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51.
Estimating the potential direct runoff for urban watersheds is essential for flood risk mitigation and rainwater harvesting. Thus, this study aims to estimate the potential runoff depth based on the natural resources conservation service (NRCS) method and delineation of the watersheds in Riyadh, Saudi Arabia. To accomplish this objective, the geographic information systems (GIS) and remote sensing technique (RST) data were integrated to save time and improve analysis accuracy. The employed data include the digital elevation model (DEM), soil map, geology map, satellite images, and daily precipitation records. Accordingly, the hydrologic soil groups (HSG), the land use/land cover (LULC), and curve number (CN) were determined for each watershed in the study area. The results of this analysis show that the study area can be delineated into 40 watersheds with a total area of 8500 km2. Furthermore, the dominant HSG is group D, which represents about 71% of the total area. The LULC maps indicate four major land types in the entire study area: urban, barren land, agricultural land, and roads. The CN of the study area ranges from 64 to 98, while the weighted CN is 92 for the city. The rainfall-runoff analysis shows that the area has a high and very high daily runoff (35–50 and >?50 mm, respectively). Therefore, in this case, the runoff leads to flooding, especially in the urban area and agricultural lands.  相似文献   
52.
Natural Hazards - Because of the disasters associated with slope failure, the analysis and forecasting of slope stability for geotechnical engineers are crucial. In this work, in order to forecast...  相似文献   
53.
A total of 6 oil samples were systematically selected from six Asmari Reservoir wells in the Cheshmeh-Khush Oilfield for geochemical evaluation of the hydrocarbon system, based on reservoir geochemistry and oil fingerprints. An investigation of the distribution patterns of normal alkanes and tricyclic and tetracyclic terpanes along with characteristic biomarkers of the depositional environment and sedimentary facies, indicated that the source rock of the studied hydrocarbons was deposited in a reducing aquatic environment with a low input of terrigenous material and predominantly carbonate lithology derived from organic algal matter. The studied oil samples exhibited moderate maturity, as was further confirmed by the parameters extracted from the light hydrocarbons. Statistical clustering based on different biomarker parameters indicated the presence of two oil families. Additionally, the application of branched and cyclic compounds in the light hydrocarbons (C5–C11) to evaluate lateral continuity of the Asmari reservoir further supported the presence of the two oil families. Other evidence proved the presence of a NE–SW trending fault separating wells X5 and X6 from the other wells in the field. In other wells across the field, good lateral reservoir continuity was observed, despite the presence of faults on the northern and southern plunges of the structure.  相似文献   
54.
A number of studies have suggested that mangrove forests and their faunal components may be pre-adapted to the impact of organic waste discharge, making them possible natural wastewater treatment wetlands. However, the results from recent research are contradictory. Some studies have shown that negative effects, sometimes subtle and difficult to observe, can be detected on specific biotic components of forests subjected to organic pollution. Therefore, the aim of the present study was to investigate possible alterations in the ecosystem engineering activities of a fiddler crab community dominating the landward belts of Kenyan mangrove forests. The total processed sediment produced by burrowing and foraging activities in a population from a peri-urban mangrove area receiving untreated domestic sewage was compared with that from a forest not affected by urban wastewater. The results showed how the peri-urban site hosted a higher biomass of crabs, which produced a significantly lower amount of processed sediment compared with the pristine site, resulting in a lower total top sediment mixing activity of the crabs. Thus, the present study showed a link between sewage exposure and top sediment reworking by crabs, which is potentially beneficial for mangrove growth and ecosystem functioning. This represents a possible example of cryptic ecological degradation in mangal systems.  相似文献   
55.
Existence of debris structures inevitably ascends the rate of scour process around bridge piers and flow area not only lead into remarkable deviation of flow but also increase the velocity around bridge piers. A myriad of experimental and field studies to understand effective parameters on the scour depth with debris effects were conducted. To reach permissible values of the scour depth for the practical uses, relationships extracted in previous investigations suffer from lack of generalization for experimental data ranges. In this way, neuro-fuzzy group method of data handling (NF-GMDH)-based self-organized models is applied to evaluate the pier scour depth. In this study, NF-GMDH network is implemented using evolutionary algorithms listed particle swarm optimization (PSO), gravitational search algorithm (GSA), and genetic algorithm (GA). In all, 243 experimental datasets including a wide range of input and output parameters to develop the proposed models were compiled from various literature. The efficiency of NF-GMDH networks for training and testing stages was perused. NF-GMDH-PSO model provided the scour depth with more precise predictions (root mean squared error (RMSE)?=?0.388 and scatter index (SI)?=?0.343) in comparison with NF-GMDH-GA (RMSE?=?0.402 and SI?=?0.361) and NF-GMDH-GSA (RMSE?=?0.456 and SI?=?0.407) networks. In addition, blockage ratio (ΔA) was taken into account as the most sumptuous parameter with utmost level of effectiveness using the sensitivity analysis.  相似文献   
56.
It is shown that sheared electron flows can generate long as well as short wavelength (in comparison with the ion gyroradius) electrostatic waves in a nonuniform magnetplasma. For this purpose, we derive dispersion relations by employing two-fluid and hybrid models; in the two-fluid model the dynamics of both the electrons and ions are governed by the hydrodynamic equations and the guiding center fluid drifts, whereas the hybrid model assumes kinetic ions and fluid electrons. Explicit expressions for the growth rates and thresholds are presented. Linearly excited waves attain finite amplitudes and start interacting among themselves. The interaction is governed by the nonlinear equations containing the Jacobian nonlinearities. Stationary solutions of the nonlinear mode coupling equations can be represented in the form of a dipolar vortex and a vortex street. Conditions under which the latter arise are given. Numerical results for the growth rates of linearly excited modes as well as for various types of vortices are displayed for the parameters that are relevant for the F-region of the Earth's ionosphere. It is suggested that the results of the present investigation are useful in understanding the properties of nonthermal electrostatic waves and associated nonlinear vortex structures in the Earth's ionosphere.  相似文献   
57.
One of the major causes of instability in geotechnical structures such as dikes or earth dams is internal erosion, an insidious process that occurs over a long period of time. Research on this topic is still fairly new and much more needs to be understood in order to solve the problems posed by this phenomenon. This paper proposes a hydromechanical model based on porous continuous medium theory to assess how internal erosion impacts the safety of earthen structures. The saturated soil is considered as a mixture of four interacting constituents: soil skeleton, erodible fines, fluidized fine particles, and fluid. The detachment and transport of the fine particles are described by a mass exchange model between the solid and the fluid phases. An elastoplastic constitutive model for sand-silt mixtures has been developed to monitor the effect of the evolution of both porosity and fines content induced by internal erosion upon the behavior of the soil skeleton. The model has been numerically solved with the finite element method. It has then been applied to the specific case study of a dike foundation subjected to internal erosion induced by the presence of a karstic cavity beneath the alluvium layer. The numerical results show the onset of erosion, the time-space evolution of the eroded zone, and the hydromechanical response of the soil constituting the dike, all of which highlights the effects of the cavity location, the erosion rate, and the fines content.  相似文献   
58.
The Portland cement manufacturing process produces considerable amount of cement kiln dust (CKD). While many facilities are able to reuse a significant portion of CKD in their production lines, a large percentage is removed as industrial waste and placed in landfills. Because of the large amount of material potentially available for use, and in an effort to cut disposal costs, alternative and beneficial uses for CKD need to be investigated. This study presents experimental results of the use of CKD in modification and stabilization of soils from the Aberdeen and Everett areas in the state of Washington. These soils are typically wet of the optimum water content and pose problems during geotechnical construction. CKD was added in percentages of 5, 10, 15, and 20% by dry weight of the soils. Laboratory tests, including drying rate of the soils, Atterberg limits, standard proctor and unconfined compressive strength were conducted. Results of the investigation showed significant improvement in drying rate and unconfined compressive strength of the CKD treated specimens as the percentage of CKD increased. It was also found that lower percentages of CKD can be used for modification purposes, whereas higher percentages of CKD can be used for both modification and stabilization purposes in geotechnical construction.  相似文献   
59.
Mesoproterozoic volcanosedimentary units and tectonic events occurring in the Río de la Plata Craton (RPC) are reviewed. A belt consisting of volcanosedimentary successions exhibiting greenschist-facies metamorphism is exposed in the eastern RPC (Nico Pérez Terrane) in Uruguay. The Parque UTE Group consists of basic volcanics and gabbros at the base (1,492?±?4?Ma, U?CPb on zircon), carbonates in its middle part and interbedded carbonates, shales and acid volcanics (1,429?±?21?Ma, U?CPb on zircon) at the top. The Mina Verdún Group is made up of rhyolites and acid pyroclastics at its base and top, and Conophyton-bearing limestones and massive dolostones in the middle. A U?CPb LA-ICP MS zircon age of 1,433?±?6?Ma is reported here for lapilli-tuffs at the base of the Mina Verdún Group (Cerro de las Víboras Formation). This age shows that the Mina Verdún Group immediately postdates the Parque UTE Group, a fact supported by carbon isotope chemostratigraphy. Both units were deformed and metamorphosed between 1.25 and 1.20?Ga, as shown by K?CAr and Ar?CAr ages. This tectonic event affected most of the RPC and led to the accretion of the Nico Pérez Terrane to the remainder of the RPC along the Sarandí del Yí megashear. We report a U?CPb LA-ICP MS zircon age (upper intercept) of 3,096?±?45?Ma for metatonalites of the La China Complex (Nico Pérez Terrane), which yield a lower intercept age of 1,252?Ma. A proto-Andean, Mesoproterozoic belt is envisaged to account for abundant Mesoproterozoic detrital zircon ages occurring in Ediacaran sandstones of the RPC. If the RPC is fringed at both sides by Mesoproterozoic, Grenville-aged belts it is likely that it occupied a rather central position in Rodinia. A possible location between Laurentia and the Kalahari Craton, and to the south of Amazonia, is suggested.  相似文献   
60.
Recently, new theories on underground geophysical and geochemical interactions which had been reported to occur during the preparation stages of earthquakes and the remotely measurable variations have been put to test and some warning factors were suggested as earthquake precursors. Data vendors are providing daily basis information from the earth's surface by combining remote sensing data and in situ observations. In this paper, we analyze atmospheric, oceanic, and surface changes in the ocean, coast, and land lying near the epicenters of two recent major earthquakes. The changes are studied in terms of the regional fault locations which have been reported by the U.S. Geological Survey as the shake triggering geological structures. Our detailed analyses showed anomalous increases of surface latent heat flux (SLHF) for both the earthquakes. Meaningfully limited to the geographical extents of the regional active faults, the SLHF variation patterns suggest pre-seismic activity 2–3 weeks before the main events. The agreement of these variations with abnormalities in other climatic and surface factors like relative humidity and temperature represents an unusual situation during the same period as well. Spatiotemporal variations of chlorophyll-a was also studied as another earthquake indicator. Abnormal rises in these factors are possibly caused by the formation of micro-cracks, heat production, evaporation, ionization, and upwelling of nutrient-rich water produced by pre-seismic activity prior to the main events.  相似文献   
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