River Seepage Conductance in Large‐Scale Regional Studies          下载免费PDF全文

Hubert J. Morel‐Seytoux  Calvin D. Miller  Cinzia Miracapillo  Steffen Mehl 《Ground water》2017,55(3):399-407

Flow exchange between surface and groundwater is of great importance be it for beneficial allocation and use of water resources or for the proper exercise of water rights. In large‐scale regional studies, most numerical models use coarse grid sizes, which make it difficult to provide an accurate depiction of the phenomenon. In particular, a somewhat arbitrary leakance coefficient in a third type (i.e., Cauchy, General Head) boundary condition is used to calculate the seepage discharge as a function of the difference of head in the river and in the aquifer, whose value is often found by calibration. A different approach is presented to analytically estimate that leakance coefficient. It is shown that a simple equivalence can be deduced from the analytical solution for the empirical coefficient, so that it provides the accuracy of the analytical solution while the model maintains a very coarse grid, treating the water‐table aquifer as a single calculation layer. Relating the empirical leakance coefficient to the exact conductance, derived from physical principles, provides a physical basis for the leakance coefficient. Factors such as normalized wetted perimeter, degree of penetration of the river, presence of a clogging layer, and anisotropy can be included with little computational demand. In addition the river coefficient in models such as MODFLOW, for example, can be easily modified when grid size is changed without need for recalibration.  相似文献   

The importance of aspect for modelling the hydrological response in a glacier catchment in Central Asia   总被引：2，自引：0，他引：2       下载免费PDF全文

Hongkai Gao  Yongjian Ding  Qiudong Zhao  Markus Hrachowitz  Hubert H.G. Savenije 《水文研究》2017,31(16):2842-2859

Understanding how explicit consideration of topographic information influences hydrological model performance and upscaling in glacier dominated catchments remains underexplored. In this study, the Urumqi glacier no. 1 catchment in northwest China, with 52% of the area covered by glaciers, was selected as study site. A conceptual glacier‐hydrological model was developed and tested to systematically, simultaneously, and robustly reproduce the hydrograph, separate the discharge into contributions from glacier and nonglacier parts of the catchment, and establish estimates of the annual glacier mass balance, the annual equilibrium line altitude, and the daily catchment snow water equivalent. This was done by extending and adapting a recently proposed landscape‐based semidistributed conceptual hydrological model (FLEX‐Topo) to represent glacier and snowmelt processes. The adapted model, FLEX^G, allows to explicitly account for the influence of topography, that is, elevation and aspect, on the distribution of temperature and precipitation and thus on melt dynamics. It is shown that the model can not only reproduce long‐term runoff observations but also variations in glacier and snow cover. Furthermore, FLEX^G was successfully transferred and up‐scaled to a larger catchment exclusively by adjusting the areal proportions of elevation and aspect without the need for further calibration. This underlines the value of topographic information to meaningfully represent the dominant hydrological processes in the region and is further exacerbated by comparing the model to a model formulation that does not account for differences in aspect (FLEX^G,nA) and which, in spite of satisfactorily reproducing the observed hydrograph, does not capture the influence of spatial variability of snow and ice, which as a consequence reduces model transferability. This highlights the importance of accounting for topography and landscape heterogeneity in conceptual hydrological models in mountainous and snow‐, and glacier‐dominated regions.  相似文献   

Evolution of cutoffs across meander necks in Powder River,Montana, USA     

Glenn R. Gay  Hubert H. Gay  William H. Gay  Holly A. Martinson  Robert H. Meade  John A. Moody 《地球表面变化过程与地形》1998,23(7):651-662

Over a period of several decades, gullies have been observed in various stages of forming, growing and completing the cutoff of meander necks in Powder River. During one episode of overbank flow, water flowing over the down-stream bank of the neck forms a headcut. The headcut migrates up-valley, forming a gully in its wake, until it has traversed the entire neck, cutting off the meander. The river then follows the course of the gully, which is subsequently enlarged as the river develops its new channel. The complete process usually requires several episodes of high water: in only one of the five cases described herein was a meander cutoff initiated and completed during a single large flood. © 1998 John Wiley & Sons, Ltd.  相似文献   

A landscape analysis of the candelaria watershed in mexico: Insights into paleoclimates affecting upland horticulture in the southern yucatan peninsula semi-karst     

Joel D. Gunn  William J. Folan  Hubert R. Robichaux 《Geoarchaeology》1995,10(1):3-42

Biocultural systems adapt to global climate change through its regional manifestations. Subsistence customs are the cultural interface between regional climate and culture at large. Swidden horticulturalists in Campeche, Mexico report that dry April followed by early onset of the wet season enhances the productivity of upland tropical gardens, or milpas. To relate regional seasonality of moisture to global climate, growing season discharge for Mexico's Candelaria River from 1958 to 1990 was analyzed relative to global average temperature. Analysis of covariance revealed a statistically significant relationship (p < 0.001). Further analysis showed that hot global climate eliminates the dry season, which lowers milpa productivity by preventing burning of the slash. Cold global climate delays the wet season and planting, also at cost of productivity. Intermediate global temperature fosters optimal wet—dry season combinations. Productivity of milpas is therefore directly related to global climate through the intervening mechanism of seasonality of moisture. A regression model reflecting these findings is used to retrodict paleohydrology for the last 3000 years. The pattern of ascendancy and decline of ancient southern Maya lowland urban centers is reviewed in the perspective of changing hydrological conditions. The model indicates that fluorescence occurred with optimal balance of wet and dry season duration and catastrophes unfolded during extended wet or dry periods. We suggest that the southern Maya lowlands have had a precipitous record of urban development and collapse in part because of complex interactions of global climate and upland horticulture. The most productive conditions for milpa issue from an inherently unstable overlay of global climate on a relatively narrow band of partially developed karst (semikarst) geological formations.  相似文献   

Meeting review: The nice symposium on the origin of the solar system     

Hubert Reeves 《Icarus》1973,19(4):604-606

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Measurements of the helium 584 Å airglow during the Cassini flyby of Venus     

J.-C. Gérard  J. Gustin  B. Hubert  G.R. Gladstone  L.W. Esposito 《Planetary and Space Science》2011,59(13):1524-1528

The helium resonance line at 584 Å has been observed with the UltraViolet Imaging Spectrograph (UVIS) Extreme Ultraviolet channel during the flyby of Venus by Cassini at a period of high solar activity. The brightness was measured along the disk from the morning terminator up to the bright limb near local noon. The mean disk intensity was ∼320 R, reaching ∼700 R at the bright limb. These values are slightly higher than those determined from previous observations. The sensitivity of the 584 Å intensity to the helium abundance is analyzed using recent cross-sections and solar irradiance measurements at 584 Å. The intensity distribution along the UVIS footprint on the disk is best reproduced using the EUVAC solar flux model and the helium density distribution from the VTS3 empirical model. It corresponds to a helium density of 8×10⁶ cm⁻³ at the level of where the CO₂ is 2×10¹⁰ cm⁻³.  相似文献   

Post-depositional redistribution of trace metals in reservoir sediments of a mining/smelting-impacted watershed (the Lot River,SW France)     

Stéphane Audry  Cécile Grosbois  Hubert Bril  Jörg Schäfer  Jakub Kierczak  Gérard Blanc 《Applied Geochemistry》2010

Mining/smelting wastes and reservoir sediment cores from the Lot River watershed were studied using mineralogical (XRD, SEM–EDS, EMPA) and geochemical (redox dynamics, selective extractions) approaches to characterize the main carrier phases of trace metals. These two approaches permitted determining the role of post-depositional redistribution processes in sediments and their effects on the fate and mobility of trace metals. The mining/smelting wastes showed heterogeneous mineral compositions with highly variable contents of trace metals. The main trace metal-bearing phases include spinels affected by secondary processes, silicates and sulfates. The results indicate a clear change in the chemical partitioning of trace metals between the reservoir sediments upstream and downstream of the mining/smelting activities, with the downstream sediments showing a 2-fold to 5-fold greater contribution of the oxidizable fraction. This increase was ascribed to stronger post-depositional redistribution of trace metals related to intense early diagenetic processes, including dissolution of trace metal-bearing phases and precipitation of authigenic sulfide phases through organic matter (OM) mineralization. This redistribution is due to high inputs (derived from mining/smelting waste weathering) at the water–sediment interface of (i) dissolved SO₄ promoting more efficient OM mineralization, and (ii) highly reactive trace metal-bearing particles. As a result, the main trace metal-bearing phases in the downstream sediments are represented by Zn- and Fe-sulfides, with minor occurrence of detrital zincian spinels, sulfates and Fe-oxyhydroxides. Sequestration of trace metals in sulfides at depth in reservoir sediments does not represent long term sequestration owing to possible resuspension of anoxic sediments by natural (floods) and/or anthropogenic (dredging, dam flush) events that might promote trace metal mobilization through sulfide oxidation. It is estimated that, during a major flood event, about 870 t of Zn, 18 t of Cd, 25 t of Pb and 17 t of Cu could be mobilized from the downstream reservoir sediments along the Lot River by resuspension-induced oxidation of sulfide phases. These amounts are equivalent to 13-fold (Cd), ∼6-fold (Zn), 4-fold (Pb) the mean annual inputs of the respective dissolved trace metals into the Gironde estuary.  相似文献   

Corrigendum to “Impact and recovery associated with the deposition of capital dredging at UK disposal sites: Lessons for future licensing and monitoring” [Marine Pollution Bulletin 60 (2010) 79–90]     

Suzanne Ware  Stefan G. Bolam  Hubert L. Rees 《Marine pollution bulletin》2010,60(12):2357

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Using salt intrusion measurements to determine the freshwater discharge distribution over the branches of a multi-channel estuary: The Mekong Delta case     

Anh Duc Nguyen  Hubert H.G. Savenije  Duc Nghia Pham  Duc Thang Tang 《Estuarine, Coastal and Shelf Science》2008

The fresh water discharge is an important parameter for modelling salt intrusion in an estuary. In alluvial converging estuaries during periods of low flow, when salinity is highest, the river discharge is generally small compared to the tidal flow. This makes the determination of the fresh water discharge a challenging task. Even if discharge observations are available during a full tidal cycle, the fresh water discharge is seldom much larger than the measurement error in the tidal discharge. Observations further upstream, outside the tidal region, do not always reflect the actual flow in the saline area due to withdrawals or additional drainage. Discharge computation is even more difficult in a complex system such as the Mekong Delta, which is a multi-channel estuary consisting of many branches, over which the freshwater discharge distribution cannot be measured directly. This paper presents a new approach to determine the freshwater discharge distribution over the branches of the Mekong Delta by means of an analytical salt intrusion model, based on measurements made during the dry season of 2005 and 2006. It appears that the analytical model agrees well with observations and with a hydraulic model. This paper demonstrates that with relatively simple and appropriate salinity measurements and making use of the analytical salt intrusion model, it is possible to obtain an accurate discharge distribution over the branches of a complex estuary system. This makes the analytical model a powerful tool to analyze the water resources in tidal regions.  相似文献   

Pillow lavas as a habitat for microbial life     

Harald Furnes  Neil R. Banerjee  Hubert Staudigel  & Karlis Muehlenbachs 《Geology Today》2007,23(4):143-146

The upper oceanic crust consists predominantly of pillow lavas that, soon after their eruption, are colonized by microbes when the ambient temperature ameliorates. During the process of microbial interaction with the glassy rims of pillows several types of bio-traces are generated, of which micro-textures are the most spectacular. Microbial textures are most useful for mapping the depth of the oceanic biosphere, and in the search for the earliest life on Earth.  相似文献