Table of Content

    25 March 2002, Volume 57 Issue 2 Previous Issue    Next Issue
    The Minimum Area Per Capita of Cultivated Land and Its Implication for the Optimization of Land Resource Allocation
    CAI Yun-long, FU Ze-qiang, DAI Er-fu
    2002, 57 (2):  127-134.  doi: 10.11821/xb200202001
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    Cultivated land, different from other resources, is fundamental to the sustainable development of Chinese agriculture, society and economy. Market mechanism inevitably drives cultivated land into industrial and urban uses. Rapid industrialization and urbanization lead the scarce cultivated land resources to more crises. So market is a failure to allocate this kind of resource which can be regarded as common property in a certain sense. Government intervention is necessary for optimization allocation of cultivated land. Current policy of macro-administration for cultivated land conservation is oriented to total quantitative control. Every province is demanded that the total number of cultivated land remains not decreased. This policy is difficult for practicing because it does not consider various situations in different regions. For example, in eastern provinces where rapid industrialization and urbanization is proceeding and reserved arable land is scarce, the total number of cultivated land will inevitably decrease unless at the cost of lowering the economic growth. Therefore, it is necessary to innovate the policy of cultivated land resources conservation and utilization. The authors put forward the concept of minimum area per capita of cultivated land (MAPCCL) as a new insight into the optimization of land resource allocation for policy making. MAPCCL can be defined as the minimum number of cultivated land that can meet the needs of food consumption under certain food self-sufficient rate and land productivity. PICL provides a threshold of cultivated land conservation. If K<1, some cultivated land may be conversed into urban and industrial uses and planting structure may be adjusted for more cash crops. If K>1, cultivated land should not be conversed into other uses or land quality and productivity should be enhanced by means of increasing input and technological innovation.

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    Spatial Characteristics of Suburbanization and Its Developing Strategies in Beijing
    ZONG Yue-guang, ZHOU Shang-yi, ZHANG Zhen-shi,GUO Rui-hua, Chen Hong-chun
    2002, 57 (2):  135-142.  doi: 10.11821/xb200202002
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    Centralization, Sub-urbanization, Counter-urbanization and Re-urbanization are the main phases in the life cycle of metropolis. Sub-urbanization is one of the most important stages in metropolitan development. There have been four tidal waves of sub-urbanization in western developed countries since the 1930s. The analyses of sub-urbanization in this paper provide some of conclusions supported by TM images in Beijing from 1985 to 2000 and GIS as well as 2000 samples of land developing markets from 1992 to 2000. There were multi-growth patterns in urban spatial growth from the analysis. At the same time, by studying the Beijing's spatial extension pattern in central urban area in different periods, five growth or diffusion types were identified. The analysis indicates that excessive land use transformation from rural area to urban area was the result of distinct center and corridor effects. This paper analyses the corridors' extension volume, extension velocity and variant tendency of urban landscape on several directions. Finally, it is illustrated that three concentrated regions, eight developing sectors and six radiate corridors have been or will be formed from 2000 to 2010. Moreover, this paper brings forward the idea of incorporating the system of natural corridors into the Beijing's metropolitan planning, namely to form a star-shaped scattering-group pattern in which artificial corridors and natural corridors are alternately distributed in order to effectively prevent built-up area from massive growth and to meet the sound environmental needs of 2008 Olympic Games.

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    Population Growth Rate and Its Spatial Association by Providence in China
    LU An-min, LI Cheng-ming, LIN Zong-jian, SHI Wen-zhong
    2002, 57 (2):  143-150.  doi: 10.11821/xb200202003
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    Spatial autocorrelation is concerned with the degree to which objects or activities are similar to other objects or activities located nearby. In contrast to other types of spatial statistical analysis, such as point pattern analysis for example, spatial autocorrelation deals simultaneously with both locational and attribute information. Spatial association statistics measure the concentration of an attribute over space. While they are constructed in a very similar way to spatial autocorrelation measures, they offer the twin advantages of being able to differentiate spatial patterns caused by clusters of low values as opposed to clusters of high values, and they can be disaggregated by polygon or point to provide much more detailed information. Both spatial autocorrelation and spatial association statistics examine the relationship of an attribute value in one polygon or for one point with the values for proximal polygons or points. The spatial data of this paper are polygons. This paper aims to examine the relationship of an attribute value in one polygon with the values for proximal polygons. So spatial autocorrelation and spatial association statistics are fitted to analyze the spatial association of population growth rate by providence in China. Population growth rate indicates population growth degree in a period. This paper analyzes population growth rate in the periods of 1982-1990 and 1990-1998 in China. The spatial association of population growth rates in the two periods is studied with spatial statistics methods as well. In 1982-1990, China is divided into four regions: lower population growth rate in northern sub-region, higher population growth rate in central and western sub-region, lower population growth rate in central and eastern sub-region and higher population growth rate in southern sub-region. In 1990-1998, China is divided into two regions: lower population growth rate in northern sub-region and higher population growth rate in southern sub-region. Although the spatial clusters of the two periods are different, there are the same features with them. The population growth rate in the southern and eastern parts of China is higher, the population growth rate in the northern part of China is lower. The reasons are analyzed in detail.

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    Theoretic and Application Research of Geo-Case Based Reasoning
    DU Yun-yan1, ZHOU Cheng-hu, SHAO Quan-qin, SU Fen-zhen,SHI Zhong-zhi, YE Shi-ren
    2002, 57 (2):  151-158.  doi: 10.11821/xb200202004
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    As an emerging branch of AI, Case-Based Reasoning (CBR) has the inborn ability of quantitative interpretation and prediction simply based on similarity of historical events even there is difficulty to get the working mechanism, principles, or build statistical models for those complex systems. Since it is a perfect model of human recognition and its working mechanism is very similar to the human primitive reasoning logic, the introduction of CBR to geographical system (Geo-case Based Reasoning) study to solve the problem of quantitative prediction was promoted. With tracking the front of international CBR research, expression and reasoning models of CBR have been promoted. And application of CBR model and method to specific geographical phenomenon has been fully discussed as well. The content of this paper can be summarized in the following aspects: (1) GeoCBR has been posed from the view of geographic case study. Furthermore, principle difference between GeoCBR and general CBR has been explored. (2) A comprehensive expression model for geographic case based reasoning has been established based on Tesseral model. (3) Geo-case based reasoning model was built in case of having fuzzy spatial-temporal distribution, a special FMP was used to calculate similarity of Geo-cases, and then reasoning model was given based on it. (4) With such a theoretical framework of Geo-CBR, a fishing ground prediction model, which can be regarded as a sample of Geo-CBR, has been built. This model has been applied to the East China Sea fishing center prediction. The validation result is satisfying.

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    Neural-network-based Cellular Automata for Realistic and Idealized Urban Simulation
    LI Xia, YEH Anthony Gar-On
    2002, 57 (2):  159-166.  doi: 10.11821/xb200202005
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    There is rapid development of CA models for simulation of land use patterns and urban systems recently. Traditional methods using multicriteria evaluation (MCE) have limitations because they only use a linear weighted combination of multiple factors for predictions. It cannot explain much of the non-linear variations presented in complex urban systems. It is most attractive that neural networks have the capabilities of nonlinear mapping which is critical for actual urban systems. The study indicates that improvement has been made by using the proposed model to simulate non-linear urban systems. The advantages of using neural networks are apparent. The method can significantly reduce much of the tedious work, such as the requirements for explicit knowledge of identify relevant criteria, assign scores, and determine criteria preference. Furthermore, variables used in spatial decision are always dependent on each other. General MCE methods are not suitable to handle relevant variables. Neural networks can learn and generalize correctly and handle redundant, inaccurate or noise data which are frequently found in land use information. Users don't need to worry about which variable should be selected or not. Knowledge and experiences can be easily learnt and stored for further simulation. General CA models also have problems in obtaining consistent parameters when there are many variables in the prediction. It is very time consuming in finding the proper values of parameters for CA models through general calibration procedures. This paper has demonstrated that neural network can be integrated in CA simulation for solving the problems in finding the values of parameters. Users don't need to pay great efforts in seeking suitable parameters or weights which are difficult to be determined by general CA methods. In the proposed method, the parameters or weights required for CA simulation are automatically determined by the training procedures instead of by users. It is convenient to embed the neural network in the CA simulation model based on the platform of GIS. The model is plausible in forecasting urban growth and formulating idealized development patterns. Different scenarios of development patterns can be easily simulated based on proper training using neural networks. Remote sensing data can be used to prepare training data sets for more realistic simulation. Based on planning objectives and development evaluation, original training data sets can be rationally modified to obtain different sets of adjusted weights through the training procedure of neural networks. These adjusted weights can be applied to the CA model in generating idealized patterns.

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    Scale-Space Theory Based Regionalization for Spatial Cells
    LUO Jian-cheng, ZHOU Cheng-hu, LEUNG Yee, ZHANG Jiang-she, HUANG Ye-fang
    2002, 57 (2):  167-173.  doi: 10.11821/xb200202006
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    Traditional regional partitioning model for spatial cells is only built upon the information of attributes in every cell. However, the spatial relationships and their spatial interaction between cells are not considered sufficiently. In this study, based on scale-space theory a new approach for regional partitioning or regionalization for spatial cells is proposed so that the elements of spatial relationship between cells could be integrated besides considering the information of attributes. By this approach, regional partitioning in multiple scale can be accomplished on the basis of the spatial clustering algorithm that at certain scale the spatial cells could be melted into one class if their connective direction is the same within the road transformation system that is built upon by a spatial interactive model. Finally, according to the social and economic statistical data of 18 years from 1978 to 1995, the experiments of regional partitioning for social and economic development level of Jiangsu Province are achieved. In the experiments, despite only the simple spatial correlative model is used as the spatial interactive model for the scale-space clustering algorithm the regional partitioning results are highly accordant with real situations.

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    The Evolution of Mangrove and Its Geographic Background in Tropical China
    HUANG Zhen-guo, ZHANG Wei-qiang
    2002, 57 (2):  174-184.  doi: 10.11821/xb200202007
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    According to palynological analysis of about thirty samples, the developing process of mangrove since the late Tertiary in the tropical zone of China is discussed. The mangrove can be divided into two types, i.e., the typical and general. The former is represented by Sonneratia, Rhizophora, etc., which only grow in the southern tropical zone. At present the north limit of typical mangrove lies in 19o30'N and that of general mangrove, about 26oN in China. The oldest sporo-pollens of mangrove have been found in the Oligocene stratum in Zhujiang River estuary basin. From Miocene to Pliocene the north limit of mangrove reached Japan. But it was returned to about 22oN, i.e., the northern part of Leizhou Peninsula of Guangdong during Early Pleistocene.It is worth noting that the Last Interglacial Period was a prosperous stage for the evolution of mangrove. The pollens of Sonneratia dated at 42 000~32 696 a BP can be seen in Chenghai of Hanjiang Delta. It shows that the north limit of typical mangrove moved northwards from 19o30'N at present to 23o40'N at that time, showing an amplitude of 2~2.5 oC of rise in temperature than present.The pollens of Sonneratia with datings of 36 230~25 410 aBP have been found also in Shenzhen, Hong Kong, Shuidong and Haikou. The eight palynological profiles from Fuzhou to Beihai indicate that the mangrove disappeared during the Last Glacial Period, which can be seen only in some profiles in South China Sea but the pollens of Sonneratia and Rhizophora were carried by the sea current from southern South China Sea. Up to Early Holocene (9 656~7 912 aBP) the mangrove revived, in which about 7 000 aBP was another prosperous stage corresponding to the Megathermal in Holocene. Sonneratia caseolaris and Bruguiera sexangula have been found from the profiles in Shenzhen and Hong Kong and thus it can be deduced that the typical mangrove developed once again in Middle Holocene and its north limit was moved northwards to 22o20'N, i.e., the estuary of Zhujiang River.It is reported that there are pollens of Acgiceras corniculatum in the Middle Holocene stratum even in Ningbo (29o50'N) of Zhejiang. However they are not developed in situ because about twenty sites of Holocene mangrove pollens are found in the seafloor of East China Sea but they are carried by the Kuroshio or Taiwan Warm Current from south.The north limit of distribution of mangrove at present (26oN) is formed in Middle Holocene. After Middle Holocene the typical mangrove disappeared north of 19o30'N in China's tropical zone but there is Sonneratia alba in Iriomote Island (25oN) of Japan at present. It is also influenced by the Kuroshio, and the cold-resistant Kandelia candel is growing in Kagoshima Bay of Japan, where is the northernmost location of mangrove in the west Pacific Ocean.

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    Interdecadal Change in Western Pacific Subtropical High and Climatic Effects
    GONG Dao-yi, HE Xue-zhao
    2002, 57 (2):  185-193.  doi: 10.11821/xb200202008
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    Western North Pacific Subtropical High is a very important atmospheric circulation system influencing the summer climate over eastern China. Its interdecadal change is analyzed in this study. There is a significant decadal shift in about 1979/1980. Since 1980, the Western North Pacific Subtropical High has enlarged, intensified, and shifted southwestward. This change gives rise to an anti-cyclonic circulation anomaly over the region from the South China Sea to Western Pacific and thus causes wet anomalies over the Yangtze River valley. During the summers of 1980-1999, the precipitation is 63.9 mm above normal, while during 1958-1979 it is 27.3 mm below normal. The difference is significant at the 99% confidence level as a t - test shown. The southwestward expanding of the Western North Pacific Subtropical High also leads to a significant warming in the southern China, during the 1980-1999 the summer mean temperature is 0.37oC warmer than that of the period 1958-1979. The strong warming is primarily due to the clearer skies associated with the stronger downward air motion as the Western North Pacific Subtropical High expanding to the west. It is also found that the relative percentage of tropical cyclones in the regions south of 20oN has been decreasing since the 1980s, but that in the regions north of 20oN has been increasing during the same period. The Western North Pacific Subtropical High responds significantly to sea surface temperature of the tropical eastern Pacific with a lag of one-two seasons and simultaneously to sea surface temperature of the tropical Indian Ocean. The changes in the sea surface temperatures are mainly responsible for the interdecadal variability of the Western North Pacific Subtropical High.

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    Impact of Land Use Change on Runoff of Taihu Basin
    GAO Jun-feng, WEN Yu-hua
    2002, 57 (2):  194-200.  doi: 10.11821/xb200202009
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    Taihu Basin is one of the most developed regions in China and its land use has withnessed great changes in recent 20 years. Based on land use survey (1986, 1996) and land use planning (2010) data, land use characteristics are analyzed in this paper. Runoff of 1986, 1996 and 2010 was calculated using precipitation pattern from May to September of 1991. It is found out: The land use changed greatly in the Taihu Basin during 1986-1996. Cultivated land decreased by 3 385 km2 and construction area increased by 2 460 km2. Land use will go on changing to 2010, but the change will be little. Spatial distribution of land use is different in the Taihu Basin. With higher per capita GDP and dense population, land use changes greater than other regions. Land use changes have increased runoff of precipitation greatly. Compared to 1986, runoff increased by 10×108 m3 in 1996 if 1991 precipitation was used. It will increase by 12×108 m3 in 2010 compared to 1986. The upper reaches have more runoff increase than the lower reaches. These calculated results are corresponding with high water levels of the Taihu Lake in the 1990s.

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    Groundwater Dynamic Drift and Response to Different Exploitation in the North China Plain: A Case Study of Luancheng County, Hebei Province
    JIA Jin-sheng, LIU Chang-mingJIA Jin-sheng, LIU Chang-ming
    2002, 57 (2):  201-209.  doi: 10.11821/xb200202010
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    The groundwater table has been declining at a rate of 0.65 m/yr in Luancheng County since pumping groundwater on a large scale in the 1960s. The decrease of the precipitation, large increase of the agricultural output, variation of the crop growing structure and the building of the hydraulic project in the headwater area all tie up with the decline of the groundwater table. On the basis of analyzing the hydrogeological condition and the water resources utilization of Luancheng County, we build a three-dimensional groundwater flow model, and simulate the groundwater flow through finite-difference method using Visual Modflow software. We divide the research field into four parts after analyzing the hydrogeological condition. After calibrating and adjusting parameters using measured data, we simulate the parameters of hydraulic conductivity and specific yield. Using the calibrated model, this article analyzes the agricultural water saving potentiality and its influence on the groundwater. The results are as follows: (1) if we decrease the pumping water by 0.14×108 m3, the average groundwater table of five observation wells in December will rise by 0.33 m; (2) if we decrease the pumping water by 0.29×108 m3, the average groundwater table of five observation wells in December will rise by 0.64 m; (3) if we increase the pumping water for 0.29×108 m3, the average groundwater table of five observation wells in December will decline by 0.45 m. So we can draw a conclusion that controlling the agricultural water use is an important way to prevent the groundwater table's decline.

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    Temporal and Spatial Variation Features of Sediment Yield Intensity on Loess Plateau
    WANG Wan-zhong, JIAO Ju-ying
    2002, 57 (2):  210-217.  doi: 10.11821/xb200202011
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    Based on the distribution of the hydrological station and it's observation series of sediment information on loess Plateau, the study area was divided into 120 hydrological control area firstly, then according to the different soil erosion type area, the 120 hydrological control area were divided into 292 soil erosion units. The main results are as following: (1) The sediment yield of loess plateau (average condition from 1955 to 1989) are mainly come from the violence erosive area with erosion modulus >5000t/km2.a, the area of it made up 42.8% of the total sediment yielding area, and the sediment from it amounted to 85.0% of the total amount of erosive sediment yield. And the mighty violence erosive area with erosion modulus >10000t/km2.a, the area of it only made up 18.4% of the total sediment yielding area, but the sediment from it amounted to 50% of the total amount of erosive sediment yield. In the 8 grade of erosion intensity, the sediment yield from the area with erosion modulus2500-15000t/km2.a amounted to about 90% of the total amount of erosive sediment yield, and the sediment from the area with erosion modulus 10000-15000t/km2.a reach 35.0%. (2) Sediment intensities have changed evidently because of rainfall factor and the effects of soil and water conservation. From the view of structural features of sediment area, the sediment area with erosion modulus >10000t/km2.a reduced rapidly, from 8.7×104km2 (1955-1969)to 2.5×104km2 (1970-1989), reduced 71.8%, and the proportion in the total area decreased from 28.2% to 7.9%. And the sediment area with erosion modulus >15000t/km2.a reduced from 2.9×104km2 to 0.6×104km2 , reduced 78.3%; the area with erosion modulus >20000t/km2.a reduced from 1.0×104km2 to only 0.2×104km2 , reduced 81.0%. In the 8 grade of erosion intensity, the sediment area with erosion modulus >20000t/km2.a , 15000-20000 t/km2.a and 10000-15000 t/km2.a decreased greatly , and the reductive degree is 81.0%,76.9% and 68.7% respectively. And from the view of structural features of sediment yield, the proportion of sediment yield of mighty violence erosive area with erosion modulus >10000t/km2.a in that of total area reduced from 66.0% to 27.8%. And sediment yield reduced more greatly is the area with erosion modulus >20000t/km2.a , 15000-20000 t/km2.a and 10000-15000 t/km2.a, the reductive degree is 77.1%, 76.7% and 71.6% respectively. (3) The regions where the sediment yield reduced evidently are mainly distributed in the mighty violence erosive area surrounding Wuding River, and the majority of Fen river, the reductive degree is above 50%. Before soil and water conservation(1955-1969), the regions with erosion modulus >10000t/km2.a were distributed in the majority of the mainstream reaches of Yellow River between Hekouzheng and Longmen area, the upper reaches of Beiluo River, the most part of upper and middle reaches of Jing River, and the much area of Hulu River and Sandu River in Wei River basin. After soil and water conservation(1970-1989), the regions with erosion modulus >10000t/km2.a were scattered in Huangpuchuan river, the lower reaches of Kuye River, Jialu River, Wuding River and Qiushui River near to the mainstream reaches of Yellow River, and the riverhead of Beiluo River and Jing River. After control, the area with erosion modulus >10000t/km2.a in Hekouzheng - Longmen area, the upper reaches of Jing River and Wei River decreased on a large scale, and the erosion modulus reduced to 5000-10000 t/km2.a. the area with <5000 t/km2.a has changed not too much. (4) The sediment yield of loess plateau, calculated according to tributaries, are mainly come from Hekouzheng - Longmen area (54.8%), next from Jing River (17.6%) and Wei River (13.3%); according to soil erosion type areas, are mainly from loess Mao hill gully region and arid loess hill gully region (50.5%), next from loess Liang hill gully region (11.0%), loess flat hillock hill gully region (9.8%), and loess plateau hill gully region (9.7%); according to soil erosion belts, are mainly from wind and water erosion belt in semi-arid steppe region and water erosion belt in semi-arid forest steppe region (67.4%), next is from water and gravity erosion belt in sub-humid broad-leaf forest region (23.6%). (5) Taking sediment yield intensity >10000t/km2.a as criterion, there are 7 sediment yield centers on Loess Plateau. The area of the 7 centers made up 15.5% of the total sediment yielding area, however, the sediment yield amounted to 42.1% of the total amount of erosive sediment yield.

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    The REE Tracer Method for the Study of Rill Erosion Process on Loess Sloping Surface
    LI Mian1, LI Zhan-bin, DING Wen-feng, LIU Pu-ling
    2002, 57 (2):  218-223.  doi: 10.11821/xb200202012
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    By the rare earth elements (REE) tracer method, four REE (Ce, Sm, Nd, Dy) were used to study the changeable process of rill erosion on loess sloping surface in runoff scouring experiments. During different stages, the erosion pattern and characteristics are different. Generally, in the process of the rill development, the soil erosion amount in the bottom section was larger, and it decreased with the increase of the flow discharge, but the situation is on the contrary to the top section, which indicated that the influence of flow discharge outweighed the gradient on the rill erosion; the rill relative erosion amount in the bottom section obviously decreased from 92% to 37%, but the other three sections gradually increased from 4.7%, 0.25%, 2.14% to 29 %, 17% and 23% respectively because of the headcut erosion. Results from the experiments have also shown that the REE tracer method can be used not only quantitatively to determine rill erosion amounts in different slope sections, but also to reveal the changeable trend of rill relative erosion amounts. It provides a reliable and effective method for the research on rill erosion process.

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    Sustainability of the Yellow River Basin Environment to Development of Water Resources
    YIN Guo-kang
    2002, 57 (2):  224-231.  doi: 10.11821/xb200202013
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    Based on the data observed from 1919 to 1999, the paper systematically analyses temporal and spatial variations in both discharge and sediment load in the lower reaches of the Yellow River, reveals causes for its drying-up and a series of environment problems arising therefrom. A numerical simulation follows on water requirement of environment of the Yellow River catchment. The main points of them are as follows: (1) Water environment of taking fluvial systems as a link, as a part of the physical environment, is a basic condition of sustainable development of environment. Therefore the water resources of a catchment can not be sucked dry or exhausted. Its development intensity must be limited by environmental sustainability. (2) Drying-up of the lower Yellow River may give rise to a series of environment problems, such as flood, land desertification along the river region, soil salinization in delta area, pollution increase in the lower reaches and seas around the river mouth, and destruction of wetland ecosystem of the river mouth region. (3) An excess of water consumption and the inconsistency between the peak period diverting water and one of oncoming flow in the Yellow River catchment are the major and direct causes for drying-up of the lower Yellow River. From present relation of runoff yield to water consumption, it can be seen that the Yellow River with a trend of ephemeral river may be returned to a normal river by means of combined regulation of Xiaolangdi reservoir and others on the main Yellow River. (4) The Yellow River catchment tends to obvious drought recently. Its annual runoff flowing into sea decreased from 480.5×108 m3 (1950-1959) to 150.0×108 m3 (1986-1999). And the ratio of sediment output to input in the lower Yellow River correspondingly decreased from some 75% to less than 53%. So deposition seriously occurred in the river channel. To satisfy a need of sediment balance, the lower Yellow River must at least export sediment of 6×108 t a year into sea. And corresponding water demand exporting the sediment load is about 225×108 m3. Therefore there is a shortage of 75×108 m3 in water demand of environment. But viewing the problem from water saving potentiality of agricultural irrigation of the Yellow River catchment, present effective utilization ratio to water in irrigation by diversion of the Yellow River amounts to only 40-50%. If it will be raised to 70-80%, water saving in quantity will be over 85×108 m3 a year. And so merely this one can full the shortage of present environment water requirement. (5) The sustainability of catchment environment to development in water resources is also associated with its harnessing level. With gradually decreasing sediment yield due to soil and water conservation, and to give an outlet to the sediment load entering into the lower reaches of the Yellow River by means of various measures, such as strengthening dykes by warping, improving soil by warping and clearing situation in stream channel and so on, water demand exporting sediment load into sea can reduce, so the water resources to be able to supply utilization will gradually increase.

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    Relations between Grain-size of Suspended Sediments and River Basin Environment in the Middle Yellow River
    LIU Ai-xia, LU Jin-fa
    2002, 57 (2):  232-237.  doi: 10.11821/xb200202014
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    A set of data on the grain-size of suspended sediments and river basin characteristics has been collected from the first order tributaries of the Middle Yellow River. A systematic study on quantitative relationships between grain-size of suspended sediments and the characteristics of these basins have been made for those river basins by using statistical methods. The following conclusions can be drawn: Precipitation, surface material, drainage density, vegetation coverage and hyperconcentrated flows act as an important controlling factor on the grain-size of suspended sediments in the Middle Yellow River. The grain-size of suspended sediments increases with an increase in drainage density, the maximum suspended sediment concentration and unevenness of precipitation, and decreases with an increase in the percentage of loess and vegetation coverage. Multiple regression analysis has shown that surface material is the most important factor influencing the grain-size of suspended sediments, followed by vegetation, hyperconcentration and precipitation. The drainage density exerts minor influence on the grain-size of suspended sediments.

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    Sediment Disasters, Their Types and Classification Principles in Drainage System
    JIN De-sheng, SHI Chang-xing, CHEN Hao, ZHANG Ou-yang
    2002, 57 (2):  238-248.  doi: 10.11821/xb200202015
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    The sediment disaster is defined as phenomena of erosion, transportation and accumulation of material on land surface, which gradually advances or surpasses threshold so as to cause casualties and economic loss. It belongs to an independent natural hazard system. The sediment disaster appears when the productivity reaches to a certain level and possesses special attributes in natural, sociology and disaster science. In accordance with dynamics, geomorphologic location, behavior and particular, it can be divided into two subsystems: natural dynamic and man-induced ones. Then a subsystem is heartily typed as the drainage network, slope and gully, channel and plain-estuary-coastline and classified into 5 patterns, i.e. erosion, transportation, accumulation, complexity and cascading, including 49 and 54 kinds for each subsystem. It is a kind of more comprehensive principle and more systematic classification of sediment disaster up to now. Based on fluvial geomorphology, sediment mechanics and disaster science, the sediment disaster is characterized by: 1) geographic-horizontal zoning, 2) vertical zoning, 3) occurring in group, 4) inherit and period, 5) gradually and sharply changing with human environment vibration, and 6) complexity and non-linear figure, etc. Further study and in-depth analysis should be conducted on real characteristics of various high-concentrated sediment disaster, their processes and mechanism, the coupling relationships among various sediment disasters and quantitative relations between the two subsystems of sediment disaster.

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