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1.
Excessive sedimentation in mountain stream ecosystems is a critical environmental problem due to the clogging of streambeds by sediment particles within the hyporheic zone,with detrimental effects on fish spawning habitat.In this research,the effects of an array of boulders in regulating the intrusion of incoming sand within a gravel substrate were evaluated by performing detailed experiments in a laboratory flume.A unique experimental setup and two different sampling techniques were utilized for measuring the infiltrated sand within the gravel bed under two bed shear stress conditions（moderate vs.high）.For comparison purposes,experiments were performed without and with the presence of partially submerged to the flow（protruding） boulders,which is typical for the average flow conditions found in mountain streams.Results indicated that sand infiltrated primarily in the upper part of the gravel bed creating a surface seal which hindered the penetration of sand particles deeper into the bed.An exponential decrease of the amount of the infiltrated sand within the hyporheic zone was observed in all experiments regardless of the presence of boulders.However,the presence of boulders promoted sediment intrusion of sand particles especially for the moderate applied bed shear stress condition,since the total amount of the infiltrated sand was found to be on average 44% greater whenboulders were present.The findings from this study can provide additional insight regarding the role of boulders on promoting downwelling of flow and sediment within the gravel substrate with potential effects on fish habitat.  相似文献   

2.
The structure of wind-sand flow under different total sand transport rates was measured with field vertical anemometer and sand trap on the crest of typical coastal transverse ridge in Changli Gold Coast of Hebei Province, which is one of the most typical coastal aeolian distribution regions in China and famous for the tall and typical coastal transverse ridges. The measurement results show that, on the conditions of approximate wind velocities and same surface materials and environments, some changes happen to the structure of wind-sand flow with the increase of total sand transport rate on the crest of coastal transverse ridge. First, the sand transport rates of layers at different heights in the wind-sand flow increase, with the maximum increase at the height layer of 4-8cm. Second, the ratios of sand transport rates of layers at different heights to total sand transport rate decrease at the low height layer （0-4cm）, but increase at the high height layer （4-60cm）. Third, the distribution of the sand transport rate in the wind-sand flow can be expressed by an exponential function at the height layer of 0-40cm, but it changes from power function model to exponential function model in the whole height layer （0-60cm） and changes into polynomial function model at the height layer of 40-60cm with the increase of total sand transport rate. Those changes have a close relationship with the limit of sand grain size of wind flow transporting and composition of sand grain size in the wind-sand flow.  相似文献   

3.
The operation and power generation of utility-scale solar energy infrastructure in desert areas are affected by changes in surface erosion processes resulting from the construction of solar photovoltaic(PV) power stations. However, few studies have addressed the interactions between solar PV arrays and aeolian erosion processes. In this study, wind flow field characteristics and the vertical distribution of sediments were investigated in the near-surface transport layer at three different locations with respect to the solar PV arrays in a 200 WM-p PV power station in the central Hobq Desert, northwestern China. The results indicate that the sediment transport varied around the panels, with the greatest transport occurring between the panels, followed by behind and in front of the panels. The sediment fluxes of all of the observation sites obey an exponential function. The secondary flow field zones formed around the PV panels: the conflux accelerating zone between the panels, the resistance decelerating zone of the under panels, and the transition zone of the rapid velocity increase in front of and behind the panels. This resulted in a greater shear force in front of the panels under the downward flow diversion effect of PV panels, and the wind erosion depressions were finally formed here. The results of this study provide information for planning better technical schemes for wind-sand hazards at solar PV power stations, which would ensure operational stability and safety in desert areas.  相似文献   

4.
根据气象常规观测资料、湛江新一代天气雷达资料、CFL-08风廓线雷达资料及卫星云图,分析2012年4月20日粤西沿海特大暴雨的天气环流形势、能量场、对流不稳定度、水汽输送和辐合辐散等环境特征及物理量场特征。结果表明:这次暴雨过程粤西地区共经历两次强降水过程,分别是受飑线系统、以及高空槽和低空切变影响;西南低空急流的出现有利于粤西暴雨的形成、维持和发展;暴雨过程粤西上空垂直累积液水含量达25~30g/m2;暴雨期间风向随高度明显逆转,有冷平流输送;约2.0 km高度以下低空急流的下传和增强与暴雨的产生有密切关系;短时间内多普勒天气雷达的速度回波低层辐合区域远远大于辐散区域是可能产生强降水的标志。  相似文献   

5.
The lateral distributions of depth-averaged velocity in open compound channels with emerged and submerged vegetated floodplains were analyzed based on the analytical solution of the depth-integrated Reynolds-Averaged Navier-Stokes equation with a term to account for the effects of vegetation. The three cases considered for open channels were two-stage rectangular channel with emerged vegetated floodplain, rectangular channel with submerged vegetated corner, and two-stage rectangular channel with submerged vegetated floodplain, respectively. To predict the depth-averaged velocity with submerged vegetated floodplains, we proposed a new method based on a two-layer approach where flow above and through the vegetation layer was described separately. Moreover, further experiments in the two-stage rectangular channel with submerged vegetated floodplain were carried out to verify the results. The analytical solutions of the cases indicated that the corresponding analytical depth-averaged velocity distributions agree well with the simulated and experimental prediction. The analytical solutions of the cases with theoretical foundation and without programming calculation were reasonable and applicable, which were more convenient than numerical simulations. The analytical solutions provided a way for future researches to solve the problems of submerged vegetation and discontinuous phenomenon of depth-averaged velocity at the stage point for compound channels. Understanding the hydraulics of flow in compound channels with vegetated floodplains is very important for supporting the management of fluvial processes.  相似文献   

6.
In this paper, the authors explored the presence of shear fronts between the Yellow Sea Coastal Current (YSCC) and the monsoon-strengthened Yellow Sea Warm Current (YSWC) in winter and their sedimentary effects within the shear zone based on a fully validated numerical model. This work added the wind force to a tidal model during simulating the winter baroclinic circulation in the Yellow Sea. The results indicate that the YSWC is significantly strengthened by wind-driven compensation due to a northeast monsoon during winter time. When this warm current encounters the North Shandong-South Yellow Sea coastal current, there is a strong reverse shear action between the two current systems, forming a reverse-S-shaped shear front that begins near 34°N in the south and extends to approximately 38°N, with an overall length of over 600 km. The main driving force for the formation of this shear front derives from the circulation system with the reverse flow. In the shear zone, temperature and salinity gradients increase, flow velocities are relatively small and the flow direction on one side of the shear zone is opposite to that on the other side. The vertical circulation structure is complicated, consisting of a series of meso- and small-scale anti-clockwise eddies. Particularly, this shear effect significantly hinders the horizontal exchange of coastal sediments carried by warm currents, resulting in fine sediments deposition due to the weak hydrodynamic regime.  相似文献   

7.
The maximum normal impact resultant force(NIRF)is usually regarded as the sum of the static earth pressure of the dead zone and the dynamic impact pressure of the flowing layer.The influence of the interaction between the flowing layer and dead zone on the impact force is ignored.In this study,we classified two impact models with respect to the pileup characteristics of the dead zone.Then,we employed the discrete element method to investigate the influences of the pileup characteristics on the impact force of dry granular flow on a tilted rigid wall.If the final pileup height is equal to the critical value,the maximum NIRF can be estimated using a hydrostatic model,because the main contribution to the maximum NIRF is the static earth pressure of the dead zone.If the final pileup height is less than the critical value,however,the particles in the dead zone are squeezed along the slope surface by the impact ofthe flowing layer on the dead zone,and because of shear effects,the flowing layer causes an entrainment in the dead zone.This results in a decrease in the volume of the dead zone at the moment of maximum NIRF with increases in the slope angle.As such,the maximum NIRF mainly comprises the instant impact force of the flowing layer,so hydro-dynamic models are effective for estimating the maximum NIRF.Impact models will benefit from further study of the components and distribution of the impact force of dry granular flow.  相似文献   

8.
The Liaodong Shoal is a group of linear sand ridges located in the east Bohai Sea of China.In this study,54 surface sediment samples have been collected,current measurements at 4 stations have been carried out and bathymetric data were obtained.The current directions are rightward deflected relative to the strikes of the sand ridges.Affected by the narrowing effect of the ridge,the current velocities exhibited an anti-‘C’type vertical profile.The velocities of the lower currents linearly correlate with the water depths.The near-bed current velocities over the troughs are estimated to be higher than those over the ridges,and this feature could be explained by the loss of kinetic energy together with the conversion between kinetic energy and gravitational potential energy.The sedimentary characteristics that are compatible with the tidal dynamics are developed across the ridges and troughs,including grain size compositions,grain size parameters,mineral compositions and Dhm indexes.The existence of the angles between the current directions and the strikes of the sand ridges is the key factor for the growth of the sand ridges.The asymmetric hydrodynamic features between the flood and ebb currents lead to the differences in the topographical and sedimentary characteristics on both sides of a sand ridge.Insufficient material supply led to the degradation of the sand ridges,and the reduction of the tidal current intensity has led to the development of the subordinate sand ridges in the troughs.Sand ridges are migrating.  相似文献   

9.
Tidal current ridges, widely distributed geomorphological phenomena over the continental shelf of the world, are studied. They are formed by tidal current and the trend of their sand bodies runs parallel to the direction of tidal current. There are two types of the plane shapes: the parallel and the fingered. Conditions of forming tidal current ridges are the velocities of tidal current ranging from 1 to 3.5 knots and the supply of abundant sediments. Tidal current ridges often develop in following morphological locations: the bays, estuaries, the mouths of channels, as well as the offshore area with strong tidal current. Tidal current ridges occur generally at a water depth of less than 35 metres. The sediments of tidal current ridges are mainly composed of sand. The grain size of the sediments is uniform and well sorted. The characteristics of grain size of the sand imply that their formation mechanism is similar to that of river sand, that is, both of them are the result of flow movements in a trongth channel controlled by boundary. There is however difference between them that the river sand is formed by one-way flow movement while the tidal current sand by two-way movement. There are two saltation populations in the log-probability curves of tidal current sand, the sorting of first saltation population is better than the second one, and having positive skewness, which differs from beach sand. In the C-M grain size pattern tidal current sand is most found in graded suspension segment. The continental shelves of the Yellow Sea, the East China Sea and the South China Sea have favourable conditions for developing tidal current ridges in massive scale and special shape, such as the tidal current ridges in the offshore of Jiangsu, the Gulf of Korea, the shoal of Liaodong, the east and west mouths of the channel of Qiongzhou, Jiaozhou Bay, the shoal of Taiwan, Lingdingyang, the north branch of Changjiang estuary. The studies of them are of vital significance in shipping, fishing, submarine engineering, military installations, oil and gas explorations, as well as in scientific research. This paper was published in Chinese inOceanologia et Limnologia Sinica 14 (3): 286–296.  相似文献   

10.
Thirteen-year satellite-derived data are used to investigate the temporal variability of net primary production (NPP) in the Oman upwelling zone and its potential forcing mechanisms. The NPP in the Oman upwelling zone is characterized by an abnormal decrease during El Ni o events. Such an NPP decrease may be related to El Ni o-driven anomalous summertime weak wind. During the summer following El Ni o, the anomalous northeasterly wind forced by southwest Indian Ocean warming weakens the southwest monsoon and warms the Arabian Sea. The abnormal wind weakens the coastal Ekman transport, offshore Ekman pumping and horizontal advection, resulting in reduced upward nutrient supply to the euphotic zone. A slightly declining trend in NPP after 2000 associated with a gradual decrease in surface monsoon winds is discussed.  相似文献   

11.
Using satellite images taken on different dates,GIS analysis of aerial photos,bathymetric maps and other field survey data,tidal troughs and major sand ridges in the northern Jiangsu coastal area were contrasted.The results show that there have been three types of movement or migration of tidal trough in this area:(1) Periodic and restricted,this type of trough usually developed along the beaches with immobile gully head as a result of the artificial dams and the swing range increased from gully head to the...  相似文献   

12.
We investigate the influence of low-frequency Rossby waves on the thermal structure of the upper southwestern tropical Indian Ocean (SWTIO) using Argo profiles, satellite altimetric data, sea surface temperature, wind field data and the theory of linear vertical normal mode decomposition. Our results show that the SWTIO is generally dominated by the first baroclinic mode motion. As strong downwelling Rossby waves reach the SWTIO, the contribution of the second baroclinic mode motion in this region can be increased mainly because of the reduction in the vertical stratification of the upper layer above thermocline, and the enhancement in the vertical stratification of the lower layer under thermocline also contributes to it. The vertical displacement of each isothermal is enlarged and the thermal structure of the upper level is modulated, which is indicative of strong vertical mixing. However, the cold Rossby waves increase the vertical stratification of the upper level, restricting the variability related to the second baroclinic mode. On the other hand, during decaying phase of warm Rossby waves, Ekman upwelling and advection processes associated with the surface cyclonic wind circulation can restrain the downwelling processes, carrying the relatively colder water to the near-surface, which results in an out-of-phase phenomenon between sea surface temperature anomaly (SSTA) and sea surface height anomaly (SSHA) in the SWTIO.  相似文献   

13.
焉耆盆地宝浪油田含油气层段位于中生界下侏罗统三工河组(J1s)，为典型的浅水缓坡型粗粒辫状河三角洲-湖泊沉积体系。储层成分成熟度和结构成熟度低．粒度概率曲线以牵引和悬浮二段式为主，C—M图以PQ段和QR段为主，宝浪油田侏罗系三工河组划分出12种有成因意义的岩石相，采用Coleman的方案将浅水辫状河三角洲划分为：上三角洲平原(洪水线之上)、下三角洲平原(枯水线-洪水线之间)和水下三角洲平原(枯水线之下)3个亚相带。研究区主要发育了(水下)分流河道微相、水下分流河道间微相、决口水道(扇)微相、溢流沉积微相、滨湖沼泽沉积微相，河口坝微相不发育。(水下)分流河道微相占研究区储层的90％以上，根据砂体的岩石相组合、冲刷程度、水流能量大小的变化规律，其又可分为：充填河道、废弃河道、进积河道3种基本类型。储层物性以废弃河道为最好，单井油气产能亦最高，充填河道次之，进积河道和决口水道(扇)则相对较差。  相似文献   

14.
We deployed two ADCP mooring systems west of the Luzon Strait in August 2008, and measured the upper ocean currents at high frequency. Two typhoons passed over the moorings during approximately one-month observation period. Using ADCP observations, satellite wind and heat flux measurements, and high-resolution model assimilation products, we studied the response of the upper ocean to typhoons. The first typhoon, Nuri, passed over one of the moorings, resulting in strong Ekman divergence and significant surface cooling. The cooling of surface water lagged the typhoon wind forcing about one day and lasted about five days. The second typhoon, Sinlaku, moved northward east of the Luzon Strait, and did not directly impact currents near the observation regions. Sinlaku increased anomalous surface water transport exchange across the Luzon Strait, which modulated the surface layer current of the Kuroshio.  相似文献   

15.
研究不同环剪条件下库岸堆积层滑坡滑带土强度特性对滑坡稳定性评价具有重要意义。针对目前在库岸堆积层滑坡滑带土力学特性方面研究薄弱的问题, 以三峡库区童家坪滑坡滑带土为研究对象, 采用ARS-E2环剪仪开展了不同剪切速率下的剪切试验, 研究了等速剪切、加速剪切以及减速剪切作用下滑带土强度变化特征。试验结果表明: 滑带土试样在恒定的低速剪切条件下更容易得到稳定的残余强度, 并且达到峰值强度后易出现"应变软化"现象; 在相同剪切应力条件下, 滑带土加速环剪和减速环剪的剪应力变化趋势基本一致, 与法向应力均呈正相关关系; 剪切速率的变化会显著影响滑带土峰值黏聚力的大小。研究成果揭示了不同环剪条件下滑带土力学特性, 可以为揭示库岸堆积层滑坡变形破坏的力学机制提供理论依据。   相似文献   

16.
Interannual variations of Pacific North Equatorial Current (NEC) transport during eastern-Pacific El Niños (EP-El Niños) and central-Pacific El Niños (CP-El Niños) are investigated by composite analysis with European Centre for Medium-Range Weather Forecast Ocean Analysis/Reanalysis System 3. During EP-El Niño, NEC transport shows significant positive anomalies from the developing to decay phases, with the largest anomalies around the mature phase. During CP-El Niño, however, the NEC transport only shows positive anomalies before the mature phase, with much weaker anomalies than those during EP-El Niño. The NEC transport variations are strongly associated with variations of the tropical gyre and wind forcing in the tropical North Pacific. During EP-El Niño, strong westerly wind anomalies and positive wind stress curl anomalies in the tropical North Pacific induce local upward Ekman pumping and westward-propagating upwelling Rossby waves in the ocean, lowering the sea surface height and generating a cyclonic gyre anomaly in the western tropical Pacific. During CP-El Niño, however, strength of the wind and associated Ekman pumping velocity are very weak. Negative sea surface height and cyclonic flow anomalies are slightly north of those during EP El Niño.  相似文献   

17.
We studied the driving force of the Kuroshio intrusion into the South China Sea (SCS) during the winter monsoon, using satellite-tracked drifters entering the Luzon Strait (LS) through the Balintany and Babuyan Channels from the Philippine Sea. Most drifters passing through the Babuyan Channel in winter entered the interior SCS without a significant change in velocity. However, half of the drifters passing through the Balintany Channel entered the SCS at ~30 cm/s, which was faster than when they entered the LS. The other half continued moving northwestward into the Kuroshio and returned to the North Pacific. Quantitative analyses, using surface climatological wind and sea surface height anomaly (SSHa) data explained both the difference in velocity of drifters between the two channels and their acceleration through the Balintany Channel. The results suggest that the positive meridional gradient of sea surface height in the Luzon Strait, caused by the pileup of seawater driven by the Northeast monsoon, as well as Ekman flow, contribute to the Kuroshio intrusion into the SCS through the Babuyan and Balintany Channels. The former may be the main driving force.  相似文献   

18.
Assessing the slope deformation is significant for landslide prediction. Many researchers have studied the slope displacement based on field data from the inclinometer in combination with complicated numerical analysis. They found that there was a shear zone above the slip surface, and they usually focused on the distribution of velocity and displacement within the shear zone. In this paper, two simple methods are proposed to analyze the distribution of displacement and velocity along the whole profile of a slope from the slip surface to the slope surface during slow movement. In the empirical method, the slope soil above the shear zone is assumed as a rigid body. Dual or triple piecewise fitting functions are empirically proposed for the distribution of velocity along the profile of a slope. In the analytical method, the slope soil is not assumed as a rigid body but as a deformable material. Continuous functions of the velocity and displacement along the profile of a slope are directly obtained by solving the Newton's equation of motion associated with the Bingham model. Using the two proposed methods respectively, the displacement and velocity along the slope profiles of three slopes are determined. A reasonable agreement between the measured data and the calculated results of the two proposed methods has been reached. In comparison with the empirical method, the analytical method would be more beneficial for slope deformation analysis in slope engineering, because the parameters are material constants in the analytical solution independent of time t, and the nonlinear viscosity of the soil can be considered.  相似文献   

19.
对2012年8月19～21日西藏持续性强降水天气过程的成因进行分析。利用加密地面观测资料、FY一2C卫星TBB资料、常规观测资料和NCEP 1°×1°再分析资料,对2012年8月19--21日西藏持续性强降水天气过程进行诊断和中尺度特征分析。此次强降水天气过程是在稳定的径向型环流背景下产生的,巴尔喀什湖附近东移南下的短波槽和500hPa低涡切变是造成此次降水过程的主要影响系统,西太平洋副热带高压边缘的西南暖湿气流为降水过程提供r有利的水汽条件;β中尺度对流云团的先后影响,为强对流发展提供了必要的热力、动力条件;而中层冷空气的侵入和强的垂直风切变加剧了大气层结的不稳定,为降水天气提供了有利的条件。该研究为西藏夏季降水的相关预报预测提供科学依据。  相似文献   

20.
Surface waves comprise an important aspect of the interaction between the atmosphere and the ocean, so a dynamically consistent framework for modelling atmosphere-ocean interaction must take account of surface waves, either implicitly or explicitly. In order to calculate the effect of wind forcing on waves and currents, and vice versa, it is necessary to employ a consistent formula- tion of the energy and momentum balance within the airflow, wave field, and water column. It is very advantageous to apply sur- face-following coordinate systems, whereby the steep gradients in mean flow properties near the air-water interface in the cross-interface direction may be resolved over distances which are much smaller than the height of the waves themselves. We may account for the waves explicitly by employing a numerical spectral wave model, and applying a suitable theory of wave–mean flow interaction. If the mean flow is small compared with the wave phase speed, perturbation expansions of the hydrodynamic equations in a Lagrangian or generalized Lagrangian mean framework are useful: for stronger flows, such as for wind blowing over waves, the presence of critical levels where the mean flow velocity is equal to the wave phase speed necessitates the application of more general types of surface-following coordinate system. The interaction of the flow of air and water and associated differences in temperature and the concentration of various substances (such as gas species) gives rise to a complex boundary-layer structure at a wide range of vertical scales, from the sub-millimetre scales of gaseous diffusion, to several tens of metres for the turbulent Ekman layer. The bal- ance of momentum, heat, and mass is also affected significantly by breaking waves, which act to increase the effective area of the surface for mass transfer, and increase turbulent diffusive fluxes via the conversion of wave energy to turbulent kinetic energy.  相似文献   

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