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    15 March 2000, Volume 55 Issue 2 Previous Issue    Next Issue
    Climate Change and Its Impacts on China’s Agriculture
    TANG Guo ping, LI Xiu bin, Guenther Fischer, Sylvia Prieler
    2000, 55 (2):  129-138.  doi: 10.11821/xb200002001
    Abstract ( )   PDF (539KB) ( )   Save
    Though analyze the potential impacts of global climate change on China’s agriculture, the meaningful reference for China’s agriculture in the future can be shown. First, according to the historical meteorological data from 310 climatological stations during 19581997, the baseline climate in China is analyzed. Then, three general circulation models, i.e., HadCM2, CGCM1 and ECHAM4 are chosen and meanwhile six climate change scenarios constructed. Three models above are used to simulate China’s climate changes under different scenarios for three periods 2020s, 2050s and 2080s. Under three model runs, air temperature is expected to increase in all regions of China. For example, under HadCM2 GX scenario, annual mean air temperature will increase 1.5℃, 2.5℃ and 3.8℃ in 2020s, 2050s, 2080s respectively. In addition, the increasing magnitude of air temperature in high latitude area is larger than that in low latitude area, and in inland area larger than that in coastal area. Finally, based on three GCMs results, an explicit geographic model, i.e., the AEZ model developed and improved at IIASA, is applied to assess the impacts of climate change on China’s agricultural land productivity. The impact assessment mainly focuses on the changes of multi cropping index, land productivity, arable land area and total potential cereal production. The findings show: (1) The average magnitude of increase in multi cropping index is larger in the southwest, central and north of China than that in the northwest and south of China. (2) Due to climate change, the increasing temperature and rainfall in the northeast, northwest and plateau of China has a positive influence on their arable land area and total potential cereal production. Conversely, the increasing temperature and decreasing rainfall in the southeast, central and southwest of China has a negative influence on their arable land area and potential cereal production. For whole China, arable land area is projected to increase in a new climate condition. The changing scope of arable land area varies from 2 5% to 16 2% under irrigated and rain fed condition, and from 2 3% to 18 0% under rain fed condition. (3) Climate change affects land productively in northeastern China positively. However, it has a negative influence on land productively in southwestern China and Tibet. On the average, climate change affects land productivity in China negatively. The decreasing scope changes from 1.5% to 7.0% under irrigated and rain fed condition, and from 1.1% to 12.6% under rain fed condition.
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    Comprehensive Indexes and Spatial Distribution Characteristics of the Regional Sustainable Development of China
    LIAO Zhi jie, LIU Yue
    2000, 55 (2):  139-150.  doi: 10.11821/xb200002002
    Abstract ( )   PDF (589KB) ( )   Save
    The sustainable development pattern of China, calculated by province from the databases of the Population, Environment and Sustainable Development Atlas of China (PESDAC), are expressed by six indexes and their maps visually. The spatial distribution characteristics are described according to the indexes and the maps. The paper is organized as follows. Firstly, the research situaction on Chinese Sustainable Development by home and abroad is introduced. Then, the dessipative structure theory is applied to the research on evolution of regional Population, Resource, Environment and Development (PRED) system. A comprehensive index named SDI is put forward with its non-linear model. Thirdly, based on the databases of the PESDAC, the indexes of population, resource, environment, development of economy and society by province are derived quantitatively. Fourthly, they are visualized into six maps. Next, a spatial analysis of the pattern of China’s sustainable development is made. Finally, the causes are analyzed and some answers to the question are given. The conclusions are drawn as follows on the overall spatial characteristics of the sustainable development of China. The social and economic development pattern is divided into three zones from east to west obviously. The ecology and environment situation is related to regional economy closely. There is a difference between North China and South China because of their natural condition; The natural resource lies mainly in the west of China. It is short relatively in the middle of China. But the resource per capita is least in the east of China;The distribution of SDI has the same pattern as the attraction to population, its shape is like two circles with the same center in Hubei province. But there is a slight difference between SDI and the attraction to population, it reflects a value deflection by which people decide to migrate nowadays. Poverty scatters mainly in the middle of China, but there is one third of poverty population not living in the counties assigned by government.
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    Landuse Change Mechanism in Shenzhen City
    SHI Pei jun, CHEN Jin, PAN Yao zhong
    2000, 55 (2):  151-160.  doi: 10.11821/xb200002003
    Abstract ( )   PDF (217KB) ( )   Save
    Based on remote sensing images in 1980, 1988 and 1994, the Shenzhen citi’s land use was conducted through methods of maximum like and probabilistie relaxation. Which revealed the city’s spatial process during 15 years. The conclusions may be distingnished as follows: (1) The results of the detection are reasonable and it is feasibility to calculate the transfer matrix of landuse to show spatial pattern of landuse distribution as unit of image pixel. (2) The main characteristics of the city’s landuse change are the obvious reduction of the existing farm and orchard lands and subsequent rapid increase of urban landuse along the coast and several major roads which are controlled by the opening policies of establishing the special economic zone in this city. (3) The characteristics of the city’s landuse changes are mainly demonstrated as follows: The urban landuse increases rapidly at the expense of occupying great amounts of farmland, showing the patterns of belt distribution along the main transportation lines and of spreading outside the Special Economic Zone. In the primary landuse such as farmland and woodland, etc, the tendency from the lower benefit landuse pattern transforming to the higher benefit one has taken place due to the influence of urbanization. Furthermore, the city’s landuse changes also demonstrate the characteristics of bare land enlargement and farmland split up, which is one of important factors recently led to serious soil erosion and no point source pollution in the city. (4) Under the policy of the special economic region produced by the central goverment of China, the external driving forces of landuse changes in Shenzhen City are the rapid growth of population, foreign investment and development of the tertiary industry which was based upon the real estate. The counter force of landuse changes in Shenzhen City are the transportation issue, topography, landuse patterns, the most importent factor is the transportation.
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    Impacts of Climatic Change on Permafrost and Cold Regions Environments in China
    JIN Hui jun, LI Shu xun, WANG Shao ling, ZHAO Lin
    2000, 55 (2):  161-173.  doi: 10.11821/xb200002004
    Abstract ( )   PDF (480KB) ( )   Save
    Permafrost area in China is about 2.15×106km2, characteristic of altitudinal permafrost. Permafrost in China can be further divided into latitudinal and altitudinal permafrost. The latter, with an areal extent of 1.73×106km2, can be further divided into plateau and apline permafrost. Significant permafrost degradation has occurred and is occurring in most parts of permafrost regions in China due to the combined influence of climatic warming and increasing anthropogenic activities. Permafrost in China has experienced major shifts in history, and may have disappeared except in very high mountains during the Quaternary. Accelerating fluctuations of climate and permafrost have been identified during the Holocene, and most areas of permafrost in China now are relics of cold climates, and are in rapid and extensive degradation, especially during the past 40 years. As a result of climatic warming of about 0.3~0.4℃ during the past 40 years characteristic of winter warming, extensive permafrost degradation in China has been interpreted and is expected in the future based on permafrost monitoring. This can be inferred from rising mean annual ground temperatures, deepening in thaw depths, disconnecting and disappearing of island permafrost, increasing and expansion of taliks and the burying of permafrost. In island permafrost zone, mean annual permafrost temperature has risen about 0.2~0.3℃ from 1970s to 1990s. In continuous permafrost zone, it has risen from 0.2 to 0.4℃. Thawed nuclei have fromed extensively on the edge of permafrost regions, where the permafrost table is buried as deep as 4~7m and where the seasonal freezing can only reach 2~3m. On the Qinghai Xizang Plateau, for example, the lower limit of permafrost distribution has increased gengrally from 40 to 80 m in elevation despits of the influence of local lithology, slope orientations and moisture conditions. The area of island permafrost zone has shrunk 35.6% on the Qinghai Xizang Plateau during the same period. Permafrost degradation has and will cast great influence on Chinese economy and environment in cold regions. Permafrost retreat and degradation has caused a lot of problems in cold regions engineering and environments in China, which have made it urgent to reconsider the permafrost protection principles for engineering constructions and operations, as well as environmental protection. The impact of permafrost degradation on water resources, thouth poorly understood due to lack of observation, will be very important for regional economy and environment in Asia.
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    The Last Greatest Lakes on the Xizang (Tibetan) Plateau
    LI Bing yuan
    2000, 55 (2):  174-182.  doi: 10.11821/xb200002005
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    The paleo lake shorelines and lake deposits are widely distributed in the lake basins on the Xizang (Tibetan) Plateau. Deduced from the highest lake shorelines, the lakes area during the last Greatest Lake Period (GLP) was several to tens times larger than their present area. However, there are still divarication on its age, e.g. some thought GLP was formed in the early and middle Holocene, some thought GLP in the Last Glacial Interval, also some thought in the early middle period of Pleistocene. There is no final conclusion related to the last GLP on the total plateau. According to the analyses of the lake deposits and 14 C dating from 12 lakes such as Tianshuihai Lake, etc., the GLP on the Xizang Plateau was formed generally from 50 ka BP to 30~20 ka BP, even some appeared in a little newer time. Because of the difference of climatic environment and lake landform in different areas, there are also differentiation on the end age of GLP and ratio of paleo and present lake area. The GLP in the northern part of the Plateau and the middle west part of Qiangtang Plateau approximately ended at 25 ka BP while the ratio was bigger between paleo and present lake area. It was a little later to the closed time of the lakes in the south and east part of the Plateau. Some big lakes even were exterior lakes in the late Holocene while the ratio was smaller between paleo and present lake area. The GLP that represented a special warm humid stage in Xizang area generally appeared from 40 to 25 ka BP. This corresponded to the third stage of marine oxygen isotope records and Last Glacial Interval. During this period, the lake areas were bigger and lakes levels were higher than those in the best period of the Holocene. Reflected by the relics of high lake level, the climate in the Xizang area was abnormally warm in the Last Glacial Interval compared with the records of environmental change from Antarctica and Greenland. This was also documented by the records from ice core and lake deposits, even reflected in the Tengger Desert to the north of the Plateau and north China area. It may be related to two factors: one was that the incidence solar radiation between 50°N 30°S was higher than that in the high latitude area in GLP; the other was that the powerful Australia high pressure might get across the equator line in that period. This caused the strong summer monsoon on the Plateau that brought plenty of water content from the south to the north interior land.
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    Reconstructing of Sea Surface Temperature in South China Sea by Useing Image Density of Coral X-ray Photograph
    HE Xue xian, PENG Zi cheng, WANG Zhao rong, NIE Bao fu, CHEN Te gu, WANG Lu
    2000, 55 (2):  183-190.  doi: 10.11821/xb200002006
    Abstract ( )   PDF (429KB) ( )   Save
    Annual density banding in reef corals was discovered by Knuston et al in 1972. X ray photographs of coral skeleton show its banding structure with more information of the past climates and ocean environments on the basis of annual variation, it is easy to date the position along with the growth axis of the corals. Annual density banding patterns can trace sea surface temperature (SST). Annual density variations obviously record cycling of one or more environmental signals. SST is the dominant factor on coral growth at the regions, where annual change of temperature is large. Annual growth length of corals and calcification rate can be used as proxies of annual average SST. The reef coral samples (SY 7 core) were collected at Xisha Yongxing Island (16°50′N, 112°20′E), South China Sea, where both of annual change and season change of SST are large due to the influence of the monsoon. It is available to use the annual density banding of coral for reconstructing the past SST. The experimental procedures show as follows: First, a 10 mm thick longitudinal slice was cut along the central of section of the coral core. Secondly, the X ray photographs of the slice were taken by a medical X ray set. At last, the values of image density were gained by using a microdesitometer along with the growing axis at the step of 0 25 mm and scan area of 0 25 mm×0 25 mm. The length of scan step and the number of scan dots can be used as the proxies of annual growth rate and annual calcification rate respectively. Growth rate can be expressed by the Equation: L=0 25×n/β . L is annual growth rate (mm/a); n is the number of scan dots per year; β is image scale; 0 25 is the length of scan step. Calcification rate proxy can be expressed by the Equation: G′=? 苮ni=1V i/β . G′ is annual calcification rate proxy; V i is the value of image density at i dot; β is image scale. Data of image density of X ray photograph, measured by use of microdesitometer in the period of 19371993, were derived for annual growth rate and annual calcification rate proxy. Both parameters were positively related to annual mean sea surface temperature, which was measured by the instruments at the oceanographic station. Growth rate thermometer and calcification rate proxy thermometer were set up using linear regression method. Both thermometers show: SST=0 1175× L+26 r=0 91 . Where SST is annual mean SST (℃); L is annual growth rate (mm/a); r is correlative coefficient; SST=0 0204× G′+26 r=0 85 . Where SST is annual mean SST in year (℃); G′ is annual calcification rate proxy; r is correlative coefficient. We can use the growth rate thermometer and the calcification rate proxy thermometer to reconstruct the past sea surface temperature records. The annual mean error between two SST records calculated by the two thermometers is ranged in (0 12℃. Annual SST records in South China Sea showed that SST was warmer in 1940s, 1980s to 1990s than that in 1950s to 1970s. The abnormal SST records can clearly reflect the influence of the ENSO phenomenon too.
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    The Coupling Relationship between the Nature and the Man in South Edge of Tarim Basin
    XIONG Hei gang, ZHONG Wei, TashPolat Tiyip, Haimiti, Nuerbayi, Hiroki Takmura, Yuichi Suzuki
    2000, 55 (2):  191-199.  doi: 10.11821/xb200002007
    Abstract ( )   PDF (279KB) ( )   Save
    Being influenced by the physical environment, the mankind has moved in large scale along south edge of Tarim basin of Xinjiang. The environmental change information of each time have been recorded by the strata of the different deposits in this special region and the many historic sites of ages, and then the routes of mankind movement can be delineated. The man hunted animals and picked fruits at the foot of the mountains in the Stone Age. Then the optimum provided a favorable subsistence environment for mankind. At this time, the man, with the tool of the production evolving, moved forward to the center of Taklamakan desert along the river in 4000~6000 a BP. With the tools of production improved and the product forces raised, the ability of mankind taming nature was great and the scope of activities was expanded quickly in 2500~4000 a BP. Some oasis cities were built in desert and oasis culture was developed. In the 2th century, the West Han Dynasty controlled the center China and unified the west regions. The steady society provided a suitable condition for the economic development. The Yutian country, which was located in the south edge of Tarim basin, became one of the politic, economic cultural centers in the 3~4th century. After wart the frequent wars destroyed the stable phase and many old countries were abandoned though the tools and skill of product developed. The 7~9th century was cold and wet. The scale of many ruins showed that the nature and human condition were suitable for man to live and develop. With the lapse of time the climate became drier. Mankind living was deficient in water resources and the desert expanded greatly. The man felled trees, destroyed the environment. At the same time the warfare was uninterrupted and the people had no means of livinghood. The development of the physical environment and the changes of human history are results of comprehensive effect of natural factors and mankind. In the wet climate, full water, unitary state, stables society and national concord period, the economy, culture and production of the oasis developed very quickly. Otherwise, the environment worsened, the oasis was discarded and the process of desert is quick. In the early period, the natural environment factors played a big part in it, while in the later, the mankind had main effect on it. Natural condition decided both the feature of the environment and the initial foundation of its evolution. The trend that mankind kept on moving up river was chiefly influenced by physical environment. The activity of mankind was the activist factor, sometimes was the decisive factor deterring the course, feature and type of natural environment. That was indicated more obviously in the district where the physical environment was extremely unstable.
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    Coupling Relationship between the Red Earth Evolution, Climate Change and Tectonic Movement in China
    HUANG Zhen guo, ZHANG Wei qiang
    2000, 55 (2):  200-208.  doi: 10.11821/xb200002008
    Abstract ( )   PDF (420KB) ( )   Save
    It is generally considered that the evolution period of red earth is corresponded with the warm period of interglacial but the relationship between climate (red earth) and tectonic movement has not discussed well. The problem is still remained whether the warm period was associated with the relatively stable period or with the active period of tectonic movement. This paper hold the former point of view. The dating and distribution of red earth during N 2, Q 1, Q 2 and Q 3 show that the formation and evolution of monsoon circulation can be divided into 5 stages in China. In addition, the relationship between red earth and climate is also presented by the unanimity each other of cycles. Since early Pleistocene there were 10, 9 and 10 cycles of earth-climate in North China, the area of middle lower reach of Yangtze River and South China, respectively. The average main periodicity is 100~120 ka and the secondary is 60~70 ka. Taking the climate cycles of loess paleosoil series as a time mark, the multi layer red earth in south area of China can be contrasted with the interculated red layers in Loess one by one. The coupling relationship between red earth and the stages of neotectonics is obvious, for example, the deformed elevation of red earth of several periods of N 2, Q 1 and Q 2 indicates three important tectonic events since late Pliocene in China. These events are regarded as the main reason causing the formation of three large stepes of China’s relief, which is marked by the distribution of red earth. The deformed emplitude of red earth is different in space and time showing the moving of block fault movement. Finally, by comparing the corresponding relation between cycles of red earth, uplift stages of Xizang Qinghai (Tibet) Plateau and development periods of monsoon circulation, three main cycles of tectonics-climate are deduced, namely the first (before 1.4Ma BP), the second (1.4~0.64 Ma BP) and the third (since 0.64 Ma BP). For each cycle, two stages can also be divided, the former is characterized by relatively stable tectonics and warm climate, the latter, the active tectonics and cold climate.
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    Mechanism of Chemical Evolution for Quaternary Groundwater in Yangtze River Estuarine Region
    SONG Bao ping, ZHANG Xian lin, FANG Zheng, CHEN Zhong yuan
    2000, 55 (2):  209-218.  doi: 10.11821/xb200002009
    Abstract ( )   PDF (412KB) ( )   Save
    Quaternary sea level fluctuation had played important role in affecting the spatial and temporal distribution of top Holocene phreatic aquifer and 5 (Ⅰ-Ⅴ) underlying late to early Pleistocene aquifers in the Yangtze estuary region. Inevitably, the evolution of groundwater chemical field of the region was closely associated with transgression and the occurrence of aquifuge in Quaternary stratigraphy. Present database was established primarily on 245 water samples obtained from these aquifers in 78 selected Quaternary hydrogeological boreholes. The analytic items included the concentrations of K +, Na+, Ca2+, Mg 2+, NH 4+, Al3+, Cl-, HCO3-, CO32-, and SO42-, and the values of PH and temperatures. Using hydrogeochemical methods, this paper deals with the nature of groundwater chemical types and chemical evolution. The results are showed as below: (1) One phreatic aquifer and five confined aquifers in study area belong to three aquifer systems, i. e. Holocene aquifer system (phreatic aquifer), mid and upper Pleistocene aquifer system (Ⅰ-Ⅲ confined aquifers), and lower Pleistocene aquifer system (Ⅳ-Ⅴ confined aquifers). (2) Spatial and temporal distributions of brackish water and salt water in sedimentary system of the study area were controlled by Quaternary transgressions. (3) There are two main types of aquifer system can be differentiated by Piper diagram, i. e. Ⅰ-Ⅲ aquifer system and Ⅳ-Ⅴ aquifers system. The former is characterized by salt water (Cl—Na·Ca and Cl—Na), and the later is dominated by fresh water (HCO3—Na and Cl·HCO3—Na) and brackish water (Cl—Na). (4) There are four types of groundwater chemical evolution in study area: ① dilution of salt water by fresh water recharge through atmospheric replacement taking place only in phreatic aquifer. ② exchange of sodium absorbed in aquifer medium by calcium in water. The ratios Na/(Na+Cl), used as an indicator of ion exchange, demonstrate that the degree of exchange in Ⅳ-Ⅴ aquifers (0 65 on average) is more intensifying than that of Ⅰ-Ⅲ aquifers (0 45 on average). ③ mixture of different water types through leaky system in the Quaternary aquifers system. The groundwater composition reveals that the mixture of brackish water character due to leaky system is of the transition in chemical property between salt water in upper aquifers and fresh water in lower aquifers. Through thermodynamical calculation, we proposed that the groundwater in study area is super saturated with calcite ( SI >0).
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    Amelioration and Effective Use of the Sandy Land in the Northwestern Shandong Province
    ZHANG Hong ye
    2000, 55 (2):  219-227.  doi: 10.11821/xb200002010
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    Large areas of sandy land are distributed in the northwest region of Shandong Province. According to the previous investigation, the area of sandy land in the northwest region of Shandong Province is 634 500 ha, accounting for 16 4% of the total area of the region. Among the four prefectures in the region, Liaocheng has the largest sandy area, which amounts to 252 100 ha, making up 39 7% of the sandy land in the northwest region of Shandong Province. There were five types of land use representing the manners of land use in different periods of the recent 50 years, including extensive forests, annual crops on shift sandy land, annual crops on fixed sandy land, thick forest belt agroforestry and high productivity agroforestry. In this paper, the five types of land use were compared in terms of the impacts on sandy land degradation and the output benefits. Cropping without the protection of forests will not sustain because of wind erosion, while the benefits from extensive forests are extremely low. It was found that sandy land in this region could be effectively used without the occurrence of wind erosion by establishing agroforestry systems. The benefits from the thick forest belt agroforestry system are 20 times of that from extensive forests. The benefits from the high productivity agroforestry system are 36~37 times of that from extensive forests, and 1 82~1 89 times of that from the thick forest belt agroforestry system. The characteristics of agroforestry systems were also analyzed in this paper. It was concluded that both mutual beneficial and mutual competitive characters would be intensified with the elapsing of time. The sustainability of land use in sandy areas is obtained because of the protection by trees. The system therefore has a tendency of decreasing output and increasing stability. Even in the last two years in the 6~years production cycle when there are the largest shading and underground competing effects, the per hectare output from the thick forest belt agroforestry system will be 17 times of that from the extensive forests, and the output from the high productivity agroforestry system will be 31~32 times of that from the extensive forests. In these two years, the output from the high productivity agroforestry system is about 1 91 times of that from the thick forest belt agroforestry system. It was also proved that the capability of protection of the thick forest belt agroforestry system and the high productivity agroforestry system is obviously increased. It was indicated in this paper that high productivity agroforestry system is the best way to use sandy land, while thick forest belt agroforestry system is the second best.
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    Evolution of Meanders with Hyperconcentrated Flow in the Loess Areas
    SHI Chang xing, ZHANG Dian
    2000, 55 (2):  228-234.  doi: 10.11821/xb200002011
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    In the loess areas, especially on the Loess Plateau in China, most of the rivers discharging hyperconcentrated flows have developed a typical meandering pattern. Based on the data of thirteen meandering rivers on the Loess Plateau and the Yangchangzi River, the properties of water flow and sediment load of these rivers, the effects of variations of flow and sediment load on channel cross sectional geometry and sinuosity, are analyzed in the paper. The data include the daily flow and sediment load and the geometry of channel cross sections recorded from 1976 to 1980 as well as the plan of channel measured on the landscape maps with a scale of 1∶50 000 or 1∶100 000. From these data we extrast parameters reflecting the characteristics of flow and sediment load, channel geometry, and sedimentation in channel and channel adjustment thereupon. Follows are the results of analyses. 1) As the rivers with low sediment concentration, the hyperconcentrated flow dominated rivers have a narrower and more sinuous channel if the fluctuation in water discharge is low. 2) With the increase of sediment concentration, the channel cross sectional geometry is usually widened in the case of the rivers with low sediment concentration. Since a narrow channel is one of the requisite conditions as well as the result of sediment transport of hyperconcentrated flows, the channels become narrow initially as the sediment concentration of hyperconcentrated flow increases. However, if the sediment concentration is larger than a certain value, the energy consumption of sediment transport is lowered down thenceforth with the increase of sediment concentration, and the flow becomes unsaturated and has a higher channel making capacity, so the channel is widened. Revealed by the instantaneous hydrological records, the transition takes place at the sediment concentration of about 400 kg/m 3. 3) Both excessive and low intensity of sedimentation in the channel is unfavorable to development of meanders. In the case of the rivers with a low sediment concentration, the energy consumption per unit distance increases with the enlargement of slope and discharge and so the capacity of channel making of the flows; therefore, the channel sinuosity increases initially and decreases later. Regarding the hyperconcentrated flow dominated rivers, the energy consumption of sediment transport is lowered and the channel making capacity as well as magnitude of sedimentation are enlarged accompanying with the increase of sediment concentration, so an initial increase of channel sinuosity is followed by a decrease also. Due to the difference of the mechanism of channel sinuosity adjustment from that of cross section changes, the existence of the asychronism in the adjustment of the two factors is reasonable.
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    The Cross-section Variation of Glacial Valley and Its Reflection to the Glaciation
    LI Ying kui, LIU Geng nian
    2000, 55 (2):  235-242.  doi: 10.11821/xb200002012
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    A new model based on the gradient wide depth ratio (GWDR) is posed and the longitudinal variation of glacial valley is presented by using this model on the basis of the investigation and measuring data of the glacial valley cross sections in the middle and west of the Tian Shan Mountains. The GWDR of a glacial valley cross section is defined as the ratio between the distance of the same contour line and its depth in the cross section, and it can describe the integrated characters of a cross section as well as the compared morphological analysis on different cross sections. Statistics show that the relationship between the GWDR and its corresponding depth conforms to the power function. Two parameters ( A f, a measure of the breadth of the valley floor, and B f, a measure of the steepness of the valley sides) are used here to describe this relationship. According to their planar shapes, glacial valleys are classified as single valleys and multi valleys, and multi valleys are subdivided into a simple valley section, a confluent valley section and a single flow section. Base on measuring data of 49 cross profiles of glacial valleys in the middle and west of the Tian Shan Mountains, the longitudinal variations of glacial valleys are concluded as follow: (1) In single valleys, two parameters ( |A f| and |B f| ) of the GWDR model increase form the head to the snow line, and the valley becomes wider and steeper in two walls. On the contrary, they decrease from the snow line to the end of the valley, and the valley becomes narrower and gentler in two walls. (2) In multi valleys, |A f| and |B f| increase form the simple valley section to the confluent valley section, and decrease from the confluent valley section to the single flow section. These characteristics reflect the differences of glaciation along the valley. The glaciation near the snowline is greater than upstream and downstream in the simple valley because the glacier reaches the maximum values in temperature, thickness, and velocity at this location. In multi valleys, the confluence action becomes the dominant influence factor of the glaciation, so the glaciation in confluence locations is greater than other locations.
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    The Pattern of Saltwater Intruding into the Changjiang Estuary and the Utilization of Freshwater Resources
    MAO Zhi chang, SHEN Huan ting, XU Peng ling
    2000, 55 (2):  243-250.  doi: 10.11821/xb200002013
    Abstract ( )   PDF (222KB) ( )   Save
    The geomorphic features of the Changjiang estuary are characterized by the multi order branching. The saltwater intrusion has the following four distinct forms:direct intrusion from the outer sea;saltwater exchange by shoal passages;saltwater downstream from other waterways;saltwater intrusion by tidal flooding. Temportal changes in the salinity of the Changjiang estuary have daily, semimonthly, seasonal and yearly variation. There exists the sharp three demarcation lines of salinity gradient along the South Branch-South Channel. Two main problems had to be solved before building reservoirs of avoide saltwater and store freshwater in the Changjiang estuary. One is to calculate the longest duration that the chlorinity exceeds 250?10 6 in the water resources area, which is the criterion value for determining the storage capacity of reservoirs. Mathematical methods including the cybernetics, the frequecncy spected analysis and mathematical modelling are adopted here to get more correct times when the chlorinity exceeds 250?10 6 . And the other is to determine reasonably site of the pumping station and the height of water intake of water pumps from the river bed. The above problems can be solved after understanding the pattern of temporal and spatial variation of the saltwater intrusion in the Changjiang estuary. The above conclusions have played an important role in forming the reservoir scheme of the Baoshan lron and Steel Plant, and supplied basic data for selection of the postion and storage capacity for the Chenhang reservoir.
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