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181.
Spatial and depth variability of streambed vertical hydraulic conductivity under the regional flow regimes
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Jinxi Song Liping Wang Xinyi Dou Fangjian Wang Hongtao Guo Junlong Zhang Guotao Zhang Qi Liu Bo Zhang 《水文研究》2018,32(19):3006-3018
This study investigated the influence of the regional flow on the streambed vertical hydraulic conductivity (Kv) within the hyporheic zone in three stream reaches of the Weihe River in July 2016. The streambed Kv with two connected depths was investigated at each test reach. Based on the sediment characteristics, the three test reaches could be divided into three categories: a sandy streambed without continuous silt and clay layer, a sandy streambed with continuous silt and clay layer, and a silt–clay streambed. The results demonstrate that the streambed Kv mainly decreases with the depth at the sandy streambed (without continuous silt and clay layer) and increases with the depth at the other two test reaches. At the sandy streambed (with continuous silt and clay layer) where streambed Kv mainly decreases with the depth, the regional upward flux can suspend fine particles and enhance the pore spacing, resulting in the elevated Kv in the upper sediment layers. At another sandy streambed, the continuous silt and clay layer is the main factor that influences the vertical distribution of fine particles and streambed Kv. An increase in streambed Kv with the depth at the silt/clay streambed is attributed to the regional downward movement of water within the sediments that may lead to more fine particles deposited in the pores in the upper sediment layers. The streambed Kv is very close to the bank in the sandy streambed without continuous silt and clay layer and the channel centre in the other two test reaches. Differences in grain size distribution of the sediments at each test reach exercise a strong controlling influence on the streambed Kv. This study promotes the understanding of dynamics influencing the interactions between groundwater and surface water and provides guidelines to scientific water resources management for rivers. 相似文献
182.
Roughness scale dependence of the relationship between tracer longitudinal dispersion and Peclet number in variable‐aperture fractures
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The relationship between the longitudinal dispersion (DL) and Peclet number (Pe) is crucial for predicting and simulating tracer through the variable‐aperture fracture. In this study, the roughness of the self‐affine fracture wall was decomposed into primary roughness (relatively large‐scale waviness) and secondary roughness (relatively small‐scale waviness) by a multiscaled wavelet analysis technique. Based on the complete dispersion mechanism (diffusion, macrodispersion, and Taylor dispersion) in the variable‐aperture fracture, three relationships (second‐order, power‐law, and linear relationships) between the DL and Pe were investigated at large and small scales, respectively. Our results showed that the primary roughness mostly controlled the Taylor dispersion mechanism, whereas the secondary roughness was a dominant factor for the macrodispersion mechanism. Increasing the Hurst exponent and removing the secondary roughness led to the decreasing range of Pe where macrodispersion mechanism dominated the solute transport. It was found that estimating the DL from the power‐law relationship based on Taylor dispersion theory resulted in considerable errors, even in the range of Pe where the Taylor dispersion mechanism dominated. The exponent of the power‐law relationship increased as the secondary roughness was removed. Analysing the linear relationship between the DL and Pe revealed that the longitudinal dispersivity αL increased linearly. However, this linear increase became weak as the Taylor dispersion mechanism dominated. In the range of Pe where the macrodispersion mechanism dominated, increasing the Hurst exponent caused the increase of αL and the secondary roughness played a significant role in enhancing the αL. As the Taylor dispersion mechanism dominated, the αL was insensitive to the influence of multiscale roughness in variable‐aperture fractures. 相似文献
183.
煤矿巷道底板冲击矿压发生的原因及控制研究 总被引:7,自引:1,他引:6
巷道底板水平应力是导致底板冲击矿压发生的主要因素,根据巷道底板冲击矿压的特点,建立了底板冲击矿压发生条件与影响因素的力学模型,初步确定了底板冲击矿压危险性系数的表达式。当底板岩层泊松比一定时,底板冲击矿压危险性系数与巷道埋深、巷道宽度的平方、水平构造应力、巨厚坚硬老顶影响系数成正比,与弹性模量、巷道底板软弱层厚度的平方成反比。通过数值模拟,发现巷道开挖后底板煤层的水平应力升高和垂直应力降低的规律,底板应力极易达到煤层破坏极限,在支护不当和外界扰动下容易发生底板冲击矿压。最后确定了底板强度弱化减冲原理,在跃进煤矿25110工作面下巷采取底板爆破卸压措施后取得了良好效果。研究成果为解决类似条件底板冲击矿压防治问题提供了理论依据和借鉴。 相似文献
184.
185.
The objective of this study is to understand the process of fluid flow in pipe and porous media with different pore structures.High-resolution Magnetic Resonance Imaging(MRI)technique was used to visualize the pore structure and measure fluid flow.The porous media was formed by packed bed of glass beads.Flow measurement was carried out by a modified spin echo sequence.The results show that the velocity distribution in pipe is annular and the linear relation between MRI velocity and actual velocity is found in pipe flow measurement.The flow distribution in porous media is rather heterogeneous,and it is consistent with heterogeneous pore structure.The flow through pores with the high volume flow rate is determined largely by geometrical effects such as pore size and cross-sectional area. 相似文献
186.
社会主义新农村建设中的防雷工作探讨 总被引:3,自引:0,他引:3
根据社会主义新农村建设中防雷工作适应新形势的需要,结合近年来农村发生的几起典型雷击事件,详细总结了农村雷击事故形成的原因,并提出加强新农村建设防雷工作的对策,切实履行气象部门监管职责,将新农村建设的防雷减灾工作落到实处. 相似文献
187.
A computationally efficient approach for estimating high-rate satellite clock corrections in realtime 总被引:9,自引:5,他引:4
Realtime satellite clock corrections are usually estimated using undifferenced phase and range observations from a global
network. Because a large number of ambiguity parameters must be estimated, the computation is time-consuming. Consequently,
only a sparse global network of limited number of stations is processed by most IGS Realtime Analysis Centers with an update
rate of 5 s. In addition, it is very desirable to build the capability to simultaneously estimate clock corrections for multi-GNSS
constellations. Although the estimation can be sped up by epoch-differenced observations that eliminate ambiguities, the derived
clocks can contain a satellite-specific bias that diminishes the contribution of range observations. We introduce a computationally
efficient approach for realtime clock estimation. Both the epoch-differenced phase and undifferenced range observations are
used together to estimate the epoch-differenced satellite clocks and the initial clock bias for each satellite and receiver.
The biased clock corrections accumulated from the estimated epoch-differenced clocks are then aligned with the estimated clock
biases and provided as the final clock corrections to users. The algorithm is incorporated into the EPOS-RT software developed
at GFZ (GeoForschungsZentrum) and experimentally validated with the IGS global network. The comparison with the GFZ rapid
products shows that the accuracy of the clock estimation with the new approach is comparable with that of the undifferenced
approach, whereas the computation time is reduced to one-tenth. As a result, estimation of high-rate satellite clocks from
a large reference network and tracking satellites of multi-GNSS constellations becomes achievable. 相似文献
188.
Regional Ecological Risk Assessment of Soil Heavy Metals in Pearl River Delta Economic Zone Based on Different Land Uses 总被引:1,自引:0,他引:1
Based on the results of regional eco-geochemical survey in Pearl River Delta Economic Zone and the local land use patterns, two conventional risk assessment models are introduced to evaluate the ecological risk of eight heavy metals in the topsoil (0~20 cm) of Pearl River Delta. The spatial distribution characteristics of risk caused by metals in the region were characterized by GIS. Results show that As、Cd、Cu and Hg in the topsoil are the primary heavy metals posing risk to the Pearl River Delta while Cr and Zn are negligible. Meanwhile, 23.89% of soil samples have a hazard index of more than 1 which suggests that it is likely to cause chronic diseases in the region. The soils with high hazard index are mainly distributed in the Quaternary area. 37.22% of soil samples have a negligible chronic risk level, of which the spatial distribution is consistent with granite area. Moreover, the spatial distribution of carcinogenic risk is similar to chronic risk, where 25.68% of samples exceed the cancer risk index (1×10-4) recommended by USEPA. Furthermore, the evaluation results presented at administrative units indicate that there are both higher chronic and cancer risk in Panyu and Nansha district where more attentions should be paid to. 相似文献
189.
西南地区晚二叠世氧、碳稳定同位素的古地理意义 总被引:22,自引:4,他引:22
对西南地区的19个晚二叠世碳酸盐岩型煤系剖面进行了碳酸岩稳定同位素的测定,探讨了其“年代效应”的校正及古盐度与古温度计算问题。结果表明:在兴文、贵阳、金沙、南桐、重庆一线以西的地区,Z值<120,δ13C值明显低于此线以东的地区,但与Schopf给出的淡水石灰岩的δ13C范围相比偏高,说明为海陆过渡相沉积;而此线以东的地区Z值>120,δ18O、δ13C均说明为海相沉积,与以前的沉积环境研究结论一致。用校正后的δ18O计算出碳酸盐岩形成时的介质古温度为14.8-50.9℃,且大多在23-31℃,说明当时该区为温暖-炎热的气候,与古地磁资料显示的当时该区处于赤道附近的热带地区的结论基本一致。 相似文献
190.
A binary homovalent ion exchange transport model governed by local chemical equilibrium is considered for a one-dimensional, steady flow in a homogeneous soil column. An analytical solution of the aqueous concentration distribution for the convex exchange is obtained by applying nonlinear shock wave theory. The main nonlinear feature is the breaking of fronts into shock waves. The corresponding mathematical theory is the method of characteristics with a special treatment of shock waves. The wave velocity and front thickness are also obtained to illustrate the front propagation and structure. The derivation of the solution presented may offer a wide range of application opportunities and may also provide a good approach for solving the binary heterovalent exchange transport model. 相似文献