Based on the long-term precipitation series with annual time resolution in the middle and lower reaches of the Yellow River and its four sub-regions during 1736-2000 reconstructed from the rainfall and snowfall archiv...Based on the long-term precipitation series with annual time resolution in the middle and lower reaches of the Yellow River and its four sub-regions during 1736-2000 reconstructed from the rainfall and snowfall archives of the Qing Dynasty, the precipitation cycles are analyzed by wavelet analysis and the possible climate forcings, which drive the precipitation changes, are explored. The results show that: the precipitation in the middle and lower reaches of the Yellow River has inter-annual and inter-decadal oscillations like 2-4a, quasi-22a and 70-80a. The 2-4a cycle is linked with El Nino events, and the precipitation is lower than normal year in the occurrence of the El Nino year or the next year; for the quasi-22a and the 70-80a cycles, Wolf Sun Spot Numbers and Pacific Decadal Oscillation (PDO) coincide with the two cycle signals. However, on a 70-80a time scale, the coincidence between solar activity and precipitation is identified before 1830, and strong (weak) solar activity is generally correlated to the dry (wet) periods; after 1830, the solar activity changes to 80-100a quasi-century long oscillation, and the adjusting action to the precipitation is becoming weaker and weaker; the coincidence between PDO and precipitation is shown in the whole time series. Moreover, in recent 100 years, PDO is becoming a pace-maker of the precipitation on the 70-80a time scale.展开更多
[ Objective] The research aimed to study community structure of the phytoplankton and its relationship with environmental factor in lower reaches of the Yellow River. [ Method] From April to June in 2011, phytoplankto...[ Objective] The research aimed to study community structure of the phytoplankton and its relationship with environmental factor in lower reaches of the Yellow River. [ Method] From April to June in 2011, phytoplankton was conducted qualitative and quantitative researches in Lijin in lower reaches of the Yellow River. By combining population characteristics of the phytoplankton, its'relationship with environmental factor was dis- cussed. [ Result] 114 species and 5 phylum of phytoplankton were observed in the whole river section. The abundance of phytoplankton was 0.90 ×104 -303.35×104 ind/m3, and mean was 27.20 ×104 ind/m3. The biomass of phytoplankton was 0.008-5.890 mg/m3, and mean was 0.641 mg/m3. Shannon-Weaver diversity index, Pielou evenness index and Simpson's diversity index were respectively 1.59, 0.36 and 0.55. SPSS data analysis indicated that transparency was the uppermost environmental factor affected phytoplankton abundance. Phytoplankton abundance had posi- tive correlation with transparency, and the regression equation was y= -393.8 +115.5×-11 .lx2 +0.35x3(n=18, R2 =0.952, F=92.665, P〈0.01 ). [ Conclusion] The community structure of phytoplankton was unstable, and transparency was the uppermost environmental factor affected phyto- plankton abundance in lower reaches of the Yellow River.展开更多
It is very important to study the archaeological culture and origin of civilization in ancient China.The changes of the channels in the lower reaches of the Yellow River in the prehistoric period are part of the natur...It is very important to study the archaeological culture and origin of civilization in ancient China.The changes of the channels in the lower reaches of the Yellow River in the prehistoric period are part of the natural environmental background of the development of the ancient civilization in that area to be explored.This paper presents a series of legends,indications,scientific evidence,and macroscopic geographical background information of the evolution in the lower reaches of the Yellow River during the Longshan period.At first the river flowed from Northern Henan and Hebei to southwestern Shandong Province and Northern Anhui–Jiangsu provinces,and the mainstream of the Yellow River changed from the southeast to return to the north and flowed into the Bohai Sea in the late Longshan Period.During this period,floods were frequent.Various ethnic groups in the northern China plains suffered natural disasters and made great migrations which also contributed to the ethnic exchanges and integration.The people of the Central Plains made more dynamic adjustments in the relationship between mankind and the land by primitively escaping from the water and self–defensively controlling the rivers then to maintaining the local ecological environment by large–scale flood control measures,which promoted the settlement of Shandong,Henan,Jiangsu and Anhui provinces,the urban cultural development,and social evolution.Based on these events,the culture symbol of Dayu's Flood Control could be formed.展开更多
Using a neutron activation analysis technique, which involves gamma-spectrometry with a Ge(Li) detector coupled to a S40 multichannel analyzer and interfaced to a PDP-11 computer, we determined thirty-eight elements i...Using a neutron activation analysis technique, which involves gamma-spectrometry with a Ge(Li) detector coupled to a S40 multichannel analyzer and interfaced to a PDP-11 computer, we determined thirty-eight elements in sediments from the lower reach (downstream from Jinan) and estuary of Huanghe. The results are discussed in this paper.From inter-elemental correlations, it ts found that a large number of metals (Mn.As, Co, Cr.Cs, Rb, Sc, Ti, Ta, V and Zn) correlate positively with Fe. Ba and Ca correlate positively with Al. Whereas some elements (e. g. , Ti and lanthanides) show no correlation with either Fe or Al. On the other hand, Hf and Zr show a negative correlation with Fe. Elements which tend to be scavenged by Fe and Al colloids or suspended particles are enriched in sediments at the Huanghe Estuary relative to its lower reach. On the other hand, the contents of some elements (e. g. , Zr,Hf,U, Ba, etc. )are higher in sediments from the lower reach of Huanghe than in the estuarine sediments,which may be related to the sorting during deposition of source materials. On the basis of their chemical property and geochemical behavior, the 38 elements we studied are classified into seven groups. (1) weathering-prone elements,group A:K,Rb, Cs and Na; (2) weathering-prone elements, group B:Mg, Ca, Ba and Al; (3) transition elements:Fe, Co.Ni, Zn, As, Sb, Mn, Cr, W,Mo,V, Ta and Sc; (4) rare elements:group A (Zr and Hf) and group B (Ti); (5) rare earth elements:the lanthanides; (6) halogens: Cl and Br; amd (7) natural radioactive elements:U and Th. The basis for this classification is discussed and we emphasize that geochemical associations of elements in the natural environment are not necessarily in accord with their chemical properties as dictated by position at the periodic table.展开更多
Evolution of the river channel downstream of reservoirs is a complex process that is closely related to the operational mode of the reservoirs and the channel boundary conditions Numerous studies have been carried out...Evolution of the river channel downstream of reservoirs is a complex process that is closely related to the operational mode of the reservoirs and the channel boundary conditions Numerous studies have been carried out on the fluvial processes of downstream reservoirs. However, only a few of them have focused on the relationship between runoff-sediment con- ditions and channel pattern indicators. Also, the impacts of river training works on fluvial processes are seldom dealt with. In this paper, the evolutionary processes of three sections in the Lower Yellow River, including Tiexie-Yiluo River mouth reach, Huayuankou-Heigangkou reach and Jiahetan-Gaocun reach, were analyzed for variations in the channel boundary line and the mainstream between 1960 and 2015. Channel pattern indicators such as sinuosity, mainstream wandering range and width/depth ratio were analyzed based on field measure- ments obtained by the Hydrological Department of the Yellow River Conservancy Commis- sion. The effects of river training works on the channel evolution are then described. Since 1960, numerous medium- and large-sized reservoirs have been built on the Yellow River, including Longyangxia Reservoir, Liujiaxia Reservoir and Xiaolangdi Reservoir. These res- ervoirs impound the runoff from upstream and retain the sediment, which changes the runoff and sediment conditions in the downstream reach. As a consequence, annual runoff and the frequency and peak of flooding have all decreased. As a result, the flow dynamics and their action on the river channel are also reduced, which changes the dynamic state of the river course. The discrimination results obtained using the single parameter discrimination rule and the discrimination equation show that the degree of wandering is weakened in the reaches studied. The variations in the channel pattern indicators show that the sinuosity in- creases and the wandering range decreases with a reduction in the total annual volume of water. However, the degree of wandering has little relationship to the sediment concentration. In addition, river training works play an important role in controlling the river course. Due to improvements in the river training works, the river course has become more stable under the same runoff and sediment conditions. A new discrimination rule that takes into account the impacts of the river training works is proposed. The discrimination results were found to fit well with the actual river pattern, which shows that the discrimination rule is applicable to the Lower Yellow River. The results show that the runoff and sediment conditions are the most important factors in the evolution of the river course. The river training works have at the same time limited the wandering range of the mainstream and played an important role in the fluvial processes. Both factors combined lead to the stabilization of the river.展开更多
Yangshao culture is the most important mid-Holocene Neolithic culture in the Yellow River catchment, and thus, a study on the impact of human activities on the environment is important. In the current study, the distr...Yangshao culture is the most important mid-Holocene Neolithic culture in the Yellow River catchment, and thus, a study on the impact of human activities on the environment is important. In the current study, the distribution pattern of the cultivated land in late Yangshao culture is reconstructed using GIS tool and site domain analysis (SDA). The results show that the cultivated land during 5.5-5.0 ka BP was mainly distributed in the Weihe River valley, Luohe River valley, northwestern Henan Plain, Fenhe River valley and eastern Gansu region, especially concentrated in the Xi'an-Baoji line of the Weihe River valley. At that time, at least 37,000 km2 of lands were reclaimed in the middle and lower reaches of the Yellow River, and 132,000 km2 of lands were affected by agricultural activities. Human activities had become the driving force of land use/land coverage. Charcoal records indicate that the ancestors of Yangshao culture burnt forests for reclamation, leading to the decrease of arbor pollen at 5 ka BP in core areas of the Yangshao culture. The areas that were significantly affected by human activities accounted for 3.2% of the Yangshao culture influenced area, while the moderately affected areas accounted for 20.1% of Yangshao culture influenced area. Meanwhile, 92% of the land areas on the edge and outside of the Yangshao culture influenced area were not affected by human activities. The arbor pollen in these areas did not decrease until 4.0 ka BP.展开更多
This paper presents the studies on groundwater resources potential of the Yellow River (YR) terrace in Zhengzhou area, China. The main aim of the research was to resolve water shortage problems induced by recent but f...This paper presents the studies on groundwater resources potential of the Yellow River (YR) terrace in Zhengzhou area, China. The main aim of the research was to resolve water shortage problems induced by recent but frequent drying ups of the YR in its lower reaches. Geologic explorations and grouped-pumping tests were conducted in the area. Based on collected data a groundwater flow net was established. The buried depth of groundwater level and water bearing potential of the aquifers were evaluated. Conventional method was used to determine recharge of the groundwater by lateral infiltration of the YR in pumping patterns. The results show that the study region has a high water bearing potential and offers conditions for the construction of large water works. However, only limited recharge by lateral infiltration from the river is available when developing large scale groundwater exploitation in the riverside of the YR. Environmental impacts induced by embankment stability of the Great dyke of the YR could be minimized or eliminated by appropriate engineering methods.展开更多
The precipitation at 17 stations over the middle and lower reaches of the Yellow River is reconstructed during the period of 1736―1910, using the snow and rainfall records in the Qing Dynasty, together with the instr...The precipitation at 17 stations over the middle and lower reaches of the Yellow River is reconstructed during the period of 1736―1910, using the snow and rainfall records in the Qing Dynasty, together with the instrumental observation data of precipitation and farmland soil moisture content. The soil physics model related to rainfall infiltration and the surface water bal-ance equation are taken as main reconstruction methodology. The field infiltration experiment by artificial rainfall is conducted to check the reliability. And the precipitation series over the middle and lower reaches of the Yellow River and its 4 sub-regions are established, going back to 1736. Analysis of the time series indicates that the abrupt change of precipitation from high to low oc-curs around 1915 over the middle and lower reaches of the Yellow River. During the three peri-ods of 1791―1805, 1816―1830 and 1886―1895, the precipitation is markedly higher than the mean of the series. While both the periods of 1916―1945 and 1981―2000 are characterized by less precipitation. Three periodicities of 22―25a, 3.9a and 2.7a are shown in the precipitation fluctuation over the middle and lower reaches of the Yellow River. Moreover, the periodical signal of 22―25a becomes weaker and weaker since the abrupt change of 1915 and disappears in the late 1940s, and then the periodical signal of 35―40a appears instead.展开更多
The channel adjustment in a braided reach is very prominent in the fluvial processes of the Lower Yel-low River, in which the process of bank erosion plays an important role, especially during the period of clear wate...The channel adjustment in a braided reach is very prominent in the fluvial processes of the Lower Yel-low River, in which the process of bank erosion plays an important role, especially during the period of clear water scouring. The process of bank erosion is closely related to soil composition and mechani-cal properties of the riverbanks. In this paper, the recent bank erosion process in a braided reach be-tween Huayuankou and Gaocun was firstly investigated after the water impoundment and sediment detention of the Xiaolangdi Reservoir, and then a field observation and indoor soil tests were con-ducted at 10 typical riverbanks in the braided reach. Through analyzing the experimental results, changes of riverbank-soil composition and mechanical properties were found, and the two real reasons causing serious bank erosion in the braided reach were identified. The following conclusions were drawn from this study: (i) the majority of riverbanks are made up of cohesive soil, and can be charac-terized by obvious vertical stratification structures of soil composition; (ii) these riverbanks are very erodible due to the lower clay-content and weak erosion-resistant strength in the bank soil, with its critical shear stress value (0.1―0.3 Pa) being much less than that of the average near-bank flow shear stress (2.0―3.0 Pa), which is one important reason causing serious bank erosion; (iii) frequent occur-rence of bank failure during flood seasons usually results from the fact that the values of shear strength parameters such as the cohesion and internal friction angle decrease with the increase of water content in riverbank soil, and the value of cohesion reduces drastically from 34 to 4 kPa with the increase of water content, which is another important reason causing serious bank erosion in the braided reach.展开更多
It is of necessity to investigate the adjustment of flood discharge capacity in the Lower Yellow River(LYR)because of its profound importance in sediment transport and flood control decision-making,and additionally it...It is of necessity to investigate the adjustment of flood discharge capacity in the Lower Yellow River(LYR)because of its profound importance in sediment transport and flood control decision-making,and additionally its magnitude is influenced by the channel and upstream boundary conditions,which have significantly varied with the ongoing implementation of soil and water conservation measures in the Loess Plateau and the operation of the Xiaolangdi Reservoir.The braided reach between two hydrometric stations of Huayuankou and Gaocun in the LYR was selected as the study area.Different parameters in the study reach during the period 1986-2015 were calculated,covering bankfull discharge(the indicator of flood discharge capacity),the pre-flood geomorphic coefficient(the indicator of channel boundary condition),and the previous five-year average fluvial erosion intensity during flood seasons(the indicator of incoming flow and sediment regime).Functional linkages at scales of section and reach were then developed respectively to quantitatively demonstrate the integrated effects of channel and upstream boundary conditions on the flood discharge capacity.Results show that:(1)the reach-scale bankfull discharge in the pre-dam stage(1986-1999)decreased rapidly by 50%,accompanied with severe channel aggradation and main-channel shrinkage.It recovered gradually as the geometry of main channel became narrower and deeper in the post-dam stage,with the geomorphic coefficient continuously reducing to less than 15 m-12.(2)The response of bankfull discharge to the channel and upstream boundary conditions varied at scales of section and reach,and consequently the determination coefficients differed for the comprehensive equations,with a smallest value at the Jiahetan station and a highest value(0.91)at reach scale.Generally,the verified results calculated using the comprehensive equations agreed well with the corresponding measured values in 2014-2015.(3)The effect of channel boundary condition was more prominent than that of upstream boundary condition on the adjustment of bankfull discharge at the Jiahetan station and the braided reach,which was proved by a larger improvement in determination coefficients for the comprehensive equations and a better performance of geomorphic coefficient on the increase of bankfull discharge.展开更多
基金National Natural Science Foundation of China, No. 40331013 No.90502009 No. 40571007, No. 40701021
文摘Based on the long-term precipitation series with annual time resolution in the middle and lower reaches of the Yellow River and its four sub-regions during 1736-2000 reconstructed from the rainfall and snowfall archives of the Qing Dynasty, the precipitation cycles are analyzed by wavelet analysis and the possible climate forcings, which drive the precipitation changes, are explored. The results show that: the precipitation in the middle and lower reaches of the Yellow River has inter-annual and inter-decadal oscillations like 2-4a, quasi-22a and 70-80a. The 2-4a cycle is linked with El Nino events, and the precipitation is lower than normal year in the occurrence of the El Nino year or the next year; for the quasi-22a and the 70-80a cycles, Wolf Sun Spot Numbers and Pacific Decadal Oscillation (PDO) coincide with the two cycle signals. However, on a 70-80a time scale, the coincidence between solar activity and precipitation is identified before 1830, and strong (weak) solar activity is generally correlated to the dry (wet) periods; after 1830, the solar activity changes to 80-100a quasi-century long oscillation, and the adjusting action to the precipitation is becoming weaker and weaker; the coincidence between PDO and precipitation is shown in the whole time series. Moreover, in recent 100 years, PDO is becoming a pace-maker of the precipitation on the 70-80a time scale.
基金Supported by Science Research Special Item of the Public Welfare Industry,Ministry of Water Resources(200901020)
文摘[ Objective] The research aimed to study community structure of the phytoplankton and its relationship with environmental factor in lower reaches of the Yellow River. [ Method] From April to June in 2011, phytoplankton was conducted qualitative and quantitative researches in Lijin in lower reaches of the Yellow River. By combining population characteristics of the phytoplankton, its'relationship with environmental factor was dis- cussed. [ Result] 114 species and 5 phylum of phytoplankton were observed in the whole river section. The abundance of phytoplankton was 0.90 ×104 -303.35×104 ind/m3, and mean was 27.20 ×104 ind/m3. The biomass of phytoplankton was 0.008-5.890 mg/m3, and mean was 0.641 mg/m3. Shannon-Weaver diversity index, Pielou evenness index and Simpson's diversity index were respectively 1.59, 0.36 and 0.55. SPSS data analysis indicated that transparency was the uppermost environmental factor affected phytoplankton abundance. Phytoplankton abundance had posi- tive correlation with transparency, and the regression equation was y= -393.8 +115.5×-11 .lx2 +0.35x3(n=18, R2 =0.952, F=92.665, P〈0.01 ). [ Conclusion] The community structure of phytoplankton was unstable, and transparency was the uppermost environmental factor affected phyto- plankton abundance in lower reaches of the Yellow River.
文摘It is very important to study the archaeological culture and origin of civilization in ancient China.The changes of the channels in the lower reaches of the Yellow River in the prehistoric period are part of the natural environmental background of the development of the ancient civilization in that area to be explored.This paper presents a series of legends,indications,scientific evidence,and macroscopic geographical background information of the evolution in the lower reaches of the Yellow River during the Longshan period.At first the river flowed from Northern Henan and Hebei to southwestern Shandong Province and Northern Anhui–Jiangsu provinces,and the mainstream of the Yellow River changed from the southeast to return to the north and flowed into the Bohai Sea in the late Longshan Period.During this period,floods were frequent.Various ethnic groups in the northern China plains suffered natural disasters and made great migrations which also contributed to the ethnic exchanges and integration.The people of the Central Plains made more dynamic adjustments in the relationship between mankind and the land by primitively escaping from the water and self–defensively controlling the rivers then to maintaining the local ecological environment by large–scale flood control measures,which promoted the settlement of Shandong,Henan,Jiangsu and Anhui provinces,the urban cultural development,and social evolution.Based on these events,the culture symbol of Dayu's Flood Control could be formed.
文摘Using a neutron activation analysis technique, which involves gamma-spectrometry with a Ge(Li) detector coupled to a S40 multichannel analyzer and interfaced to a PDP-11 computer, we determined thirty-eight elements in sediments from the lower reach (downstream from Jinan) and estuary of Huanghe. The results are discussed in this paper.From inter-elemental correlations, it ts found that a large number of metals (Mn.As, Co, Cr.Cs, Rb, Sc, Ti, Ta, V and Zn) correlate positively with Fe. Ba and Ca correlate positively with Al. Whereas some elements (e. g. , Ti and lanthanides) show no correlation with either Fe or Al. On the other hand, Hf and Zr show a negative correlation with Fe. Elements which tend to be scavenged by Fe and Al colloids or suspended particles are enriched in sediments at the Huanghe Estuary relative to its lower reach. On the other hand, the contents of some elements (e. g. , Zr,Hf,U, Ba, etc. )are higher in sediments from the lower reach of Huanghe than in the estuarine sediments,which may be related to the sorting during deposition of source materials. On the basis of their chemical property and geochemical behavior, the 38 elements we studied are classified into seven groups. (1) weathering-prone elements,group A:K,Rb, Cs and Na; (2) weathering-prone elements, group B:Mg, Ca, Ba and Al; (3) transition elements:Fe, Co.Ni, Zn, As, Sb, Mn, Cr, W,Mo,V, Ta and Sc; (4) rare elements:group A (Zr and Hf) and group B (Ti); (5) rare earth elements:the lanthanides; (6) halogens: Cl and Br; amd (7) natural radioactive elements:U and Th. The basis for this classification is discussed and we emphasize that geochemical associations of elements in the natural environment are not necessarily in accord with their chemical properties as dictated by position at the periodic table.
文摘Evolution of the river channel downstream of reservoirs is a complex process that is closely related to the operational mode of the reservoirs and the channel boundary conditions Numerous studies have been carried out on the fluvial processes of downstream reservoirs. However, only a few of them have focused on the relationship between runoff-sediment con- ditions and channel pattern indicators. Also, the impacts of river training works on fluvial processes are seldom dealt with. In this paper, the evolutionary processes of three sections in the Lower Yellow River, including Tiexie-Yiluo River mouth reach, Huayuankou-Heigangkou reach and Jiahetan-Gaocun reach, were analyzed for variations in the channel boundary line and the mainstream between 1960 and 2015. Channel pattern indicators such as sinuosity, mainstream wandering range and width/depth ratio were analyzed based on field measure- ments obtained by the Hydrological Department of the Yellow River Conservancy Commis- sion. The effects of river training works on the channel evolution are then described. Since 1960, numerous medium- and large-sized reservoirs have been built on the Yellow River, including Longyangxia Reservoir, Liujiaxia Reservoir and Xiaolangdi Reservoir. These res- ervoirs impound the runoff from upstream and retain the sediment, which changes the runoff and sediment conditions in the downstream reach. As a consequence, annual runoff and the frequency and peak of flooding have all decreased. As a result, the flow dynamics and their action on the river channel are also reduced, which changes the dynamic state of the river course. The discrimination results obtained using the single parameter discrimination rule and the discrimination equation show that the degree of wandering is weakened in the reaches studied. The variations in the channel pattern indicators show that the sinuosity in- creases and the wandering range decreases with a reduction in the total annual volume of water. However, the degree of wandering has little relationship to the sediment concentration. In addition, river training works play an important role in controlling the river course. Due to improvements in the river training works, the river course has become more stable under the same runoff and sediment conditions. A new discrimination rule that takes into account the impacts of the river training works is proposed. The discrimination results were found to fit well with the actual river pattern, which shows that the discrimination rule is applicable to the Lower Yellow River. The results show that the runoff and sediment conditions are the most important factors in the evolution of the river course. The river training works have at the same time limited the wandering range of the mainstream and played an important role in the fluvial processes. Both factors combined lead to the stabilization of the river.
基金National Natural Science Foundation of China, No.41161018 No.41121001+2 种基金 China Geological Survey, No. 1212011120046 Humanities and Social Sciences Youth Fund Project of Ministry c,f Education of China, No. 10YJCZH041 and The "Strategic Priority Research Program" of the CAS, No.XDA05120501.
文摘Yangshao culture is the most important mid-Holocene Neolithic culture in the Yellow River catchment, and thus, a study on the impact of human activities on the environment is important. In the current study, the distribution pattern of the cultivated land in late Yangshao culture is reconstructed using GIS tool and site domain analysis (SDA). The results show that the cultivated land during 5.5-5.0 ka BP was mainly distributed in the Weihe River valley, Luohe River valley, northwestern Henan Plain, Fenhe River valley and eastern Gansu region, especially concentrated in the Xi'an-Baoji line of the Weihe River valley. At that time, at least 37,000 km2 of lands were reclaimed in the middle and lower reaches of the Yellow River, and 132,000 km2 of lands were affected by agricultural activities. Human activities had become the driving force of land use/land coverage. Charcoal records indicate that the ancestors of Yangshao culture burnt forests for reclamation, leading to the decrease of arbor pollen at 5 ka BP in core areas of the Yangshao culture. The areas that were significantly affected by human activities accounted for 3.2% of the Yangshao culture influenced area, while the moderately affected areas accounted for 20.1% of Yangshao culture influenced area. Meanwhile, 92% of the land areas on the edge and outside of the Yangshao culture influenced area were not affected by human activities. The arbor pollen in these areas did not decrease until 4.0 ka BP.
文摘This paper presents the studies on groundwater resources potential of the Yellow River (YR) terrace in Zhengzhou area, China. The main aim of the research was to resolve water shortage problems induced by recent but frequent drying ups of the YR in its lower reaches. Geologic explorations and grouped-pumping tests were conducted in the area. Based on collected data a groundwater flow net was established. The buried depth of groundwater level and water bearing potential of the aquifers were evaluated. Conventional method was used to determine recharge of the groundwater by lateral infiltration of the YR in pumping patterns. The results show that the study region has a high water bearing potential and offers conditions for the construction of large water works. However, only limited recharge by lateral infiltration from the river is available when developing large scale groundwater exploitation in the riverside of the YR. Environmental impacts induced by embankment stability of the Great dyke of the YR could be minimized or eliminated by appropriate engineering methods.
基金This study was supported by the Key Project from the National Natural Science Foundation of China(Grant No.40331013)the project from the Chinese Academy of Sciences(Grant No.KZCX3-SW-321).
文摘The precipitation at 17 stations over the middle and lower reaches of the Yellow River is reconstructed during the period of 1736―1910, using the snow and rainfall records in the Qing Dynasty, together with the instrumental observation data of precipitation and farmland soil moisture content. The soil physics model related to rainfall infiltration and the surface water bal-ance equation are taken as main reconstruction methodology. The field infiltration experiment by artificial rainfall is conducted to check the reliability. And the precipitation series over the middle and lower reaches of the Yellow River and its 4 sub-regions are established, going back to 1736. Analysis of the time series indicates that the abrupt change of precipitation from high to low oc-curs around 1915 over the middle and lower reaches of the Yellow River. During the three peri-ods of 1791―1805, 1816―1830 and 1886―1895, the precipitation is markedly higher than the mean of the series. While both the periods of 1916―1945 and 1981―2000 are characterized by less precipitation. Three periodicities of 22―25a, 3.9a and 2.7a are shown in the precipitation fluctuation over the middle and lower reaches of the Yellow River. Moreover, the periodical signal of 22―25a becomes weaker and weaker since the abrupt change of 1915 and disappears in the late 1940s, and then the periodical signal of 35―40a appears instead.
基金the National Natural Science Foundation of China (Grant No. 50409002)the Ministry of Science and Technology of China under the frame of Program Strategic Scientific Alliances between China and the Netherlands (Grant No. 2004CB720402)the National Natural Science Foundation of China for Creative Research Groups (Grant No. 50221903)
文摘The channel adjustment in a braided reach is very prominent in the fluvial processes of the Lower Yel-low River, in which the process of bank erosion plays an important role, especially during the period of clear water scouring. The process of bank erosion is closely related to soil composition and mechani-cal properties of the riverbanks. In this paper, the recent bank erosion process in a braided reach be-tween Huayuankou and Gaocun was firstly investigated after the water impoundment and sediment detention of the Xiaolangdi Reservoir, and then a field observation and indoor soil tests were con-ducted at 10 typical riverbanks in the braided reach. Through analyzing the experimental results, changes of riverbank-soil composition and mechanical properties were found, and the two real reasons causing serious bank erosion in the braided reach were identified. The following conclusions were drawn from this study: (i) the majority of riverbanks are made up of cohesive soil, and can be charac-terized by obvious vertical stratification structures of soil composition; (ii) these riverbanks are very erodible due to the lower clay-content and weak erosion-resistant strength in the bank soil, with its critical shear stress value (0.1―0.3 Pa) being much less than that of the average near-bank flow shear stress (2.0―3.0 Pa), which is one important reason causing serious bank erosion; (iii) frequent occur-rence of bank failure during flood seasons usually results from the fact that the values of shear strength parameters such as the cohesion and internal friction angle decrease with the increase of water content in riverbank soil, and the value of cohesion reduces drastically from 34 to 4 kPa with the increase of water content, which is another important reason causing serious bank erosion in the braided reach.
基金National Natural Science Foundation of China,No.51725902,No.51579186。
文摘It is of necessity to investigate the adjustment of flood discharge capacity in the Lower Yellow River(LYR)because of its profound importance in sediment transport and flood control decision-making,and additionally its magnitude is influenced by the channel and upstream boundary conditions,which have significantly varied with the ongoing implementation of soil and water conservation measures in the Loess Plateau and the operation of the Xiaolangdi Reservoir.The braided reach between two hydrometric stations of Huayuankou and Gaocun in the LYR was selected as the study area.Different parameters in the study reach during the period 1986-2015 were calculated,covering bankfull discharge(the indicator of flood discharge capacity),the pre-flood geomorphic coefficient(the indicator of channel boundary condition),and the previous five-year average fluvial erosion intensity during flood seasons(the indicator of incoming flow and sediment regime).Functional linkages at scales of section and reach were then developed respectively to quantitatively demonstrate the integrated effects of channel and upstream boundary conditions on the flood discharge capacity.Results show that:(1)the reach-scale bankfull discharge in the pre-dam stage(1986-1999)decreased rapidly by 50%,accompanied with severe channel aggradation and main-channel shrinkage.It recovered gradually as the geometry of main channel became narrower and deeper in the post-dam stage,with the geomorphic coefficient continuously reducing to less than 15 m-12.(2)The response of bankfull discharge to the channel and upstream boundary conditions varied at scales of section and reach,and consequently the determination coefficients differed for the comprehensive equations,with a smallest value at the Jiahetan station and a highest value(0.91)at reach scale.Generally,the verified results calculated using the comprehensive equations agreed well with the corresponding measured values in 2014-2015.(3)The effect of channel boundary condition was more prominent than that of upstream boundary condition on the adjustment of bankfull discharge at the Jiahetan station and the braided reach,which was proved by a larger improvement in determination coefficients for the comprehensive equations and a better performance of geomorphic coefficient on the increase of bankfull discharge.