Evolution of river systems under the background of human activities has been a heated topic among geographers and hydrologists. Spatial and temporal variations of river systems during the 1960s-2010s in the Yangtze Ri...Evolution of river systems under the background of human activities has been a heated topic among geographers and hydrologists. Spatial and temporal variations of river systems during the 1960s-2010s in the Yangtze River Delta （YRD） were investigated based on streams derived from the topographic maps in the 1960s, 1980s and 2010s. A list of indi- ces, drainage density （Dd）, water surface ratio （WSR）, ratio of area to length of main streams （R）, evolution coefficient of tributaries （K） and box dimension （D）, were classified into three types （quantitative, structural, and complex indices） and used to quantify the variations of stream structure. Results showed that： （1） quantitative indices （Dd, WSR） presented de- creasing trend in the past 50 years, and Dd in Wuchengxiyu, Hangjiahu and Yindongnan have decreased most, about 20%. Structurally, the Qinhuai River basin was characterized by sig- nificant upward R, and K value in Hangjiahu went down dramatically by 46.8% during the 1960s-2010s. Decreasing tendency in D was found dominating across the YRD, and de- creasing magnitude in Wuchengxiyu and Hangjiahu peaks for 7.8% and 6.5%, respectively in the YRD. （2） Urbanization affected the spatial pattern of river system, and areas with high level of urbanization exhibited least Dd （2.18 km/km2）, WSR （6.52%）, K （2.64） and D （1.42）, compared to moderate and low levels of urbanization. （3） Urbanization also affected the evo- lution of stream system. In the past 50 years, areas with high level of urbanization showed compelling decreasing tendency in quantitative （27.2% and 19.3%） and complex indices （4.9%） and trend of enlarging of main rivers （4.5% and 7.9% in periods of the 1960s-1980s and the 1980s-2010s）. In the recent 30 years, areas with low level of urbanization were detected with significant downward trend in Dd and K. （4） Expanding of urban land, construction of hydraulic engineering and irrigation and water conservancy activities were the main means which degraded the river system in the YRD.展开更多
With both sides of the Taklimakan Desert highway line as the study area, three typical aeolian sand landforms, i.e. complex dune ridge, barchan dune and flat sand land, were selected as sand beds for the observation, ...With both sides of the Taklimakan Desert highway line as the study area, three typical aeolian sand landforms, i.e. complex dune ridge, barchan dune and flat sand land, were selected as sand beds for the observation, analysis and research of the characteristics of aeolian sand movement such as aeolian sand stream structure, sand transport intensity, etc. in the Taklimakan Desert. The results show that there is a linear relation between the height and the log of sand transport rate over transverse dune chain, longitudinal dune ridge and flat sand land, i.e. the sand transport percentage decreases exponentially with increasing height. Sand transport rate within the 10 cm height above the bed surface accounts for 80%-95% of the total sand transport rate of the observed height (40 cm), while the sand transport rate in 20 cm occupies 98% of the total amount. Sand transport rate (g·cm-1·min-1) differs greatly with respect to different landform types and different topographic positions. Based on the investigation and analysis on aeolian sand landform origin, morphological type and distribution feature, the two typical landform assemblages, complex transverse dune chain-alluvial plain and huge longitudinal dune ridge-interridge lowland in the Taklimakan Desert were divided into several characteristic zones of aeolian sand movement states. From this one can qualitatively judge the types and severities of sand disasters at various topographic positions in the engineering installation region and further put forward concrete schemes and measures to control sand damages.展开更多
基金National Natural Science Foundation of China,No.41371046The Commonwealth and Specialized Program for Scientific Research,Ministry of Water Resources of China,No.201201072,No.201301075Natural Science Foundation of Jiangsu Province,No.BK20131278
文摘Evolution of river systems under the background of human activities has been a heated topic among geographers and hydrologists. Spatial and temporal variations of river systems during the 1960s-2010s in the Yangtze River Delta （YRD） were investigated based on streams derived from the topographic maps in the 1960s, 1980s and 2010s. A list of indi- ces, drainage density （Dd）, water surface ratio （WSR）, ratio of area to length of main streams （R）, evolution coefficient of tributaries （K） and box dimension （D）, were classified into three types （quantitative, structural, and complex indices） and used to quantify the variations of stream structure. Results showed that： （1） quantitative indices （Dd, WSR） presented de- creasing trend in the past 50 years, and Dd in Wuchengxiyu, Hangjiahu and Yindongnan have decreased most, about 20%. Structurally, the Qinhuai River basin was characterized by sig- nificant upward R, and K value in Hangjiahu went down dramatically by 46.8% during the 1960s-2010s. Decreasing tendency in D was found dominating across the YRD, and de- creasing magnitude in Wuchengxiyu and Hangjiahu peaks for 7.8% and 6.5%, respectively in the YRD. （2） Urbanization affected the spatial pattern of river system, and areas with high level of urbanization exhibited least Dd （2.18 km/km2）, WSR （6.52%）, K （2.64） and D （1.42）, compared to moderate and low levels of urbanization. （3） Urbanization also affected the evo- lution of stream system. In the past 50 years, areas with high level of urbanization showed compelling decreasing tendency in quantitative （27.2% and 19.3%） and complex indices （4.9%） and trend of enlarging of main rivers （4.5% and 7.9% in periods of the 1960s-1980s and the 1980s-2010s）. In the recent 30 years, areas with low level of urbanization were detected with significant downward trend in Dd and K. （4） Expanding of urban land, construction of hydraulic engineering and irrigation and water conservancy activities were the main means which degraded the river system in the YRD.
文摘With both sides of the Taklimakan Desert highway line as the study area, three typical aeolian sand landforms, i.e. complex dune ridge, barchan dune and flat sand land, were selected as sand beds for the observation, analysis and research of the characteristics of aeolian sand movement such as aeolian sand stream structure, sand transport intensity, etc. in the Taklimakan Desert. The results show that there is a linear relation between the height and the log of sand transport rate over transverse dune chain, longitudinal dune ridge and flat sand land, i.e. the sand transport percentage decreases exponentially with increasing height. Sand transport rate within the 10 cm height above the bed surface accounts for 80%-95% of the total sand transport rate of the observed height (40 cm), while the sand transport rate in 20 cm occupies 98% of the total amount. Sand transport rate (g·cm-1·min-1) differs greatly with respect to different landform types and different topographic positions. Based on the investigation and analysis on aeolian sand landform origin, morphological type and distribution feature, the two typical landform assemblages, complex transverse dune chain-alluvial plain and huge longitudinal dune ridge-interridge lowland in the Taklimakan Desert were divided into several characteristic zones of aeolian sand movement states. From this one can qualitatively judge the types and severities of sand disasters at various topographic positions in the engineering installation region and further put forward concrete schemes and measures to control sand damages.
