilization in the burned watershed. Phosphorus transported from Jones Creek basin averaged 0.011 mmol ha^–1 s^–1 during summer 1989, but fell to 0.004 mg ha^–1 s^–1 in subsequent years. Received: 28 May 1997 · Accepted: 18 November 1997  相似文献   

Accretion column eclipses in the X-ray pulsars GX 1+4 and RX J0812.4−3114     

D.K. Galloway †  A.B. Giles ‡  K. Wu  J.G. Greenhill 《Monthly notices of the Royal Astronomical Society》2001,325(1):419-425

Sharp dips observed in the pulse profiles of three X-ray pulsars (GX 1+4, RX J0812.4−3114 and A 0535+26) have previously been suggested to arise from partial eclipses of the emission region by the accretion column occurring once each rotation period. We present pulse-phase spectroscopy from Rossi X-ray Timing Explorer satellite observations of GX 1+4 and RX J0812.4−3114, which for the first time confirms this interpretation. The dip phase corresponds to the closest approach of the column axis to the line of sight, and the additional optical depth of photons escaping from the column in this direction gives rise to both the decrease in flux and increase in the fitted optical depth measured at this phase. Analysis of the arrival time of individual dips in GX 1+4 provides the first measurement of azimuthal wandering of a neutron star accretion column. The column longitude varies stochastically with a standard deviation ranging between 2° and 6° depending on the source luminosity. Measurements of the phase width of the dip both from mean pulse profiles and from the individual eclipses demonstrate that the dip width is proportional to the flux. The variation is consistent with that expected if the azimuthal extent of the accretion column depends only upon the Keplerian velocity at the inner disc radius, which varies as a consequence of the accretion rate M˙ .  相似文献   

Periodic variation in natural radioactivity of lake Bouchet sediments   总被引：1，自引：0，他引：1  

J. Xanthakis  I. Liritzis  R. B. Galloway 《Earth, Moon, and Planets》1992,59(3):191-200

Low level counting of alpha and beta particles has been carried out on a 5 long sediment core from the lake La Bouchet in France, spanning the past around 24 000 years. A total of around 60 data points were spectrally analysed with the successive approximations method. Several whole or quasi-periodicities were located for the two radioactivity data sets, in different time intervals; for the alpha counting, periods of 1000–1200, 2000, 6000 and 24 000 years and for the beta counting periods of 1000, 3000, 4000, 8000 and 24 000 years were obtained. The non-stationarity nature of the obtained periods are discussed in relation to (a) palaeoclimatic fluctuations impact on mineral carrying natural radiosotopes partitioning of the sediment deposition of the last glacial and (b) other solar-terrestrial agents.  相似文献   

Middle to late Holocene chironomid-inferred July temperatures for the central Northwest Territories,Canada     

Lindsay M. Upiter  Jesse C. Vermaire  R. Timothy Patterson  Carley A. Crann  Jennifer M. Galloway  Andrew L. Macumber  Lisa A. Neville  Graeme T. Swindles  Hendrik Falck  Helen M. Roe  Michael F. J. Pisaric 《Journal of Paleolimnology》2014,52(1-2):11-26

We analyzed subfossil chironomids, sediment organic matter and sediment particle size data from a 1.11-m-long freeze core collected from Carleton Lake (unofficial name), located approximately 120 km north of the modern treeline. This well-dated core spans the last ca. 6,500 years. Two chironomid transfer functions were applied to infer mean July air temperatures. Our results indicated that the chironomid-inferred temperatures from this lake sediment record did not pass a significance test, suggesting that other factors in addition to temperature may have been important in structuring the chironomid community through time. Although not statistically significant, the chironomid-inferred temperatures from this site do follow a familiar pattern, with highest inferred temperatures occurring during the Holocene Thermal Maximum (~6–4 cal kyr BP), followed by a long-term cooling trend, which is reversed during the last 600 years. The largest change in the chironomid assemblage, which occurred between ca. 4,600 and 3,900 cal yr BP is possibly related to the well-documented northward advance and subsequent retreat of treeline in this region.  相似文献   

Securing the future of ground water resources in the Great Lakes basin     

Galloway G  Pentland R 《Ground water》2005,43(5):737-743

Ground water is a vital, but underappreciated, natural resource in the Great Lakes basin. It meets many human needs and contributes significantly to the hydrology of the Great Lakes and the health of ecosystems. This paper provides an overview of ground water in the Great Lakes and the institutional and legal setting that governs the use, protection, diversion, and removal of water from the basin and proposes a citizen-centered vision for management of ground water in the 21st century.  相似文献