Volume 19,Issue 4,2021 Table of Contents
2021, 19(4):625-635.
Abstract:
The hardening of the urban underlying surface and its hydrological effects have aroused widespread concern in the international community.The communication channels between the water sources are hindered or even cut off by the impervious surface,changing the natural hydrological process.Exploring the impact mechanism of urban underlying surface changes on runoff processes is of critical significance to regional flood control and water safety construction. The central urban area of Jiujiang were focused on.The time variant gain model was improved to analyze the changes of underlying surface and the evolution trend of multi-year runoff.We aimed to quantify the response relationship between runoff process and impervious surface expansion was aimed to qualified,and support for understanding the hydrological effects of impervious surface expansion was provided in typical cities in the middle reaches of the Yangtze River. ENVI and ArcGIS software was employed to realize the interpretation and classification of remote sensing images,and the variation of land use dynamics was analyzed in the study area from 1987 to 2018.In view of the difference in runoff features of underlying surfaces based on the time variant gain model,an improvement on the structure of the original model was made by dividing underlying surfaces into permeable area and impervious area.The former included arable land,green land,and water bodies,while the latter referred to the impervious surfaces in construction land.The urban time variant gain model was established to calculate the runoff coefficient over the years and the runoff process of a typical year. From 1987 to 2018,the main features of underlying changes in the studying area are listed as follows:(1) The construction land expanded from 8.23 km2 to 189.93 km2,with the fastest expansion rate in the period from 2009 to 2012.(2) A fluctuation occurred in the change of arable land, woodland and grassland, which occupied a large percentage of the total area.Before 2012,the area of arable land increased from 601.42 km2 to 806.72 km2,and the proportion of woodland and grassland decreased to 145%.From 2012 to 2018,the area of arable land has declined while the proportion of woodland and grassland increased to 24.9%.(3) The water body has shown a shrinking trend since 2006,and decreased from 217.02 km2 to 168.28 km2 from 2015 to 2018. Model calculations based on rainfall data from meteorological stations shows some fluctuations in the increasing trend of the runoff coefficient under the circumstance of impervious area expansion year by year.From 1995 to 2000,the increase in the proportion of green space caused the runoff coefficient to decrease instead.This finding revealed that runoff generation process in the study area is influenced by the changes of various underlying surface types and meteorological conditions.Under the same meteorological conditions,a high consistency existed between the change characteristics of runoff and impervious surface ratio over the years.The runoff coefficient ascended from 0.31 to 0.38,and the runoff depth increased from 44487 mm to 557.76 mm,respectively.In a typical rainstorm event,the peak flow has increased from 1 504.64 m3/s to 1 649.77 m3/s from 1987 to 2018,while the flow curve dropped in some part of 2006 and 2015,which could be attributed to the increase of green land and water bodies that acted as rainwater saver in the early rainy period. Conclusions(1) The land use in the study area shows a transforming trend from pervious to impervious area.There′s a fluctuation in the area of arable land, woodland and grassland and a shrinking trend in the water body.Especially, the area of construction land has been increasing year by year. (2) The influence factors of runoff coefficient is a combination of the underlying surface changes and the rainfall process,while the impervious surface ratio is dominant in the study area. Under the same meteorological conditions,the proportion of impervious area is increased from 0.49% to 10.58%, and the runoff coefficient is ascended from 0.31 to 0.38 from 1987 to 2018 in the study area. (3) Under a typical rainstorm event, the peak flow is increased by 10%,the flood process line became steeper,and the recession process was significantly slowed down from 1987 to 2018.Green land and water bodies could alleviate the amplification effect of runoff brought about by the urbanization process to a certain extent.
The hardening of the urban underlying surface and its hydrological effects have aroused widespread concern in the international community.The communication channels between the water sources are hindered or even cut off by the impervious surface,changing the natural hydrological process.Exploring the impact mechanism of urban underlying surface changes on runoff processes is of critical significance to regional flood control and water safety construction. The central urban area of Jiujiang were focused on.The time variant gain model was improved to analyze the changes of underlying surface and the evolution trend of multi-year runoff.We aimed to quantify the response relationship between runoff process and impervious surface expansion was aimed to qualified,and support for understanding the hydrological effects of impervious surface expansion was provided in typical cities in the middle reaches of the Yangtze River. ENVI and ArcGIS software was employed to realize the interpretation and classification of remote sensing images,and the variation of land use dynamics was analyzed in the study area from 1987 to 2018.In view of the difference in runoff features of underlying surfaces based on the time variant gain model,an improvement on the structure of the original model was made by dividing underlying surfaces into permeable area and impervious area.The former included arable land,green land,and water bodies,while the latter referred to the impervious surfaces in construction land.The urban time variant gain model was established to calculate the runoff coefficient over the years and the runoff process of a typical year. From 1987 to 2018,the main features of underlying changes in the studying area are listed as follows:(1) The construction land expanded from 8.23 km2 to 189.93 km2,with the fastest expansion rate in the period from 2009 to 2012.(2) A fluctuation occurred in the change of arable land, woodland and grassland, which occupied a large percentage of the total area.Before 2012,the area of arable land increased from 601.42 km2 to 806.72 km2,and the proportion of woodland and grassland decreased to 145%.From 2012 to 2018,the area of arable land has declined while the proportion of woodland and grassland increased to 24.9%.(3) The water body has shown a shrinking trend since 2006,and decreased from 217.02 km2 to 168.28 km2 from 2015 to 2018. Model calculations based on rainfall data from meteorological stations shows some fluctuations in the increasing trend of the runoff coefficient under the circumstance of impervious area expansion year by year.From 1995 to 2000,the increase in the proportion of green space caused the runoff coefficient to decrease instead.This finding revealed that runoff generation process in the study area is influenced by the changes of various underlying surface types and meteorological conditions.Under the same meteorological conditions,a high consistency existed between the change characteristics of runoff and impervious surface ratio over the years.The runoff coefficient ascended from 0.31 to 0.38,and the runoff depth increased from 44487 mm to 557.76 mm,respectively.In a typical rainstorm event,the peak flow has increased from 1 504.64 m3/s to 1 649.77 m3/s from 1987 to 2018,while the flow curve dropped in some part of 2006 and 2015,which could be attributed to the increase of green land and water bodies that acted as rainwater saver in the early rainy period. Conclusions(1) The land use in the study area shows a transforming trend from pervious to impervious area.There′s a fluctuation in the area of arable land, woodland and grassland and a shrinking trend in the water body.Especially, the area of construction land has been increasing year by year. (2) The influence factors of runoff coefficient is a combination of the underlying surface changes and the rainfall process,while the impervious surface ratio is dominant in the study area. Under the same meteorological conditions,the proportion of impervious area is increased from 0.49% to 10.58%, and the runoff coefficient is ascended from 0.31 to 0.38 from 1987 to 2018 in the study area. (3) Under a typical rainstorm event, the peak flow is increased by 10%,the flood process line became steeper,and the recession process was significantly slowed down from 1987 to 2018.Green land and water bodies could alleviate the amplification effect of runoff brought about by the urbanization process to a certain extent.
2021, 19(4):636-644,668.
Abstract:
Luanhe River basin is located in the north of BeijingTianjinHebei area with obvious monsoon climate characteristics and frequent dryness/wetness variations.It is an ecologically fragile area and is sensitive to climate change.Under the background of climate warming,it is of great significance to study the characteristics of typical dryness/wetness field modes and their responses to large-scale climate factors.The existing research focused on the analysis of the evolution characteristics of dryness/wetness and the impacts of climate factors,or the decomposition of the spatial and temporal patterns of drought and flood.However,there are relatively few studies on the spatiotemporal decomposition of dryness/wetness characteristics and the periodic identification and impact of climate factors. The standardized precipitation index was used to analyze the dryness/wetness change trend of Luanhe River basin from 1957 to 2016.The MannKendall method was used to test the evolution trend of dryness/wetness characteristics.The empirical orthogonal function (EOF)decomposition was used to decompose the dryness/wetness field,and its temporal and spatial characteristics and periodicity were discussed.The crosswavelet analysis was used to analyze the response relationship between large-scale climate factors and typical dryness/wetness conditions.The reference was provided for objective assessment and accurate prediction of drought and flood disasters in Luanhe River basin,so as to reduce the losses caused by extreme climate eventsand enhance people′s adaptability to climate change. In the study on the trend of wet and dry changes in the Luanhe River basin,the MannKendall method was used to analyze the trend and abrupt changes of SPI12 (12-month SPI) from 1957 to 2016.The wet and dry conditions in the basin had abrupt changes in 1989 and the drought trend became more serious.Before 1989,there were 29 years of extreme waterlogging events in the basin,and 2 years of extreme drought events,affecting 1972 and 1980-1984.After 1989,the intensity of drought events in the basin increased,and interannual drought events occurred frequently,with a total of 27 years of severe and extreme drought events.In the study of the characteristics of dryness/wetness changes in the typical modalities of the Luanhe River basin,the EOF method was used to decompose SPI12 in time and space,and the cumulative contribution rate of the first two spatial function eigenvalues was 72.3%.The distribution of dryness/wetness fields from 1957 to 2016 is dominated by mode 1,and the slope of PC1 (the first principal component) is -0.054,indicating that the degree of drought in the basin has an increasing trend.The continuous wavelet transform power spectrum and the wavelet variance graph show that the time-frequency structure of PC1 and PC2 in the dryness/wetness fields are similar,and both have a 1.5 to 4.0 year main period.In the study of the influence of largescale climate factors on the dryness/wetness fields in Luanhe River basin,the resonant period and phase relationship between largescale climate factors and PC1 and PC2 in time-frequency domain are evaluated by cross wavelet transform.The two typical modes of dryness/wetness changes in Luanhe River basin are closely related to Nina 3.4 and SOI (Southern Oscillation Index),and they have similar 1.5–6.0–year period but opposite correlation to the dryness/wetness fields.The influence of AO (Arctic Oscillation) and NAO (North Atlantic Oscillation) on the dryness/wetness fields is general,which is mainly reflected in the phase relationship of 2-4 year period. Conclusions（1) The dryness/wetness conditions of the Luanhe River basin experienced abrupt changes in 1989.Before the abrupt change,the basin was relatively humid,and drought and flood events occurred alternately;after the abrupt change,the drought trend in the basin is further strengthened,and interannual drought events occurred frequently; （2) The dryness/wetness evolution of the Luanhe River basin showed two modes:the same type of dryness/wetness in the whole area and the reverse type of upstream and downstream in the basin,with a cumulative contribution rate of 723%.The dryness/wetness field of the river basin was of the same type of dryness/wetness in the whole area.The trends of the time variables of the two modalities show that the degree of drought in the basin has an increasing trend;the two time variables have a similar timefrequency structure,and both have a 1.5 to 4.0 year main cycle;（3) Nina 3.4 and SOI,which characterize ENSO (El Nio/Southern Oscillation) events,and the two modes both have a period of 1.5 to 6.0 years;ENSO has the most significant impact on the spatialand temporal distribution of dryness and wetness in the Luanhe River basin,followed by AO and NAO,which are related to the weakest AMO and PDO;the impact of the six climatic factors on the basin′s dryness/wetness fields is mainly reflected in changing the basin′s dryness/wetness consistency
Luanhe River basin is located in the north of BeijingTianjinHebei area with obvious monsoon climate characteristics and frequent dryness/wetness variations.It is an ecologically fragile area and is sensitive to climate change.Under the background of climate warming,it is of great significance to study the characteristics of typical dryness/wetness field modes and their responses to large-scale climate factors.The existing research focused on the analysis of the evolution characteristics of dryness/wetness and the impacts of climate factors,or the decomposition of the spatial and temporal patterns of drought and flood.However,there are relatively few studies on the spatiotemporal decomposition of dryness/wetness characteristics and the periodic identification and impact of climate factors. The standardized precipitation index was used to analyze the dryness/wetness change trend of Luanhe River basin from 1957 to 2016.The MannKendall method was used to test the evolution trend of dryness/wetness characteristics.The empirical orthogonal function (EOF)decomposition was used to decompose the dryness/wetness field,and its temporal and spatial characteristics and periodicity were discussed.The crosswavelet analysis was used to analyze the response relationship between large-scale climate factors and typical dryness/wetness conditions.The reference was provided for objective assessment and accurate prediction of drought and flood disasters in Luanhe River basin,so as to reduce the losses caused by extreme climate eventsand enhance people′s adaptability to climate change. In the study on the trend of wet and dry changes in the Luanhe River basin,the MannKendall method was used to analyze the trend and abrupt changes of SPI12 (12-month SPI) from 1957 to 2016.The wet and dry conditions in the basin had abrupt changes in 1989 and the drought trend became more serious.Before 1989,there were 29 years of extreme waterlogging events in the basin,and 2 years of extreme drought events,affecting 1972 and 1980-1984.After 1989,the intensity of drought events in the basin increased,and interannual drought events occurred frequently,with a total of 27 years of severe and extreme drought events.In the study of the characteristics of dryness/wetness changes in the typical modalities of the Luanhe River basin,the EOF method was used to decompose SPI12 in time and space,and the cumulative contribution rate of the first two spatial function eigenvalues was 72.3%.The distribution of dryness/wetness fields from 1957 to 2016 is dominated by mode 1,and the slope of PC1 (the first principal component) is -0.054,indicating that the degree of drought in the basin has an increasing trend.The continuous wavelet transform power spectrum and the wavelet variance graph show that the time-frequency structure of PC1 and PC2 in the dryness/wetness fields are similar,and both have a 1.5 to 4.0 year main period.In the study of the influence of largescale climate factors on the dryness/wetness fields in Luanhe River basin,the resonant period and phase relationship between largescale climate factors and PC1 and PC2 in time-frequency domain are evaluated by cross wavelet transform.The two typical modes of dryness/wetness changes in Luanhe River basin are closely related to Nina 3.4 and SOI (Southern Oscillation Index),and they have similar 1.5–6.0–year period but opposite correlation to the dryness/wetness fields.The influence of AO (Arctic Oscillation) and NAO (North Atlantic Oscillation) on the dryness/wetness fields is general,which is mainly reflected in the phase relationship of 2-4 year period. Conclusions（1) The dryness/wetness conditions of the Luanhe River basin experienced abrupt changes in 1989.Before the abrupt change,the basin was relatively humid,and drought and flood events occurred alternately;after the abrupt change,the drought trend in the basin is further strengthened,and interannual drought events occurred frequently; （2) The dryness/wetness evolution of the Luanhe River basin showed two modes:the same type of dryness/wetness in the whole area and the reverse type of upstream and downstream in the basin,with a cumulative contribution rate of 723%.The dryness/wetness field of the river basin was of the same type of dryness/wetness in the whole area.The trends of the time variables of the two modalities show that the degree of drought in the basin has an increasing trend;the two time variables have a similar timefrequency structure,and both have a 1.5 to 4.0 year main cycle;（3) Nina 3.4 and SOI,which characterize ENSO (El Nio/Southern Oscillation) events,and the two modes both have a period of 1.5 to 6.0 years;ENSO has the most significant impact on the spatialand temporal distribution of dryness and wetness in the Luanhe River basin,followed by AO and NAO,which are related to the weakest AMO and PDO;the impact of the six climatic factors on the basin′s dryness/wetness fields is mainly reflected in changing the basin′s dryness/wetness consistency
SHEN Yuanyuan
,
GUO Gaoxuan
,
OU Zhiliang
,
XIN Baodong
,
NAN Yinghua
,
WANG Liya
,
WANG Shufang
,
LIU Jiurong
2021, 19(4):645-655.
Abstract:
Yuquanshan spring,located in the foothills of Beijing Xishan,is an essential source of water supply for ecology and environment of Beijing.However,the famous karst spring had been dry since 1974.Since the South-to-North Water Transfer Project was implemented at the end of 2014,the mountainous areas in western Beijing have been planned as "ecological conservation belts". The resurrection of Yuquanshan spring has become a new topic to many researchers.Several hydrogeological surveys of water supply have been carried out in the Beijing Xishan.The hydrogeological conditions have been identified,the exploitation potential of karst groundwater resources has been evaluated,and some preliminary discussions have been made on Yuquanshan spring′s recovery. Based on the comprehensive analysis of the hydrogeological conditions in Yuquanshan areas,a heterogeneous and anisotropic unsteady threedimensional numerical model of groundwater flow is established,which includes the Yuquanshan-Tanzhesi karst water system and the quaternary groundwater system in the upper part of Yongding River alluvialproluvial fan.The study area is divided into 200 m×200 m grids,and the aquifer is generalized into five layers in the vertical direction.The simulation period is from September 2012 to September 2015,with one month as a stress period and a time step of 10 days. The numerical simulation results showed that the groundwater system was in a negative balance during the simulation period.The main factors that played significant roles in the karst water system′s equilibrium were the Yongding River′s seepage (54.72% of the total recharge) and the extraction of karst water (93.55% of entire drainage).Supposing the groundwater level in this area was to be restored,it is necessary to make up the groundwater artificially and adjust the groundwater exploitation layout to reduce the groundwater exploitation according to the background of the South-to-North Water Transfer Project′s operation. In order to evaluate the feasibility of Yuquanshan spring recovery,six recharge and exploitation schemes were designed based on the seepage of Yongding River,the recharge of wells,and groundwater extraction as variable factors.These schemes included the current exploiting plans,extreme reduction exploiting plans,plans for increasing infiltration and reducing extraction,a long-term recovery plan with the goal of spring recovery by 2050,the short-term plans (until 2030) and longterm plans (until 2050) for recharging wells with sandpits at western outskirt in Beijing. If the channel seepage is increased by 0.8×10.8 in the Yongding River gorge and the groundwater extraction is suppressed to 71% of the present situation,the Yuquanshan spring is expected to recover in 2050;if the groundwater extraction is reduced to 45% and the seepage of the river channel is increased by 0.8×10.8m3/a,it is possible to recover in 2030.Besides,to avoid new environmental problems caused by the excessive groundwater levels when Yuquanshan spring is recovered,the appropriate groundwater level for restoration should be considered in groundwater system restoration.The seepage rate can be increased by 0.3×108 m3/a in the Yongding River gorge.At the same time,the groundwater is suppressed to 24%.Although the Yuquanshan spring can not guarantee recovery in a short time,the loss of groundwater resources will be reduced year by year.The groundwater system′s ecological environment will be gradually restored,which is more in line with the actual conditions and conducive to sustainable water resource utilization in this region.
Yuquanshan spring,located in the foothills of Beijing Xishan,is an essential source of water supply for ecology and environment of Beijing.However,the famous karst spring had been dry since 1974.Since the South-to-North Water Transfer Project was implemented at the end of 2014,the mountainous areas in western Beijing have been planned as "ecological conservation belts". The resurrection of Yuquanshan spring has become a new topic to many researchers.Several hydrogeological surveys of water supply have been carried out in the Beijing Xishan.The hydrogeological conditions have been identified,the exploitation potential of karst groundwater resources has been evaluated,and some preliminary discussions have been made on Yuquanshan spring′s recovery. Based on the comprehensive analysis of the hydrogeological conditions in Yuquanshan areas,a heterogeneous and anisotropic unsteady threedimensional numerical model of groundwater flow is established,which includes the Yuquanshan-Tanzhesi karst water system and the quaternary groundwater system in the upper part of Yongding River alluvialproluvial fan.The study area is divided into 200 m×200 m grids,and the aquifer is generalized into five layers in the vertical direction.The simulation period is from September 2012 to September 2015,with one month as a stress period and a time step of 10 days. The numerical simulation results showed that the groundwater system was in a negative balance during the simulation period.The main factors that played significant roles in the karst water system′s equilibrium were the Yongding River′s seepage (54.72% of the total recharge) and the extraction of karst water (93.55% of entire drainage).Supposing the groundwater level in this area was to be restored,it is necessary to make up the groundwater artificially and adjust the groundwater exploitation layout to reduce the groundwater exploitation according to the background of the South-to-North Water Transfer Project′s operation. In order to evaluate the feasibility of Yuquanshan spring recovery,six recharge and exploitation schemes were designed based on the seepage of Yongding River,the recharge of wells,and groundwater extraction as variable factors.These schemes included the current exploiting plans,extreme reduction exploiting plans,plans for increasing infiltration and reducing extraction,a long-term recovery plan with the goal of spring recovery by 2050,the short-term plans (until 2030) and longterm plans (until 2050) for recharging wells with sandpits at western outskirt in Beijing. If the channel seepage is increased by 0.8×10.8 in the Yongding River gorge and the groundwater extraction is suppressed to 71% of the present situation,the Yuquanshan spring is expected to recover in 2050;if the groundwater extraction is reduced to 45% and the seepage of the river channel is increased by 0.8×10.8m3/a,it is possible to recover in 2030.Besides,to avoid new environmental problems caused by the excessive groundwater levels when Yuquanshan spring is recovered,the appropriate groundwater level for restoration should be considered in groundwater system restoration.The seepage rate can be increased by 0.3×108 m3/a in the Yongding River gorge.At the same time,the groundwater is suppressed to 24%.Although the Yuquanshan spring can not guarantee recovery in a short time,the loss of groundwater resources will be reduced year by year.The groundwater system′s ecological environment will be gradually restored,which is more in line with the actual conditions and conducive to sustainable water resource utilization in this region.
2021, 19(4):656-668.
Abstract:
Background As an important ecological barrier,the upper Yongding River basin plays a key role for preventing sandstorm and protecting water resources for the downstream where the capital city located.With the impact of climate change and high-intensity human activities,the ecological environment in the basin has undergone significant changes in the past 50 years,and water shortage and water environment deterioration have become increasingly prominent.The impact of climate change and human activities on water quantity and quality is highly related to climate change,basin location and other factors,yet it has obvious spatial heterogeneity.Therefore,revealing the characteristics of regional-scale environmental changes and quantitative and qualitative evolution of water resources and their driving factors is highly needed,which is of great significance for water resources management and water environmental protection in the upper Yongding River basin. Findings(1) The mean temperature of the upper Yongding River basin showed an "abrupt" increasing trend in the past 50 years,and the temperature increased significantly especially after 2000.The magnitude of minimum temperature increase is greater than that of maximum temperature,and the warming trend in winter and spring is higher than that in other seasons.Temperature may have an increase tendency in future.(2) The annual average precipitation in the basin showed a decreasing trend but not statistically significant,while the summer precipitation decreased significantly.The days and the amount of heavy rain and rainstorm showed an extremely significant decreasing trend.Annual precipitation may increase in future.(3) Both the pan evaporation and potential evapotranspiration in the basin have a decreasing tendency,yet not statistically significant.The actual evapotranspiration does not increase with the increase of temperature.(4) The land use change changed dramatically in the basin,with the increase of woodland and construction land and the decrease of cultivated land,unused land and water area as main characteristics.Land use change dynamics are more obvious after 2000 in the basin.(5) Runoff has a significant decreasing trend and water quality is partly polluted in the upper Yongding River basin.High intensity human activity is the main reason for runoff decline and water quality deterioration in the upper Yongding River basin. [WTHZ]Conclusions[WTBZ] (1) The carrying capacity of water resources and water environment are seriously insufficient in the upper Yongding River basin.How to improve the water use efficiency regards to the limited water resources,and how to coordinate the relationship between water resources,ecology and social economic development are highly needed for regional sustainable development and ecological civilization in the upper Yongding River basin.(2) Under the influence of climate change and human activities,the mechanism of water cycle and the process of pollutant migration and transformation will change significantly.How to reveal hydrological cycle and solute migration in the basin under changing environment,and evaluate and predict their effects are hotspots for water security research.(3) Strengthening monitoring,promoting data sharing and improving the models of coupling simulation of water quantity and quality are necessary for water resources research.(4) The upper Yongding River basin has a large drainage area and spans five different provinces.How to plan and promote the comprehensive river basin management is still a key issue which needs to be solved urgently.
Background As an important ecological barrier,the upper Yongding River basin plays a key role for preventing sandstorm and protecting water resources for the downstream where the capital city located.With the impact of climate change and high-intensity human activities,the ecological environment in the basin has undergone significant changes in the past 50 years,and water shortage and water environment deterioration have become increasingly prominent.The impact of climate change and human activities on water quantity and quality is highly related to climate change,basin location and other factors,yet it has obvious spatial heterogeneity.Therefore,revealing the characteristics of regional-scale environmental changes and quantitative and qualitative evolution of water resources and their driving factors is highly needed,which is of great significance for water resources management and water environmental protection in the upper Yongding River basin. Findings(1) The mean temperature of the upper Yongding River basin showed an "abrupt" increasing trend in the past 50 years,and the temperature increased significantly especially after 2000.The magnitude of minimum temperature increase is greater than that of maximum temperature,and the warming trend in winter and spring is higher than that in other seasons.Temperature may have an increase tendency in future.(2) The annual average precipitation in the basin showed a decreasing trend but not statistically significant,while the summer precipitation decreased significantly.The days and the amount of heavy rain and rainstorm showed an extremely significant decreasing trend.Annual precipitation may increase in future.(3) Both the pan evaporation and potential evapotranspiration in the basin have a decreasing tendency,yet not statistically significant.The actual evapotranspiration does not increase with the increase of temperature.(4) The land use change changed dramatically in the basin,with the increase of woodland and construction land and the decrease of cultivated land,unused land and water area as main characteristics.Land use change dynamics are more obvious after 2000 in the basin.(5) Runoff has a significant decreasing trend and water quality is partly polluted in the upper Yongding River basin.High intensity human activity is the main reason for runoff decline and water quality deterioration in the upper Yongding River basin. [WTHZ]Conclusions[WTBZ] (1) The carrying capacity of water resources and water environment are seriously insufficient in the upper Yongding River basin.How to improve the water use efficiency regards to the limited water resources,and how to coordinate the relationship between water resources,ecology and social economic development are highly needed for regional sustainable development and ecological civilization in the upper Yongding River basin.(2) Under the influence of climate change and human activities,the mechanism of water cycle and the process of pollutant migration and transformation will change significantly.How to reveal hydrological cycle and solute migration in the basin under changing environment,and evaluate and predict their effects are hotspots for water security research.(3) Strengthening monitoring,promoting data sharing and improving the models of coupling simulation of water quantity and quality are necessary for water resources research.(4) The upper Yongding River basin has a large drainage area and spans five different provinces.How to plan and promote the comprehensive river basin management is still a key issue which needs to be solved urgently.
WANG Qingming，JIANG Shan，LI Sen
,
ZHANG Yue，HE Guohua，ZHAO Yong，LI Haihong，ZHU Yongnan，ZHAI Jiaqi，WANG Lizhen
2021, 19(4):669-679.
Abstract:
Runoff attenuation has been a serious threat to the natural ecological and social production of the river basins,and it was usually attributed to climate change and human activities.The research methods were generally divided into two types,one was based on statistical data to identify the impact of climate factors and human activities factors by the difference of the relationship between precipitation and runoff in two periods.The other approach was based on the hydrological model that simulate the difference in runoff under different climate conditions and different surface conditions to distinguish the effect of climate and human activities.Due to the limitation of data acquisition,there is no mature attribution method for the contribution of vegetation,soil and water conservation projects and other factors to runoff attenuation.Therefore,Daqing River basin was taken as the study area to analyze the influence mechanisms of different factors on runoff and investigate the contribution of each factor to runoff attenuation. Runoff changes at three typical hydrological stations in the Daqing River basin were analyzed,and the abrupt change of surface runoff was analyzed using the Pettitt mutation test.The first abrupt change occurred in 1983,and the second abrupt change occurred in 1997.Thus,the runoff series from 1961 to 2016 was divided into three periods (T1,T2 and T3) based on the above mentioned two mutation points.Additionally,the evolution patterns of rainfall in flood season and non-flood season,potential evapotranspiration,mountain water conservation and reservoir construction were analyzed in the three periods,respectively.Sensitivity analysis method was applied to evaluate the contribution of each influencing factor to runoff attenuation in the Daqing River basin. The results showed that there has no significant change in the rainfall in the three periods in the Daqing River basin,but the rainfall decreases in flood season and increases in non-flood season,which is one of the important reasons for the decrease of runoff.In the mountainous area of the Daqing River basin,the heavy rainfall showed a decreasing trend,while the medium and small rainfall showed an increasing trend.The rainfall intensity in the mountainous area of the Daqing River basin gradually decreases,which leads to the decrease of storm runoff.The potential evaporation in the Daqing River basin decreases and then increases during the annual,flood and nonflood seasons.The increase of evapotranspiration capacity in the flood season during the T3 period means the increase of regional actual evapotranspiration and the corresponding decrease of runoff from precipitation decline.The annual maximum NDVI in Daqing Mountain has shown an increasing trend since the 1980 s,with an average annual growth rate of 0.002 3.Vegetation conditions have become better and more precipitation was retained by the canopy and evaporated into the atmosphere,thus reducing the runoff formed by precipitation.The reservoirs led to an increase in evaporation,with evaporation loss of 37.96 million m3 and 36.59 million m3 from the reservoirs in the T2 and T3 periods,respectively. In conclusion,the influence of precipitation on surface runoff in mountainous area of the Daqing River basin is mainly reflected in the flood season.The decrease of precipitation and the weakening of rain intensity in the flood season reduced runoff,while the increase of evaporation capacity leads to the increase of actual evaporation loss in the flood season,which further aggravatesthe attenuation of runoff.The increased interception of vegetation canopy and the enhancement of soil water storage capacity caused by the water conservation project were important reasons for the attenuation of surface runoff in the T2 and T3 periods.The change of precipitation in flood season in the T1 period is the main reason for affecting runoff.The large increase of terrace area in the T2 period is the main reason for the decrease of surface runoff.In the T3 period,precipitation decreased in flood season and the increase of the proportion of evaporation to precipitation due to the improvement of vegetation quality lead to the decrease of runoff.
Runoff attenuation has been a serious threat to the natural ecological and social production of the river basins,and it was usually attributed to climate change and human activities.The research methods were generally divided into two types,one was based on statistical data to identify the impact of climate factors and human activities factors by the difference of the relationship between precipitation and runoff in two periods.The other approach was based on the hydrological model that simulate the difference in runoff under different climate conditions and different surface conditions to distinguish the effect of climate and human activities.Due to the limitation of data acquisition,there is no mature attribution method for the contribution of vegetation,soil and water conservation projects and other factors to runoff attenuation.Therefore,Daqing River basin was taken as the study area to analyze the influence mechanisms of different factors on runoff and investigate the contribution of each factor to runoff attenuation. Runoff changes at three typical hydrological stations in the Daqing River basin were analyzed,and the abrupt change of surface runoff was analyzed using the Pettitt mutation test.The first abrupt change occurred in 1983,and the second abrupt change occurred in 1997.Thus,the runoff series from 1961 to 2016 was divided into three periods (T1,T2 and T3) based on the above mentioned two mutation points.Additionally,the evolution patterns of rainfall in flood season and non-flood season,potential evapotranspiration,mountain water conservation and reservoir construction were analyzed in the three periods,respectively.Sensitivity analysis method was applied to evaluate the contribution of each influencing factor to runoff attenuation in the Daqing River basin. The results showed that there has no significant change in the rainfall in the three periods in the Daqing River basin,but the rainfall decreases in flood season and increases in non-flood season,which is one of the important reasons for the decrease of runoff.In the mountainous area of the Daqing River basin,the heavy rainfall showed a decreasing trend,while the medium and small rainfall showed an increasing trend.The rainfall intensity in the mountainous area of the Daqing River basin gradually decreases,which leads to the decrease of storm runoff.The potential evaporation in the Daqing River basin decreases and then increases during the annual,flood and nonflood seasons.The increase of evapotranspiration capacity in the flood season during the T3 period means the increase of regional actual evapotranspiration and the corresponding decrease of runoff from precipitation decline.The annual maximum NDVI in Daqing Mountain has shown an increasing trend since the 1980 s,with an average annual growth rate of 0.002 3.Vegetation conditions have become better and more precipitation was retained by the canopy and evaporated into the atmosphere,thus reducing the runoff formed by precipitation.The reservoirs led to an increase in evaporation,with evaporation loss of 37.96 million m3 and 36.59 million m3 from the reservoirs in the T2 and T3 periods,respectively. In conclusion,the influence of precipitation on surface runoff in mountainous area of the Daqing River basin is mainly reflected in the flood season.The decrease of precipitation and the weakening of rain intensity in the flood season reduced runoff,while the increase of evaporation capacity leads to the increase of actual evaporation loss in the flood season,which further aggravatesthe attenuation of runoff.The increased interception of vegetation canopy and the enhancement of soil water storage capacity caused by the water conservation project were important reasons for the attenuation of surface runoff in the T2 and T3 periods.The change of precipitation in flood season in the T1 period is the main reason for affecting runoff.The large increase of terrace area in the T2 period is the main reason for the decrease of surface runoff.In the T3 period,precipitation decreased in flood season and the increase of the proportion of evaporation to precipitation due to the improvement of vegetation quality lead to the decrease of runoff.
2021, 19(4):680-688.
Abstract:
In recent years,with the continuous acceleration of industrialization,rapid social and economic development and continuous population growth,water consumption in various industries is increasing,and the contradiction between supply and demand is aggravating.Water consumption includes not only physical water but also virtual water in products and services.The purpose of water footprint theory is to study invisible water in the public consumption and service process.Beijing is a typical water consumption city,but there is no research on water resources utilization from the perspective of water footprint theory.Therefore,based on water footprint theory,it is necessary to evaluate the utilization of water resources in urban physical water,virtual water,and trade. The internal water footprint and external water footprint are calculated based on water footprint theory,including agricultural virtual water consumption,industrial virtual water consumption,domestic water consumption,ecological environment water consumption,virtual water outlet,and external water footprint is virtual water inlet.At the same time,the LMDI model is applied to decompose different factors such as structure effect,technology effect,and population effect of water footprint change. The total water footprint of Beijing showed a fluctuating downward trend from 2003 to 2011 and from 2011 to 2018,respectively.Among them,agricultural and industrial water footprint has a downward trend year after year,living and ecological water footprint has an upward trend;virtual water quantity of import is greater than virtual water quantity of export.In terms of water footprint structure,the selfsufficiency rate of water resources is generally on the rise,exceeding 70% by 2015,and the dependence on water resources imports is on the decline side.In case of water footprint sustainability,the water footprint growth index is mostly negative and the available water resources growth index is positive.In terms of ecological safety of water resources,both the water shortage index and pressure index are greater than 1,and the water resource pressure index is on the decline as a whole.Likewise,in terms of water footprint benefits,the economic benefits of water footprint are on the rise,the water load index is on the rise,the net trade value of water footprint and the contribution rate of water resources are on the fluctuating stage from 2003 to 2011,and from 2011 to 2018.Among the drivers of water footprint,the proportion of population effect is less than 10%,the economic effect is less than 40%,and the technical effect is more than 50%,respectively. Water footprint accounts for about 70% in Beijing,mainly in agriculture.However,with the acceleration of urbanization,population growth, industrial structure changes,agricultural water footprint is getting lower and lower,and ecological water footprint and living water footprint are increasing.The total water footprint is on a downward trend and its dependence on imports is decreasing.Water resources are developing in Beijing,and the import dependence is high.From the perspective of the water footprint development trend,the overall development of Beijing is in two stages,fluctuating from 2003 to 2011 and declining from 2012 to 2018.Since 2012,the sustainable development of water resources in Beijing has been benign and in a sustainable state.Due to the shortage of local water resources in Beijing,both the water shortage index and pressure index are relatively high,and the ecological safety of water resources is in a serious overload situation.Although the internal economic benefit of water resources is increasing continuously,the external water diversion still needs to be increased due to heavy load. Based on the LMDI model analysis,it can be seen that the driving factors of water resources change in the process of urbanization are technology effect>economy effect>population effect.Only technical effect is driven in the opposite direction,while economic effect and population effect are both driven in the positive direction.It indicates that great attention should be paid to the increase of water consumption brought by economic development and population growth in the process of urbanization and that sustainable attention should be paid to the development of water-saving technology,the optimization and adjustment of industrial structure, and the improvement of water resource utilization efficiency to realize the sustainable development of water resources.
In recent years,with the continuous acceleration of industrialization,rapid social and economic development and continuous population growth,water consumption in various industries is increasing,and the contradiction between supply and demand is aggravating.Water consumption includes not only physical water but also virtual water in products and services.The purpose of water footprint theory is to study invisible water in the public consumption and service process.Beijing is a typical water consumption city,but there is no research on water resources utilization from the perspective of water footprint theory.Therefore,based on water footprint theory,it is necessary to evaluate the utilization of water resources in urban physical water,virtual water,and trade. The internal water footprint and external water footprint are calculated based on water footprint theory,including agricultural virtual water consumption,industrial virtual water consumption,domestic water consumption,ecological environment water consumption,virtual water outlet,and external water footprint is virtual water inlet.At the same time,the LMDI model is applied to decompose different factors such as structure effect,technology effect,and population effect of water footprint change. The total water footprint of Beijing showed a fluctuating downward trend from 2003 to 2011 and from 2011 to 2018,respectively.Among them,agricultural and industrial water footprint has a downward trend year after year,living and ecological water footprint has an upward trend;virtual water quantity of import is greater than virtual water quantity of export.In terms of water footprint structure,the selfsufficiency rate of water resources is generally on the rise,exceeding 70% by 2015,and the dependence on water resources imports is on the decline side.In case of water footprint sustainability,the water footprint growth index is mostly negative and the available water resources growth index is positive.In terms of ecological safety of water resources,both the water shortage index and pressure index are greater than 1,and the water resource pressure index is on the decline as a whole.Likewise,in terms of water footprint benefits,the economic benefits of water footprint are on the rise,the water load index is on the rise,the net trade value of water footprint and the contribution rate of water resources are on the fluctuating stage from 2003 to 2011,and from 2011 to 2018.Among the drivers of water footprint,the proportion of population effect is less than 10%,the economic effect is less than 40%,and the technical effect is more than 50%,respectively. Water footprint accounts for about 70% in Beijing,mainly in agriculture.However,with the acceleration of urbanization,population growth, industrial structure changes,agricultural water footprint is getting lower and lower,and ecological water footprint and living water footprint are increasing.The total water footprint is on a downward trend and its dependence on imports is decreasing.Water resources are developing in Beijing,and the import dependence is high.From the perspective of the water footprint development trend,the overall development of Beijing is in two stages,fluctuating from 2003 to 2011 and declining from 2012 to 2018.Since 2012,the sustainable development of water resources in Beijing has been benign and in a sustainable state.Due to the shortage of local water resources in Beijing,both the water shortage index and pressure index are relatively high,and the ecological safety of water resources is in a serious overload situation.Although the internal economic benefit of water resources is increasing continuously,the external water diversion still needs to be increased due to heavy load. Based on the LMDI model analysis,it can be seen that the driving factors of water resources change in the process of urbanization are technology effect>economy effect>population effect.Only technical effect is driven in the opposite direction,while economic effect and population effect are both driven in the positive direction.It indicates that great attention should be paid to the increase of water consumption brought by economic development and population growth in the process of urbanization and that sustainable attention should be paid to the development of water-saving technology,the optimization and adjustment of industrial structure, and the improvement of water resource utilization efficiency to realize the sustainable development of water resources.
2021, 19(4):689-699.
Abstract:
Watershed runoff forecasting has been a research focus on hydrological model and flooding prediction.In China,Xinanjiang (XAJ) model is a widely used for flood forecasting,which is of significance to areas with booming economy,dense population,and high flooding risks,such as those located in central China.The Fu River basin located in Jiangxi Province is a rainy area with abundant precipitation (average annual rainfall is 1 761 mm).A lumped hydrological model,three-source XAJ model based on excess storage runoff generation,was established to simulate 18 rainstorms and floods in Fu River basin from 1981 to 1995.Muskingen′s piecewise continuous algorithm was used to calculate river flood routing and the flow process line.The processes of the flow and flood were determined by linear superposition of all the flow processes.Parameters were calibrated by daily data and frequency data.Results showed that the average deterministic coefficient of the model in the field flood simulation was 0911,the average error of runoff depth for model calibration was 4.73%,and the average error of runoff depth for validation was 8.21%.Therefore,the three-source XAJ model could be used as a useful forecasting model in the flood forecasting system of Fu River basin.The useful references were provided for flood forecasting research in the rainy central China.
Watershed runoff forecasting has been a research focus on hydrological model and flooding prediction.In China,Xinanjiang (XAJ) model is a widely used for flood forecasting,which is of significance to areas with booming economy,dense population,and high flooding risks,such as those located in central China.The Fu River basin located in Jiangxi Province is a rainy area with abundant precipitation (average annual rainfall is 1 761 mm).A lumped hydrological model,three-source XAJ model based on excess storage runoff generation,was established to simulate 18 rainstorms and floods in Fu River basin from 1981 to 1995.Muskingen′s piecewise continuous algorithm was used to calculate river flood routing and the flow process line.The processes of the flow and flood were determined by linear superposition of all the flow processes.Parameters were calibrated by daily data and frequency data.Results showed that the average deterministic coefficient of the model in the field flood simulation was 0911,the average error of runoff depth for model calibration was 4.73%,and the average error of runoff depth for validation was 8.21%.Therefore,the three-source XAJ model could be used as a useful forecasting model in the flood forecasting system of Fu River basin.The useful references were provided for flood forecasting research in the rainy central China.
2021, 19(4):700-707,728.
Abstract:
The Grand Canal is an important cultural heritage in China,which has important economic,ecological and cultural significance.With the development and utilization of water resources,water pollution is becoming a serious issue.Government at all levels implement the river chief system to ensure the sustainable development of water resources and promote the protection and inheritance of the Grand Canal.Therefore,remote sensing information technology is applied to the investigation and evaluation stage of the river head system to monitor the temporal and spatial changes of the river basin. With the support of remote sensing and geographic information system technology,based on Gaofen-2 remote sensing image,the change of water body and vegetation coverage in the core monitoring area of the Grand Canal from 2015 to 2019 was analyzed.First,the two types of land use,water,and vegetation are extracted and the change of area in the time interval is analyzed.Then,according to the high-resolution image of Google Earth,validation samples are generated to verify the accuracy,and the classification accuracy meets the research requirements.Finally,the landscape pattern index was used to analyze the changing trend of each landscape in the study area.From 2015 to 2017,the vegetation area decreased by 82.94 km2,accounting for 38.82% of the original area,and the water area decreased by 0.01 km2.From 2017 to 2019,the vegetation area increased by 205.53 km2,accounting for 157.27% of the originalarea,and the water area increased by 1.79 km2,accounting for 10.86% of the original area.The total number of plaques first increased and then decreased,and the patch density fluctuated greatly.Edge density,aggregation degree,weighted average shape index also showed an upward trend.On the whole,the establishment of the construction team of the Grand Canal cultural belt and the river chief system by the staff of Beijing Municipality has achieved good results in the strict control of the water quality and the greening along the Grand Canal. The qualitative and quantitative evaluation of the comprehensive treatment results of the Beijing section of the Grand Canal is realized,and the actual situation of the study area is directly reflected through remote sensing images and column statistical charts.Combined the results with the landscape pattern index analysis of the study area,the scientificity and accuracy of the evaluation process are ensured,mobilizing the enthusiasm of the staff,reducing the risk of corruption to a certain extent,and promoting innovation of China′s administrative system.
The Grand Canal is an important cultural heritage in China,which has important economic,ecological and cultural significance.With the development and utilization of water resources,water pollution is becoming a serious issue.Government at all levels implement the river chief system to ensure the sustainable development of water resources and promote the protection and inheritance of the Grand Canal.Therefore,remote sensing information technology is applied to the investigation and evaluation stage of the river head system to monitor the temporal and spatial changes of the river basin. With the support of remote sensing and geographic information system technology,based on Gaofen-2 remote sensing image,the change of water body and vegetation coverage in the core monitoring area of the Grand Canal from 2015 to 2019 was analyzed.First,the two types of land use,water,and vegetation are extracted and the change of area in the time interval is analyzed.Then,according to the high-resolution image of Google Earth,validation samples are generated to verify the accuracy,and the classification accuracy meets the research requirements.Finally,the landscape pattern index was used to analyze the changing trend of each landscape in the study area.From 2015 to 2017,the vegetation area decreased by 82.94 km2,accounting for 38.82% of the original area,and the water area decreased by 0.01 km2.From 2017 to 2019,the vegetation area increased by 205.53 km2,accounting for 157.27% of the originalarea,and the water area increased by 1.79 km2,accounting for 10.86% of the original area.The total number of plaques first increased and then decreased,and the patch density fluctuated greatly.Edge density,aggregation degree,weighted average shape index also showed an upward trend.On the whole,the establishment of the construction team of the Grand Canal cultural belt and the river chief system by the staff of Beijing Municipality has achieved good results in the strict control of the water quality and the greening along the Grand Canal. The qualitative and quantitative evaluation of the comprehensive treatment results of the Beijing section of the Grand Canal is realized,and the actual situation of the study area is directly reflected through remote sensing images and column statistical charts.Combined the results with the landscape pattern index analysis of the study area,the scientificity and accuracy of the evaluation process are ensured,mobilizing the enthusiasm of the staff,reducing the risk of corruption to a certain extent,and promoting innovation of China′s administrative system.
2021, 19(4):708-719,757.
Abstract:
Vegetation as an important part of the terrestrial ecosystem,it links the atmosphere,hydrosphere,and soil circle,and is a reflection and indication of regional climate characteristics.With the construction advancement of the ThreeNorth Shelterbelt and the conversion of farmland to forest and grassland,vegetation growth is being affected by human activities.Hebei Province has a forest coverage rate of 34% by the end of 2018.At the same time,it has fully promoted the threeyear national land greening initiative.In 2019,684,000 hectares of afforestation were completed,accounting onetenth of the total number of afforestation in the country.The semihumid and semiarid continental monsoon climate in Hebei Province and the geographical location of the farmingpastoral zone determine its ecological environment selfregulation ability,and it is extremely vulnerable to meteorological disasters,especially drought.Therefore,in the context of global warming,the accelerated frequency of climate extremes,and the increase in the intensity of human activities,comprehensive exploration of vegetation growth characteristics and attribution analysis has an important practical significance. The research methods include SPEI (standardized precipitation evapotranspiration index) and correlation analysis.The SPEI index not only considers precipitation and evapotranspiration but also retains the sensitivity to temperature and precipitation such as SPI (standardized precipitation index) and PDSI (palmer drought index).Describing drought objectively,correlation analysis and the inverse distance weighted interpolation method is used in ArcGIS,SPEI raster map combined with NDVI image to calculate the spatial correlation distribution map of NDVI and SPEI,and conduct a significance test to analyze the spatial relationship between NDVI and drought index. Hebei Province′s multiyear average NDVI fluctuates and rises on the time scale,especially in 2003,and it display a rapid increase of 0.028/(10 a),showing the distribution characteristics of high and low in the middle on the spatial scale.The increase of temperature is significant,and the spatial distribution shows an increasing trend from northwest to southeast in Hebei Province.Precipitation presents a low-medium-high distribution pattern from northwestcentralnortheast.The area and frequency of droughts are the highest in spring,and the high frequency area of summer drought is located in Tangshan in Zhangjiakou,the frequency of drought is the lowest in autumn,and light drought is dominant in winter.The correlation between vegetation NDVI and SPEI is strongest in summer (0.529),followed by spring and autumn,and relatively weak in winter.The central area of Yuxian Station,Zhangbei Station and Chengde Station are mainly negatively correlated,and the positively correlated are mainly distributed in the central region. Conclusions (1) The multi-scale SPEI (1/3/12) value of Hebei Province has a large range of changes,and the seasonal drought has obvious changes with phase characteristics,which mostly occur in spring,summer and winter.The annual scale SPEI judgment shows that the drought is serious and has a large deviation "Hebei Meteorological Bulletin".The seasonal scale SPEI value shows the drought situation in Hebei Province is more reasonable,but there is a degree of deviation in some years.(2) The correlation between NDVI and SPEI on a seasonal scale,with the strongest correlation in summer,followed by spring and autumn,and the weakest in winter.On the annual scale,the correlation between vegetation NDVI and SPEI has obvious regional differences.
Vegetation as an important part of the terrestrial ecosystem,it links the atmosphere,hydrosphere,and soil circle,and is a reflection and indication of regional climate characteristics.With the construction advancement of the ThreeNorth Shelterbelt and the conversion of farmland to forest and grassland,vegetation growth is being affected by human activities.Hebei Province has a forest coverage rate of 34% by the end of 2018.At the same time,it has fully promoted the threeyear national land greening initiative.In 2019,684,000 hectares of afforestation were completed,accounting onetenth of the total number of afforestation in the country.The semihumid and semiarid continental monsoon climate in Hebei Province and the geographical location of the farmingpastoral zone determine its ecological environment selfregulation ability,and it is extremely vulnerable to meteorological disasters,especially drought.Therefore,in the context of global warming,the accelerated frequency of climate extremes,and the increase in the intensity of human activities,comprehensive exploration of vegetation growth characteristics and attribution analysis has an important practical significance. The research methods include SPEI (standardized precipitation evapotranspiration index) and correlation analysis.The SPEI index not only considers precipitation and evapotranspiration but also retains the sensitivity to temperature and precipitation such as SPI (standardized precipitation index) and PDSI (palmer drought index).Describing drought objectively,correlation analysis and the inverse distance weighted interpolation method is used in ArcGIS,SPEI raster map combined with NDVI image to calculate the spatial correlation distribution map of NDVI and SPEI,and conduct a significance test to analyze the spatial relationship between NDVI and drought index. Hebei Province′s multiyear average NDVI fluctuates and rises on the time scale,especially in 2003,and it display a rapid increase of 0.028/(10 a),showing the distribution characteristics of high and low in the middle on the spatial scale.The increase of temperature is significant,and the spatial distribution shows an increasing trend from northwest to southeast in Hebei Province.Precipitation presents a low-medium-high distribution pattern from northwestcentralnortheast.The area and frequency of droughts are the highest in spring,and the high frequency area of summer drought is located in Tangshan in Zhangjiakou,the frequency of drought is the lowest in autumn,and light drought is dominant in winter.The correlation between vegetation NDVI and SPEI is strongest in summer (0.529),followed by spring and autumn,and relatively weak in winter.The central area of Yuxian Station,Zhangbei Station and Chengde Station are mainly negatively correlated,and the positively correlated are mainly distributed in the central region. Conclusions (1) The multi-scale SPEI (1/3/12) value of Hebei Province has a large range of changes,and the seasonal drought has obvious changes with phase characteristics,which mostly occur in spring,summer and winter.The annual scale SPEI judgment shows that the drought is serious and has a large deviation "Hebei Meteorological Bulletin".The seasonal scale SPEI value shows the drought situation in Hebei Province is more reasonable,but there is a degree of deviation in some years.(2) The correlation between NDVI and SPEI on a seasonal scale,with the strongest correlation in summer,followed by spring and autumn,and the weakest in winter.On the annual scale,the correlation between vegetation NDVI and SPEI has obvious regional differences.
2021, 19(4):720-728.
Abstract:
The rapid social-economic development has caused serious water environmental pollution,and water quality assessment is the basis of environmental water management.However,different assessment methods may yield different water quality grades results.The downstream reaches of the Liao River,Daliao River,and the estuary were focused on Water quality assessment was conducted based on several pollutants,and the applicability of the different methods was discussed.This study may provide scientific references for water quality assessment and management for the terrestrial-marine system. In September 2019 and June 2020,30 sites in the downstream reaches of the Liao River,Daliao River,and the estuary were sampled.Dissolved oxygen (DO),total phosphorus, ammonia nitrogen,and permanganate index were selected as the evaluation indexes for rivers,and dissolved oxygen (DO),active phosphate,and inorganic nitrogen were selected as the evaluation indexes of estuarine waters.The single factor method and fuzzy variable method were selected for water quality assessment.The single factor method defines the grade of the worst single index as the comprehensive water quality grade.The fuzzy variable method uses the concept of opposite fuzzy sets to construct the relative subordinate degree matrix and to determine the weight of each index.Finally, the comprehensive relative subordinate degree was used to evaluate the water quality grade.Two methods were applied to determine the weights of indexes,i.e.,the ordered binary comparison method and the entropy weight method. Results of single factor method showed that in the rivers,DO and permanganate indexes were the major pollutants in 2019,and the water quality varied from Grades Ⅱ to Ⅳ for all sampling sites.In 2020,the total phosphorus was the major pollutant,and 17 sampling sites have the water quality inferior to Grade V.For the estuary,water quality for all sampling sites was inferior to Glade Ⅳ due to the high mass concentrations of inorganic nitrogen.As for the fuzzy variable method,the water quality of the river water varied from Grade Ⅱ to Ⅳ,the estuary water were Grade Ⅱ and Ⅲ based on the ordered binary comparison method.Likewise,the water quality grades based on the entropy weight method were better than the ordered binary comparison method.In comparison,the water quality grades obtained by the fuzzy variable method were generally superior to single factor method both for the rivers and estuary water samples.The results proved that the fuzzy variable method can comprehensively consider the impact of each index on water quality grade by the index weight.The single factor evaluation method often produces "over-protection" results,but it can better reflect the strict requirements of water environment management and is more simple and feasible to implement. Overall,the results indicated that the water quality grades obtained by the fuzzy variable method were generally superior to single factor method.The major pollutants of river water were DO,permanganate index and total phosphorous,and the water quality grades were Ⅳ and inferior to Ⅴ based on the single factor method, while Ⅰ to Ⅲ based on fuzzy variable method.The major pollutants in the estuary were inorganic nitrogen.The single factor method is assessed based on the grade of the worst index,while the fuzzy variable method weighs the impacts of all indexes.Water quality grades using different assessment methods should be comprehensively considered in water environmental management.
The rapid social-economic development has caused serious water environmental pollution,and water quality assessment is the basis of environmental water management.However,different assessment methods may yield different water quality grades results.The downstream reaches of the Liao River,Daliao River,and the estuary were focused on Water quality assessment was conducted based on several pollutants,and the applicability of the different methods was discussed.This study may provide scientific references for water quality assessment and management for the terrestrial-marine system. In September 2019 and June 2020,30 sites in the downstream reaches of the Liao River,Daliao River,and the estuary were sampled.Dissolved oxygen (DO),total phosphorus, ammonia nitrogen,and permanganate index were selected as the evaluation indexes for rivers,and dissolved oxygen (DO),active phosphate,and inorganic nitrogen were selected as the evaluation indexes of estuarine waters.The single factor method and fuzzy variable method were selected for water quality assessment.The single factor method defines the grade of the worst single index as the comprehensive water quality grade.The fuzzy variable method uses the concept of opposite fuzzy sets to construct the relative subordinate degree matrix and to determine the weight of each index.Finally, the comprehensive relative subordinate degree was used to evaluate the water quality grade.Two methods were applied to determine the weights of indexes,i.e.,the ordered binary comparison method and the entropy weight method. Results of single factor method showed that in the rivers,DO and permanganate indexes were the major pollutants in 2019,and the water quality varied from Grades Ⅱ to Ⅳ for all sampling sites.In 2020,the total phosphorus was the major pollutant,and 17 sampling sites have the water quality inferior to Grade V.For the estuary,water quality for all sampling sites was inferior to Glade Ⅳ due to the high mass concentrations of inorganic nitrogen.As for the fuzzy variable method,the water quality of the river water varied from Grade Ⅱ to Ⅳ,the estuary water were Grade Ⅱ and Ⅲ based on the ordered binary comparison method.Likewise,the water quality grades based on the entropy weight method were better than the ordered binary comparison method.In comparison,the water quality grades obtained by the fuzzy variable method were generally superior to single factor method both for the rivers and estuary water samples.The results proved that the fuzzy variable method can comprehensively consider the impact of each index on water quality grade by the index weight.The single factor evaluation method often produces "over-protection" results,but it can better reflect the strict requirements of water environment management and is more simple and feasible to implement. Overall,the results indicated that the water quality grades obtained by the fuzzy variable method were generally superior to single factor method.The major pollutants of river water were DO,permanganate index and total phosphorous,and the water quality grades were Ⅳ and inferior to Ⅴ based on the single factor method, while Ⅰ to Ⅲ based on fuzzy variable method.The major pollutants in the estuary were inorganic nitrogen.The single factor method is assessed based on the grade of the worst index,while the fuzzy variable method weighs the impacts of all indexes.Water quality grades using different assessment methods should be comprehensively considered in water environmental management.
LING Yanchen
,
,
SU Yuliang
,
HU Kewu
,
YUAN Hanhong
,
WU Bin
,
HUANG Hongbo
,
FANG Li
,
WU Jie
,
HUANG Tianyin
,
AO Xiuwei
,
SUN Wenjun
2021, 19(4):729-738.
Abstract:
The water supply system in Zhuhai City presents the characteristics of multiple water sources.The Xijiang River is the main drinking water source,and various reservoirs are auxiliary water sources.The reservoirs are responsible for the important function of water storage and water diversion.The water supply system combing the river and reservoirs in Zhuhai City makes the water quality not only affected by point and nonpoint source pollution in the river basin,but also interfered by the internal source pollution in the reservoir,which leads to the difficulty in controlling the stability of the water quality.The water quality of reservoirs in Zhuhai has gradually declined in recent years,and the algae content of the water body has continued to be high.The trend of eutrophication is becoming more and more obvious.However, there is still a lack of theoretical research into the impact of complex water supply system on algae in water sources,and technical guidance for algae control is therefore difficult and highly needed. The single factor analysis was used to compare the measured data and the regulated values of national standard,which aims to evaluate the water quality of four typical reservoirs (Meixi,Zhuyin,Dajingshan and Fenghuangshan reservoirs) in Zhuhai City from 2016 to 2019.The water quality characteristics and the spatial and temporal distribution of algae density in each reservoir were analyzed by the statistical method.The correlation between algae density and 10 water quality indexes (total nitrogen,total phosphorus,5-day biochemical oxygen demand,ammonianitrogen,total organic carbon,permanganate index,dissolved oxygen,2-methylisoborneol,geosmin,and turbidity) was studied by the bivariate analysis.The stepwise regression analysis was used to study and establish a regression model for preliminarily predicting the water quality of the reservoirs,with algae density,taste and odor compounds as dependent variables,and other environmental factors mentioned above as independent variables,respectively.Considering the current operational and problems of water plans in Zhuhai City, suitable solutions for solving the algae problems were analyzed and proposed from two perspectives: pollution source control and process transformation. The water quality of the reservoirs in Zhuhai City basically conformed to the standard of Class III surface water bodies from 2016 to 2019.However,the contents of total nitrogen and total phosphorus in some reservoirs exceeded the standard.From 2016 to 2019,the average algae density in the four reservoirs were 17.90 million cells/L in Meixi reservoir,18.78 million L-1in Zhuyin reservoir,9.43 million L-1in Fenghuangshan reservoir and 108.39 million L-1in Dajingshan reservoir,respectively.Under the influence of climate and water environment quality,the increase of algae density mostly occurred in spring,while the content of taste and odor compounds in the reservoirs were higher in autumn and winter,which could reach 5 times of the maximum odor threshold.Regression analysis showed that the water quality factors affecting algae density in Zhuhai reservoir involved total nitrogen and organic matter.The permanganate index was positively correlated with algal density,while total nitrogen and 5-day biochemical oxygen demand had negative correlation with the algal density.In addition,turbidity,organic matter and ammonianitrogen may contribute to the formation of taste and odor compounds in the reservoirs.And ammonianitrogen was the dominant factor and positively correlated with geosmin.Taking the monthly mean algae density of Zhuyin reservoir as the dependent variable while total nitrogen as the independent variable,a wellfitting regression model was established (R2=0.911,P<0.001,n=9).Furthermore,taking geosmin as the dependent variable while turbidity,permanganate index ammonianitrogen as the independent variables,a well-fitted regression model was developed (R2=0.911,P<0.001,n=54). High algae density,high taste and odor substances were the main water pollution problems in Zhuhai City.Ammonianitrogen and organic matter were the key factors affecting algae density and the production of taste and odor compounds in the reservoirs,algae problems in drinking water sources in Zhuhai City can be effectively solved by source control combined with the end treatment of ozone activated carbon or other advanced treatment technologies.
The water supply system in Zhuhai City presents the characteristics of multiple water sources.The Xijiang River is the main drinking water source,and various reservoirs are auxiliary water sources.The reservoirs are responsible for the important function of water storage and water diversion.The water supply system combing the river and reservoirs in Zhuhai City makes the water quality not only affected by point and nonpoint source pollution in the river basin,but also interfered by the internal source pollution in the reservoir,which leads to the difficulty in controlling the stability of the water quality.The water quality of reservoirs in Zhuhai has gradually declined in recent years,and the algae content of the water body has continued to be high.The trend of eutrophication is becoming more and more obvious.However, there is still a lack of theoretical research into the impact of complex water supply system on algae in water sources,and technical guidance for algae control is therefore difficult and highly needed. The single factor analysis was used to compare the measured data and the regulated values of national standard,which aims to evaluate the water quality of four typical reservoirs (Meixi,Zhuyin,Dajingshan and Fenghuangshan reservoirs) in Zhuhai City from 2016 to 2019.The water quality characteristics and the spatial and temporal distribution of algae density in each reservoir were analyzed by the statistical method.The correlation between algae density and 10 water quality indexes (total nitrogen,total phosphorus,5-day biochemical oxygen demand,ammonianitrogen,total organic carbon,permanganate index,dissolved oxygen,2-methylisoborneol,geosmin,and turbidity) was studied by the bivariate analysis.The stepwise regression analysis was used to study and establish a regression model for preliminarily predicting the water quality of the reservoirs,with algae density,taste and odor compounds as dependent variables,and other environmental factors mentioned above as independent variables,respectively.Considering the current operational and problems of water plans in Zhuhai City, suitable solutions for solving the algae problems were analyzed and proposed from two perspectives: pollution source control and process transformation. The water quality of the reservoirs in Zhuhai City basically conformed to the standard of Class III surface water bodies from 2016 to 2019.However,the contents of total nitrogen and total phosphorus in some reservoirs exceeded the standard.From 2016 to 2019,the average algae density in the four reservoirs were 17.90 million cells/L in Meixi reservoir,18.78 million L-1in Zhuyin reservoir,9.43 million L-1in Fenghuangshan reservoir and 108.39 million L-1in Dajingshan reservoir,respectively.Under the influence of climate and water environment quality,the increase of algae density mostly occurred in spring,while the content of taste and odor compounds in the reservoirs were higher in autumn and winter,which could reach 5 times of the maximum odor threshold.Regression analysis showed that the water quality factors affecting algae density in Zhuhai reservoir involved total nitrogen and organic matter.The permanganate index was positively correlated with algal density,while total nitrogen and 5-day biochemical oxygen demand had negative correlation with the algal density.In addition,turbidity,organic matter and ammonianitrogen may contribute to the formation of taste and odor compounds in the reservoirs.And ammonianitrogen was the dominant factor and positively correlated with geosmin.Taking the monthly mean algae density of Zhuyin reservoir as the dependent variable while total nitrogen as the independent variable,a wellfitting regression model was established (R2=0.911,P<0.001,n=9).Furthermore,taking geosmin as the dependent variable while turbidity,permanganate index ammonianitrogen as the independent variables,a well-fitted regression model was developed (R2=0.911,P<0.001,n=54). High algae density,high taste and odor substances were the main water pollution problems in Zhuhai City.Ammonianitrogen and organic matter were the key factors affecting algae density and the production of taste and odor compounds in the reservoirs,algae problems in drinking water sources in Zhuhai City can be effectively solved by source control combined with the end treatment of ozone activated carbon or other advanced treatment technologies.
2021, 19(4):739-749,767.
Abstract:
Heavy metals in sediments were one of the most harmful and longlasting sources of pollution in the lake basin.The distribution characteristics,source analysis,change trend,occurrence form,adsorption,release rules, and risk assessment of heavy metals in the sediments of Dongting Lake have already been studied by domestic scholars.Based on the sampling investigation of the three lakes and four rivers in the Dongting Lake and the previous research results,the pollution status and possible pollution sources of heavy metals were analyzed comprehensively,which provided a basis for the control of heavy metal pollution in the Dongting Lake. In August 2019,thirtynine and fourteen sampling sites were set up to collect sediments from the lake and four rivers.The samples were cryopreserved to the laboratory.Aqua regia extraction and inductively coupled plasma mass spectrometry (ICPMS) were used to detect the heavy metal content in sediment samples.The heavy metal pollution in Dongting Lake was evaluated by the ground accumulation index and the ecological risk assessment method. [JP3]The average mass fraction of heavy metals were Zn（121.01 mg/kg）>Cr（66.39 mg/kg）>Ni（33.34 mg/kg）>Pb（31.14 mg/kg）>Cu（30.57 mg/kg）>[JP]As（16.58 mg/kg）>Cd（2.88 mg/kg）,respectively.The spatial variation coefficient of Cd was 159.91%.The average content of Cd in the three lakes has decreased in recent 10 years,especially in the West Dongting Lake and the South Dongting Lake,which was up to 19%~74%.However,the East Dongting Lake was relatively more stable and the heavy metal content was still high.According to the ground cumulative index value mean,the pollution of 7 kinds of heavy metals showed.According to single heavy metal hazard index value,the comprehensive potential ecological risk of heavy metal elements was as follows:East Dongting Lake (high)>West Dongting Lake (medium)>South Dongting Lake (low);The inflow rivers were Zishui (high)>Yuanjiang (high)>Xiangjiang (high)>Lishui (low).The overall comprehensive ecological risk index value of Dongting Lake was 308.35,which was at a high ecological risk level. Conclusions(1) The spatial distribution of seven heavy metal elements in the surface sediments of Dongting Lake and the rivers was significantly different.The contents of elements were 0.51,0.57,0.51,0.45,0.29,7.72 and 0.34 times higher than the background values.Compared with other lakes in China,the content of Cd in Dongting Lake was at a higher level,and the contents of the other six heavy metals were at an intermediate level.(2) The results of the two methodslike the ground accumulation index,and the ecological risk assessment method,had shown a Cd for the most serious heavy metal pollution damage elements in East Dongting Lake and water of the lake district,respectively,and the most serious area of sediment pollution in rivers was seriously polluted and high potential ecological risk in Dongting Lake valley. Ni,Cr,Cu and Zn were heavy metals with moderate pollution and low risk.Pb and As were heavy metals with mild pollution and low risk.(3) According to the correlation analysis and principal component analysis,the seven kinds of heavy metal elements may be divided into three categories,including Cd and Zn,respectively,according to the situation of Dongting Lake basin′s natural and human activity,Cd probably from pesticides,fertilizers and sewage may also come from steel manufacturing,paint,etc.,Zn may come from zinc mining or rock weathering and erosion of minerals,and As were the third category and may belong to natural sources.Based on the results of this study,it was suggested that the next step should be the regional classification of pollution levels in Dongting Lake.The environmental protection inspectors and other relevant departments are urged to strengthen the control of Cd input from sources inside and outside the river basin.Comprehensive measures of ectopic or in situ treatment should be adopted.The ecological restoration of Dongting Lake sediments was carried out to eliminate the heavy metal pollution of sediments and improve the overall ecological environment level.
Heavy metals in sediments were one of the most harmful and longlasting sources of pollution in the lake basin.The distribution characteristics,source analysis,change trend,occurrence form,adsorption,release rules, and risk assessment of heavy metals in the sediments of Dongting Lake have already been studied by domestic scholars.Based on the sampling investigation of the three lakes and four rivers in the Dongting Lake and the previous research results,the pollution status and possible pollution sources of heavy metals were analyzed comprehensively,which provided a basis for the control of heavy metal pollution in the Dongting Lake. In August 2019,thirtynine and fourteen sampling sites were set up to collect sediments from the lake and four rivers.The samples were cryopreserved to the laboratory.Aqua regia extraction and inductively coupled plasma mass spectrometry (ICPMS) were used to detect the heavy metal content in sediment samples.The heavy metal pollution in Dongting Lake was evaluated by the ground accumulation index and the ecological risk assessment method. [JP3]The average mass fraction of heavy metals were Zn（121.01 mg/kg）>Cr（66.39 mg/kg）>Ni（33.34 mg/kg）>Pb（31.14 mg/kg）>Cu（30.57 mg/kg）>[JP]As（16.58 mg/kg）>Cd（2.88 mg/kg）,respectively.The spatial variation coefficient of Cd was 159.91%.The average content of Cd in the three lakes has decreased in recent 10 years,especially in the West Dongting Lake and the South Dongting Lake,which was up to 19%~74%.However,the East Dongting Lake was relatively more stable and the heavy metal content was still high.According to the ground cumulative index value mean,the pollution of 7 kinds of heavy metals showed.According to single heavy metal hazard index value,the comprehensive potential ecological risk of heavy metal elements was as follows:East Dongting Lake (high)>West Dongting Lake (medium)>South Dongting Lake (low);The inflow rivers were Zishui (high)>Yuanjiang (high)>Xiangjiang (high)>Lishui (low).The overall comprehensive ecological risk index value of Dongting Lake was 308.35,which was at a high ecological risk level. Conclusions(1) The spatial distribution of seven heavy metal elements in the surface sediments of Dongting Lake and the rivers was significantly different.The contents of elements were 0.51,0.57,0.51,0.45,0.29,7.72 and 0.34 times higher than the background values.Compared with other lakes in China,the content of Cd in Dongting Lake was at a higher level,and the contents of the other six heavy metals were at an intermediate level.(2) The results of the two methodslike the ground accumulation index,and the ecological risk assessment method,had shown a Cd for the most serious heavy metal pollution damage elements in East Dongting Lake and water of the lake district,respectively,and the most serious area of sediment pollution in rivers was seriously polluted and high potential ecological risk in Dongting Lake valley. Ni,Cr,Cu and Zn were heavy metals with moderate pollution and low risk.Pb and As were heavy metals with mild pollution and low risk.(3) According to the correlation analysis and principal component analysis,the seven kinds of heavy metal elements may be divided into three categories,including Cd and Zn,respectively,according to the situation of Dongting Lake basin′s natural and human activity,Cd probably from pesticides,fertilizers and sewage may also come from steel manufacturing,paint,etc.,Zn may come from zinc mining or rock weathering and erosion of minerals,and As were the third category and may belong to natural sources.Based on the results of this study,it was suggested that the next step should be the regional classification of pollution levels in Dongting Lake.The environmental protection inspectors and other relevant departments are urged to strengthen the control of Cd input from sources inside and outside the river basin.Comprehensive measures of ectopic or in situ treatment should be adopted.The ecological restoration of Dongting Lake sediments was carried out to eliminate the heavy metal pollution of sediments and improve the overall ecological environment level.
2021, 19(4):750-757.
Abstract:
The riverside groundwater source area has both river and groundwater characteristics.Due to the particularity of its location and the complexity of recharge conditions,it is difficult to divide the protection area.In 2018,the Ministry of Environmental Protection of the People′s Republic of China issued the Technical Specification for the Division of Drinking Water Source Protection Zones(HJ 338—2018),the regulation only stipulates that the boundary of the protected area should be divided according to the source of river water and the source of groundwater,both of them should be combined as the final boundary of the protected area.Operability does not provide a method and procedure for the classification of riverfront groundwater sources because of their special characteristics. To accurately determine the type of water source area,the land area of the protected area is calculated by empirical formula,and the results of pumping test are used to calculate the parameters of a complete well of phreatic water.The hydraulic gradient of group well is calculated accurately by the iterative operation of the interpolation method.The radius of the protected area is finally calculated with the radius of the empirical value.The analogy and empirical method are used to divide the water area of the protected area,taking into account the surrounding river and the influence of factors such as the distribution of upstream pollution sources,the size of risk sources,and river water quality on the size of the protected area.Finally,the scope of the protected area is revised according to the surrounding terrain and ground conditions. The type of Wangmu water source area is medium and small-sized pore phreatic water source area.The lithology of the phreatic water aquifer is mainly medium-coarse sand.The radius of the land area of the first-class protection area is 66.5 m and that of the-secondclass protection area is 665.0 m.The water area of the first-class protected area divided by analogy and is extended to 1 000 m to the upper reaches and 100 m to the lower reaches of the Hutuo River.The water area of the second-class protected area extends 2 000 m to the upper reaches of the Hutuo River and 770 m to the lower reaches of the first-class protected area. Conclusions (1) The investigation of the basic environmental conditions of the riverside groundwater sources and the nearby rivers is an important prerequisite for the division of the protection zones,and the flow direction and velocity of groundwater and surface water should be fully considered,according to the distribution of pollution sources,the migration and diffusion of pollutants,the pollution source type and risk grade can be determined accurately.(2) Taking into full account the hydrogeological characteristics of the region,combining with the geomorphological features and genetic analysis of the rivers near the region,comprehensively utilizing the information of well structure map and hydrogeological section map,etc.,accurately judging the type of riverfront groundwater source area.(3) When choosing the method of the protection zone division of riverfront groundwater source area,the relationship between groundwater and river and the influence of groundwater exploitation on the quality and quantity of river water are fully considered.The radius of the protected area is calculated by the empirical formula method and the land area is divided,and the water area is divided by the analogy empirical method,the combination of the two methods is suitable for the division of the groundwater source protection area near the river,which is closely connected with the surrounding rivers.(4) The definition of the scope of the riverside groundwater source protection area should be based on the actual situation of the topography and topography of the area,the distribution of pollution sources,the flow direction of groundwater and surface water,etc.,to facilitate the daily environmental management of the protected area,the boundary of the union area divided by the rivertype water source and the groundwatertype water source is revised,wherever possible,clearly marked features should be used as the boundary of the protected area.
The riverside groundwater source area has both river and groundwater characteristics.Due to the particularity of its location and the complexity of recharge conditions,it is difficult to divide the protection area.In 2018,the Ministry of Environmental Protection of the People′s Republic of China issued the Technical Specification for the Division of Drinking Water Source Protection Zones(HJ 338—2018),the regulation only stipulates that the boundary of the protected area should be divided according to the source of river water and the source of groundwater,both of them should be combined as the final boundary of the protected area.Operability does not provide a method and procedure for the classification of riverfront groundwater sources because of their special characteristics. To accurately determine the type of water source area,the land area of the protected area is calculated by empirical formula,and the results of pumping test are used to calculate the parameters of a complete well of phreatic water.The hydraulic gradient of group well is calculated accurately by the iterative operation of the interpolation method.The radius of the protected area is finally calculated with the radius of the empirical value.The analogy and empirical method are used to divide the water area of the protected area,taking into account the surrounding river and the influence of factors such as the distribution of upstream pollution sources,the size of risk sources,and river water quality on the size of the protected area.Finally,the scope of the protected area is revised according to the surrounding terrain and ground conditions. The type of Wangmu water source area is medium and small-sized pore phreatic water source area.The lithology of the phreatic water aquifer is mainly medium-coarse sand.The radius of the land area of the first-class protection area is 66.5 m and that of the-secondclass protection area is 665.0 m.The water area of the first-class protected area divided by analogy and is extended to 1 000 m to the upper reaches and 100 m to the lower reaches of the Hutuo River.The water area of the second-class protected area extends 2 000 m to the upper reaches of the Hutuo River and 770 m to the lower reaches of the first-class protected area. Conclusions (1) The investigation of the basic environmental conditions of the riverside groundwater sources and the nearby rivers is an important prerequisite for the division of the protection zones,and the flow direction and velocity of groundwater and surface water should be fully considered,according to the distribution of pollution sources,the migration and diffusion of pollutants,the pollution source type and risk grade can be determined accurately.(2) Taking into full account the hydrogeological characteristics of the region,combining with the geomorphological features and genetic analysis of the rivers near the region,comprehensively utilizing the information of well structure map and hydrogeological section map,etc.,accurately judging the type of riverfront groundwater source area.(3) When choosing the method of the protection zone division of riverfront groundwater source area,the relationship between groundwater and river and the influence of groundwater exploitation on the quality and quantity of river water are fully considered.The radius of the protected area is calculated by the empirical formula method and the land area is divided,and the water area is divided by the analogy empirical method,the combination of the two methods is suitable for the division of the groundwater source protection area near the river,which is closely connected with the surrounding rivers.(4) The definition of the scope of the riverside groundwater source protection area should be based on the actual situation of the topography and topography of the area,the distribution of pollution sources,the flow direction of groundwater and surface water,etc.,to facilitate the daily environmental management of the protected area,the boundary of the union area divided by the rivertype water source and the groundwatertype water source is revised,wherever possible,clearly marked features should be used as the boundary of the protected area.
2021, 19(4):758-767.
Abstract:
Bank slope instability is a common geological hazard,which extremely threatens people′s property and life in China.Rainfall is an important cause of bank slope instability,and the slope angle and the slope material directly control the stability of the bank slope.Therefore,it is meaningful to study the influence of slope angle and slope material on bank slope stability under rainfall conditions. To explore the influence of slope angle and slope material on the instability of water banks under heavy rainfall,5 model tests were carried out by taking different slope angles,slope materials and the deformation characteristics of bank slope were observed at different times.The change of pore water pressure and earth pressure in different positions of the slope were monitored by a pore water pressure gauge and earth pressure gauge. By comparing the failure process of 5 model tests at different times,the results showed that heavy rainfall had a significant effect on the stability of the slope surface structure.Under the action of rainfall,the surface structure rapidly saturated,the shear strength was greatly reduced and the stability deteriorates.However,the internal structure was less affected because the water was difficult to penetrate.At 60° slope angle,there were obvious cracks in the bank slope after 10 minutes of rainfall,and the cracks became larger as the rainfall time increased.After 2 hours of rainfall,the slope angle changed from 60° to 47°,and there were many obvious cracks on the surface of the bank slope.When the slope angle was 30° and 45°,there was no obvious damage on the bank slopes.The change in bank slope with different slope materials was also significantly different.There was little obvious damage to the clay slope during the whole test.When the sand content was 20%,the bank slope had erosion damage after 40 minutes of rainfall,and as the rainfall time increased,the damage gradually increased,Eventually,a collapse occurred on the surface of the bank slope when the sand content was 40%,and it was also noted that the bank slope had obvious cracks after 5 minutes of rainfall.About 70 minutes,there was a scour groove in the middle of the bank slope,which gradually widened with the increase of rainfall time. Under the rainfall,the bank slope became heavier and the sliding force increased.Moreover,with the increase of the water content of the bank slope,the shear strength decreased sharply,then induced bank slope instability.The slope angle had a great influence on bank stability.The bigger the slope angle,the deeper the rain seep,and the sliding force and infiltration force become stronger,which was not conducive to the stability of the bank slope,the influence was 60°＞45°＞30°,respectively.The slope material affected the bank slope stability directly,and different materials had different permeability.When the sand content was 40%,the permeability was best,and bank slope was damaged at 5 minutes and the response of pore water pressure was fast,the instability probability was higher with the worst permeability.When the bank slope was pure clay,and no damage obviously,and the response of pore water pressure was slow,the impact of rainfall on bank slope stability was low relatively.
Bank slope instability is a common geological hazard,which extremely threatens people′s property and life in China.Rainfall is an important cause of bank slope instability,and the slope angle and the slope material directly control the stability of the bank slope.Therefore,it is meaningful to study the influence of slope angle and slope material on bank slope stability under rainfall conditions. To explore the influence of slope angle and slope material on the instability of water banks under heavy rainfall,5 model tests were carried out by taking different slope angles,slope materials and the deformation characteristics of bank slope were observed at different times.The change of pore water pressure and earth pressure in different positions of the slope were monitored by a pore water pressure gauge and earth pressure gauge. By comparing the failure process of 5 model tests at different times,the results showed that heavy rainfall had a significant effect on the stability of the slope surface structure.Under the action of rainfall,the surface structure rapidly saturated,the shear strength was greatly reduced and the stability deteriorates.However,the internal structure was less affected because the water was difficult to penetrate.At 60° slope angle,there were obvious cracks in the bank slope after 10 minutes of rainfall,and the cracks became larger as the rainfall time increased.After 2 hours of rainfall,the slope angle changed from 60° to 47°,and there were many obvious cracks on the surface of the bank slope.When the slope angle was 30° and 45°,there was no obvious damage on the bank slopes.The change in bank slope with different slope materials was also significantly different.There was little obvious damage to the clay slope during the whole test.When the sand content was 20%,the bank slope had erosion damage after 40 minutes of rainfall,and as the rainfall time increased,the damage gradually increased,Eventually,a collapse occurred on the surface of the bank slope when the sand content was 40%,and it was also noted that the bank slope had obvious cracks after 5 minutes of rainfall.About 70 minutes,there was a scour groove in the middle of the bank slope,which gradually widened with the increase of rainfall time. Under the rainfall,the bank slope became heavier and the sliding force increased.Moreover,with the increase of the water content of the bank slope,the shear strength decreased sharply,then induced bank slope instability.The slope angle had a great influence on bank stability.The bigger the slope angle,the deeper the rain seep,and the sliding force and infiltration force become stronger,which was not conducive to the stability of the bank slope,the influence was 60°＞45°＞30°,respectively.The slope material affected the bank slope stability directly,and different materials had different permeability.When the sand content was 40%,the permeability was best,and bank slope was damaged at 5 minutes and the response of pore water pressure was fast,the instability probability was higher with the worst permeability.When the bank slope was pure clay,and no damage obviously,and the response of pore water pressure was slow,the impact of rainfall on bank slope stability was low relatively.
2021, 19(4):768-775.
Abstract:
Aiming at the reliability analysis of gravity dams by traditional probabilistic reliability analysis methods,the analysis process has poor convergence,low accuracy,and long time consumption due to the influence of the structural performance uncertainty and the high nonlinearity of the function.Combined with improved particle swarm optimization (IPSO) and the Kriging model,a reliability analysis method of gravity dam based on the IPSO-Kriging model is proposed.The particle swarm optimization (PSO) algorithm is reconstructed employing mutation operation,inertial weight,and Gaussian weight,to improve the traditional PSO algorithm′s slow convergence speed and early maturity.The IPSO and Kriging model are integrated to establish the reliability optimization model of gravity dam based on the IPSO-Kriging model. Under the synergistic action of many factors,such as static and dynamic load,bad environment,and aging of materials,the functional function of a gravity dam is often highly nonlinear,which is difficult to be described by an explicit mathematical model.This leads to the limitation of the traditional analysis method in the process of gravity dam engineering reliability.To break through the constraints of highly nonlinear and non-dominant structural function,it is intended to explore a reasonable optimization scheme based on the basic principle of the Kriging model to make it have higher fitting ability and robustness,to achieve accurate and efficient calculation of reliability of complex gravity dam engineering. Considering the traditional Kriging model,the pattern search method has poor global optimization ability and is sensitive to the initial value.The PSO algorithm is adopted and variation operation,inertial weight,and Gaussian weight are implemented to improve the algorithm.On this basis,the IPSO algorithm is used to optimize the Kriging model to overcome the defects of the pattern search method and build the IPSO-Kriging model with stronger and stable predictive ability.Finally,on the premise of explicit numerical examples to verify the accuracy and efficiency of the established method,the ABAQUS simulation software and Matlab implementation program are used in combination with the actual engineering to realize the efficient calculation of gravity dam reliability. Based on the actual gravity dam engineering,considering the highly nonlinear and nondominant characteristics of gravity dam function,the constructed IPSO-Kriging model and the reliability index optimization calculation method are applied to realize the efficient calculation of the reliability index of gravity dam.This is mainly attributed to the following unique advantages of the IPSO-Kriging model in reliability analysis of complex structural engineering with high nonlinear degree:(1) The variation operation,inertial weight,and Gaussian weight of PSO algorithm are improved and introduced into the Kriging model.An IPSO algorithm based optimization Kriging model is proposed,which could effectively solve the problems of the local optimal solution and difficult initial value selection in the traditional Kriging model.(2) The reliability index optimization calculation model is established based on the organic combination of reliability index definition and optimization algorithm,and the reliability index optimization design method of a gravity dam is proposed based on the IPSO-Kriging model.The method presented can improve the calculation accuracy and reduce the number of simulations to save the calculation cost.(3) Based on the advantages of the established IPSO-Kriging model and the high efficiency of the proposed method,the finite element model of structural limit state reliability is built with the help of the advantages of the finite element simulation platform,and the corresponding implementation program is developed.Compared with other methods,this method has higher calculation accuracy and efficiency,and good adaptability and robustness.
Aiming at the reliability analysis of gravity dams by traditional probabilistic reliability analysis methods,the analysis process has poor convergence,low accuracy,and long time consumption due to the influence of the structural performance uncertainty and the high nonlinearity of the function.Combined with improved particle swarm optimization (IPSO) and the Kriging model,a reliability analysis method of gravity dam based on the IPSO-Kriging model is proposed.The particle swarm optimization (PSO) algorithm is reconstructed employing mutation operation,inertial weight,and Gaussian weight,to improve the traditional PSO algorithm′s slow convergence speed and early maturity.The IPSO and Kriging model are integrated to establish the reliability optimization model of gravity dam based on the IPSO-Kriging model. Under the synergistic action of many factors,such as static and dynamic load,bad environment,and aging of materials,the functional function of a gravity dam is often highly nonlinear,which is difficult to be described by an explicit mathematical model.This leads to the limitation of the traditional analysis method in the process of gravity dam engineering reliability.To break through the constraints of highly nonlinear and non-dominant structural function,it is intended to explore a reasonable optimization scheme based on the basic principle of the Kriging model to make it have higher fitting ability and robustness,to achieve accurate and efficient calculation of reliability of complex gravity dam engineering. Considering the traditional Kriging model,the pattern search method has poor global optimization ability and is sensitive to the initial value.The PSO algorithm is adopted and variation operation,inertial weight,and Gaussian weight are implemented to improve the algorithm.On this basis,the IPSO algorithm is used to optimize the Kriging model to overcome the defects of the pattern search method and build the IPSO-Kriging model with stronger and stable predictive ability.Finally,on the premise of explicit numerical examples to verify the accuracy and efficiency of the established method,the ABAQUS simulation software and Matlab implementation program are used in combination with the actual engineering to realize the efficient calculation of gravity dam reliability. Based on the actual gravity dam engineering,considering the highly nonlinear and nondominant characteristics of gravity dam function,the constructed IPSO-Kriging model and the reliability index optimization calculation method are applied to realize the efficient calculation of the reliability index of gravity dam.This is mainly attributed to the following unique advantages of the IPSO-Kriging model in reliability analysis of complex structural engineering with high nonlinear degree:(1) The variation operation,inertial weight,and Gaussian weight of PSO algorithm are improved and introduced into the Kriging model.An IPSO algorithm based optimization Kriging model is proposed,which could effectively solve the problems of the local optimal solution and difficult initial value selection in the traditional Kriging model.(2) The reliability index optimization calculation model is established based on the organic combination of reliability index definition and optimization algorithm,and the reliability index optimization design method of a gravity dam is proposed based on the IPSO-Kriging model.The method presented can improve the calculation accuracy and reduce the number of simulations to save the calculation cost.(3) Based on the advantages of the established IPSO-Kriging model and the high efficiency of the proposed method,the finite element model of structural limit state reliability is built with the help of the advantages of the finite element simulation platform,and the corresponding implementation program is developed.Compared with other methods,this method has higher calculation accuracy and efficiency,and good adaptability and robustness.
2021, 19(4):776-785.
Abstract:
The calculation of bridge backwater of piers played an important role in both the riverbanks and the floodplain.Previous studies showed that the bridge backwater of piers could not be ignored.However,in the simulation of floodplain inundation caused by river overbank,the influence of bridge was not considered in river flood simulation.Bridge hole clogging is a common phenomenon in narrow rivers of mountainous areas,it is,therefore,necessary to study the influence of bridge hole clogging.For this reason,the contribution of bridge backwater of piers and bridge clogging to flooding is explored,which provides the foundation for the actual bridge maintenance and protection and floodplain disaster reduction. A catastrophic flood took place in the Honglai Town of the downriver reaches of the Meixi River catchment during the typhoon "Meranti" in 2016.As a result,the inundation depth of the floodplain around the Meixi River was nearly 3 m.The typhoon "Meranti" caused a total of 6881 billion direct losses according to statistics from the government.The bridge backwater of piers may play an important role in the flooding during the typhoon "Meranti".Therefore,eight bridges along the Meixi River in Honglai Town were selected.To relatively veritably reflect the different shapes and structures of bridges and riverbeds,a refined three-dimensional model was built by three-dimensional hydrodynamic software (FLOW3D).According to the measurement result by unmanned aerial vehicle oblique photography,the surface data was obtained with 1 meter DEM resolution in the Honglai Town.After that,the river channel and adjacent floodplain three-dimension models were generated.In addition,associated with field investigation of each bridge,the refined three-dimensional model of each bridge was also depicted in equal proportion by FLOW3D. The model calculated the river water level changes and the backwater of piers of each bridge in five return periods.The observed water level data of different locations along the Meixi River was used to validate the FLOW3D model in 10-year,20-year,and 50-year return periods.The maximum relative error between the simulated value and the data value is 0.19 meters in a single point.The simulated value using the average water level of each cross-section might be one of the reasons for explaining the error.As a whole,most of the simulated water level values were larger than the observed data values.In addition,it was verified that the absolute errors of the abovementioned three return periods are less than 0.1 meters.The average absolute errors of the 10year,20year,and 50year return period were 0.02 meter,0.05 meter and 0.04 meter,respectively.The Nash coefficients were 0.83,0.77,and 0.81 respectively,which indicated that the simulated values fit the observed data well.Based on the verified FLOW3D model,the backwater of piers for each bridge in different return periods were calculated.The influence of bridge hole clogging degree was also simulated.The results show that most of the upstream bridge′s backwater values were greater than the downstream bridges.Among them,the backwater of bridge number seven had the greatest impact.The river water will overflow to the floodplain near the bridge when the return periods larger than 10 year since its obstruction effect can even reach to 47% in channel crosssection.When the return period was more than 20-year,its contribution to the floodplain′s maximum inundation depth was more than 15% in front of the bridge number seven.In almost all return periods,the average velocity under bridge number seven was greater than the calculated critical velocity,which may cause scouring of the riverbank.The increasing proportion of the bridge hole clogging degree was linear with the increase of water level in front of the bridge.Compared with the situation without clogging,the contribution ratio with 20% clogging to the floodplain maximum inundation depth in front of the bridge will increase 21%.The average water level in front of bridge number seven with 20% clogging in 50-year was larger than that in 100-year without clogging. The variations of backwater of piers in front of each bridge along the Meixi River were calculated and the inundation contribution of each bridge to its adjacent floodplain was revealed.The flow simulated velocity and calculated velocity under each bridge were compared for all five return periods and all bridges can be used to simply estimate flood scouring to the riverbank.The effect of bridge hole clogging on upstream water level rising was determined.It is implied that reducing the obstruction in channel crosssection will have a relatively significant effect on decreasing adjacent floodplain inundation extent.It is suggested that removing the retaining part of piers extending into the river channel of bridge number seven.If no corresponding measures can be taken,monitoring equipment should be installed at bridge number seven to prevent the bridge from clogging.The abovementioned findings can provide important references for flood control,disaster reduction,and bridge safety.
The calculation of bridge backwater of piers played an important role in both the riverbanks and the floodplain.Previous studies showed that the bridge backwater of piers could not be ignored.However,in the simulation of floodplain inundation caused by river overbank,the influence of bridge was not considered in river flood simulation.Bridge hole clogging is a common phenomenon in narrow rivers of mountainous areas,it is,therefore,necessary to study the influence of bridge hole clogging.For this reason,the contribution of bridge backwater of piers and bridge clogging to flooding is explored,which provides the foundation for the actual bridge maintenance and protection and floodplain disaster reduction. A catastrophic flood took place in the Honglai Town of the downriver reaches of the Meixi River catchment during the typhoon "Meranti" in 2016.As a result,the inundation depth of the floodplain around the Meixi River was nearly 3 m.The typhoon "Meranti" caused a total of 6881 billion direct losses according to statistics from the government.The bridge backwater of piers may play an important role in the flooding during the typhoon "Meranti".Therefore,eight bridges along the Meixi River in Honglai Town were selected.To relatively veritably reflect the different shapes and structures of bridges and riverbeds,a refined three-dimensional model was built by three-dimensional hydrodynamic software (FLOW3D).According to the measurement result by unmanned aerial vehicle oblique photography,the surface data was obtained with 1 meter DEM resolution in the Honglai Town.After that,the river channel and adjacent floodplain three-dimension models were generated.In addition,associated with field investigation of each bridge,the refined three-dimensional model of each bridge was also depicted in equal proportion by FLOW3D. The model calculated the river water level changes and the backwater of piers of each bridge in five return periods.The observed water level data of different locations along the Meixi River was used to validate the FLOW3D model in 10-year,20-year,and 50-year return periods.The maximum relative error between the simulated value and the data value is 0.19 meters in a single point.The simulated value using the average water level of each cross-section might be one of the reasons for explaining the error.As a whole,most of the simulated water level values were larger than the observed data values.In addition,it was verified that the absolute errors of the abovementioned three return periods are less than 0.1 meters.The average absolute errors of the 10year,20year,and 50year return period were 0.02 meter,0.05 meter and 0.04 meter,respectively.The Nash coefficients were 0.83,0.77,and 0.81 respectively,which indicated that the simulated values fit the observed data well.Based on the verified FLOW3D model,the backwater of piers for each bridge in different return periods were calculated.The influence of bridge hole clogging degree was also simulated.The results show that most of the upstream bridge′s backwater values were greater than the downstream bridges.Among them,the backwater of bridge number seven had the greatest impact.The river water will overflow to the floodplain near the bridge when the return periods larger than 10 year since its obstruction effect can even reach to 47% in channel crosssection.When the return period was more than 20-year,its contribution to the floodplain′s maximum inundation depth was more than 15% in front of the bridge number seven.In almost all return periods,the average velocity under bridge number seven was greater than the calculated critical velocity,which may cause scouring of the riverbank.The increasing proportion of the bridge hole clogging degree was linear with the increase of water level in front of the bridge.Compared with the situation without clogging,the contribution ratio with 20% clogging to the floodplain maximum inundation depth in front of the bridge will increase 21%.The average water level in front of bridge number seven with 20% clogging in 50-year was larger than that in 100-year without clogging. The variations of backwater of piers in front of each bridge along the Meixi River were calculated and the inundation contribution of each bridge to its adjacent floodplain was revealed.The flow simulated velocity and calculated velocity under each bridge were compared for all five return periods and all bridges can be used to simply estimate flood scouring to the riverbank.The effect of bridge hole clogging on upstream water level rising was determined.It is implied that reducing the obstruction in channel crosssection will have a relatively significant effect on decreasing adjacent floodplain inundation extent.It is suggested that removing the retaining part of piers extending into the river channel of bridge number seven.If no corresponding measures can be taken,monitoring equipment should be installed at bridge number seven to prevent the bridge from clogging.The abovementioned findings can provide important references for flood control,disaster reduction,and bridge safety.
2021, 19(4):786-794,813.
Abstract:
The arch dam is a three-dimensional shell structure with a complex operating environment and complicated stress state,its actual working behavior is different from the design condition.During the operation of a high arch dam,the temperature load,which is determined by the difference between the temperature field during operation and its joint closure temperature field,is one of the main loads.Generally speaking,it is easy to obtain the temperature field of arch sealing.However,thermal analysis of the arch dam during operation is difficult due to the influence of climate conditions,structural form,and operation modes.In addition,as the main waterholding structure,the stress state of the arch dam during operation is sophisticated.The mechanical parameters of concrete may differ from the experimental values.Therefore,the research on the real working behavior of the Xiaowan arch dam is of great significance. The material parameters of the Xiaowan arch dam were investigated and the stress distribution was simulated by the finite element method.The temperature distribution on the dam surfaces was fitted by the polynomial as the thermal boundary condition based on the measured temperature.Then transient temperature field of the Xiaowan arch dam was calculated step by step.The elastic modulus of dam concrete and foundation rocks were continuously adjusted to minimize the differentials between the numerical displacements calculated by FEM and the actual displacement measured by the plumb lines.The elastic modulus with the smallest displacement errors was viewed as the actual material parameters.The simulation of stress distribution of the Xiaowan arch dam was carried out based on the inversion results of the temperature field and material parameters. Conclusions (1)The feedback temperature field could represent the temperature field distribution of the Xiaowan arch dam during the operation period.The temperature of the upstream dam surface was mainly affected by the reservoir water.Besides,the temperature of the upstream dam surface near the foundation was higher,between 17 ℃ and 19 ℃ due to the influence of the ground temperature and slag in front of the dam.The temperature of the downstream dam surface was mainly affected by atmospheric temperature,showing a phenomenon that the temperature was higher on both sides than in the middle section.(2) The elastic modulus of the dam concrete during the operation was increased by about 30% relative to the test value.Besides,the deformation modulus of the bedrock was 20%~45% higher than the test value.(3) The calculated displacement agreed well with the measured data with the same trend.The displacement of the Xiaowan arch dam was closely related to the upstream water level.The dam had a trend of slow deformation to the downstream because the aging effect had not yet fully converged at present.(4) The upstream dam surface was basically in a pressure state.Besides,the maximum compressive stress,which was located at the height of 975 m,was about 10 MPa.However,the dam surface above the water level was under tension in winter,and the maximum tensile stress was about 0.6 MPa.The downstream dam surface was basically in a compressive state,and the maximum compressive stress could reach to 17.3 MPa,which was located at the dam toe.Besides,the te2nsile stress zone appeared near the interface between the dam body and the foundation due to the stress concentration,and the global maximum tensile stress was about 0.8 MPa,although the operating state of the dam was still in the safe scope. Conclusions（1）The temperature of the downstream dam surface was mainly affected by atmospheric temperature,showing a phenomenon that the temperature was higher on both sides than the middle section.（2） The elastic modulus of the dam concrete during the operation was increased by about 30% relative to the test value.（3）The stress distributions of the Xiaowan arch dam revealed that its operating state was still in the safe scope.
The arch dam is a three-dimensional shell structure with a complex operating environment and complicated stress state,its actual working behavior is different from the design condition.During the operation of a high arch dam,the temperature load,which is determined by the difference between the temperature field during operation and its joint closure temperature field,is one of the main loads.Generally speaking,it is easy to obtain the temperature field of arch sealing.However,thermal analysis of the arch dam during operation is difficult due to the influence of climate conditions,structural form,and operation modes.In addition,as the main waterholding structure,the stress state of the arch dam during operation is sophisticated.The mechanical parameters of concrete may differ from the experimental values.Therefore,the research on the real working behavior of the Xiaowan arch dam is of great significance. The material parameters of the Xiaowan arch dam were investigated and the stress distribution was simulated by the finite element method.The temperature distribution on the dam surfaces was fitted by the polynomial as the thermal boundary condition based on the measured temperature.Then transient temperature field of the Xiaowan arch dam was calculated step by step.The elastic modulus of dam concrete and foundation rocks were continuously adjusted to minimize the differentials between the numerical displacements calculated by FEM and the actual displacement measured by the plumb lines.The elastic modulus with the smallest displacement errors was viewed as the actual material parameters.The simulation of stress distribution of the Xiaowan arch dam was carried out based on the inversion results of the temperature field and material parameters. Conclusions (1)The feedback temperature field could represent the temperature field distribution of the Xiaowan arch dam during the operation period.The temperature of the upstream dam surface was mainly affected by the reservoir water.Besides,the temperature of the upstream dam surface near the foundation was higher,between 17 ℃ and 19 ℃ due to the influence of the ground temperature and slag in front of the dam.The temperature of the downstream dam surface was mainly affected by atmospheric temperature,showing a phenomenon that the temperature was higher on both sides than in the middle section.(2) The elastic modulus of the dam concrete during the operation was increased by about 30% relative to the test value.Besides,the deformation modulus of the bedrock was 20%~45% higher than the test value.(3) The calculated displacement agreed well with the measured data with the same trend.The displacement of the Xiaowan arch dam was closely related to the upstream water level.The dam had a trend of slow deformation to the downstream because the aging effect had not yet fully converged at present.(4) The upstream dam surface was basically in a pressure state.Besides,the maximum compressive stress,which was located at the height of 975 m,was about 10 MPa.However,the dam surface above the water level was under tension in winter,and the maximum tensile stress was about 0.6 MPa.The downstream dam surface was basically in a compressive state,and the maximum compressive stress could reach to 17.3 MPa,which was located at the dam toe.Besides,the te2nsile stress zone appeared near the interface between the dam body and the foundation due to the stress concentration,and the global maximum tensile stress was about 0.8 MPa,although the operating state of the dam was still in the safe scope. Conclusions（1）The temperature of the downstream dam surface was mainly affected by atmospheric temperature,showing a phenomenon that the temperature was higher on both sides than the middle section.（2） The elastic modulus of the dam concrete during the operation was increased by about 30% relative to the test value.（3）The stress distributions of the Xiaowan arch dam revealed that its operating state was still in the safe scope.
2021, 19(4):795-804.
Abstract:
The Menglou-Qifang inverted siphon is a pressurized water delivery system with ultra-long pipelines and large diameters.Its safe operation is directly related to the normal and stable operation of the entire project.Under sudden accident conditions,complex changes such as water hammers and partial negative pressure may occur,and untimely emergency response or unreasonable scheduling measures may lead to serious accidental damage and water interruption.Therefore,it is of great significance to study the hydraulic response and emergency dispatch of long-distance water conveyance inverted siphon. Taking the Menglou-Qifang inverted siphon (72 km) in the North Hubei Water Resources Allocation Project as the research object,a onedimensional unsteady flow numerical calculation model for accidental conditions was established.The water delivery channel system simulation and control software (SCCS Version 1.0) was used to simulate the hydraulic response characteristics of the long inverted siphon under accidental conditions.The hydraulic response characteristics of different gate dispatching schemes were analyzed and compared,and gate dispatching strategies were proposed accordingly. The hydraulic response characteristics of the long inverted siphon are quite different under different dispatch gate modes.When the gate adopts the asynchronous same speed scheduling rule by keeping the closing time of each gate constant,increase the time interval at which the gate starts to close,and the pressure head of the inverted siphon will increase significantly.If the time interval increases to more than 15 minutes its peak value will exceed the limit.At the same time interval,different closing speeds have little effect on the hydraulic response process of the long inverted siphon,and the pressure range is only 0.49 m.When the gate adopts the synchronous all-speed dispatching rule,the closing time of the inverted siphon outlet has a significant impact on the water head along with the inverted siphon.The shorter the closing time,the more severe the hydraulic response and the easier it is to exceed the limit.When the closing time is less than 30 minutes,the pressure will exceed the limit.Extending the closing time of the inlet and upstream gates will cause more pressure water to enter the inverted siphon section,which is detrimental to the safety of the inverted siphon under accident conditions.When the closing time of the inlet and upstream gates exceeds 30 minutes,the pressure peak of the control section exceeds the design limit. Conclusions (1) In the emergency dispatch of the accident,the hydraulic response process of the inverted siphon is very rapid due to the large gap between the pressure wave velocity and the gravity wave velocity.It will climb to the peak pressure in a short time,and the pressure water will be discharged from the outlet gate in a short time so that the pressure along the entire inverted siphon will eventually stabilize at a safe level.(2) Compared with the synchronous all-speed and asynchronous samespeed scheduling methods,the synchronous all-speed scheduling method is more conducive to the safety of the inverted siphon.(3) Under the synchronous allometric scheduling rules,delaying the inverted siphon inlet and upstream gate closing time,extending the inlet and upstream gate closing time,or quickly closing the inverted siphon outlet and the downstream gate will inhibit the internal pressure water release process of the inverted siphon and make the pressure peaks rise rapidly,increasing the risk of pressure overruns.(4) Under the synchronous all-speed dispatching rules,for the water resources allocation project in northern Hubei,it is recommended that the inverted siphon inlet and upstream gates start to operate no later than 30 minutes after the exit and downstream gates start to close,and the inverted siphon outlet and downstream gates are closed for a long time,it should not be shorter than 30 min,and the closing time of the inverted siphon inlet and the upstream gate should not exceed 30 min.This is a reference set of emergency dispatch combinations for control gates.
The Menglou-Qifang inverted siphon is a pressurized water delivery system with ultra-long pipelines and large diameters.Its safe operation is directly related to the normal and stable operation of the entire project.Under sudden accident conditions,complex changes such as water hammers and partial negative pressure may occur,and untimely emergency response or unreasonable scheduling measures may lead to serious accidental damage and water interruption.Therefore,it is of great significance to study the hydraulic response and emergency dispatch of long-distance water conveyance inverted siphon. Taking the Menglou-Qifang inverted siphon (72 km) in the North Hubei Water Resources Allocation Project as the research object,a onedimensional unsteady flow numerical calculation model for accidental conditions was established.The water delivery channel system simulation and control software (SCCS Version 1.0) was used to simulate the hydraulic response characteristics of the long inverted siphon under accidental conditions.The hydraulic response characteristics of different gate dispatching schemes were analyzed and compared,and gate dispatching strategies were proposed accordingly. The hydraulic response characteristics of the long inverted siphon are quite different under different dispatch gate modes.When the gate adopts the asynchronous same speed scheduling rule by keeping the closing time of each gate constant,increase the time interval at which the gate starts to close,and the pressure head of the inverted siphon will increase significantly.If the time interval increases to more than 15 minutes its peak value will exceed the limit.At the same time interval,different closing speeds have little effect on the hydraulic response process of the long inverted siphon,and the pressure range is only 0.49 m.When the gate adopts the synchronous all-speed dispatching rule,the closing time of the inverted siphon outlet has a significant impact on the water head along with the inverted siphon.The shorter the closing time,the more severe the hydraulic response and the easier it is to exceed the limit.When the closing time is less than 30 minutes,the pressure will exceed the limit.Extending the closing time of the inlet and upstream gates will cause more pressure water to enter the inverted siphon section,which is detrimental to the safety of the inverted siphon under accident conditions.When the closing time of the inlet and upstream gates exceeds 30 minutes,the pressure peak of the control section exceeds the design limit. Conclusions (1) In the emergency dispatch of the accident,the hydraulic response process of the inverted siphon is very rapid due to the large gap between the pressure wave velocity and the gravity wave velocity.It will climb to the peak pressure in a short time,and the pressure water will be discharged from the outlet gate in a short time so that the pressure along the entire inverted siphon will eventually stabilize at a safe level.(2) Compared with the synchronous all-speed and asynchronous samespeed scheduling methods,the synchronous all-speed scheduling method is more conducive to the safety of the inverted siphon.(3) Under the synchronous allometric scheduling rules,delaying the inverted siphon inlet and upstream gate closing time,extending the inlet and upstream gate closing time,or quickly closing the inverted siphon outlet and the downstream gate will inhibit the internal pressure water release process of the inverted siphon and make the pressure peaks rise rapidly,increasing the risk of pressure overruns.(4) Under the synchronous all-speed dispatching rules,for the water resources allocation project in northern Hubei,it is recommended that the inverted siphon inlet and upstream gates start to operate no later than 30 minutes after the exit and downstream gates start to close,and the inverted siphon outlet and downstream gates are closed for a long time,it should not be shorter than 30 min,and the closing time of the inverted siphon inlet and the upstream gate should not exceed 30 min.This is a reference set of emergency dispatch combinations for control gates.
2021, 19(4):805-813.
Abstract:
Submersible agitator,also known as submersible propeller,is widely used in the sewage treatment plant process.Recently,the use of CFD software is used to simulate the flow field changes in the stirred tank,more clearly provides us with theoretical support.It is the emergence of this numerical simulation technology that the research of submersible agitators has entered a new stage.Therefore,researchers from the design parameters of the submersible mixer,installation position,speed adjustment,and other aspects,to not only improve the mixing effect of the submersible mixer,but also achieve the purpose of effective energy saving. Up to now,the installation scheme of submersible agitators has been studied more or less.However,how the blade angle of the submersible agitator affects the flow field has not been studied.Therefore,based on the previous research,the influence of blade angle on the performance of submersible agitators is simulated.The change of impeller blade setting angle is realized by rotating the corresponding angle around the y-axis in turbogrid.The y-axis rotates 2°in the positive direction (clockwise),that is,the blade setting angle is adjusted to -2°(clockwise is negative,counterclockwise is positive),and so on.The purpose is to study the flow characteristics in the stirred tank with different blade placement angles (-4°,-2°,0°,2° and 4°),to provide a reference for selecting the appropriate blade placement angle according to the mixing requirements and energysaving effect. To study the influence of different blade angles (-4°,-2°,0°,2° and 4°) on the flow field in the stirred tank,the numerical simulation of the submerged agitator with different blade angles is carried out,and the flow field is analyzed by CFD-Post software.According to the results of numerical simulation,it is concluded that:(1) The velocity field in the mixing tank is axisymmetric concerning the submersible agitator.The flow is pushed forward along the center of the submersible agitator.When the central jet moves to the other side of the tank wall,the flow diffuses around.The area of velocity distribution cloud diagram in the mixing tank to achieve effective mixing becomes larger and larger with the increase of blade angle,which indicates that the mixing effect of submersible agitator becomes better and better when the blade angle increases from -4° to 4°.(2) The pressure distribution characteristics of the impeller pressure surface are almost the same under different blade placement angles,that is,the high-pressure area is mainly concentrated in the inlet area of the impeller,and the negative pressure area is concentrated in the area near the blade flange and impeller outlet.The pressure on the blade working surface increases with the increase of blade placement angle,that is,the area of the highpressure area increases continuously.At the same time,the shaft power and thrust of the submersible agitator are increasing with the increase of blade angle.(3) Compared with the mixing effect,the effective mixing ratio and effective unit energy consumption of submersible agitators increase with the increase of blade angle.When the blade angle is -4°,the effective unit energy consumption of the submersible mixer is the minimum,and the effective mixing area in the mixing tank is only about half,and a part of low-speed zone or even dead zone will appear in the flow field,which affects the mixing effect.When the blade angle is increased to 4°,the mixing area of the submersible mixer is about 70% (the mixing effect of the submersible mixer has been improved in practical engineering application).Most of the fluid in the flow field has been stirred,which meets the design requirements,and the stirring effect is good.(4) Finally,to prove the accuracy of the numerical simulation results of submersible agitator,the experimental verification is carried out when the blade setting angle is 0°and the error between the numerical simulation and experimental verification is less than 5%,which proves the accuracy of the numerical simulation results.It shows that the research on the blade setting angle of the submersible agitator is feasible and provides a reference for the future research of submersible agitator certain reference. [WTHZ]Conclusions[WTBZ] (1) With the increase of blade angle,the effective mixing area of velocity distribution nephogram in the mixing tank is increasingly larger,and the mixing performance of submersible agitator is improved.(2) When the blade angle increases from -4° to 4°,the shaft power and thrust of submersible agitator motor increase continuously.At the same time,with the increase of blade angle,the corresponding effective mixing ratio and effective unit energy consumption are also increasing.(3) The accuracy and rationality of the numerical simulation results are verified by experiments,which provides certain reference for the future research of submersible agitator.
Submersible agitator,also known as submersible propeller,is widely used in the sewage treatment plant process.Recently,the use of CFD software is used to simulate the flow field changes in the stirred tank,more clearly provides us with theoretical support.It is the emergence of this numerical simulation technology that the research of submersible agitators has entered a new stage.Therefore,researchers from the design parameters of the submersible mixer,installation position,speed adjustment,and other aspects,to not only improve the mixing effect of the submersible mixer,but also achieve the purpose of effective energy saving. Up to now,the installation scheme of submersible agitators has been studied more or less.However,how the blade angle of the submersible agitator affects the flow field has not been studied.Therefore,based on the previous research,the influence of blade angle on the performance of submersible agitators is simulated.The change of impeller blade setting angle is realized by rotating the corresponding angle around the y-axis in turbogrid.The y-axis rotates 2°in the positive direction (clockwise),that is,the blade setting angle is adjusted to -2°(clockwise is negative,counterclockwise is positive),and so on.The purpose is to study the flow characteristics in the stirred tank with different blade placement angles (-4°,-2°,0°,2° and 4°),to provide a reference for selecting the appropriate blade placement angle according to the mixing requirements and energysaving effect. To study the influence of different blade angles (-4°,-2°,0°,2° and 4°) on the flow field in the stirred tank,the numerical simulation of the submerged agitator with different blade angles is carried out,and the flow field is analyzed by CFD-Post software.According to the results of numerical simulation,it is concluded that:(1) The velocity field in the mixing tank is axisymmetric concerning the submersible agitator.The flow is pushed forward along the center of the submersible agitator.When the central jet moves to the other side of the tank wall,the flow diffuses around.The area of velocity distribution cloud diagram in the mixing tank to achieve effective mixing becomes larger and larger with the increase of blade angle,which indicates that the mixing effect of submersible agitator becomes better and better when the blade angle increases from -4° to 4°.(2) The pressure distribution characteristics of the impeller pressure surface are almost the same under different blade placement angles,that is,the high-pressure area is mainly concentrated in the inlet area of the impeller,and the negative pressure area is concentrated in the area near the blade flange and impeller outlet.The pressure on the blade working surface increases with the increase of blade placement angle,that is,the area of the highpressure area increases continuously.At the same time,the shaft power and thrust of the submersible agitator are increasing with the increase of blade angle.(3) Compared with the mixing effect,the effective mixing ratio and effective unit energy consumption of submersible agitators increase with the increase of blade angle.When the blade angle is -4°,the effective unit energy consumption of the submersible mixer is the minimum,and the effective mixing area in the mixing tank is only about half,and a part of low-speed zone or even dead zone will appear in the flow field,which affects the mixing effect.When the blade angle is increased to 4°,the mixing area of the submersible mixer is about 70% (the mixing effect of the submersible mixer has been improved in practical engineering application).Most of the fluid in the flow field has been stirred,which meets the design requirements,and the stirring effect is good.(4) Finally,to prove the accuracy of the numerical simulation results of submersible agitator,the experimental verification is carried out when the blade setting angle is 0°and the error between the numerical simulation and experimental verification is less than 5%,which proves the accuracy of the numerical simulation results.It shows that the research on the blade setting angle of the submersible agitator is feasible and provides a reference for the future research of submersible agitator certain reference. [WTHZ]Conclusions[WTBZ] (1) With the increase of blade angle,the effective mixing area of velocity distribution nephogram in the mixing tank is increasingly larger,and the mixing performance of submersible agitator is improved.(2) When the blade angle increases from -4° to 4°,the shaft power and thrust of submersible agitator motor increase continuously.At the same time,with the increase of blade angle,the corresponding effective mixing ratio and effective unit energy consumption are also increasing.(3) The accuracy and rationality of the numerical simulation results are verified by experiments,which provides certain reference for the future research of submersible agitator.
2021, 19(4):814-821.
Abstract:
China has serious water shortage problems,and the regional distribution of water resources is very unbalanced.The water diversion project may solve the water shortage problem and uneven spatial distribution,but also affect the water situation in the receiving area, making the local water source and the pump station reservoir interrelated and interdependent.It is of great significance for improving the efficiency and reducing the cost of water transfer to master the changing process and influencing factors of water storage level in water transfer projects.As traditional methods are difficult to analyze the action mechanism of multiple influencing factors,several scholars begin to apply the intelligent method based on the "black box" processing of mapping relationship to analyze the reducing water level under the influence of multiple factors and start to use intelligent algorithms such as artificial intelligence algorithm,BP neural network and correlation vector machine to seek the relationship between the regulating and storing water level and various influencing factors. Relevance vector machine (RVM) is a sparse probability model based on Sparse Bayes,which has many advantages such as its kernel functions without the restriction of Mercer′s conditions,and automatically determined relevance vectors.Many factors are influencing the change of the water level before the pump,and there is a complex nonlinear relationship with the water level before the pump.Given the limitations of the BP neural network model,through the analysis and comparison of a large number of experimental data,the selection of pump stations open time,adjust the water level,flow,the analysisof the existing data collection,sorting out of the water diversion scheme fitting data set and build learning samples and fitting training, to regulate water level and forecasting model.The RVM model predicted results are compared with BP neural network prediction model. By selecting reasonable kernel function and kernel width parameters,the prediction results of RVM model are obtained,the application of example shows that the root mean squared error and mean absolute error for RVM prediction model are smaller than BP neural network prediction model using the same sample,prediction accuracy is higher.However,due to the insufficient number of learning samples,the RVM prediction model is not as good as the BP neural network prediction model in reflecting the trend and amplitude in the water level prediction,but the BP neural network prediction model has greater discretization in the result prediction because the main reason is that the model has low accuracy in predicting the samples. Aimed at the complex nonlinear relationship between the water level and its influencing factors,a prediction model of water level for water transfer project based on RVM is established.The model has high precision and low dispersion,which provides a new way for the prediction of water levels for water transfer projects.The prediction results show that the BP neural network prediction can reflect the trend and amplitude,but the RVM prediction model has the advantages of higher accuracy,shorter time consumption,and better generalization ability.In practical application,the advantages of the two different models can be played,the BP neural network model is used to predict the overall trend of the water level,and the RVM model is used to predict the corresponding sample value,to provide more reliable reference for engineers and technicians.
China has serious water shortage problems,and the regional distribution of water resources is very unbalanced.The water diversion project may solve the water shortage problem and uneven spatial distribution,but also affect the water situation in the receiving area, making the local water source and the pump station reservoir interrelated and interdependent.It is of great significance for improving the efficiency and reducing the cost of water transfer to master the changing process and influencing factors of water storage level in water transfer projects.As traditional methods are difficult to analyze the action mechanism of multiple influencing factors,several scholars begin to apply the intelligent method based on the "black box" processing of mapping relationship to analyze the reducing water level under the influence of multiple factors and start to use intelligent algorithms such as artificial intelligence algorithm,BP neural network and correlation vector machine to seek the relationship between the regulating and storing water level and various influencing factors. Relevance vector machine (RVM) is a sparse probability model based on Sparse Bayes,which has many advantages such as its kernel functions without the restriction of Mercer′s conditions,and automatically determined relevance vectors.Many factors are influencing the change of the water level before the pump,and there is a complex nonlinear relationship with the water level before the pump.Given the limitations of the BP neural network model,through the analysis and comparison of a large number of experimental data,the selection of pump stations open time,adjust the water level,flow,the analysisof the existing data collection,sorting out of the water diversion scheme fitting data set and build learning samples and fitting training, to regulate water level and forecasting model.The RVM model predicted results are compared with BP neural network prediction model. By selecting reasonable kernel function and kernel width parameters,the prediction results of RVM model are obtained,the application of example shows that the root mean squared error and mean absolute error for RVM prediction model are smaller than BP neural network prediction model using the same sample,prediction accuracy is higher.However,due to the insufficient number of learning samples,the RVM prediction model is not as good as the BP neural network prediction model in reflecting the trend and amplitude in the water level prediction,but the BP neural network prediction model has greater discretization in the result prediction because the main reason is that the model has low accuracy in predicting the samples. Aimed at the complex nonlinear relationship between the water level and its influencing factors,a prediction model of water level for water transfer project based on RVM is established.The model has high precision and low dispersion,which provides a new way for the prediction of water levels for water transfer projects.The prediction results show that the BP neural network prediction can reflect the trend and amplitude,but the RVM prediction model has the advantages of higher accuracy,shorter time consumption,and better generalization ability.In practical application,the advantages of the two different models can be played,the BP neural network model is used to predict the overall trend of the water level,and the RVM model is used to predict the corresponding sample value,to provide more reliable reference for engineers and technicians.
2021, 19(4):822-832.
Abstract:
Pumping station is an important water conservancy infrastructure,which plays a key role in flood control and drainage,cross-basin water diversion for farmland,and regional irrigation.The analysis of the natural vibration characteristics of the shaft system in water and air makes the natural frequency of the structure avoid the possible excitation frequency of the outside world and prevent resonance,which is of special importance to improve the safety and stability of the pump unit in the process of operation and prolong the life of the unit. A large shaft tubular pump is taken as the research object,based on the equation of SST(shear stress transport)model considers the transmission of turbulent shear stress,and through the modal analysis,it can provide a reference basis for the optimization of the vibration characteristics of the structure and in the process of structural design so that the inherent frequency of the structure can avoid the possible external excitation frequency,which can prevent the structure from resonance. It is found that:the water flow in the outlet channel will produce some vortex bands,which have some influence on the performance of the pump,among which the angle of placement +2° vortex band is the most obvious.The runner inlet pressure pulsation has good periodicity,and its main frequency is 8.6 Hz,which is 2 times the runner blade frequency,and the second frequency is 4.3 Hz,which is the runner blade frequency.Under 3.2 and 3.8 m head conditions,the main frequency of pressure pulsation at the outlet of the runner is 4.3 Hz,i.e.the blade passing frequency,while the opposite is true under the low head condition of 0.5 m,which indicates that the main pressure pulsation at the outlet of the runner is caused by the rotation of the runner,whereas the flow is more unstable under the low head condition.The inherent frequencies of the impeller rotor in the air at different angles are calculated for the first eight orders.It can be seen that more blade is deflected to the negative angle (-2°),its inherent frequency has a decreasing trend,but the difference is small.The inherent frequencies of the first eight steps of each scheme are calculated,with the increase of shaft diameter,the inherent frequencies of each step gradually increased,and the first step frequency increased by 18%.With the increase of shaft length,the inherent frequencies of each step gradually decreased,while with the gradual growth of bearing length,the inherent frequencies of each step also increased,and the first step frequency increased by 83%.It can be seen that the influence of the change of support position and shaft diameter on the inherent frequency is more obvious. Conclusions(1) Comparing the flow field distribution under different heads and different placement angles,the pump streamlines flow pattern is better under the design head and placement angle of -2° working condition.(2) The pressure pulsation at the inlet of the runner has good periodicity,its main frequency is 2 times the runner blade frequency.The second frequency is the runner blade frequency,the rotation of the runner is the main cause of the pressure pulsation.The main frequency at the outlet of the runner is the blade passing frequency,indicating that the main pressure pulsation is caused by the rotation of the runner,and the flow is more unstable under low head conditions.The amplitude of pressure pulsation at the exit point of the runner is smaller than that at the inlet of the runner,and the runner has the role of stabilizing the water flow.(3) Comparing the inherent vibration pattern of the runner in air and water,it can be seen that part of the kinetic energy is transferred to the water body,which leads to the decrease of the inherent frequency of the runner in the water body,but the decrease is small,and the higherorder frequencies of the dry and wet modes are the same.Comparing the nonconstant calculation results and modal analysis results,the main frequency of pressure pulsation is mostly the rotational frequency,which has a large gap with the inherent frequency of the runner and is not easy to cause resonance and meet the structural strength requirements.(4) The effect of increasing the support position and increasing the shaft diameter on the inherent frequency is more obvious,and the firstorder frequency increases by 83% and 18%,respectively.
Pumping station is an important water conservancy infrastructure,which plays a key role in flood control and drainage,cross-basin water diversion for farmland,and regional irrigation.The analysis of the natural vibration characteristics of the shaft system in water and air makes the natural frequency of the structure avoid the possible excitation frequency of the outside world and prevent resonance,which is of special importance to improve the safety and stability of the pump unit in the process of operation and prolong the life of the unit. A large shaft tubular pump is taken as the research object,based on the equation of SST(shear stress transport)model considers the transmission of turbulent shear stress,and through the modal analysis,it can provide a reference basis for the optimization of the vibration characteristics of the structure and in the process of structural design so that the inherent frequency of the structure can avoid the possible external excitation frequency,which can prevent the structure from resonance. It is found that:the water flow in the outlet channel will produce some vortex bands,which have some influence on the performance of the pump,among which the angle of placement +2° vortex band is the most obvious.The runner inlet pressure pulsation has good periodicity,and its main frequency is 8.6 Hz,which is 2 times the runner blade frequency,and the second frequency is 4.3 Hz,which is the runner blade frequency.Under 3.2 and 3.8 m head conditions,the main frequency of pressure pulsation at the outlet of the runner is 4.3 Hz,i.e.the blade passing frequency,while the opposite is true under the low head condition of 0.5 m,which indicates that the main pressure pulsation at the outlet of the runner is caused by the rotation of the runner,whereas the flow is more unstable under the low head condition.The inherent frequencies of the impeller rotor in the air at different angles are calculated for the first eight orders.It can be seen that more blade is deflected to the negative angle (-2°),its inherent frequency has a decreasing trend,but the difference is small.The inherent frequencies of the first eight steps of each scheme are calculated,with the increase of shaft diameter,the inherent frequencies of each step gradually increased,and the first step frequency increased by 18%.With the increase of shaft length,the inherent frequencies of each step gradually decreased,while with the gradual growth of bearing length,the inherent frequencies of each step also increased,and the first step frequency increased by 83%.It can be seen that the influence of the change of support position and shaft diameter on the inherent frequency is more obvious. Conclusions(1) Comparing the flow field distribution under different heads and different placement angles,the pump streamlines flow pattern is better under the design head and placement angle of -2° working condition.(2) The pressure pulsation at the inlet of the runner has good periodicity,its main frequency is 2 times the runner blade frequency.The second frequency is the runner blade frequency,the rotation of the runner is the main cause of the pressure pulsation.The main frequency at the outlet of the runner is the blade passing frequency,indicating that the main pressure pulsation is caused by the rotation of the runner,and the flow is more unstable under low head conditions.The amplitude of pressure pulsation at the exit point of the runner is smaller than that at the inlet of the runner,and the runner has the role of stabilizing the water flow.(3) Comparing the inherent vibration pattern of the runner in air and water,it can be seen that part of the kinetic energy is transferred to the water body,which leads to the decrease of the inherent frequency of the runner in the water body,but the decrease is small,and the higherorder frequencies of the dry and wet modes are the same.Comparing the nonconstant calculation results and modal analysis results,the main frequency of pressure pulsation is mostly the rotational frequency,which has a large gap with the inherent frequency of the runner and is not easy to cause resonance and meet the structural strength requirements.(4) The effect of increasing the support position and increasing the shaft diameter on the inherent frequency is more obvious,and the firstorder frequency increases by 83% and 18%,respectively.
Mobile website
® 2024 All Rights Reserved
冀公网安备13010502002656号
冀公网安备13010502002656号 冀ICP备14004744号-5