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211.
The effects of incoherency and wave-passage on the nonlinear responses of concrete arch dams are investigated in this study. A double curvature arch dam is selected as a numerical example. The reservoir is modeled as a compressible material and the foundation is modeled as a massless medium. Ground motion time-histories are artificially generated using the Monte Carlo simulation approach. Four different finite element models (FEM) are considered: uniform excitation; incoherence effect; wave passage effect; and both incoherence and wave passage effects. It was revealed that modeling multiple-supports excitation could have a significant impact on the structural response of the dam by inducing a pseudo-static effect. Also, it was concluded that the coherency effect overshadows the wave passage effect and the results obtained from non-uniform excitation of FEM, including the wave passage effect, is close to the results of the FEM when it is uniformly excited. 相似文献
212.
The coastal water quality of Çanakkale Dardanelles (Turkey) was assessed based on bacteriological data and physical–chemical parameters. Total coliform (TC), fecal coliform (FC), and enterococci (ENT) bacteria along with physicochemical parameters were measured monthly up to a year at 12 different sampling sites located through both coastal lines of the strait. The fecal bacteria were abounded at several sampling sites such as B1, B3, G3, and G4 due to direct wastewater discharges and septic leakages or overloading. Storm water runoff and sediment resuspension were important pathways for the transport of coliform and ENT bacteria to the Dardanelles, as the region receives high precipitation and strong winds for most part of the year. The values of pH, temperature, and salinity were in typical ranges for the studied area. The microbiological and physicochemical data were correlated individually and in combination. The best fit correlations for bacterial data were attained between TC and FC or TC and ENT (R = 0.67 or ?0.68), while those for the combined data were obtained for TC with temperature (R = 0.94) and TC with salinity (R = ? 0.70). 相似文献
213.
Hasan ?av?ak 《Studia Geophysica et Geodaetica》2012,56(1):185-195
Uniform tetrahedra are commonly used elementary bodies for gravity calculations from which arbitrary polyhedra can be composed.
A simple derivation of the gravity effect is presented for the apex P of the tetrahedron expanded from P to an arbitrarily
oriented plane triangle. Integration of its potential effect in a rotated coordinate system applies vector algebra and renders
the anomalous potential depending on the distance of P over the triangle plain and a function of the triangle coordinates.
Partial differentiation by moving P infinitesimally in z-direction leads to two terms, a simple and a complex one; they can
be understood as describing the same difference from two points of view: leaving P at the apex of the changed polyhedron or
moving P off the unchanged polyhedron. Both views imply the same shape change and the sum over the polyhedron is thus numerically
equal. Hence we need to calculate only the one of the terms of the differential which is simpler. The calculation of the gravity
effect is numerically simplified and more stable. This has been tested for many models and is demonstrated by two examples. 相似文献
214.
Hahn Chul Jung James Hamski Michael Durand Doug Alsdorf Faisal Hossain Hyongki Lee A. K. M. Azad Hossain Khaled Hasan Abu Saleh Khan A.K.M. Zeaul Hoque 《地球表面变化过程与地形》2010,35(3):294-304
The Surface Water and Ocean Topography (SWOT) satellite mission will provide global, space‐based estimates of water elevation, its temporal change, and its spatial slope in fluvial environments, as well as across lakes, reservoirs, wetlands, and floodplains. This paper illustrates the utility of existing remote sensing measurements of water temporal changes and spatial slope to characterize two complex fluvial environments. First, repeat‐pass interferometric SAR measurements from the Japanese Earth Resources Satellite are used to compare and contrast floodplain processes in the Amazon and Congo River basins. Measurements of temporal water level changes over the two areas reveal clearly different hydraulic processes at work. The Amazon is highly interconnected by floodplain channels, resulting in complex flow patterns. In contrast, the Congo does not show similar floodplain channels and the flow patterns are not well defined and have diffuse boundaries. During inundation, the Amazon floodplain often shows sharp hydraulic changes across floodplain channels. The Congo, however, does not show similar sharp changes during either infilling or evacuation. Second, Shuttle Radar Topography Mission measurements of water elevation are used to derive water slope over the braided Brahmaputra river system. In combination with in situ bathymetry measurements, water elevation and slope allow one to calculate discharge estimates within 2.3% accuracy. These two studies illustrate the utility of satellite‐based measurements of water elevation for characterizing complex fluvial environments, and highlight the potential of SWOT measurements for fluvial hydrology. Copyright © 2010 John Wiley & Sons, Ltd. 相似文献
215.
Koichi Unami Felix Kofi Abagale Macarius Yangyuoru Abul Hasan M. Badiul Alam Gordana Kranjac-Berisavljevic 《Stochastic Environmental Research and Risk Assessment (SERRA)》2010,24(5):725-733
Droughts and floods are two opposite but related hydrological events. They both lie at the extremes of rainfall intensity
when the period of that intensity is measured over long intervals. This paper presents a new concept based on stochastic calculus
to assess the risk of both droughts and floods. An extended definition of rainfall intensity is applied to point rainfall
to simultaneously deal with high intensity storms and dry spells. The mean-reverting Ornstein–Uhlenbeck process, which is
a stochastic differential equation model, simulates the behavior of point rainfall evolving not over time, but instead with
cumulative rainfall depth. Coefficients of the polynomial functions that approximate the model parameters are identified from
observed raingauge data using the least squares method. The probability that neither drought nor flood occurs until the cumulative
rainfall depth reaches a given value requires solving a Dirichlet problem for the backward Kolmogorov equation associated
with the stochastic differential equation. A numerical model is developed to compute that probability, using the finite element
method with an effective upwind discretization scheme. Applicability of the model is demonstrated at three raingauge sites
located in Ghana, where rainfed subsistence farming is the dominant practice in a variety of tropical climates. 相似文献
216.
M. Aziz Hasan Prosun Bhattacharya Ondra Sracek Kazi Matin Ahmed Mattias von Brmssen Gunnar Jacks 《Journal of Hydrology》2009,378(1-2):105-118
Hydrogeochemical investigations along an E–W transect in the middle Meghna basin show groundwater chemistry and redox condition vary considerably with the change in geology. Groundwater in the Holocene shallow (<150 m bgl) alluvial aquifer in western part of the transect is affected by high arsenic concentration (As > 10 μg/l) and salinity. On the other hand, groundwater from the Pliocene Dupi Tila sandy aquifer in the eastern part is fresh and low in As (<10 μg/l). The Holocene shallow aquifers are high in dissolved As, , Fe and dissolved organic carbon (DOC), but generally low in and . High concentrations (250–716 mg/l) together with high DOC concentrations (1.4–21.7 mg/l) in these aquifers reflect active sources of degradable natural organic matter that drives the biogeochemical process. There is generally de-coupling of As from other redox-sensitive elements. In contrast, the Pliocene aquifers are low in As, and DOC. Molar ratio of /H4SiO4 suggests that silicate weathering is dominant in the deeper Holocene aquifers and in the Pliocene aquifers. Molar ratios of Cl−/ and Na+/Cl− suggest mixing of relict seawater with the fresh water as the origin of groundwater salinity. Speciation calculations show that saturation indices for siderite and rhodochrosite vary significantly between the Holocene and Pliocene aquifers. Stable isotopes (δ2H and δ18O) in groundwater indicate rapid infiltration without significant effects of evaporation. The isotopic data also indicates groundwater recharge from monsoonal precipitation with some impact of altitude effect at the base of the Tripura Hills in the east. The results of the study clearly indicate geological control (i.e. change in lithofacies) on groundwater chemistry and distribution of redox-sensitive elements such as As along the transect. 相似文献
217.
218.
219.
Sina Maghami Nick Nadim K. Copty Selen Deviren Saygın Hasan Sabri Öztürk Burak Demirel S. Mehdi Emadian Günay Erpul Majid Sedighi Masoud Babaei 《水文研究》2024,38(3):e15135
Soil salt accumulation is a widespread problem leading to diminished crop yield and threatening food security in many regions of the world. The soil salinization problem is particularly acute in areas that lack adequate soil water drainage and where a saline shallow water table (WT) is present. In this study, we present laboratory-scale column experiments, extending over a period of more than 400 days that focus on the processes contributing to soil salinization. We specifically examine the combined impact of soil compaction, surface water application model and water quality on salt dynamics in the presence of a saline shallow WT. The soil columns (60 cm height and 16 cm diameter) were packed with an agricultural soil with bulk densities of 1.15 and 1.34 g/cm−3 for uncompacted and compacted layers, respectively, and automatically monitored for water content, salinity and pressure. Two surface water compositions are considered: fresh (deionized, DI) and saline water (~3.4 mS/cm). To assess the sensitivity of compaction on salt dynamics, the experiments were numerically modelled with the HYDRUS-1D computer program. The results show that the saline WT led to rapid salinization of the soil column due to capillarity, with the salinity reaching levels much higher than that at the WT. However, compaction layer provided a barrier that limited the downwards moisture percolation and solute transport. Furthermore, the numerical simulations showed that the application of freshwater can temporarily reverse the accumulation of salts in agricultural soils. This irrigation strategy can help, in the short-term, alleviate soil salinization problem. The soil hydraulic properties, WT depth, water quality, evaporation demand and the availability of freshwater all play a role in the practicability of such short-term solutions. The presence of a saline shallow WT would, however, rapidly reverse these temporary measures, leading to the recurrence of topsoil salinization. 相似文献
220.
Evidence for Elevated Levels of Arsenic in Public Wells of Bangladesh Due To Improper Installation 下载免费PDF全文
I. Choudhury K. M. Ahmed M. Hasan M. R. H. Mozumder P. S. K. Knappett T. Ellis A. van Geen 《Ground water》2016,54(6):871-877
One of the mainstays of mitigation to reduce the exposure of the rural population of Bangladesh to arsenic (As) from private, mostly <90‐m deep wells over the past 15 years has been the installation of over 300,000 deeper community wells. A comprehensive testing campaign previously conducted across a 180 km2 of area of Bangladesh identified 9 out of total of 927 wells >90 m deep that contained >50 µg/L arsenic. We show here that for five of these nine wells, conductivity profiles obtained after spiking the well bore with salt indicate a shallow leak that could explain the high As in the well water. In two of the five leaky wells, the presence of additional screens at the depth of the leak was documented with a downhole camera. The downhole camera did not detect anomalies in the construction of the remaining three leaky wells or in the four wells that did not leak. The four wells that did not leak were all >150‐m deep and located in two villages separated by less than 500 m. Excluding these two villages and a handful of leaky wells, the results indicate an aquifer that is consistently low in As over a sizeable area at depths >90 m. Isolated cases of public wells that are elevated in As that have been reported elsewhere in Bangladesh may therefore reflect improper installation rather than actual contamination of the deep aquifer. 相似文献