1 Introduction Morphological analysis on the planform migration structure of meandering river is an important basis for the reconstruction of evolution of paleochannel.Besides,it is a significant method for restoratio...1 Introduction Morphological analysis on the planform migration structure of meandering river is an important basis for the reconstruction of evolution of paleochannel.Besides,it is a significant method for restoration of rivers through the展开更多
River ice is a natural phenomenon in cold regions, influenced by meteorology, geomorphology, and hydraulic conditions. River ice processes involve complex interactions between hydrodynamic, mechanical, and thermal pro...River ice is a natural phenomenon in cold regions, influenced by meteorology, geomorphology, and hydraulic conditions. River ice processes involve complex interactions between hydrodynamic, mechanical, and thermal processes, and they are also influenced by weather and hydrologic conditions. Because natural rivers are serpentine, with bends, narrows, and straight reaches, the commonly-used one-dimensional river ice models and two-dimensional models based on the rectangular Cartesian coordinates are incapable of simulating the physical phenomena accurately. In order to accurately simulate the complicated river geometry and overcome the difficulties of numerical simulation resulting from both complex boundaries and differences between length and width scales, a two-dimensional river ice numerical model based on a boundary-fitted coordinate transformation method was developed. The presented model considers the influence of the frazil ice accumulation under ice cover and the shape of the leading edge of ice cover during the freezing process. The model is capable of determining the velocity field, the distribution of water temperature, the concentration distribution of frazil ice, the transport of floating ice, the progression, stability, and thawing of ice cover, and the transport, accumulation, and erosion of ice under ice cover. A MacCormack scheme was used to solve the equations numerically. The model was validated with field observations from the Hequ Reach of the Yellow River. Comparison of simulation results with field data indicates that the model is capable of simulating the river ice process with high accuracy.展开更多
Many debris flows have occurred in the areas surrounding the epicenter of the Wenchuan earthquake. Susceptibility assessment of debris flows in this area is especially important for disaster prevention and mitigation....Many debris flows have occurred in the areas surrounding the epicenter of the Wenchuan earthquake. Susceptibility assessment of debris flows in this area is especially important for disaster prevention and mitigation. This paper studies one of the worst hit areas, the Subao river valley, and the susceptibility assessment of debris flows is performed based on field surveys and remote sensing interpretation. By investigating the formation conditions of debris flows in the valley, the following assessment factors are selected： mixture density of landslides and rock avalanches, distance to the seismogenic fault, stratum lithology, ground roughness, and hillside angle. The weights of the assessment factors are determined by the analytic hierarchy process （AHP） method. Each of the assessment factors is further divided into five grades. Then, the assessment model is built using the multifactor superposition method to assess the debris flow susceptibility. Based on the assessment results, the Subao river valley is divided into three areas： high susceptibility areas, medium susceptibility areas, and low susceptibility areas. The high susceptibility areas are concentrated in the middle of the valley, accounting for 17.6%of the valley area. The medium susceptibility areas are in the middle and lower reaches, most of which are located on both sides of the high susceptibility areas and account for 45.3% of the valley area. The remainders are clas-sified as low susceptibility areas. The results of the model are in accordance with the actual debris flow events that occurred after the earthquake in the valley, confirming that the proposed model is capable of assessing the debris flow susceptibility. The results can also provide guidance for reconstruction planning and debris flow prevention in the Subao river valley.展开更多
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 an...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 rainfall ISO and the heavy precipitation process over LYRV were also discussed.It is found that the rainfall over LYRV in May―August is mainly of periodic oscillations of 10―20,20―30 and 60―70 days,and the interannual variation of the intensity of its 20―30-day oscillation has a strongly positive correlation with the number of the heavy precipitation process.Two modes(POP1,POP2)are revealed by POP for the 20―30-day oscillation of the global 850 hPa geopotential height.One is a circumglobal telecon-nection wave train in the middle latitude of the Southern Hemisphere(SCGT)with an eastward propagation,and the other is the southward propagation pattern in the tropical western Pacific(TWP).The POP modes explain 7.72%and 7.66%of the variance,respectively.These two principal ISO patterns are closely linked to the low frequency rainfall and heavy precipitation process over LYRV,in which the probability for the heavy precipitation process over LYRV is 54.9%and 60.4%for the positive phase of the imaginary part of POP1 and real part of POP2,respectively.Furthermore,the models of the global atmospheric circulation for the 20―30-day oscillation in association with or without the heavy pre-cipitation process over LYRV during the Northern Hemisphere summer are set up by means of the composite analysis method.Most of the heavy precipitation processes over LYRV appear in Phase 4 of SCGT or Phase 6 of TWP.When the positive phases of 20―30-day oscillations for the rainfall over LYRV are associated with(without)the heavy precipitation process,a strong westerly stream appears(disappears)from the Arabian Sea via India and Bay of Bengal(BOB)to southern China and LYRV for the global 850 hPa filtered wind field during Phase 4 of SCGT.This situation is favorable(unfavorable)for the forming of the heavy precipitation process over LYRV.Similarly,a strong(weak)western wind belt forms from India through BOB to southern China and LYRV and the subtropical northwestern Pacific and central and eastern equatorial Pacific during Phase 6 of TWP for the cases with(without)the heavy precipitation process.The evolutions of these ISO patterns related to the 20―30-day oscillation are excited by either the interaction of extratropical circulation in both hemispheres or the heat source forcing in Asia monsoon domain and internal interaction of circulation in East Asia.These two global circulation models might therefore provide valuable information for the extended-range forecast of the heavy precipitation process over LYRV during the 10―30 days.展开更多
基金supported by National Natural Sciences Fund (No. 41372125)Fund of Ministry of Education of Hubei Province (No. Q20121210)
文摘1 Introduction Morphological analysis on the planform migration structure of meandering river is an important basis for the reconstruction of evolution of paleochannel.Besides,it is a significant method for restoration of rivers through the
基金supported by the National Natural Science Foundation of China(Grant No.50579030)
文摘River ice is a natural phenomenon in cold regions, influenced by meteorology, geomorphology, and hydraulic conditions. River ice processes involve complex interactions between hydrodynamic, mechanical, and thermal processes, and they are also influenced by weather and hydrologic conditions. Because natural rivers are serpentine, with bends, narrows, and straight reaches, the commonly-used one-dimensional river ice models and two-dimensional models based on the rectangular Cartesian coordinates are incapable of simulating the physical phenomena accurately. In order to accurately simulate the complicated river geometry and overcome the difficulties of numerical simulation resulting from both complex boundaries and differences between length and width scales, a two-dimensional river ice numerical model based on a boundary-fitted coordinate transformation method was developed. The presented model considers the influence of the frazil ice accumulation under ice cover and the shape of the leading edge of ice cover during the freezing process. The model is capable of determining the velocity field, the distribution of water temperature, the concentration distribution of frazil ice, the transport of floating ice, the progression, stability, and thawing of ice cover, and the transport, accumulation, and erosion of ice under ice cover. A MacCormack scheme was used to solve the equations numerically. The model was validated with field observations from the Hequ Reach of the Yellow River. Comparison of simulation results with field data indicates that the model is capable of simulating the river ice process with high accuracy.
基金supported by the National Natural Science Foundation of China (Grant No. 41372301)the National Science and Technology Support Program (Grant No. 2012BAC06B02)
文摘Many debris flows have occurred in the areas surrounding the epicenter of the Wenchuan earthquake. Susceptibility assessment of debris flows in this area is especially important for disaster prevention and mitigation. This paper studies one of the worst hit areas, the Subao river valley, and the susceptibility assessment of debris flows is performed based on field surveys and remote sensing interpretation. By investigating the formation conditions of debris flows in the valley, the following assessment factors are selected： mixture density of landslides and rock avalanches, distance to the seismogenic fault, stratum lithology, ground roughness, and hillside angle. The weights of the assessment factors are determined by the analytic hierarchy process （AHP） method. Each of the assessment factors is further divided into five grades. Then, the assessment model is built using the multifactor superposition method to assess the debris flow susceptibility. Based on the assessment results, the Subao river valley is divided into three areas： high susceptibility areas, medium susceptibility areas, and low susceptibility areas. The high susceptibility areas are concentrated in the middle of the valley, accounting for 17.6%of the valley area. The medium susceptibility areas are in the middle and lower reaches, most of which are located on both sides of the high susceptibility areas and account for 45.3% of the valley area. The remainders are clas-sified as low susceptibility areas. The results of the model are in accordance with the actual debris flow events that occurred after the earthquake in the valley, confirming that the proposed model is capable of assessing the debris flow susceptibility. The results can also provide guidance for reconstruction planning and debris flow prevention in the Subao river valley.
基金Supported by the Program for the Fundamental Research of China Meteorological Administration(Grant No.200726)
文摘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 rainfall ISO and the heavy precipitation process over LYRV were also discussed.It is found that the rainfall over LYRV in May―August is mainly of periodic oscillations of 10―20,20―30 and 60―70 days,and the interannual variation of the intensity of its 20―30-day oscillation has a strongly positive correlation with the number of the heavy precipitation process.Two modes(POP1,POP2)are revealed by POP for the 20―30-day oscillation of the global 850 hPa geopotential height.One is a circumglobal telecon-nection wave train in the middle latitude of the Southern Hemisphere(SCGT)with an eastward propagation,and the other is the southward propagation pattern in the tropical western Pacific(TWP).The POP modes explain 7.72%and 7.66%of the variance,respectively.These two principal ISO patterns are closely linked to the low frequency rainfall and heavy precipitation process over LYRV,in which the probability for the heavy precipitation process over LYRV is 54.9%and 60.4%for the positive phase of the imaginary part of POP1 and real part of POP2,respectively.Furthermore,the models of the global atmospheric circulation for the 20―30-day oscillation in association with or without the heavy pre-cipitation process over LYRV during the Northern Hemisphere summer are set up by means of the composite analysis method.Most of the heavy precipitation processes over LYRV appear in Phase 4 of SCGT or Phase 6 of TWP.When the positive phases of 20―30-day oscillations for the rainfall over LYRV are associated with(without)the heavy precipitation process,a strong westerly stream appears(disappears)from the Arabian Sea via India and Bay of Bengal(BOB)to southern China and LYRV for the global 850 hPa filtered wind field during Phase 4 of SCGT.This situation is favorable(unfavorable)for the forming of the heavy precipitation process over LYRV.Similarly,a strong(weak)western wind belt forms from India through BOB to southern China and LYRV and the subtropical northwestern Pacific and central and eastern equatorial Pacific during Phase 6 of TWP for the cases with(without)the heavy precipitation process.The evolutions of these ISO patterns related to the 20―30-day oscillation are excited by either the interaction of extratropical circulation in both hemispheres or the heat source forcing in Asia monsoon domain and internal interaction of circulation in East Asia.These two global circulation models might therefore provide valuable information for the extended-range forecast of the heavy precipitation process over LYRV during the 10―30 days.
