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1.
The Yellow River(YR) capture of the Huai River had a profound effect on the landscape evolution,ecology, and social development in China, disrupting the evolution of some vital shallow floodplain lakes.Because of the absence of lacustrine sediment provenance analysis, previous studies were inadequate in distinguishing the influence of YR capture on paleoenvironmental changes in these lakes, especially on landscape evolution, redox conditions, lake level changes, and organic productivity. The cur...  相似文献   

2.
Following a new train of thinking, this paper has explored first the potential information in the ground resistivity data observed by the existing geoelectric observation system, investigated and proposed a new dimensionless geoelectric precursor factor, the degree of ground resistivity anisotropy, S, and studied the characteristics of dynamic evolution pattern of S during the seismogenic process. The results show that, during the seismogenic process, the degree of ground resistivity anisotropy (S) displays a process of 'normal' →'abnormal strengthening (amplitude, range)' →abnormal weakening' → 'earthquake occurrence'→ 'normal'. The earthquake would occur at the time when the S value has entered the late stage of strengthening and turns to weaken and in the gradient belt on the margin of S anomaly region. The dynamic evolution pattern of S reflects the changes of the tectonic stress field during the seismogenic process. Therefore, it would be possible to trace the process of earthquake generation and occurrence from the dynamic evolution pattern of S so as to service earthquake prediction.  相似文献   

3.
Based on long-term measurements at three gauging stations, Toudaoguai, Fugu and Hequ, and one meteorological station, this article discusses the features of discharge (Q) and sediment concentration (Cs) of a river reach of the Yellow River with a reservoir located in the Loess Plateau. The impacts of the local sub-watershed between Toudaoguai and Fugu gauging stations on sediment budget to the Yellow River have been analyzed. In addition, the deposition processes in the Tianqiao Reservoir have been investigated. Results show over 80% of the precipitation that falls in the local subwatershed is unable to contribute to the Yellow River runoff process. It is found that the annualmaximum sediment concentration is usually less than 30 kg/m^3 during flood seasons at Toudaoguai Gauging Station, but the sediment concentration varies dramatically at Fugu Gauging Station. About 35% of the sediment eroded in the sub-watersheds between Toudaoguai and Fugu gauging stationswas produced from the Huangfuchuan sub-watershed which has a drainage area accounting only for 10% of the drainage area between Toudaoguai and Fugu gauging stations. The Tianqiao Reservoir generally has deposition during the summer flood season, and scouring during the non-flood season.On average, over 85% of deposited sediment in the reservoir occurs in the 12 km long lower reservoir reach. The volume of annual deposition in the reservoir mainly depends on the volume of water from the local region between Hequ and Fugu gauging stations.  相似文献   

4.
The Tongling area is one of the most important ore cluster areas in the middle to lower Yangtze River metallogenic belt. The ore-forming process in Tongling region was mainly resulted from the me- dium-acidic magma intrusion activity during Yansha- nian epoch[1―4]. Lots of research of the structure sys- tem and intrusion series were carried out in recent decades and the following aspects were mainly fo- cused on: (1) Accurate determination of the petrologic structure, chemical composition a…  相似文献   

5.
The equilibrium relations for water and sediment transport refer to the relative balance of sediment transport and the relative stability of river courses formed by the automatic adjustment of riverbeds.This is the theoretical basis for the comprehensive management of sediment in the Yellow River.Based on the theories of sediment carrying capacity and the delayed response of riverbed evolution,in this study,the equilibrium relations for water and sediment transport in the Yellow River are established.These relations include the equilibrium relationships between water and sediment transport and bankfull discharge in the upper and lower Yellow River and between water and sediment transport and the Tongguan elevation in the middle Yellow River.The results reveal that for the Ningmeng reach,the Tongguan reach,and the lower Yellow River,erosion and deposition in the riverbeds are adjusted automatically,and water and sediment transport can form highly constrained equilibrium relationships.These newly established equilibrium relationships can be applied to calculate the optimal spatial allocation scheme for sediment in the Yellow River.  相似文献   

6.
Spatiotemporal variations of Chinese Loess Plateau vegetation cover during 1981-2006 have been investigated using GIMMS and SPOT VGT NDVI data and the cause of vegetation cover changes has been analyzed, considering the climate changes and human activities. Vegetation cover changes on the Loess Plateau have experienced four stages as follows: (1) vegetation cover showed a continued increasing phase during 1981―1989; (2) vegetation cover changes came into a relative steady phase with small fluctuations during 1990―1998; (3) vegetation cover declined rapidly during 1999―2001; and (4) vegetation cover increased rapidly during 2002―2006. The vegetation cover changes of the Loess Plateau show a notable spatial difference. The vegetation cover has obviously increased in the Inner Mongolia and Ningxia plain along the Yellow River and the ecological rehabilitated region of Ordos Plateau, however the vegetation cover evidently decreased in the hilly and gully areas of Loess Plateau, Liupan Mountains region and the northern hillside of Qinling Mountains. The response of NDVI to climate changes varied with different vegetation types. NDVI of sandy land vegetation, grassland and cultivated land show a significant increasing trend, but forest shows a decreasing trend. The results obtained in this study show that the spatiotemporal variations of vegetation cover are the outcome of climate changes and human activities. Temperature is a control factor of the seasonal change of vegetation growth. The increased temperature makes soil drier and unfavors vegetation growth in summer, but it favors vegetation growth in spring and autumn because of a longer growing period. There is a significant correlation between vegetation cover and precipitation and thus, the change in precipitation is an important factor for vegetation variation. The improved agricultural production has resulted in an increase of NDVI in the farmland, and the implementation of large-scale vegetation construction has led to some beneficial effect in ecology.  相似文献   

7.
Channel evolution refers to boundary changes of rivers affected by fluvial actions. This paper provides an analysis of the development and formation of stream patterns in the lower Yellow River and presents intensive studies of several critical problems relating to channel evolution, including thresholds of channel gradient and longitudinal profile adjustment, channel surface morphology, response of channel pattern to boundary conditions, critical discrimination of cross sections and the discrimination of channel pattern changes using hydrologic parameters.  相似文献   

8.
Deterioration of air quality as a result of rapid eco- nomic development in the Yangtze River Delta (YRD) has attracted much scientific and public attention[1―7]. To explore the air quality of a region, measurement of pollutants in locations reflecting the “background” atmospheric conditions of the region is essential. The Regional Baseline Air Quality Monitoring Station of the Chinese Academy of Meteorological Sciences (CAMS) at Lin’an is located in such an area in Zhe- jiang Pro…  相似文献   

9.
The temporal and spatial evolution characteristics of the geomagnetic secular acceleration(SA) are investigated, based on CHAOS-4 core field model during the period of 1997–2013. The SA evolution on a short time scale is associated with the phenomenon of the geomagnetic jerk. More details of the global extent and the occurrence time of the successive jerks(the 1999, 2003, 2007, and 2011 jerks) are obtained. The location, size and reversed polarity pattern for the 1999 jerk are similar to those for the 2003 jerk in the Asian-Indian sector. While the 2007 and 2011 jerks mainly take place in the Atlantic sector. The direction and speed of the shift for the four jerks are different, identified by the occurrence time of the jerks. The zonal motions of the SA patches exhibit an oscillation pattern in the Asian-Indian sector, whereas a purely westward drifting pattern is along the equator in the Atlantic sector. It is believed that the shift of the jerks is related to the motion of SA-B_r patches observed at the core-mantle boundary(CMB).  相似文献   

10.
For almost two decades, the relationship between prehistoric natural disasters that struck the Guanting Basin in northeast Tibetan Plateau and the destruction of Lajia, an archeological site, has attracted scholarly attention and been widely discussed. Whereas most studies have focused on the impacts of disasters on a single site within the Guanting Basin, few have examined patterns of spatiotemporal evolution of human settlements from the Neolithic to the Bronze Age. Consequently, there is a lack of clarity on the processes and mechanisms underlying the evolution of prehistoric human-land relationships in the Guanting Basin. We therefore examined spatiotemporal variations in settlements in the Guanting Basin during the period, based on the locations, altitudes, and areas of archaeological sites. We found that four sites were located on the third terrace of the Yellow River during the late Yangshao period(5500–5000 cal yr BP) and distributed within a small area. During the period between the Majiayao and Qijia cultures(5300–3600 cal yr BP), the number of sites evidently increased and the scale and distribution of settlements expanded, with settlements generally shifting toward the lower elevation areas of the Guanting Basin.During the Xindian period(3400–2700 cal yr BP), the number and scale of sites showed a downward trend and the distribution of settlements contracted. The Xindian settlement underwent altitude-based spatial differentiation, with some groups moving to areas at higher altitudes and others remained in lower altitude areas. Moreover, we found that the number, scale, and distribution range of Neolithic and Bronze Age sites in the Guanting Basin were closely related to the evolution and distribution patterns of prehistoric cultures in the regions of Gansu and Qinghai, which were further affected by climate change and agricultural development. Furthermore, there is no evidence that the altitudinal distribution pattern of Neolithic and Bronze Age settlements in the Guanting Basin was influenced by paleofloods rather it was primarily influenced by changes in subsistence strategies.  相似文献   

11.
Fluids in the deep subduction zones play an impor-tant role in the process of crust-mantle interaction. This has been proved by a large number of studies on the geochemistry of island arc volcanic rocks[1―9]. Study on high-pressure metamorphic rocks within orogen shows that the dehydration and devolatilization of subducted oceanic crust and sediments can release amounts of water during progressive metamorph- ism[10―13]. The origin of the fluids in the subduction zones provides important info…  相似文献   

12.
Based on the observational data in summer, the variations of intraseasonal oscillation (ISO) of the daily rainfall over the lower reaches of the Yangtze River valley (LYRV) were studied by using the non-integer spectrum analysis. The NCEP/NCAR reanalysis data for the period of 1979―2005 were analyzed by principal oscillation pattern analysis (POP) to investigate the spatial and temporal characteristics of principal ISO patterns of the global circulation. The relationships of these ISO patterns to the rainfa...  相似文献   

13.
The Southern Yellow Sea Cold Water Mass(YSCWM) is closely related to the modern circulation system of the east China shelf seas, which has significantly influenced regional marine environmental changes. The study of the Holocene evolution of the YSCWM will greatly improve our understanding of the mechanisms of regional environmental change. Benthic foraminifera are sensitive to bottom water environmental changes and can serve as useful indicators in bottom water environmental reconstruction. In this study, benthic foraminifera were analyzed in core N02 from the northwestern margin of the southern Yellow Sea Mud to decipher the phase evolution of the YSCWM during the last 7 kyr. Benthic foraminifera census counts and Q-mode factor analysis indicate that the Holocene sedimentary environment can be divided into three stages: From6.9–5.0 ka, the fauna was dominated by Ammonia ketienziensis, indicating that the YSCWM was at its strongest during the last 7 kyr, while the Yellow Sea Coastal Current(YSCC) had a weak influence on the bottom water of the study area. From 5.0–2.9 ka,the relative abundance of Hanzawaia nipponica remarkably increased while the abundance of A. ketienziensis decreased significantly, reflecting that the strength of the YSCWM was relatively weak and the range of the YSCWM might have contracted. The influence of the YSCC on the bottom water might have slightly increased, although its influence was still weak during this time. A notable increase in low-temperature and low-salinity species, such as Protelphidium tuberculatum and Buccella spp. has occurred since 2.9 ka, indicating that the YSCC has had a strong influence on bottom water during this period,while the strength of the YSCWM has been at its weakest during the last 7 kyr. Generally, the influence of the YSCWM and the YSCC on the bottom water properties of the study area show an obvious seesaw pattern, with one's influence increasing while the other's influence decreases and vice versa. The fluctuations in the strength of YSCWM during the Holocene may be caused by the different effect allocations of regional climatic factors(i.e. El Ni?o Southern Oscillation, East Asian Winter Monsoon,summer insolation in the northern hemisphere, etc.) acting on the circulation system during different periods.  相似文献   

14.
Using annual precipitation and discharge data measured in the past five decades,this paper analyzed the regional differences over west China in terms of climate and discharge variations,and investigated the relationship between the regional characteristics and the activities of South and East Asian sum-mer monsoon. Results revealed that the precipitation and discharge in the upper reaches of the Yellow River (Central West China) have a negative correlation with those in Xinjiang (northwest China) and the Yarlung Zangbo River (the upper reaches of the Brahmaputra Rive,southwest China) regions. The geographical patterns of precipitation and discharge variations are different over west China,i.e. the regional climate displays the alteration of dry-wet-dry or wet-dry-wet from north to south in west China. The negative correlation of annual discharges between Xinjiang and the upper reaches of the Yellow River is found statistically significant in the decadal scale,and that between the Yarlung Zangbo River and the upper reaches of the Yellow River is found active in the interannual scale. The regional char-acteristics indicate that the discharge/precipitation variations in the upper reaches of the Yellow River are dominated by the East Asian summer monsoon while their variations in Xinjiang are affected by both the west wind and East Asian summer monsoon.  相似文献   

15.
I. CHAncEL CHANGal m THE FLOODED AREA ArVER BREACHING AT TONGWAXIANG AND THEIR IMPACTSIn mid--June of 1855 a great flood occurred in the lower reaches of the Yellow River. The findmainly came down from the main stem of the river and itS tributary Qinhe River. In the meantimethe riparian area of the Yellow River had just been subjected to a heavy rain, and large amountS of water from mountains and hills were flowing into the river and lakes were also full. The Weis…  相似文献   

16.
Monthly data of Self-Calibrated Palmer Drought Severity Index (PDSI) from 1951 to 2000 are calculated using historical precipitation and temperature data for Chinese 160 stations. Temporal and spatial pat-terns of the first empirical orthogonal function (EOF) of the PDSI reveals a fairly linear trend resulting from trends in precipitation and surface temperature, which is similar to the linear PDSI trend during 1951―2000 calculated using all monthly data. The EOF analysis also reveals that the leading mode correlates significantly with ENSO events in time and space. The ENSO EOF shows that during the typical warm phase of ENSO, surface conditions are drier in most regions of China, especially North China, but wetter than normal in the southern regions of Changjiang River, and Northwest China. During the typical cold phase of ENSO, these anomalies reverse sign. From 1951 to 2000, there are large multi-year to decadal variations in droughts and wet spells over China, which are all closely related to strong El Nio events. In other words, when one strong El Nio event happens, there is a possible big variability in droughts and wet spells over China on the multi-year or decadal scale. Studies also sug-gest that during the last 2―3 decades climate changes over China, especially North China's drying and northwest China's wetting, are closely related to the shift in ENSO towards warmer events and global warming since the late 1970s. The instability of the relationship is also studied. It is revealed that there is a good correlation between ENSO and Chinese variations in droughts and wet spells in the 3―8-year band, but the correlation between ENSO and Chinese variations in droughts and wet spells is instable. Studies suggest that there are decadal changes in the correlation: the wavelet coherency between ENSO and Chinese variations in droughts and wet spells is high during 1951―1962 and 1976―1991, but low during 1963―1975 and 1992―2000.  相似文献   

17.
Observation of the operation of the Sanmenxia Reservoir on the Yellow River has led to the conclusion that to preserve a certain effective storage volume for reservoirs built on heavily silt-laden rivers is feasible if the reservoir is operated according to the principle known as“storing the clear water and discharging the muddy flow”. The relative stability of the bed elevation at the end of the backwater and the reservoir‘s erosion and deposition equilibrium depend on the compatibility of the pool level maintained in non-flood seasons with the conditions of flow and sediment load during flood seasons. Operating the reservoir to regulate the flood and sediment load during flood seasons can reduce the rate ofaggradation in the Lower Yellow River. The basic condition for applying the operation mode of “storing the clear water and discharging the muddy flow” is that a sufficient amount of water should be used for discharging sediment during flood seasons. Under the condition of extremely low flow years, reservoir sedimentation cannot be avoided even if this operation mode is adopted.  相似文献   

18.
The variations of the Earth’s geometry (ETP) pre-dominate climate changes such as monsoon on the Earth[1], serving as its external forcing. The loess/ paleosol sequence in Central China provides a good record of terrestrial deposition to study the evolution of the east Asian monsoon[2―4]. However, the deep sea deposition, due to its high resolution dating and abun-dant climate proxies, should be able to provide more climatic information in the geological time, such as the forcing mechanis…  相似文献   

19.
The present work explores relations between stream power,braiding intensities and bank erosion in certain stretches of the Brahmaputra River.In this paper,an objective approach is presented to enable quantitative assessment of spatio-temporal behaviour of channel braiding process of the Brahmaputra River by using the Plan Form Index and corresponding estimation of stream power to establish a behavioural pattern of variability of potential energy expenditure.The braiding index is compared for discrete years to understand the morphological behaviour.Subsequently,a real time estimation of stream power for certain stretches of Brahmaputra River is done in order to analyse its variability in braiding intensity and bank erosion.The paper presents the dynamic behaviour of the channel pattern of the Brahmaputra River System in Assam valley of India over a time span of 18 years.The procedure addresses the selection of input parameters from digital satellite images,comprising scenes for the years 1990,1997 and 2007 with specific dates,from Dhubri near Indo-Bangladesh Border to Upper Assam.Deployment of GIS technique has been made to extract the required parameters to derive Plan Form Indices for the entire study reach.Stream power estimation is done for corresponding latest floods and for corresponding dates of image scenes.The study indicated that due to consistent aggradation of riverbed inducing temporal declination of stream power,there is an occurrence of wide spread braiding.This in turn incurs substantial yearly land loss due to bank erosion,caused by flow concentrations due to temporal evolution of multiple channels in the Brahmaputra River.  相似文献   

20.
A theoretical model for river evolution including riverbed formation and meandering pattern formation is presented in this paper.Based on nonlinear mathematic theory,the nonlinear river dynamic theory is set up for river dynamic process.Its core content includes the stability and tropism characteristics of flow motion in river and river selves＇ evolution.The stability of river dynamic process depends on the response of river selves to the external disturbance,if the disturbance and the resulting response will eventually attenuate,and the river dynamics process can be restored to new equilibrium state,the river dynamic process is known as stable;otherwise,the river dynamic process is unstable.The river dynamic process tropism refers to that the evolution tendency of river morphology after the disturbance.As an application of this theory,the dynamical stability of the constant curvature river bend is calculated for its coherent vortex disturbance and response.In addition,this paper discusses the nonlinear evolution of the river peristaltic process under a large-scale disturbance,showing the nonlinear tendency of river dynamic processes,such as river filtering and butterfly effect.  相似文献   

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