Inverse modeling and uncertainty analysis of potential groundwater recharge to the confined semi-fossil Ohangwena II Aquifer,Namibia     

Markus Wallner  Georg Houben  Christoph Lohe  Martin Quinger  Thomas Himmelsbach 《Hydrogeology Journal》2017,25(8):2303-2321

The identification of potential recharge areas and estimation of recharge rates to the confined semi-fossil Ohangwena II Aquifer (KOH-2) is crucial for its future sustainable use. The KOH-2 is located within the endorheic transboundary Cuvelai-Etosha-Basin (CEB), shared by Angola and Namibia. The main objective was the development of a strategy to tackle the problem of data scarcity, which is a well-known problem in semi-arid regions. In a first step, conceptual geological cross sections were created to illustrate the possible geological setting of the system. Furthermore, groundwater travel times were estimated by simple hydraulic calculations. A two-dimensional numerical groundwater model was set up to analyze flow patterns and potential recharge zones. The model was optimized against local observations of hydraulic heads and groundwater age. The sensitivity of the model against different boundary conditions and internal structures was tested. Parameter uncertainty and recharge rates were estimated. Results indicate that groundwater recharge to the KOH-2 mainly occurs from the Angolan Highlands in the northeastern part of the CEB. The sensitivity of the groundwater model to different internal structures is relatively small in comparison to changing boundary conditions in the form of influent or effluent streams. Uncertainty analysis underlined previous results, indicating groundwater recharge originating from the Angolan Highlands. The estimated recharge rates are less than 1% of mean yearly precipitation, which are reasonable for semi-arid regions.  相似文献   

The Riddle of the Springs of Dilmun—Does the Gilgamesh Epic Tell the Truth?     

Randolf Rausch  Heiko Dirks  Andreas Kallioras  Christoph Schüth 《Ground water》2014,52(4):640-644

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Can GPS-Derived Surface Loading Bridge a GRACE Mission Gap?     

Roelof Rietbroek  Mathias Fritsche  Christoph Dahle  Sandra-Esther Brunnabend  Madlen Behnisch  Jürgen Kusche  Frank Flechtner  Jens Schröter  Reinhard Dietrich 《Surveys in Geophysics》2014,35(6):1267-1283

We investigated two ‘gap-filler’ methods based on GPS-derived low-degree surface loading variations (GPS-I and GPS-C) and a more simple method (REF-S) which extends a seasonal harmonic variation into the expected Gravity Recovery and Climate Experiment (GRACE) mission gap. We simulated two mission gaps in a reference solution (REF), which is derived from a joint inversion of GRACE (RL05) data, GPS-derived surface loading and simulated ocean bottom pressure. The GPS-I and GPS-C methods both have a new type of constraint applied to mitigate the lack of GPS station network coverage over the ocean. To obtain the GPS-C solution, the GPS-I method is adjusted such that it fits the reference solution better in a 1.5 year overlapping period outside of the gap. As can be expected, the GPS-I and GPS-C solutions contain larger errors compared to the reference solution, which is heavily constrained by GRACE. Within the simulated gaps, the GPS-C solution generally fits the reference solution better compared to the GPS-I method, both in terms of spherical harmonic loading coefficients and in terms of selected basin-averaged hydrological mass variations. Depending on the basin, the RMS-error of the water storage variations (scaled for leakage effects) ranges between 1.6 cm (Yukon) and 15.3 cm (Orinoco). In terms of noise level, the seasonal gap-filler method (REF-S) even outperforms the GPS-I and GPS-C methods, which are still affected by spatial aliasing problems. However, it must be noted that the REF-S method cannot be used beyond the study of simple harmonic seasonal variations.  相似文献   

Impact of channel bar form and grain size variability on estimated stranding risk of juvenile brown trout during hydropeaking          下载免费PDF全文

Christoph Hauer  Günther Unfer  Patrick Holzapfel  Marlene Haimann  Helmut Habersack 《地球表面变化过程与地形》2014,39(12):1622-1641

Hydropeaking leads to artificial fluctuations in discharge and corresponding water levels with pronounced dewatering areas between base and peak flow along gravel bars and channel banks. In the present study, 16 hydropeaking reaches in Austria were investigated to assess possible differences in the estimated stranding risk for young of the year brown trout according to different gravel bar types and differences in microtopography roughness. Based on hydrodynamic‐numerical modelling, a predictive habitat modelling approach was implemented in the study design. Accompanied by grain size sampling along the various channel bars, a conceptual stranding risk model (SRM) was developed. The results showed that a high variability in estimated stranding risk exists for the tested sites considering discharge ratios of 1:3, 1:5 and 1:10. With respect to the discussion of establishing legal thresholds for ramping ratios in discharge, it was documented that, exemplarily, a discharge ratio base flow/peak flow of 1:5 (winter base flow conditions) could cause minor differences in the spatial extent of dewatering areas and the related estimated stranding risk for juvenile brown trout compared to a ratio of 1:2 for summer base flow conditions. Microtopographic roughness was addressed due to sampling and analysis of grain size distributions. Statistical testing of grain size distributions revealed significant differences between the surface material compositions of the investigated gravel bars. Those differences are evident, particularly for the coarser fraction (d₉₀), which is important as cover for young of the year brown trout. These aspects of grain size in habitat use and hydraulics have been addressed in the conceptual SRM. The results showed that point bar morphology, in particular, was less sensitive to the risk of stranding compared to, for example, alternating gravel bars. Considering the multiple pressures for alpine rivers, the improvement of structural features due to bar formation and related self‐forming processes is discussed as a possible alternative for future mitigation measures to reduce the negative impacts of hydropeaking. Copyright © 2014 John Wiley & Sons, Ltd.  相似文献   

A large sedimentary basin in the Terra Sirenum region of the southern highlands of Mars     

Alfonso F. Davila  Christoph Gross  Alberto G. Fairén  Thomas Kneissl  James M. Dohm 《Icarus》2011,212(2):579-589

Different lines of evidence point to hydrological cycling in the martian past. The extent, duration, and magnitude of this cycling remains unclear, as well as the magnitude of aqueous processes on the surface. Here, we provide geomorphic and mineralogic evidence of a large inter-crater sedimentary basin located in the Terra Sirenum region, which was once covered by a body of liquid water with an areal extent of at least 30,000 km² and a depth of approximately 200 m. The topographic basin, which is modified by a number of large impact craters, is partly controlled by ancient impact and tectonic structures. As a result of evaporation of the large body of water, salt flats formed in the lowest topographic reaches of the basin. Hydrated phyllosilicates occur in close proximity to the salt flats and in the ejecta and rim materials of small impact craters with stratigraphic relations that suggest that they underlie the evaporite deposits. Crater statistics place the maximum age of aqueous activity during the Late Noachian epoch. The relatively pristine mineral deposits in the basin have a high potential to yield information of the geochemistry and water activity during the ancient Noachian Period when conditions were seemingly more conducive to life.  相似文献   

Neoproterozoic calc‐alkaline peraluminous granitoids of the Deleihimmi pluton,Central Eastern Desert,Egypt: implications for transition from late‐ to post‐collisional tectonomagmatic evolution in the northern Arabian–Nubian Shield     

Esam S. Farahat  Rafat Zaki  Christoph Hauzenberger  Mabrouk Sami 《Geological Journal》2011,46(6):544-560

The widely distributed late‐collisional calc‐alkaline granitoids in the northern Arabian–Nubian Shield (ANS) have a geodynamic interest as they represent significant addition of material into the ANS juvenile crust in a short time interval (∼630–590 Ma). The Deleihimmi granitoids in the Egyptian Central Eastern Desert are, therefore, particularly interesting since they form a multiphase pluton composed largely of late‐collisional biotite granitoids enclosing granodiorite microgranular enclaves and intruded by leuco‐ and muscovite granites. Geochemically, different granitoid phases share some features and distinctly vary in others. They display slightly peraluminous (ASI = 1–1.16), non‐alkaline (calc‐alkaline and highly fractionated calc‐alkaline), I‐type affinities. Both biotite granitoids and leucogranites show similar rare earth element (REE) patterns [(La/Lu)_N = 3.04–2.92 and 1.9–1.14; Eu/Eu* = 0.26–0.19 and 0.11–0.08, respectively) and related most likely by closed system crystal fractionation of a common parent. On the other hand, the late phase muscovite granites have distinctive geochemical features typical of rare‐metal granites. They are remarkably depleted in Sr and Ba (4–35 and 13–18 ppm, respectively), and enriched in Rb (381–473 ppm) and many rare metals. Moreover, their REE patterns show a tetrad effect (TE_1,3 = 1.13 and 1.29) and pronounced negative Eu anomalies (Eu/Eu* = 0.07 and 0.08), implying extensive open system fractionation via fluid–rock interaction during the magmatic stage. Origin of the calc‐alkaline granitoids by high degree of partial melting of mafic lower crust with subsequent crystal fractionation is advocated. The broad distribution of late‐collisional calc‐alkaline granitoids in the northern ANS is related most likely to large areal and intensive lithospheric delamination subsequent to slab break‐off and crustal/mantle thickening. Such delamination caused both crustal uplift and partial melting of the remaining mantle lithosphere in response to asthenospheric uprise. The melts produced underplate the lower crust to promote its melting. The presence of microgranular enclaves, resulting from mingling of mantle‐derived mafic magma with felsic crustal‐derived liquid, favours this process. The derivation of the late‐phase rare‐metal granites by open system fractionation via fluid interaction is almost related to the onset of extension above the rising asthenosphere that results in mantle degassing during the switch to post‐collisional stage. Consequently, the switch from late‐ to post‐collisional stage of crustal evolution in the northern ANS could be potentially significant not only geodynamically but also economically. Copyright © 2011 John Wiley & Sons, Ltd.  相似文献   

Origin and dynamics of groundwater salinity in the alluvial plains of western Delhi and adjacent territories of Haryana State,India   总被引：1，自引：0，他引：1  

Gunnar Lorenzen  Christoph Sprenger  Paul Baudron  Dinesh Gupta  Asaf Pekdeger 《水文研究》2012,26(15):2333-2345

Groundwater salinity is a widespread problem and a challenge to water resources management. It is an increasing concern in the alluvial plains of Delhi and neighbouring Haryana state as well as a risk for agricultural production water supply and sustainable development. This study aims to identify potential sources of dissolved salts and the driving mechanisms of salinity ingress in the shallow aquifer. It combines a comprehensive review of environmental conditions and the analysis of groundwater samples from 25 sampling points. Major ions are analysed to describe the composition and distribution of saline groundwater and dissolution/precipitation dynamics. Density stratification and local upconing of saline waters were identified by multilevel monitoring and temperature logging. Bromide–chloride ratios hold information on the formation of saline waters, and nitrate is used as an indicator for anthropogenic influences. In addition, stable isotope analysis helps to identify evaporation and to better understand recharge processes and mixing dynamics in the study region. The results lead to the conclusion that surface water and groundwater influx into the poorly drained semiarid basin naturally results in the accumulation of salts in soil, sediments and groundwater. Human‐induced changes of environmental conditions, especially the implementation of traditional canal and modern groundwater irrigation, have augmented evapotranspiration and led to waterlogging in large areas. In addition, water‐level fluctuations and perturbation of the natural hydraulic equilibrium favour the mobilisation of salts from salt stores in the unsaturated zone and deeper aquifer sections. The holistic approach of this study demonstrates the importance of various salinity mechanisms and provides new insights into the interference of natural and anthropogenic influences. Copyright © 2011 John Wiley & Sons, Ltd.  相似文献   

Inclined lidar observations of boundary layer aerosol particles above the Kongsfjord,Svalbard     

Astrid Lampert  Johan Ström  Christoph Ritter  Roland Neuber  Young Jun Yoon  Nam Yi Chae  Masataka Shiobara 《Acta Geophysica》2012,60(5):1287-1307

An inclined lidar with vertical resolution of 0.4 m was used for detailed boundary layer studies and to link observations at Zeppelin Mountain (474 m) and Ny-Ålesund, Svalbard. We report on the observation of aerosol layers directly above the Kongsfjord. On 29 April 2007, a layer of enhanced backscatter was observed in the lowest 25 m above the open water surface. The low depolarization ratio indicated spherical particles. In the afternoon, this layer disappeared. The ultrafine particle concentration at Zeppelin and Corbel station (close to the Kongsfjord) was low. On 1 May 2007, a drying process in the boundary layer was observed. In the morning, the atmosphere up to Zeppelin Mountain showed enhanced values of the backscatter coefficient. Around noon, the top of the highly reflecting boundary layer decreased from 350 to 250 m. The top of the boundary layer observed by lidar was confirmed by radiosonde data.  相似文献   

Estimating economic impacts in New Zealand: Technical issues     

Christoph Schumacher  Paul Spoonley 《New Zealand geographer》2008,64(3):221-227

Abstract: This technical paper describes the techniques used to calculate future economic impacts, using two quite different situations: a technology park in a major urban area and the suspension of fees at a tertiary institution in a provincial town. A number of issues arose which required assumptions to be made. Notable among these were the lack of regionalized input–output tables and estimating the ‘leakage’ to economies outside the specified target area.  相似文献   

Synchronizing seismic networks with ambient noise   总被引：1，自引：0，他引：1  

Christoph Sens-Schönfelder 《Geophysical Journal International》2008,174(3):966-970

The technique of retrieving Green's functions by pairwise correlation of a random wavefield is used to estimate the stability of the timing system of a seismic network. The method is demonstrated with data from a network consisting of stations with four independent clocks and GPS-receivers. For a two years period, daily measurements of the timing error of each of the four systems are obtained. These measurements can be used to correct the timing of the data in periods without GPS reception. The accuracy of this method can exceed the precision of the internal station clocks already after a single day of uncorrected drift.  相似文献