Spatial variation in fluvial hydraulics with major bed erosion zone: a study of Kharsoti river of India in the post monsoon period     

Md Kutubuddin Dhali  Mehebub Sahana 《Arabian Journal of Geosciences》2017,10(20):451

This study attempts to assess the spatial variation of fluvial hydraulics with special emphasis on hydrological components at upper, middle and lower part of the Kharsoti river basin. The study encompasses the scenario of a micro bedrock river of India in the post monsoon period. This paper includes the study of hydrological components such as discharge, velocity, shear stress, stream power, specific stream power, width-depth relation and roughness and its interrelationships with different parts of the river basin with related mathematical equations and identification of major river bed erosive zones coupled with geo-hydrological components with geological explanation. Kharsoti is a typical example of rejuvenated antecedent tributary river of Subarnarekha River basin in Chota Nagpur Plateau. It is necessary to give a new threshold to the quantitative methods regarding the fluvial hydraulic studies under a systematic scientific geographical and hydrological background. The results also involve some specific techniques, equations and GIS mapping. The result of this study will help to open the scenario of hydraulics of a micro river basin in a contemporary method.  相似文献   

Hydrodynamics and suspended sediment transport at tidal inlets of Salut Mengkabong Lagoon,Sabah,Malaysia     

Md. Azharul HOQUE  Bobita Golam AHAD  Ejria SALEH 《国际泥沙研究》2010,25(4):399-410

Salut-Mengabong Lagoon is located at the west coast of Sabah facing the South China Sea. At the bay side of the main inlet the lagoon splits into Salut and Mengabong Channels. Sediment dynamics at the inlets of the lagoon have recently received considerable attention. But any direct measurement of hydrodynamics and sediment flux are yet to be well documented. This study covers the field measurements of current velocity, water flux, suspended sediment concentration and sediment flux across the three transects (main inlet, Salut entrance and Mengkabong entrance) during typical spring and neap tidal cycles in southwest monsoon and northeast monsoon. Temporal variations and time-averaged values of measured parameters are discussed. The inlets of Salut-Mengkabong Lagoon are found to be ebb-dominated. The time-averaged velocities during spring tidal measurements are found to be higher in the main inlet followed by Mengkabong entrance and Salut entrance. Suspended sediment concentration and sediment fluxes are substantially higher in spring tidal cycles compared to the same in neap tidal cycles. During spring tidal cycles, ebb tidal sediment fluxes are higher than the flood tidal fluxes. The ebb dominated flux across the main inlet led to the large ebb shoal.  相似文献   

Numerical simulation of stress distributions and displacements around an entry roadway with igneous intrusion and potential sources of seam gas emission of the Barapukuria coal mine, NW Bangladesh   总被引：4，自引：0，他引：4  

Md. Rafiqul Islam  Ryuichi Shinjo 《International Journal of Coal Geology》2009,78(4):249-262

This paper uses two-dimensional boundary element method (BEM) numerical modeling to analyze the deformation and failure behavior of a coal seam and to understand the nature of gas flow into a roadway entering the Barapukuria coal mine in Bangladesh. The Barapukuria basin contains Permian-aged Gondwana coals with high volatile B bituminous rank. Three models (A, B, and C) are presented here. Model A assumes horseshoe-shaped geometry, model B assumes trapezoid-shaped geometry, and model C assumes horseshoe-shaped geometry coupled with a roof fall-induced cave generated by the break-up of rock materials along the vertical dimension of an igneous dyke. The simulation results show that there is little difference in strata deformation between models A and B. In model A, there is no horizontal tensional stress and the overall horizontal stress patterns are compressive, while the distribution and magnitude of vertical stress show higher tensional stresses on the immediate rib sides and floor. In model B, both horizontal and vertical stress distributions indicate low to medium tensional stresses on the immediate roof, floor, and rib sides, but compressive stresses are prominent toward the interior of the coal seam. Deformation vectors indicate that failure extends laterally to about 7.5 m around the excavation geometry.On the contrary, for model C, the distributions and magnitudes of horizontal and vertical stress show higher tensional stresses in both rib sides of the roof fall zone. The deformation around the dyke-induced perturbation zone affects a large volume of coal. The deformation vectors with high magnitudes are nearly horizontal and propagate laterally up to 30 m; whereas, low-magnitude deformation vectors extend about 25 m toward the roof and 20 m toward the floor. The vertical tensional displacement, which is concentrated in the floor and the left and right hand sides of the roof, propagates about 30 m on both sides and about 22 m in the floor. From these simulation results, it is thought that the extension of the dyke-induced perturbation zone toward the roof, floor, and rib sides of the entry roadway initially creates small tensional cracks that gradually grow into large-scale tensional features. These features could also be responsible for high concentrations of gas, which are emitted into the mine from fractured coals due to insufficient mine ventilation and low atmospheric pressure.  相似文献   

Effect of soil cohesion and friction angles on reverse faults     

Mehdi Ghafari  Haslinda Nahazanan  Zainuddin Md Yusoff  Vahed Ghiasi 《地震工程与工程振动(英文版)》2021,20(2):329-334

Severe faults have caused many earthquakes around the world throughout history.More recently,earthquakes have occurred in Taiwan,China(Chi-Chi fault),and elsewhere,causing loss of lives and destroying many buildings and structures.These tectonic movements have gained attention from engineers,and in the past 15 years,the focus has been on faulting mechanisms.In this study,a physical model(1 g)was fabricated and used to evaluate the impact of a reverse fault in a field with a tunnel.In the 1 g model,researchers installed additional gauges on the tunnel,so that all the displacements could be adjusted,and all the responses could be monitored during faulting.An experimental study of various soil properties(cohesion and friction angles)in reverse faults on the tunnel lining were carried out and are described herein.A comparison of results for different levels of soil cohesion revealed that it can dramatically reduce the displacement by as much as 40%,and that friction angles of 27ocan record approximately 60%more displacements than at 37o.Furthermore,a comparison of fault angles of 30oand 60oindicates that the displacements can be different by more than 43%in cohesionless soil and about 64%for a friction angle of 27o.  相似文献   

Flood susceptibility modelling using advanced ensemble machine learning models     

Abu Reza Md Towfiqul Islam  Swapan Talukdar  Susanta Mahato  Sonali Kundu  Kutub Uddin Eibek  Quoc Bao Pham  Alban Kuriqi  Nguyen Thi Thuy Linh 《地学前缘(英文版)》2021,12(3):60-77

Floods are one of nature's most destructive disasters because of the immense damage to land, buildings, and human fatalities.It is difficult to forecast the areas that are vulnerable to flash flooding due to the dynamic and complex nature of the flash floods.Therefore, earlier identification of flash flood susceptible sites can be performed using advanced machine learning models for managing flood disasters.In this study, we applied and assessed two new hybrid ensemble models, namely Dagging and Random Subspace(RS) coupled with Artificial Neural Network(ANN), Random Forest(RF), and Support Vector Machine(SVM) which are the other three state-of-the-art machine learning models for modelling flood susceptibility maps at the Teesta River basin, the northern region of Bangladesh.The application of these models includes twelve flood influencing factors with 413 current and former flooding points, which were transferred in a GIS environment.The information gain ratio, the multicollinearity diagnostics tests were employed to determine the association between the occurrences and flood influential factors.For the validation and the comparison of these models, for the ability to predict the statistical appraisal measures such as Freidman, Wilcoxon signed-rank, and t-paired tests and Receiver Operating Characteristic Curve(ROC) were employed.The value of the Area Under the Curve(AUC) of ROC was above 0.80 for all models.For flood susceptibility modelling, the Dagging model performs superior, followed by RF,the ANN, the SVM, and the RS, then the several benchmark models.The approach and solution-oriented outcomes outlined in this paper will assist state and local authorities as well as policy makers in reducing flood-related threats and will also assist in the implementation of effective mitigation strategies to mitigate future damage.  相似文献   

Floods in Bangladesh: A question of disciplining the rivers     

Gazi Md. Khalil 《Natural Hazards》1990,3(4):379-401

Bangladesh has been experiencing floods more frequently than ever before. Since 1947, she has been hit by extremely devastating floods in 1954, 1955, 1956, 1962, 1963, 1966, 1968, 1969, 1970, 1971, 1974, 1976, 1984, 1987, and 1988. Each year's highest flood record and damage costs have been broken by that of the subsequent year. All means of communication become paralysed. People lose food grains, domestic animals, homesteads, and lives. They remain marooned without food and drinking water until relief arrives. Despite huge spending on flood control, the intensity of the floods has been increasing. Therefore, speculation is naturally rife about the causes.The aim of this paper is to identify the factors which contribute to these devastating floods, and then to recommend an appropriate strategy for effective flood control. The geography, geology, and hydrology of Bangladesh are briefly discussed. The whole of the country is a huge river basin criss-crossed by as many as seven hundred rivers, tributaries, and distributaries, having a total length of 22 155 km.The river-beds are rendered shallow by heavy deposits of alluvial earth each year and tend easily to cause inundations. The quantum of silt carried by the river systems into Bangladesh is estimated to be 2.4 × 10⁹ tonnes/yr.Disciplining the rivers means keeping the rivers navigable all year round, removing excessive deposits of silt where they threaten to block a channel, preventing widening by erosion, contracting the width where the river is excessively wide, and last but not least, preventing construction whose eventual impact might prove harmful.Natural disasters do not respect political frontiers, nothing can stop them, but their adverse impact could be minimised. The author emphasises the need for employing the abundant cheap manpower, local materials, and indigenous technology for flood control projects.  相似文献   

Seed supply for coastal brackishwater shrimp farming: environmental impacts and sustainability     

Islam MS  Wahab MA  Tanaka M 《Marine pollution bulletin》2004,48(1-2):7-11

Globally, shrimp farming has been a significant agro-based economic activity since the early 1970s. Because it offered a huge immediate economic return, shrimp farming showed a booming expansion and soon became a multimillion dollar industry. However, it has been under extreme criticism because of its devastating ecological and socio-economic impacts. Because seed is the primary input, the impact from farming has started from the source of seed supply, so that not only are natural stocks of shrimp seeds now overexploited worldwide but seed collection activities also significantly reduce stocks of other living resources. Although hatcheries were developed as potential alternative and have replaced the natural seed source to a great extent, large-scale hatchery productions provide a potential source of coastal pollution. However, this area is still poorly studied. The present paper provides a review of the environmental impacts of the wild shrimp seed fishery as well as the possibility of environmental degradation from artificial shrimp seed production in hatcheries.  相似文献   

Climate change in Bangladesh: a spatio-temporal analysis and simulation of recent temperature and rainfall data using GIS and time series analysis model     

Md.?Rejaur?RahmanEmail author  Habibah?LatehEmail author 《Theoretical and Applied Climatology》2017,128(1-2):27-41

In this paper, temperature and rainfall data series were analysed from 34 meteorological stations distributed throughout Bangladesh over a 40-year period (1971 to 2010) in order to evaluate the magnitude of these changes statistically and spatially. Linear regression, coefficient of variation, inverse distance weighted interpolation techniques and geographical information systems were performed to analyse the trends, variability and spatial patterns of temperature and rainfall. Autoregressive integrated moving average time series model was used to simulate the temperature and rainfall data. The results confirm a particularly strong and recent climate change in Bangladesh with a 0.20 °C per decade upward trend of mean temperature. The highest upward trend in minimum temperature (range of 0.80–2.4 °C) was observed in the northern, northwestern, northeastern, central and central southern parts while greatest warming in the maximum temperature (range of 1.20–2.48 °C) was found in the southern, southeastern and northeastern parts during 1971–2010. An upward trend of annual rainfall (+7.13 mm per year) and downward pre-monsoon (?0.75 mm per year) and post-monsoon rainfall (?0.55 mm per year) trends were observed during this period. Rainfall was erratic in pre-monsoon season and even more so during the post-monsoon season (variability of 44.84 and 85.25 % per year, respectively). The mean forecasted temperature exhibited an increase of 0.018 °C per year in 2011–2020, and if this trend continues, this would lead to approximately 1.0 °C warmer temperatures in Bangladesh by 2020, compared to that of 1971. A greater rise is projected for the mean minimum (0.20 °C) than the mean maximum (0.16 °C) temperature. Annual rainfall is projected to decline 153 mm from 2011 to 2020, and a drying condition will persist in the northwestern, western and southwestern parts of the country during the pre- and post-monsoonal seasons.  相似文献   

Numerical study on wave-induced filtration flow across the beach face and its effects on swash zone sediment transport   总被引：2，自引：0，他引：2  

Md. Azharul Hoque  Toshiyuki Asano 《Ocean Engineering》2007,34(14-15):2033-2044

A numerical model, coupling an analysis of beach groundwater flow with an analysis of swash wave motion over a uniform slope, is presented. Model calculations are performed to investigate the variations of swash-induced filtration flows across the beach face for different input parameters. Swash zone sediment transport under the influence of such filtration flow across the beach face is investigated through modification of effective weight of sediment particle and modification of swash boundary layer thickness. These effects are quantified based on a bed load transport model with a modified Shields parameter.  相似文献   

Estimation of Mining Project Values Through Real Option Valuation Using a Combination of Hedging Strategy and a Mean Reversion Commodity Price     

Md. Aminul Haque  Erkan Topal  Eric Lilford 《Natural Resources Research》2016,25(4):459-471

Cash flows generated from mining projects are typically highly volatile and significantly influenced by a number of exogenous factors including commodity price as one of the most influential uncertainties. In addition, mining projects are complex and many of their executed investment decisions are irreversible. Therefore, management needs to address this potential risk exposure before making an investment decision. Due to the deterioration and fluctuation of mineral commodity prices for a successful mining project acquisition or development, an important and appropriate investment strategy should include a hedging strategy for reducing potential losses suffered by a company. The discounted cash flow methods, which are commonly used to calculate mining project values, often fail to respond to this identified economic uncertainty and also to incorporate de-risking hedging strategies. Therefore, this study approximates the numerical value or value ranges of a mining project considering the combination of a mean reverting commodity price and hedging strategies using continuous time modeling. A novel time-dependent partial differential equation has been proposed using a continuous time, mean reverting model, and hedging strategy to approximate the mining project value. Application of a new real options valuation technique demonstrated its superiority by providing the advantage of mitigating financial losses and procuring financial gains. In this study, some key results are deferral option and expansion option enhanced the maximum values of the project which are, respectively, 2.51 % and 4.4 % compared to the base case. Furthermore, the country risk has a great impact on project values, as when we considered the country risk premium is zero in our model, the project value increases up to 0.97 %.  相似文献