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111.
Jeffery Tyler McGarr Corey D. Wallace Dimitrios Ntarlagiannis Daniel M. Sturmer Mohamad Reza Soltanian 《水文研究》2021,35(9):e14358
Hyporheic exchange influences water quality and controls numerous physical, chemical, and biological processes. Despite its importance, hyporheic exchange and the associated dynamics of solute mixing are often difficult to characterize due to spatial (e.g., sedimentary heterogeneity) and temporal (e.g., river stage fluctuation) variabilities. This study coupled geophysical techniques with physical and chemical sediment analyses to map sedimentary architecture and quantify its influence on hyporheic exchange dynamics within a compound bar deposit in a gravel-dominated river system in southwestern Ohio. Electromagnetic induction (EMI) was used to quantify variability in electrical conductivity within the compound bar. EMI informed locations of electrode placement for time-lapse electrical resistivity imaging (ERI) surveys, which were used to examine changes in electrical resistivity driven by hyporheic exchange. Both geophysical methods revealed a zone of high electrical conductivity in the center of the bar, identified as a fine-grained cross-bar channel fill. The zone acts as a baffle to flow, evidenced by stable electrical conditions measured by time-lapse ERI over the study period. Large changes in electrical resistivity throughout the survey period indicate preferential flowpaths through higher permeability sands and gravels. Grain size analyses confirmed sedimentological interpretations of geophysical data. Loss on ignition and x-ray fluorescence identified zones with higher organic matter content that are locations for potentially enhanced geochemical activity within the cross-bar channel fill. Differences in the physical and geochemical characteristics of cross-bar channel fills play an important role in hyporheic flow dynamics and nutrient processing within riverbed sediments. These findings enhance our understanding of the applications of geophysical methods in mapping riverbed heterogeneity and highlight the importance of accurately representing geomorphologic features and heterogeneity when studying hyporheic exchange processes. 相似文献
112.
Groundwater is a primary source of drinking water worldwide, but excess nutrients and emerging contaminants could compromise groundwater quality and limit its usage as a drinking water source. As such contaminants become increasingly prevalent in the biosphere, a fundamental understanding of their fate and transport in groundwater systems is necessary to implement successful remediation strategies. The dynamics of surface water-groundwater (hyporheic) exchange within a glacial, buried-valley aquifer system are examined in the context of their implications for the transport of nutrients and contaminants in riparian sediments. High conductivity facies act as preferential flow pathways which enhance nutrient and contaminant delivery, especially during storm events, but transport throughout the aquifer also depends on subsurface sedimentary architecture (e.g. interbedded high and low conductivity facies). Temperature and specific conductance measurements indicate extensive hyporheic mixing close to the river channel, but surface water influence was also observed far from the stream-aquifer interface. Measurements of river stage and hydraulic head indicate that significant flows during storms (i.e., hot moments) alter groundwater flow patterns, even between consecutive storm events, as riverbed conductivity and, more importantly, the hydraulic connectivity between the river and aquifer change. Given the similar mass transport characteristics among buried-valley aquifers, these findings are likely representative of glacial aquifer systems worldwide. Our results suggest that water resources management decisions based on average (base) flow conditions may inaccurately represent the system being evaluated, and could reduce the effectiveness of remediation strategies for nutrients and emerging contaminants. 相似文献
113.
Mohamad?Reza?SoltanianEmail author Zhenxue?Dai Changbing?Yang Mohammad?Amin?Amooie Joachim?Moortgat 《Stochastic Environmental Research and Risk Assessment (SERRA)》2018,32(1):295-310
This paper presents a stochastic model for multicomponent competitive monovalent cation exchange in hierarchical porous media. Reactive transport in porous media is highly sensitive to heterogeneities in physical and chemical properties, such as hydraulic conductivity (K), and cation exchange capacity (CEC). We use a conceptual model for multimodal reactive mineral facies and develop a Eulerian-based stochastic theory to analyze the transport of multiple cations in heterogeneous media with a hierarchical organization of reactive minerals. Numerical examples investigate the retardation factors and dispersivities in a chemical system made of three monovalent cations (Na+, K+, and Cs+). The results demonstrate how heterogeneity influences the transport of competitive monovalent cations, and highlight the importance of correlations between K and CEC. Further sensitivity analyses are presented investigating how the dispersion and retardation of each cation are affected by the means, variances, and integral scales of K and CEC. The volume fraction of organic matter is shown to be another important parameter. The Eulerian stochastic framework presented in this work clarifies the importance of each system parameters on the migration of cation plumes in formations with hierarchical organization of facies types. Our stochastic approach could be used as an alternative to numerical simulations for 3D reactive transport in hierarchical porous media, which become prohibitively expensive for the multicomponent applications considered in this work. 相似文献
114.
Earthquake engineers have made a lot of efforts to derive a comprehensive set of closed form expressions for performance evaluation of frames, which are already presented in guidelines such as SAC/FEMA. These analytical expressions have been developed to estimate the annual probability of exceeding a limit state. In the process of such seismic assessments, some essential assumptions are adopted to simplify the process. One of these fundamental assumptions declares that drift demand at any seismic intensity level follows a lognormal distribution around its median. To investigate the validity of this assumption, this paper describes a case study of the types of errors that could be produced by using the sample median as the central tendency. Based on the Maximum Likelihood Estimation method as well as other statistical evidence, this paper proposes the use of the sample geometric mean instead of the sample median for the central tendency. Further, the results of seismic reliability evaluations of 4 sample frames are compared based on utilizing both the geometric mean and the sample median. In this process, both first and second order power law fits of the hazard curve are implemented to compare the effects of hazard estimation and the selection of the central tendency on the final results. It is observed in the application example that the sample geometric mean could lead to more accurate results. 相似文献
115.
Relocation of hypocenters from DOMERAPI and BMKG networks: a preliminary result from DOMERAPI project
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Mohamad Ramdhan Sri Widiyantoro Andri Dian Nugraha Jean-Philippe Métaxian Asep Saepuloh Said Kristyawan Andry Syaly Sembiring Agus Budi Santoso Antoine Laurin Ahmad Ali Fahmi 《地震科学(英文版)》2017,30(2):67-79
Merapi volcano located in central Java, Indonesia, is one of the most active stratovolcanoes in the world. Many Earth scientists have conducted studies on this volcano using various methods. The geological features around Merapi are very attractive to be investigated because they have been formed by a complex tectonic process and volcanic activities since tens of millions of years ago. The southern mountain range, Kendeng basin and Opak active fault located around the study area resulted from these processes. DOMERAPI project was conducted to understand deep magma sources of the Merapi volcano comprehensively. The DOMERAPI network was running from October 2013 to mid-April 2015 by deploying 46 broad-band seismometers around the volcano. Several steps, i.e., earthquake event identification, arrival time picking of P and S waves, hypocenter determination and hypocenter relocation, were carried out in this study. We used Geiger’s method (Geiger 1912) for hypocenter determination and double-difference method for hypocenter relocation. The relocation result will be used to carry out seismic tomographic imaging of structures beneath the Merapi volcano and its surroundings. For the hypocenter determination, the DOMERAPI data were processed simultaneously with those from the Agency for Meteorology, Climatology and Geophysics (BMKG) seismic network in order to minimize the azimuthal gap. We found that the majority of earthquakes occurred outside the DOMERAPI network. There are 464 and 399 earthquakes obtained before and after hypocenter relocation, respectively. The hypocenter relocation result successfully detects some tectonic features, such as a nearly vertical cluster of events indicating a subduction-related backthrust to the south of central Java and a cluster of events to the east of Opak fault suggesting that the fault has an eastward dip. 相似文献
116.
Ahmad Safuan A Rashid Mohammad Gharehzadeh Shirazi Ramli Nazir Hisham Mohamad Fauzan Sahdi 《Marine Georesources & Geotechnology》2020,38(6):755-760
AbstractThis article presents the performance of the short-term bearing capacity on soft clay soil treated by Kenaf geotextile under vertical loading via a small-scale modelling test at unit gravity. The ground model was formulated by consolidating kaolin in a rigid testing compartment. In the loading test, the strip footing was represented by a rigid footing. For the treated case, a series of tests were performed to examine the effects of the burial depth of the Kenaf geotextile on the bearing capacity of the soft soil. The Kenaf geotextile was laid beneath the rigid footing (at the ground surface) and at 50, 75 and 100?mm depth from the soil surface. All the measured results of the Kenaf geotextile treated ground were compared with the untreated ground. The incorporation of Kenaf fibre geotextile was observed to enhance the bearing capacity of soft cohesive clay up to 281% depending upon the depth of the installed geotextile. The geotextile at the surface provided the highest bearing capacity and sustained the highest displacement at failure. The outcome of this research will promote the use of natural fibre geotextiles as sustainable earth reinforcement in temporary earthwork applications. 相似文献
117.
Sedaghati Parshan Gerami Mohsen Naderpour Hosein 《Bulletin of Earthquake Engineering》2022,20(11):6267-6305
Bulletin of Earthquake Engineering - Since post-mainshock events following a major earthquake are likely to occur, it is imperative to have an understanding of the functionality status of... 相似文献
118.
Zohreh NOWROUZI Asadollah MAHBOUBI Reza MOUSSAVI-HARAMI Mohammad Hossein MAHMUDY GHARAIE Farzin GHAEMI 《《地质学报》英文版》2015,89(4):1276-1295
Two sections from the Silurian deposits in the Central Iran Micro and Turan Plates were measured and sampled. These deposits are mostly composed of submarine volcanic rocks, skeletal and non-skeletal limestone, shale and sandstone that were deposited in low to high energy conditions (from tidal flat to deep open marine). According to gradual deepening trend, wide lateral distribution of facies as well as absence of resedimentation deposits, a depositional model of a homoclinal ramp was proposed for these deposits. Field observations and facies distribution indicate that, two depositional sequences were recognized in both sections. These sections show similarities in facies and depositional sequence during the Early Silurian in the area. Although there are some opinions and evidences that demonstrated Paleo-Tethys rifting phase started at the Late Ordovician-Early Silurian, similarities suggest that the Turan and Iran Plates were not completely detached tectonic block during this time, and that their depositional conditions were affected by global sea level changes and tectonic events. 相似文献
119.
Building more realistic reservoir optimization models using data mining - A case study of Shelbyville Reservoir 总被引:1,自引:0,他引:1
Mohamad I. HejaziXiming Cai 《Advances in water resources》2011,34(6):701-717
In this paper, we promote a novel approach to develop reservoir operation routines by learning from historical hydrologic information and reservoir operations. The proposed framework involves a knowledge discovery step to learn the real drivers of reservoir decision making and to subsequently build a more realistic (enhanced) model formulation using stochastic dynamic programming (SDP). The enhanced SDP model is compared to two classic SDP formulations using Lake Shelbyville, a reservoir on the Kaskaskia River in Illinois, as a case study. From a data mining procedure with monthly data, the past month’s inflow (Qt−1), current month’s inflow (Qt), past month’s release (Rt−1), and past month’s Palmer drought severity index (PDSIt−1) are identified as important state variables in the enhanced SDP model for Shelbyville Reservoir. When compared to a weekly enhanced SDP model of the same case study, a different set of state variables and constraints are extracted. Thus different time scales for the model require different information. We demonstrate that adding additional state variables improves the solution by shifting the Pareto front as expected while using new constraints and the correct objective function can significantly reduce the difference between derived policies and historical practices. The study indicates that the monthly enhanced SDP model resembles historical records more closely and yet provides lower expected average annual costs than either of the two classic formulations (25.4% and 4.5% reductions, respectively). The weekly enhanced SDP model is compared to the monthly enhanced SDP, and it shows that acquiring the correct temporal scale is crucial to model reservoir operation for particular objectives. 相似文献
120.
This contribution is an attempt to enlarge the current knowledge about the focal mechanisms as well as the seismotectonic
settings in Syria. The seismologically active zones have been identified by applying an appropriate methodology to the events
recorded during the period 1995–2003 by the Syrian National Seismological Network (SNSN). The recorded events in Syria were
classified as weak during the research period. It was extremely important to propose and apply an appropriate methodology
to identify the focal mechanisms generating this seismic activity. The proposed methodology consists of applying a combination
of two techniques: the multiplet and the composite focal mechanisms. The combination of many events in one composite focal
mechanism was realized by a multiplet technique using the spectral coherence of the events as a measure of similarity. The
application of the proposed methodology allows a data set of composite fault plane solutions to be obtained. Most of the composite
fault plane solutions had strike-slip mechanisms which are in agreement with the configuration of seismogenic belts in Syria. 相似文献