Slope‐area thresholds of road‐induced gully erosion and consequent hillslope–channel interactions          下载免费PDF全文

Harry Alexander Katz  J. Michael Daniels  Sandra Ryan 《地球表面变化过程与地形》2014,39(3):285-295

Pikes Peak Highway is a partially paved road between Cascade, Colorado and the summit of Pikes Peak. Significant gully erosion is occurring on the hillslopes due to the concentration of surface runoff, the rearrangement of drainage pathways along the road surface and adjacent drainage ditches, and the high erodibility of weathered Pikes Peak granite that underlies the area. As a result, large quantities of sediment are transported to surrounding valley networks causing significant damage to water quality and aquatic, wetland, and riparian ecosystems. This study establishes the slope/drainage area threshold for gullying along Pikes Peak Highway and a cesium‐137 based sediment budget highlighting rates of gully erosion and subsequent valley deposition for a small headwater basin. The threshold for gullying along the road is S_cr = 0 · 21A^–0·45 and the road surface reduces the critical slope requirement for gullying compared to natural drainages in the area. Total gully volume for the 20 gullies along the road is estimated at 5974 m³, with an erosion rate of 64 m³ yr^–1 to 101 m³ yr^–1. Net valley deposition is estimated at 162 m³ yr^–1 with 120 m³ yr^–1 unaccounted for by gullying. The hillslope–channel interface is decoupled with minimal downstream sediment transport which results in significant local gully‐derived sedimentation. Copyright © 2013 John Wiley & Sons, Ltd.  相似文献   

Validation and Application of the Second Generation Three Dimensional Hydrodynamic Model of Chesapeake Bay     

Wang  Harry V.  Johnson  Billy H. 《Water Quality and Ecosystems Modeling》2000,1(1-4):51-90

The validation and subsequent application of the current three-dimensional numerical hydrodynamic model of Chesapeake Bay is presented. The numerical model solves conservation equations for water mass, momentum, salinity, and heat on a boundary-fitted grid in the horizontal plane and a Cartesian z-grid in the vertical. A generalized ADI finite difference scheme is employed in conjunction with mode splitting technique, solving external and the internal modes. The 10-year boundary conditions including tide, slinity, temperature, wind, heat exchange coefficient, river and non-point source flows were constructed. Model validation was accomplished by demonstrating the model's ability to reproduce observed data over time scales ranging from tidal to seasonal periods. The major parameters compared include tidal elevation, intra-tidal and residual velocities, salinity, temperature, stratification, and flux calculated through the Bay mouth.After validation, the model was applied to simulate bay hydrodynamics for the 10 years of 1985–94. These results were used to drive the three-dimensional water quality model of Chesapeake Bay, which is discussed in a companion paper.  相似文献   

Loads on a 3D body due to second-order waves and a current     

Jesper Skourup  Kwok Fai Cheung  Harry B. Bingham  Bjarne Büchmann 《Ocean Engineering》2000,27(7)

Non-linear loads on a fixed body due to waves and a current are investigated. Potential theory is used to describe the flow, and a three-dimensional (3D) boundary element method (BEM), combined with a time-stepping procedure, is used to solve the problem. The exact free-surface boundary conditions are expanded about the still-water level by Taylor series so that the solution is evaluated on a time-invariant geometry. A formulation correct to second order in the wave steepness and to first order in the current speed is used. Numerical results are obtained for the first-order and the second-order oscillatory forces and for the second-order mean force on a fixed vertical circular cylinder in waves and a current. The second-order oscillatory forces on the body in waves and current are new results, while the remaining force components are verified by comparison with established numerical and analytical models. It is shown that the current can have a significant influence on the forces, and especially on the amplitude of the second-order oscillatory component.  相似文献   

Differentiations of geographic distribution and subsistence strategies between Tibetan and other major ethnic groups are determined by the physical environment in Hehuang Valley   总被引：1，自引：0，他引：1  

Xin JIA  Harry F.LEE  Mengchun CUI  Guoquan CHENG  Yang ZHAO  Hong DING  Ricci P.H.YUE  Huayu LU 《中国科学:地球科学(英文版)》2019,(2)

The people of the Tibetan Plateau have received extensive attention from scholars because of their unique adaptability to the low temperature and anoxic environments. However, the Tibetan communities and their habitats in the low-altitude regions of the plateau have rarely been studied in a scientific manner. Based on the extraction of geographic information of 197 towns in the Hehuang Valley and on variance analysis, this study examines the habitats and subsistence strategies of the Tibetans and other major ethnic groups in the low-latitude region of the Tibetan Plateau. Our statistical results show that the annual average temperature of Tibetan habitats in the Hehuang Valley is relatively high. The relatively warm environment of the valley allows the Tibetans in that area to cultivate wheat and barley and raise cattle and sheep—a subsistence strategy significantly different from that of other Tibetans in the high-altitude regions in the Tibetan Plateau. In addition, the Tibetan communities in the Hehuang Valley include similar agri-pastoral ethnic groups (including Hui and Salar), both of which adopt similar subsistence strategies. The agricultural ethnic groups (Han and Tu) live in a relatively cool and humid environment facilitating agricultural production, while the agri-pastoral ethnic groups (Tibetan, Hui, and Salar) inhabit relatively warm and arid environment in the valley. Due to the lack of agricultural activities, agri-pastoral groups must also engage in animal husbandry to supplement their diet. In the Ando Tibetan region, the subsistence strategies of the ethnic groups are closely related to their physical environment.Those ethnic groups communicate among themselves, integrate, and influence each other, resulting in a diversified culture. This study proves that the habitat variation at a regional scale corresponds significantly to the variation of subsistence strategies. Our findings may further refine knowledge about the human-environmental relationships of Tibetans and lead future research towards using quantitative methods to analyse the intersection of physical environment and ethnic groups' distribution.  相似文献   

Hydrocarbon-derived carbonate buildups of the northern Gulf of Mexico continental slope: A review of submersible investigations   总被引：15，自引：3，他引：15  

Harry H. Roberts  Paul Aharon 《Geo-Marine Letters》1994,14(2-3):135-148

Hydrocarbon-derived and microbially mediated authigenic carbonates occur over the entire depth range of the northern Gulf of Mexico slope. These carbonates consist of nodules and incipient nodules in surface sediments, hardgrounds and isolated slabs, and moundlike buildups of up to 10–20 m relief above the surrounding seafloor. The authigenic carbonates are characterized by ¹³C negative values in the range –18 to –55 (PDB) suggesting mixing of seawater carbon with¹³C-depleted carbon sources ranging from crude oil to biogenic methane. Near the shelf edge, carbonates are diluted with biogenic material produced by reefs—bioherms developed at low sea level stands. Fossil-poor carbonates over salt diapirs of the upper and middle slope formed in the shallow subsurface and have been exhumed by the combined processes of uplift and physical erosion. Middle and lower slope carbonates are generally rich in fossil shells of chemosynthetic organisms. Mg calcite pelloidal matrix and acicular to botryoidal aragonitic void-filling cements are common petrographic features of these hydrocarbonderived carbonates. At two sites carbonates are mixed with barite.  相似文献   

Resolving the contributing factors to Mississippi Delta subsidence: Past and Present     

Bruce C. Frederick  Michael Blum  Richard Fillon  Harry Roberts 《Basin Research》2019,31(1):171-190

To date, quantification of individual components that contribute to shallow and deep‐seated subsidence in passive margin deltas worldwide has proven problematic. A new, regional gridded chronostratigraphic dataset for the Lower Mississippi Delta region, derived from 80,928 well reports across the northern Gulf of Mexico (GOM), has bridged the disparity between geodetic mean rates measuring total land surface subsidence across annual‐to‐decadal timescales and the deep‐seated stratigraphic subsidence rates that record isostatic response over timescales of >10⁴ years. Through a quantitative assessment of gridded chronostratigraphic surfaces, sections, and subsidence rates extending from the Middle Pleistocene (0.58 Ma) to the Late Pliocene (3.85 Ma), we identify both temporal and spatial variability in deep‐seated subsidence across the northern GOM. Targeted deep‐seated subsidence data extracted across prior GOM Holocene sea‐level sample locations have revealed more than an order of magnitude greater rates of isostatic compensation in the Mississippi depocentre versus similar GOM sea‐level control sites in Florida and Alabama, casting doubt on efforts towards a representative Holocene sea‐level curve. Spatial variability in subsidence was also assessed locally in both the strike and dip directions to assess the contributions of growth faults. Fault throw displacement magnitude was discovered to decrease with depth, accounting for less than half of the total deep‐seated subsidence record of the Middle Pleistocene. Temporal subsidence complexities were also revealed including a direct, inverse logarithmic relationship between subsidence rate and time indicating variable subsidence component controls across different timescales. Despite the spatial and temporal complexities, this dataset serves as the first regional baseline for deep‐seated subsidence rates across the northern GOM.  相似文献   

Isotopic constraints on time scales and mechanisms of slab material transport in the mantle wedge: evidence from the Simcoe mantle xenoliths, Washington, USA     

Alan D. Brandon  Harry Becker  Richard W. Carlson  Steven B. Shirey 《Chemical Geology》1999,160(4):239-407

Spinel harzburgite and websterite mantle xenoliths from Simcoe volcano in southern Washington represent fragments of mantle lithosphere from the back-arc side of the Cascade arc front. Previous studies have shown that metasomatism by either silica-rich fluids or hydrous melts crystallized phlogopite, imparted high oxygen fugacities (0.3 to 1.4 log units above QFM), and more radiogenic Os isotopic compositions on these peridotites. These features are consistent with part or all of the metasomatic agent being derived from the Juan de Fuca slab. New Re–Os, Sm–Nd, Sr, and U–Th–Pb isotopic data shed further light on the origin and composition of the metasomatic agent. The clinopyroxenes from the xenoliths have correlated Pb isotopic compositions (²⁰⁶Pb/²⁰⁴Pb=18.63–19.55, ²⁰⁷Pb/²⁰⁴Pb=15.56–15.63, ²⁰⁸Pb/²⁰⁴Pb=38.22–38.87). The most radiogenic Pb isotopic compositions extend beyond the most radiogenic Pb isotopic compositions for the Cascade arc lavas and display a shallower trend. Mixtures between Juan de Fuca basalts and pelagic or terrigenous sediments would result in Pb isotopic compositions that are not radiogenic enough in ²⁰⁷Pb/²⁰⁴Pb and ²⁰⁸Pb/²⁰⁴Pb at the high ²⁰⁶Pb/²⁰⁴Pb end of this array. Therefore, models for rapid transfer of components from the slab to the mantle lithosphere are not viable in this case. Instead, a multi-stage model is preferred. In the first stage, the slab component is transferred via fluid or melt into, and reacts with the hanging wall mantle. This results in a residual slab depleted in Pb relative to U and Th, and consequent high U/Pb and Th/Pb. Additional dehydration or melting of the slab imparts this chemical signature to the peridotite in the hanging wall. In the second stage, the hybridized hanging wall peridotite evolves for tens of million years until corner flow drags it down to deeper levels in the mantle wedge where melting occurs in response to higher temperatures. In the third stage, this melt migrates upward where it metasomatizes the mantle lithosphere represented by the Simcoe xenoliths. Trace element compositions of the clinopyroxenes, and the presence of high alkali glasses in the xenoliths, are consistent with the metasomatic agent derived from the hybridized hanging wall being alkali-rich, and possibly similar to potassic-rich lavas found in arc and back-arc settings. These data therefore demonstrate the importance of the hybridized hanging wall mantle above slabs as a source for melts which can be metasomatic agents in the upper mantle, and as a site for storage of material derived from the slab for periods of at least tens of million years.  相似文献   

Temperature dependence of specific heat capacity and its effect on asteroid thermal models     

Amitabha GHOSH  Harry Y. McSWEEN 《Meteoritics & planetary science》1999,34(1):121-127

Abstract— Asteroid thermal models have typically employed a constant value of specific heat capacity, although this parameter is a function of temperature. We examine whether incorporation of the temperature dependence of specific heat capacity is a necessary refinement and find that including it produces considerable differences in thermal history. Though the temperature effect is demonstrated in a representative calculation for a chondritic asteroid with ²⁶Al decay as a heat source, this result also has implications for asteroidal thermal models based on electromagnetic induction heating or heating by impact, as well as for thermal models of the terrestrial planets.  相似文献   

Northwest Africa 5790: A previously unsampled portion of the upper part of the nakhlite pile          下载免费PDF全文

J. Brian Balta  Matthew E. Sanborn  Rhiannon G. Mayne  Meenakshi Wadhwa  Harry Y. McSween Jr  Samuel D. Crossley 《Meteoritics & planetary science》2017,52(1):36-59

We present a geochemical study of recently discovered Martian meteorite Northwest Africa (NWA) 5790 and use our results to constrain its origin and relationship with the other nakhlites. This nakhlite is a clinopyroxene cumulate composed of phenocrysts of augite, olivine, and rare oxides surrounded by a mesostasis composed of vitrophyric glass, feldspars, oxides, phosphates, and fine‐grained olivines and augite. Petrography, and major and trace element compositions of the phases present are consistent with derivation of NWA 5790 from a parental magma common to all the nakhlites. Olivine cores grew from a distinct, incompatible‐element enriched magma and are surrounded by rims containing augite inclusions that grew from the nakhlite parental liquid, supporting previous arguments for xenocrystic olivine cores in nakhlites. Rare earth element microdistributions suggest derivation of NWA 5790 augites from an evolved, relatively oxidized magma, produced by augite fractionation from the common nakhlite parental liquid. Augite grain shapes and CSD patterns are consistent with rapid cooling and derivation near the top of the nakhlite cumulate pile, but patterns are distinct from other nakhlites thought to have formed near the stratigraphic top. The high mesostasis abundance (~44 vol%) indicates solidification near the top of the nakhlite pile close to locations suggested for nakhlites NWA 817 and Miller Range (MIL) 03346. However, the geochemical and petrographic characteristics of these three samples do not permit their placement in a simple stratigraphic order as would occur in a single lava flow. This lack of simple ordering suggests that the nakhlite lava flow split into multiple sections as would occur during breakouts from a single lava flow. Finally we note that NWA 5790 is unique among currently available nakhlites in having phenocryst abundances low enough to allow it to flow.  相似文献   

Approximate computer analysis of pile groups subjected to loads and ground movements     

Harry G. Poulos 《国际地质力学数值与分析法杂志》1999,23(10):1021-1041

This paper describes the development of an approximate approach for the analysis and design of piles subjected to axial and lateral loading and also to vertical and horizontal ground movements. The analysis involves a number of simplifications in order to make it feasible to implement. For example, it considers the behaviour of a ‘representative’ pile in a group to characterize the behaviour of all piles in the group, and adopts approximations to derive free-field interaction factors from the conventional interaction factors for direct loading. The analysis has been implemented via a computer program called EMbankment PIle Group (EMPIG) and has the ability to incorporate the following features:

• 1. single piles or pile groups,
• 2. applied vertical, lateral and moment loading on the pile cap,
• 3. the effects of axial and lateral soil movements caused by embankment construction,
• 4. a layered soil profile,
• 5. non-linear axial and lateral response of the piles.

Comparisons between solutions from EMPIG and other independent programs suggest that it is capable of providing results of adequate accuracy for practical design purposes. The analysis has been used to investigate the effects of pile rake on a typical bridge abutment group. The presence of raked piles can have a detrimental effect on group behaviour, especially in the presence of ground movements. Large lateral deflections can be generated and axial forces and moments in the piles are increased. Comparisons are also made with the results of centrifuge model tests on abutment pile groups. Copyright © 1999 John Wiley & Sons, Ltd.  相似文献