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61.
Formation of point bars through rising and falling flood stages: Evidence from bar morphology,sediment transport and bed shear stress 
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下载免费PDF全文 Flow processes and sediment transport in a channel bend and associated point bar have been studied in modern rivers, theoretical models and physical experiments: however, the relationship between flow process and point‐bar morphology has rarely been explained due to the complex nature of open channel flow. Plan‐view exposures of an ancient point‐bar complex, exposed at the top of the Cretaceous Ferron Sandstone Member of the Mancos Shale Formation, south‐central Utah, allowed reconstruction of bar morphology, sediment transport and bed shear stress, which were used to extrapolate flow processes. Studies of these outcrops show that compound point bars and scroll bars were probably formed during falling and rising flood stages, respectively. A simulation model of plan‐view channel form shows that channel dimensions, such as radius of curvature and sinuosity of the point‐bar complex, range between 205 m and 351 m and 1·04 and 1·22, respectively, throughout the evolution of the channel bend. Variations in strength of the helical flow were interpreted as the main control on facies architecture and bar morphology. Strong helical flow was related to the deposition of the scroll bars, while strength of helical flow is decreased for compound bars. The use of cross‐beds as a common palaeocurrent indicator was found to be inconsistent with mean flow directions and channel margin orientation. 相似文献
62.
Muhammad Dawood Atta-ur Rahman Sami Ullah Ghani Rahman Kamran Azam 《Arabian Journal of Geosciences》2018,11(16):471
The present study explores the spatial and temporal deviations in temperature using Monte Carlo (MC) and Sen’s slope (SS) approaches in the Hindu Kush (HK) region. Climate change holds sturdy association against the temperature trend that has generated adverse impacts in the form of floods. In this attempt, for trend analysis, temperature has been selected as a meteorological parameter. This study mainly focuses on exploring the tendency in average temperature with respect to time and the consequential flood recurrences in the region. For the current study, data regarding temperature were typically collected from Pakistan Meteorological Department. In the study region, there are a total of seven meteorological station falls namely Dir, Chitral, Drosh, Saidu, Malam Jabba, Kalam, and Timergara. The temperature time series data was calculated and analyzed using MC and SS approaches for trend detection in order to demonstrate the kind of fluctuation in the Hindu Kush region. The resultant analysis further revealed that in the meteorological station of Dir, a more significant positive trend (α?=?0.0001) was found in mean monthly maximum, minimum, and monthly normal temperature. Likewise, at Drosh, a positive trend is detected in mean monthly maximum (α?=?0.04), monthly minimum (α?=?0.003), and monthly average (α?=?0.0005). Moreover, at Saidu met station, there is also a trend detected in temperature sub-variables such as monthly maximum (α?=?0.0001) and monthly minimum (α?=?0.001). In addition to these, at Kalam, there is a temperature trend noted for monthly minimum (α?=?0.01) and monthly average (α?=?0.02). Furthermore, the analysis demonstrates that there is no trend detected in the remaining stations, i.e., Chitral, Malam Jabba, Drosh, and Timergara. The overall analysis discovered that there is a sturdy relationship between climate change phenomenon and temperature variability. After using SS test to the temperature data of mean monthly maximum (TMMMax), the results explored that Kalam station grips the highest magnitude, i.e., Q?=?0.76; however, Timergara shows the lowermost, i.e., Q?=???0.34. For the monthly minimum temperature (TMMMin), at Kalam again, the highest value (Q?=?0.005) was detected; however, other stations revealed a negative trend, except Drosh which express no change in terms of magnitude. Similarly, in terms of monthly normal temperature (TMNor), Timergara station (Q?=???0.4) verified a negative trend magnitude and Malam Jabba station again trendless. Among all, the met station of Malam Jabba which holds an altitude of 2591 m is a hilly station just followed by Kalam having 2103 m height; however, Dir holds 1375 m height and the rest of the met stations show low elevation. The main reason for the temperature difference is the altitude of the study region. 相似文献
63.
H. Ullah N. U. Khan F. Ali A. Khan I. Zeb M. J. Khan 《International Journal of Environmental Science and Technology》2018,15(12):2519-2530
Characterization of content and source of heavy metals in soils are necessary to establish quality standards on a regional level. In relation to this, two zones, (sampling zone-1) and (sampling zone-2) depending on nature and intensity of wastewater disposal along the peri-urban area of Peshawar, Pakistan were selected. Thirty-six samples of wastewater and topsoil each were collected to determine the content of Pb, Cr, Cd, Cu, Zn, Ni, Fe and Mn, and physico-chemical parameters like pH, electrical conductivity, total solids, total dissolved solids, total suspended solids, and organic matter. Analytical determinations were performed by atomic absorption spectroscopy after microwave sample digestion in acid solution. Chemometric techniques which include hierarchical cluster analysis, principal component analysis, correlation analysis, and tukey test were applied. Concentrations of physico-chemical properties in wastewater and soil were higher in sampling zone-2. Concentrations of six heavy metals in wastewater and two in soil exceeded permissible limits of World Health Organization (Guidelines for drinking water quality, 4th edition, 2011), European Union (Heavy metals in wastes, European commission on environment. http://ec.europa.eu/environment/waste/studies/pdf/heavymetalsreport, 2002). Hierarchical cluster analysis grouped eight heavy metals into two clusters for wastewater and five clusters for soils. Principal component analysis describes four factors possessing Eigenvalues greater than 1.0 and explained the cumulative total variance of 84% with factor 1, having positive loading of anthropogenic metals (Cd, Cu, and Ni). Significant correlation was found between anthropogenic metals like Ni and Cd in water and between Cu and Cr in soil. Further research in other agricultural lands in peri-urban region would improve the basis for proposing such soil quality standards. 相似文献
64.
While historically significant for ancient civilizations, the Indus basin is also known for its floods and complex anthropogenic management history. Resulting from years of modifications by the pre-British era Mughal rulers followed by the post-partition division of river waters among the two neighbors, India and Pakistan, Pakistan faces severe management and financial challenges of water management. This study investigates the intricacies arising from this complicated management doctrine for the lower Indus basin. A detailed remote sensing-based analysis of the significant floods to hit the lower Indus basin since 2000 has been provided. Flood years were identified, and Moderate Resolution Imaging Spectroradiometer (MODIS) data for the years 2003, 2005, 2006, 2010, 2011, 2012, 2015, and 2016 were used to map their spatiotemporal extents. Almost all the flood water accumulated in the north is released in one river channel of the lower Indus basin. Further, the challenges were exacerbated due to the excessive rainfall in 2011 and 2012 in southeastern Sindh. A trend analysis of rainfall data shows an increase in the southern basin in the last 21 years, particularly toward the central plains and Sindh Province. The floodwater accumulated in the lower basin for as many as?~?425 days on average, stretching to?~?800 days of stagnancy in some places. The water stagnation period has been the highest in the river floodplain, highly populated and cultivated. The analyses of the current study suggest that the riverine channel has been better managed after the 2010 floods; however, the monsoon’s shift in 2011 and 2012 led to widespread disaster in low-lying regions of Sindh Province.
相似文献65.
Displacement measurement‐based estimations of loads and utilization degrees in shotcrete tunnel shells as part of the New Austrian Tunneling Method (NATM), have become standard tools in tunnel practice; their quality, however, may crucially depend on the knowledge of the actual shotcrete composition after spraying. To shed light on this issue, we here determine, based on experimentally validated micromechanical representations of shotcrete, the hydration degree‐dependent elastic, creep, and strength properties of different shotcretes, characterized by water cement ratios (w/c) between 0.4 and 0.6, aggregate cement ratios (a/c) between 3.5 and 5, and Young's modulus of aggregates (Eagg) between 40 and 80 GPa. These properties are fed into a structural shell model of the Sieberg tunnel, and this model is subjected to displacement fields approximated from daily displacement measurements at five selected points along the shell's inner surface. Resulting stresses and forces in the tunnel shell allow for analyzing the influence of shotcrete composition on load‐level estimation in NATM tunnel shells: The magnitudes of circumferential and longitudinal normal forces increase significantly with decreasing w/c, while a/c and Eagg have the inverse and relatively minor effect. The utilization degree is virtually insensitive to changes in w/c(especially at early ages), and only slightly decreases with decreasing a/c and Eagg. The location of maximum loading is unaffected by the shotcrete composition underlying the analysis. Conclusively, location and magnitude of maximum utilization degrees are very robust estimates (not affected by limited knowledge on the shotcrete composition), whereas realistic estimation of stresses and forces does require more accurate consideration of shotcrete composition. Copyright © 2011 John Wiley & Sons, Ltd. 相似文献
66.
Raza Ullah Ganesh P. Shivakoti Farhad Zulfiqar Muhammad Nadeem Iqbal Ashfaq Ahmad Shah 《Natural Hazards》2017,87(3):1361-1375
Agriculture sector is exposed to a variety of risks and uncertainties which can lead to sizeable losses in crop yields and alter farm incomes. Risk management is, therefore, an essential element of the overall farm management process. Farmers have number of options in managing farm risks; however, smallholders, due to their small operations and limited financial capabilities, find it difficult to adopt sophisticated risk management strategies to overcome yield and income instabilities at farm level. This study is, therefore, designed to investigate the enabling environment for small farmers to manage climatic risks at farm level. A total of 330 sampled respondents from Khyber Pakhtunkhwa Province of Pakistan are randomly selected for the study using multistage sampling technique. Analysis of variance technique is employed to compare the risk management adoption decision of small, medium and large farmers. A post hoc analysis is also performed to highlight the difference in means and the magnitude of differences. The results indicate that smallholders have significantly lower access to credit (both formal and informal), formal information sources along with significantly higher perceptions of pest and diseases. Smallholders are also at the tail end in the adoption of precautionary savings and agricultural credit to manage climatic risk at farm level. The study urges for risk management policies particularly in favor of the small farmers and intervention in the existing information and credit provision programs to facilitate smallholders in managing farm risks. 相似文献