Both winter DJF （December, January, February） months and DJF season means long-term data series of 50 regulated rivers discharges rates and the NAO indices were analyzed for different spans. This study is dictated ...Both winter DJF （December, January, February） months and DJF season means long-term data series of 50 regulated rivers discharges rates and the NAO indices were analyzed for different spans. This study is dictated for： （1） detecting the exclusive impacts of the positive phases of NAO indices on rivers discharges rates by estimating the Linear Correlation Coefficient; （2） modeling the interrelations between the discharges rates and NAO indices by estimating the Linear Regression Models, both for manifesting the impact of the positive phase of NAO index; （3） estimating the Linear Trend Coefficient in the discharge series, for manifesting the contribution of the positive phase of NAO index. Discharge rates are mainly influenced by the two mechanisms： the positive phase of NAO index and the environmental conditions in specific catchments, that is where, the positive phase of the NAO index manifest its impact on the related rivers discharges and its contribution in the related configured trends. The discharges fluctuations patterns show some increase in the discharges values have been occurred in regions around the Northern Baltic Proper as well as in Southern Finland and Sweden. The rivers such as Lagan, Nissan, Helgean, Venta, Pamu, Porvoonjoki, Lapuanjoki, Oulujoki, Kyronjoki, Wisla, Eurajoki, Odra, Lielupe, Gota alv, Motala strom, Nykopingsan, Vuoksi, Kalajoki and Simojoki haven not linear discharges changes registered depending on the specificity of the environmental conditions at the catchments areas for those rivers. The positive phase of NAO index has a linear relation with impacted river discharge.展开更多
Coastal hazards induced by meteo-marine forcing are exacerbated by sea level change along the West African coastline. Changes in sea level are induced by ocean processes such as ocean heat content and river discharge....Coastal hazards induced by meteo-marine forcing are exacerbated by sea level change along the West African coastline. Changes in sea level are induced by ocean processes such as ocean heat content and river discharge. However, although these processes control largely change in sea level, they remain poorly understood. This study analyzes changes in ocean heat content, river discharge, and sea level and establishes an interconnection between these parameters using several statistical methods over the 1993-2021 period. Results showed a significant correlation between sea level and ocean heat content at 2000 m depth. The yearly minimum value appears in July from Cote d’Ivoire to Benin, whilst this value appears in June in Nigeria. The temporal variability of ocean heat content, river discharge and sea level along the West African coastline exhibits three or four periods interrupted by some breakpoints with unequal duration. The results indicate that the 1993-2000 period was dominated by an increasing ocean heat content along the coastline, while the period after the 2000s exhibits mostly a decreasing trend. Positive and negative trends characterized river discharge and sea level along this coastline. The result of multiple linear regression between sea level, river discharge and ocean heat content is a good approximation of sea level trend along the West African coastline. The results of this study could be used to predict future sea level trends along the coast.展开更多
The ZRE is a very complicated estuary with multi-river inlets. The total sum of river discharge in the upstream (away from the tidal influence region) of the Zhujiang River can be easily measured. However, when the to...The ZRE is a very complicated estuary with multi-river inlets. The total sum of river discharge in the upstream (away from the tidal influence region) of the Zhujiang River can be easily measured. However, when the total river discharges into the estuary from eight inlets, it is a very difficult task to obtain a continuous river discharge flux data from each branch of the Zhujiang River. However, the different ratios of river discharges between the river branches can significantly affect the estuarine circulation feature and baroclinic process. Moreover, the accuracy of numerical forecast for the estuarine circulation is very much dependent on the accuracy of the time history of the river discharge flux for each branch. Therefore, it is important to estimate river discharge from each branch in order to improve the accuracy of the model forecast for the circulation of the ZRE. The development of a new estimation method of the river discharges is focused on based on the system identification theory, numerical modeling and the time history data from the CODAR observed sea surface current. The new approach has been applied to estimating the time history (hourly) of river discharge from each branch in the upstream of the ZRE.展开更多
River runoff is affected by many factors, including long-term effects such as climate change that alter rainfall-runoff relationships, and short-term effects related to human intervention(e.g., dam construction, land-...River runoff is affected by many factors, including long-term effects such as climate change that alter rainfall-runoff relationships, and short-term effects related to human intervention(e.g., dam construction, land-use and land-cover change(LUCC)). Discharge from the Yellow River system has been modified in numerous ways over the past century, not only as a result of increased demands for water from agriculture and industry, but also due to hydrological disturbance from LUCC, climate change and the construction of dams. The combined effect of these disturbances may have led to water shortages. Considering that there has been little change in long-term precipitation, dramatic decreases in water discharge may be attributed mainly to human activities, such as water usage, water transportation and dam construction. LUCC may also affect water availability, but the relative contribution of LUCC to changing discharge is unclear. In this study, the impact of LUCC on natural discharge(not including anthropogenic usage) is quantified using an attribution approach based on satellite land cover and discharge data. A retention parameter is used to relate LUCC to changes in discharge. We find that LUCC is the primary factor, and more dominant than climate change, in driving the reduction in discharge during 1956–2012, especially from the mid-1980 s to the end-1990 s. The ratio of each land class to total basin area changed significantly over the study period. Forestland and cropland increased by about 0.58% and 1.41%, respectively, and unused land decreased by 1.16%. Together, these variations resulted in changes in the retention parameter, and runoff generation showed a significant decrease after the mid-1980 s. Our findings highlight the importance of LUCC to runoff generation at the basin scale, and improve our understanding of the influence of LUCC on basin-scale hydrology.展开更多
A large sand bar develops in the inner Qiantang River Estuary,China.It is a unique sedimentary system,elongating landwards by about 130 km.Based on long-term series of bathymetric data in each April,July,and November ...A large sand bar develops in the inner Qiantang River Estuary,China.It is a unique sedimentary system,elongating landwards by about 130 km.Based on long-term series of bathymetric data in each April,July,and November since the 1960s,this study investigated the morphological behavior of this bar under natural conditions and the influence of a large-scale river narrowing project(LRNP)implemented in the last decades.The results show that three timescales,namely the seasonal,interannual and decadal timescales,can be distinguished for the sand bar evolution.The first two are related to the seasonal and interannual variations of river discharge.During high discharge seasons or years,erosion took place at the upper reach and sedimentation at the lower reach.Consequently,the bar apex shifted seaward.The opposite development took place during low discharge seasons or years.The decadal timescale is related to LRNP.Due to the implementation of LRNP,the upper reach has experienced apparent erosion and currently a new equilibrium state has been reached;whereas the lower reach has been accumulated seriously and the accumulation still continues.Nonlinear relationships for how the bar apex location and elevation depend on the river discharge over various stages of LRNP have been established.Compared with the earlier stage of LRNP,the bar apex at present has shifted seaward by about 12 km and lowered by about 1 m.The sand bar movement has significant feedback on the hydrographic conditions along the estuary and has practical implications for coastal management.展开更多
The historical, informational and literary sources regarding flooding have been studied. Based on the statistical processing of multiyear stationary observation data the river maximal discharge parameters are specifie...The historical, informational and literary sources regarding flooding have been studied. Based on the statistical processing of multiyear stationary observation data the river maximal discharge parameters are specified. According tendency of their dynamics the flooding strengthening has been revealed on rivers nourished by glaciers, on the contrary in other rivers they reduced, in some regions evaporation has been increased and desertifieation has been detected. For mitigation negative impacts of those processes the recommendations of prevention measures are drafted.展开更多
The gauged river data play an important role in modeling, planning and management of the river basins. Among the hydrological data, the daily discharge data seem to be more significant for determining the amount of en...The gauged river data play an important role in modeling, planning and management of the river basins. Among the hydrological data, the daily discharge data seem to be more significant for determining the amount of energy production and the control the risks of floods and drought. Hence, the data need correct measurement, analysis, and reliable estimates. The purpose of the paper is to investigate the question whether all the stations in a river basin exhibit chaotic behavior. For this purpose, the daily discharge data of four gauge stations are examined by using three nonlinear data analysis methods: 1) phase space reconstruction;2) correlation dimension;and 3) local approximation where all those methods provide identification of chaotic behaviors. The results show that all stations exhibit chaotic character. Taking into account the proven chaotic characteristic of the stations, local approximation method is applied to observe the prediction accuracy. Considering the fact that global warming is a serious threat on natural resources, the prediction accuracy is becoming a key factor to ensure sustainability. Hence, this study is a good example on the implementation of chaotic analysis by means of the obtained results from the methods.展开更多
We studied the flood, ebb and tidal averaged along (net) water diversion ratio (WDR) during dry season in the Changjiang (Yangtze) estuary, China, along with the effects of northerly wind, river discharge, tide and th...We studied the flood, ebb and tidal averaged along (net) water diversion ratio (WDR) during dry season in the Changjiang (Yangtze) estuary, China, along with the effects of northerly wind, river discharge, tide and their interactions on WDR using the improved version of three-dimensional numerical model ECOM. Using data for annual mean wind speed and river discharge during January, we determined that the flood, ebb, net WDR values in the North Branch of the estuary were 3.48%, 1.68%,-4.06% during spring tide, and 4.82%, 2.34%,-2.79% during neap tide, respectively. Negative net WDR values denote the transport of water from the North Branch into the South Branch. Using the same data, the corresponding ratios were 50.09%, 50.92%, 54.97%, and 52.33%, 50.15%, 43.86% in the North Channel and 38.56%, 44.78%, 103.96%, and 36.92%, 43.17%, 60.97% in the North Passage, respectively. When northerly wind speed increased, landward Ekman transport was enhanced in the North Branch, increasing the flood WDR, while the ebb WDR declined and the net WDR exhibited a significant decrease. Similarly, in the North Channel, the flood WDR is increased, the ebb WDR reduced, and the net WDR showed a marked decrease. In the North Passage, the flood WDR also increased while the ebb and net WDR declined. As the river discharge increased, the flood and ebb WDR of the North Branch increased slightly and the net WDR increased markedly. In the North Channel the flood and ebb WDR changed very slightly, while the net WDR declined during spring tides and increased during neap tides. The WDR in the North Passage changed slightly during flood and ebb tides while the net WDR showed a marked increase. The WDR values of different bifurcations and the responses to northerly wind, river discharge, and tide are discussed in comparison with variations in river topography, horizontal wind-induced circulation, and tidal-induced residual current.展开更多
This study aims to determine the relationships between local meteorological conditions,proglacial river discharge and biogeochemical processes operating in a periglacial basin located in the Polar Ural mountain range,...This study aims to determine the relationships between local meteorological conditions,proglacial river discharge and biogeochemical processes operating in a periglacial basin located in the Polar Ural mountain range, Russia. Fieldwork was conducted in the catchment of Obruchev Glacier(13 km2) during the summer peak flow period in 2008. River discharge was dominated by snowmelt and changed from 3300 l s-1 to less than 1000 l s-1. The mean daily air temperatures of stations situated in the mountain tundra and near Obruchev Glacier from July 11 th to August 1st 2008 were 14.4°C and 10.3°C, respectively. The glacial river had low total dissolved solids varying from 4.5 to 9 mg l-1 and coefficients of correlation between Na+ and Cl-, K+ and Cl-, as well as NH4+ and Cl- were 0.94, 0.90 and 0.84, respectively. Rainfall events affected the snowmelt initiation and provided an essential part of the discharge during the intense snowmelt period, which occurred from July 11 th to July 18 th 2008. Data showed that Na+ and K+ in the surface water derived from snowmelt rather than chemical weathering of silicates. Also, it was obtained that NO3- derived from the melting snowpack, whereas ammonification occurring under the snowpacks was the primary source for NH4+.展开更多
A combined numerical model for computing mixing areas of pollution vertical jet discharging into tidal flows has been developed. This numerical model is composed of a 2-D depth-averaged dynamic far-field numerical mod...A combined numerical model for computing mixing areas of pollution vertical jet discharging into tidal flows has been developed. This numerical model is composed of a 2-D depth-averaged dynamic far-field numerical model and a 2-D vertical dynamic near-field numerical model. The former uses finite node method to compute velocity, and improved finite node method to compute pollutant concentration distribution; the latter is a k-e turbulence model, and uses SIMPLE (Semi-Implicit Method for Pressure Linked Equations) method to compute velocity. At the same time, the former provides boundary conditions for the latter. This model can simulate both far- field pollutant concentration distribution and near-field vertical recirculation quickly and precisely. This model has been verified by measured data of pollutant F of the Dachang reach of the Changjing River and test data presented by Chen el al. (1992). On the basis of verification, the authors use a designed hydrograph to compute this mixing area for a certain amount of wastewater discharging into the river.展开更多
The variations of current, salt intrusion and vertical stratification under different conditions of river flow and wind in the Oujiang River Estuary （ORE） were investigated in this article using the Environmental Fl...The variations of current, salt intrusion and vertical stratification under different conditions of river flow and wind in the Oujiang River Estuary （ORE） were investigated in this article using the Environmental Fluid Dynamics Code （EFDC）. The model was verified against water level variation, velocity, and salinity variations in June 2005. The simulation results agreed well with measured data. Six sensitivity tests were conducted for different conditions of river flow and wind specified in the model. Model results show that salinity intrudes further upstream under scenarios with low flow and downriver local wind conditions. In contrast, the responses of salinity stratification to different environmental forcing functions were different in different portions of the estuary. Salinity stratification was enhanced under high flow condition. Model results also show that wind is not crucial to the salt intrusion and salinity stratification in the ORE.展开更多
Simple statistical models were developed to relate available meteorological data with daily river discharge （RD） for rivers not influenced by melting of ice and snow. In a case study of the Vouga River （Portugal）,...Simple statistical models were developed to relate available meteorological data with daily river discharge （RD） for rivers not influenced by melting of ice and snow. In a case study of the Vouga River （Portugal）, the RD could be determined by a linear combination of the recent （PR） and non-recent （PNR） atmospheric precipitation history. It was found that a simple linear model including only PR and PnR cannot account for low RD. The model was improved by including non-linear terms of precipitation that accounted for the water loss. Additional improvement of the models was possible by including average monthly air temperature （7）. The best model was robust when up to 60% of the original data were randomly removed. The advantage is the simplicity of the models, which take into account only PR, PNR and T. These models can provide a useful tool for RD estimation from current meteorological data.展开更多
A significant large number of dams have been constructed in the past two centuries in the United States. These dams＇ ability to regulate downstream flooding has received world-wide attention. In this study, data from...A significant large number of dams have been constructed in the past two centuries in the United States. These dams＇ ability to regulate downstream flooding has received world-wide attention. In this study, data from 38 rivers distributed over the entire conterminous Untied States with extensive pre- and post-dam annual peak discharge records, were collected to research the impacts of various dams on the flood behaviors at a national scale. The results indicate that dams have led to significant reductions in flood magnitude for nearly all of the sites; the decrease rate in the mean of annual peak discharge varies between 7.4% and 95.14%, except for the Dead River, which increased by 1.46%. Because of dams＇ effective- ness, the probability density curve of annual peak flow changes from a flat to peaked shape because both the range and magnitude of high discharges are decreased. More- over, the potential impact of dams on flood characteristics were closely related to the dam＇s geographic location and function, the ratio of the storage capacity of the dam to the mean annual runoff of the river （C/R）, and the ratio of reservoir storage capacity to the area of its drainage （C/D）. Specifically, the effects of dams on annual peak flows were more related to latitude than longitude. Compared with dams built for other purposes, the dam exclusively used for flood management cut off more flood peaks. Increases in the ratios of C/R and C/D increased the degree of modification of annual maximum discharge.展开更多
Semi-arid and arid areas exhibit great temporal variability in water availability. In some of these regions, a one- or two-day rainfall is followed by intervening dry periods of variable length. In recent decades, man...Semi-arid and arid areas exhibit great temporal variability in water availability. In some of these regions, a one- or two-day rainfall is followed by intervening dry periods of variable length. In recent decades, many rivers of the semi-arid portion of the Jequitinhonha Basin have been undergoing a progressive discharge reduction, mainly of their base flow, the Aracuai River is one of them. In order to understand this transformation, a long-term analysis of the annual water balance of the Aracuai River Basin was performed, the results of which are presented herein. Satellite images, hydrometeorological and river discharge data were analyzed; mean and variance tests were conducted to determine temporal homogeneity. Historical pluviometric data analysis shows no corresponding precipitation reduction and temperature undergoes only a slight increase in the same period. On the other hand, evaporation is extremely high, higher than precipitation during most of the year, leaving almost no water for infiltration （aquifer recharge） and runoff. Furthermore, the Aracuai head- waters of its tributaries are now occupied by a monoculture, Eucaliptus sp., used for paper production. Because of the decreased fluvial discharges, its lowlands, usually used for agriculture and pasture, are abandoned and partially eroded.展开更多
A 2-D vertical dynamic near-field numerical model is developed for the simulation of a vertical jet discharging into tidal flows. This model is a k-εturbulent model. The semi-implicit method for pressure-linked equat...A 2-D vertical dynamic near-field numerical model is developed for the simulation of a vertical jet discharging into tidal flows. This model is a k-εturbulent model. The semi-implicit method for pressure-linked equations is used to solve all the governing equations, which are discretized by control volume method. The model has been tested by water channel experiments. On this basis, the designed hydrological condition for one plan of wastewater of the Dachang district discharging into the Changjiang River has been obtained by this model.展开更多
Rapid development and urbanization in recent years have contributed to a reduction in freshwater discharge and intensified saltwater intrusion in the Pearl River Delta. This comprises a significant threat to potable w...Rapid development and urbanization in recent years have contributed to a reduction in freshwater discharge and intensified saltwater intrusion in the Pearl River Delta. This comprises a significant threat to potable water supplies and overall estuary ecosystem health. In this study, the environmental flows of the Modaomen Estuary, one of the estuaries of the Pear/River Delta in China, were determined based on the salinity demand of keystone species and the linear relationship between river discharge and estuarine salinity. The estimated minimum and optimal annual environmental flows in the Modaomen Estuary were 116.8 ~ I09m3 and 273.8 ~ 109m3, respectively, representing 59.3% and 139.0% of the natural runoff. Water quality assessments in recent years indicate that the environmental flows have not been satisfied most of the time, particularly the optimal environmental flow, despite implementation of various water regulations since 2005. Therefore, water regulations and wetland network recov- eries based on rational environmental flows should be implemented to alleviate saltwater intrusion and for the creation of an ideal estuarine habitat.展开更多
文摘Both winter DJF （December, January, February） months and DJF season means long-term data series of 50 regulated rivers discharges rates and the NAO indices were analyzed for different spans. This study is dictated for： （1） detecting the exclusive impacts of the positive phases of NAO indices on rivers discharges rates by estimating the Linear Correlation Coefficient; （2） modeling the interrelations between the discharges rates and NAO indices by estimating the Linear Regression Models, both for manifesting the impact of the positive phase of NAO index; （3） estimating the Linear Trend Coefficient in the discharge series, for manifesting the contribution of the positive phase of NAO index. Discharge rates are mainly influenced by the two mechanisms： the positive phase of NAO index and the environmental conditions in specific catchments, that is where, the positive phase of the NAO index manifest its impact on the related rivers discharges and its contribution in the related configured trends. The discharges fluctuations patterns show some increase in the discharges values have been occurred in regions around the Northern Baltic Proper as well as in Southern Finland and Sweden. The rivers such as Lagan, Nissan, Helgean, Venta, Pamu, Porvoonjoki, Lapuanjoki, Oulujoki, Kyronjoki, Wisla, Eurajoki, Odra, Lielupe, Gota alv, Motala strom, Nykopingsan, Vuoksi, Kalajoki and Simojoki haven not linear discharges changes registered depending on the specificity of the environmental conditions at the catchments areas for those rivers. The positive phase of NAO index has a linear relation with impacted river discharge.
文摘Coastal hazards induced by meteo-marine forcing are exacerbated by sea level change along the West African coastline. Changes in sea level are induced by ocean processes such as ocean heat content and river discharge. However, although these processes control largely change in sea level, they remain poorly understood. This study analyzes changes in ocean heat content, river discharge, and sea level and establishes an interconnection between these parameters using several statistical methods over the 1993-2021 period. Results showed a significant correlation between sea level and ocean heat content at 2000 m depth. The yearly minimum value appears in July from Cote d’Ivoire to Benin, whilst this value appears in June in Nigeria. The temporal variability of ocean heat content, river discharge and sea level along the West African coastline exhibits three or four periods interrupted by some breakpoints with unequal duration. The results indicate that the 1993-2000 period was dominated by an increasing ocean heat content along the coastline, while the period after the 2000s exhibits mostly a decreasing trend. Positive and negative trends characterized river discharge and sea level along this coastline. The result of multiple linear regression between sea level, river discharge and ocean heat content is a good approximation of sea level trend along the West African coastline. The results of this study could be used to predict future sea level trends along the coast.
文摘The ZRE is a very complicated estuary with multi-river inlets. The total sum of river discharge in the upstream (away from the tidal influence region) of the Zhujiang River can be easily measured. However, when the total river discharges into the estuary from eight inlets, it is a very difficult task to obtain a continuous river discharge flux data from each branch of the Zhujiang River. However, the different ratios of river discharges between the river branches can significantly affect the estuarine circulation feature and baroclinic process. Moreover, the accuracy of numerical forecast for the estuarine circulation is very much dependent on the accuracy of the time history of the river discharge flux for each branch. Therefore, it is important to estimate river discharge from each branch in order to improve the accuracy of the model forecast for the circulation of the ZRE. The development of a new estimation method of the river discharges is focused on based on the system identification theory, numerical modeling and the time history data from the CODAR observed sea surface current. The new approach has been applied to estimating the time history (hourly) of river discharge from each branch in the upstream of the ZRE.
基金Under the auspices of Key Program of Chinese Academy of Sciences(No.KJZD-EW-TZ-G10)National Key Research and Development Program of China(No.2016YFA0602704)Breeding Project of Institute of Geographic Sciences and Natural Resources Research,CAS(No.TSYJS04)
文摘River runoff is affected by many factors, including long-term effects such as climate change that alter rainfall-runoff relationships, and short-term effects related to human intervention(e.g., dam construction, land-use and land-cover change(LUCC)). Discharge from the Yellow River system has been modified in numerous ways over the past century, not only as a result of increased demands for water from agriculture and industry, but also due to hydrological disturbance from LUCC, climate change and the construction of dams. The combined effect of these disturbances may have led to water shortages. Considering that there has been little change in long-term precipitation, dramatic decreases in water discharge may be attributed mainly to human activities, such as water usage, water transportation and dam construction. LUCC may also affect water availability, but the relative contribution of LUCC to changing discharge is unclear. In this study, the impact of LUCC on natural discharge(not including anthropogenic usage) is quantified using an attribution approach based on satellite land cover and discharge data. A retention parameter is used to relate LUCC to changes in discharge. We find that LUCC is the primary factor, and more dominant than climate change, in driving the reduction in discharge during 1956–2012, especially from the mid-1980 s to the end-1990 s. The ratio of each land class to total basin area changed significantly over the study period. Forestland and cropland increased by about 0.58% and 1.41%, respectively, and unused land decreased by 1.16%. Together, these variations resulted in changes in the retention parameter, and runoff generation showed a significant decrease after the mid-1980 s. Our findings highlight the importance of LUCC to runoff generation at the basin scale, and improve our understanding of the influence of LUCC on basin-scale hydrology.
基金The National Natural Science Foundation of China under contract Nos 41676085 and 42176170the Zhejiang Provincial Hydraulic Science and Technology Planning Project under contract No.RB2033the Zhejiang Provincial Natural Science Foundation of China under contract No.LY16D060004.
文摘A large sand bar develops in the inner Qiantang River Estuary,China.It is a unique sedimentary system,elongating landwards by about 130 km.Based on long-term series of bathymetric data in each April,July,and November since the 1960s,this study investigated the morphological behavior of this bar under natural conditions and the influence of a large-scale river narrowing project(LRNP)implemented in the last decades.The results show that three timescales,namely the seasonal,interannual and decadal timescales,can be distinguished for the sand bar evolution.The first two are related to the seasonal and interannual variations of river discharge.During high discharge seasons or years,erosion took place at the upper reach and sedimentation at the lower reach.Consequently,the bar apex shifted seaward.The opposite development took place during low discharge seasons or years.The decadal timescale is related to LRNP.Due to the implementation of LRNP,the upper reach has experienced apparent erosion and currently a new equilibrium state has been reached;whereas the lower reach has been accumulated seriously and the accumulation still continues.Nonlinear relationships for how the bar apex location and elevation depend on the river discharge over various stages of LRNP have been established.Compared with the earlier stage of LRNP,the bar apex at present has shifted seaward by about 12 km and lowered by about 1 m.The sand bar movement has significant feedback on the hydrographic conditions along the estuary and has practical implications for coastal management.
基金This study was supported by the Grant of the Georgian Shota Rustaveli National Science Foundation No. GNSF/ST08/5-444. Any idea in this research is possessed by opinion of the Foundation itself.
文摘The historical, informational and literary sources regarding flooding have been studied. Based on the statistical processing of multiyear stationary observation data the river maximal discharge parameters are specified. According tendency of their dynamics the flooding strengthening has been revealed on rivers nourished by glaciers, on the contrary in other rivers they reduced, in some regions evaporation has been increased and desertifieation has been detected. For mitigation negative impacts of those processes the recommendations of prevention measures are drafted.
文摘The gauged river data play an important role in modeling, planning and management of the river basins. Among the hydrological data, the daily discharge data seem to be more significant for determining the amount of energy production and the control the risks of floods and drought. Hence, the data need correct measurement, analysis, and reliable estimates. The purpose of the paper is to investigate the question whether all the stations in a river basin exhibit chaotic behavior. For this purpose, the daily discharge data of four gauge stations are examined by using three nonlinear data analysis methods: 1) phase space reconstruction;2) correlation dimension;and 3) local approximation where all those methods provide identification of chaotic behaviors. The results show that all stations exhibit chaotic character. Taking into account the proven chaotic characteristic of the stations, local approximation method is applied to observe the prediction accuracy. Considering the fact that global warming is a serious threat on natural resources, the prediction accuracy is becoming a key factor to ensure sustainability. Hence, this study is a good example on the implementation of chaotic analysis by means of the obtained results from the methods.
基金Supported by the Funds for Creative Research Groups of China (No. 40721004)the National Natural Science Foundation of China (Nos. 40776012, 40976056)the Special Funds of the State Key Laboratory of Estuarine and Coastal Research (No. 2008KYYW03)
文摘We studied the flood, ebb and tidal averaged along (net) water diversion ratio (WDR) during dry season in the Changjiang (Yangtze) estuary, China, along with the effects of northerly wind, river discharge, tide and their interactions on WDR using the improved version of three-dimensional numerical model ECOM. Using data for annual mean wind speed and river discharge during January, we determined that the flood, ebb, net WDR values in the North Branch of the estuary were 3.48%, 1.68%,-4.06% during spring tide, and 4.82%, 2.34%,-2.79% during neap tide, respectively. Negative net WDR values denote the transport of water from the North Branch into the South Branch. Using the same data, the corresponding ratios were 50.09%, 50.92%, 54.97%, and 52.33%, 50.15%, 43.86% in the North Channel and 38.56%, 44.78%, 103.96%, and 36.92%, 43.17%, 60.97% in the North Passage, respectively. When northerly wind speed increased, landward Ekman transport was enhanced in the North Branch, increasing the flood WDR, while the ebb WDR declined and the net WDR exhibited a significant decrease. Similarly, in the North Channel, the flood WDR is increased, the ebb WDR reduced, and the net WDR showed a marked decrease. In the North Passage, the flood WDR also increased while the ebb and net WDR declined. As the river discharge increased, the flood and ebb WDR of the North Branch increased slightly and the net WDR increased markedly. In the North Channel the flood and ebb WDR changed very slightly, while the net WDR declined during spring tides and increased during neap tides. The WDR in the North Passage changed slightly during flood and ebb tides while the net WDR showed a marked increase. The WDR values of different bifurcations and the responses to northerly wind, river discharge, and tide are discussed in comparison with variations in river topography, horizontal wind-induced circulation, and tidal-induced residual current.
基金supported by the Institute of Geography and Spatial Management at Jagiellonian University
文摘This study aims to determine the relationships between local meteorological conditions,proglacial river discharge and biogeochemical processes operating in a periglacial basin located in the Polar Ural mountain range, Russia. Fieldwork was conducted in the catchment of Obruchev Glacier(13 km2) during the summer peak flow period in 2008. River discharge was dominated by snowmelt and changed from 3300 l s-1 to less than 1000 l s-1. The mean daily air temperatures of stations situated in the mountain tundra and near Obruchev Glacier from July 11 th to August 1st 2008 were 14.4°C and 10.3°C, respectively. The glacial river had low total dissolved solids varying from 4.5 to 9 mg l-1 and coefficients of correlation between Na+ and Cl-, K+ and Cl-, as well as NH4+ and Cl- were 0.94, 0.90 and 0.84, respectively. Rainfall events affected the snowmelt initiation and provided an essential part of the discharge during the intense snowmelt period, which occurred from July 11 th to July 18 th 2008. Data showed that Na+ and K+ in the surface water derived from snowmelt rather than chemical weathering of silicates. Also, it was obtained that NO3- derived from the melting snowpack, whereas ammonification occurring under the snowpacks was the primary source for NH4+.
文摘A combined numerical model for computing mixing areas of pollution vertical jet discharging into tidal flows has been developed. This numerical model is composed of a 2-D depth-averaged dynamic far-field numerical model and a 2-D vertical dynamic near-field numerical model. The former uses finite node method to compute velocity, and improved finite node method to compute pollutant concentration distribution; the latter is a k-e turbulence model, and uses SIMPLE (Semi-Implicit Method for Pressure Linked Equations) method to compute velocity. At the same time, the former provides boundary conditions for the latter. This model can simulate both far- field pollutant concentration distribution and near-field vertical recirculation quickly and precisely. This model has been verified by measured data of pollutant F of the Dachang reach of the Changjing River and test data presented by Chen el al. (1992). On the basis of verification, the authors use a designed hydrograph to compute this mixing area for a certain amount of wastewater discharging into the river.
基金supported by the National Basic Research Program of China (973 Program,Grant No.2006CB403302)the National Natural Science Foundation of China (Grant Nos.50839001,50779006)
文摘The variations of current, salt intrusion and vertical stratification under different conditions of river flow and wind in the Oujiang River Estuary （ORE） were investigated in this article using the Environmental Fluid Dynamics Code （EFDC）. The model was verified against water level variation, velocity, and salinity variations in June 2005. The simulation results agreed well with measured data. Six sensitivity tests were conducted for different conditions of river flow and wind specified in the model. Model results show that salinity intrudes further upstream under scenarios with low flow and downriver local wind conditions. In contrast, the responses of salinity stratification to different environmental forcing functions were different in different portions of the estuary. Salinity stratification was enhanced under high flow condition. Model results also show that wind is not crucial to the salt intrusion and salinity stratification in the ORE.
文摘Simple statistical models were developed to relate available meteorological data with daily river discharge （RD） for rivers not influenced by melting of ice and snow. In a case study of the Vouga River （Portugal）, the RD could be determined by a linear combination of the recent （PR） and non-recent （PNR） atmospheric precipitation history. It was found that a simple linear model including only PR and PnR cannot account for low RD. The model was improved by including non-linear terms of precipitation that accounted for the water loss. Additional improvement of the models was possible by including average monthly air temperature （7）. The best model was robust when up to 60% of the original data were randomly removed. The advantage is the simplicity of the models, which take into account only PR, PNR and T. These models can provide a useful tool for RD estimation from current meteorological data.
文摘A significant large number of dams have been constructed in the past two centuries in the United States. These dams＇ ability to regulate downstream flooding has received world-wide attention. In this study, data from 38 rivers distributed over the entire conterminous Untied States with extensive pre- and post-dam annual peak discharge records, were collected to research the impacts of various dams on the flood behaviors at a national scale. The results indicate that dams have led to significant reductions in flood magnitude for nearly all of the sites; the decrease rate in the mean of annual peak discharge varies between 7.4% and 95.14%, except for the Dead River, which increased by 1.46%. Because of dams＇ effective- ness, the probability density curve of annual peak flow changes from a flat to peaked shape because both the range and magnitude of high discharges are decreased. More- over, the potential impact of dams on flood characteristics were closely related to the dam＇s geographic location and function, the ratio of the storage capacity of the dam to the mean annual runoff of the river （C/R）, and the ratio of reservoir storage capacity to the area of its drainage （C/D）. Specifically, the effects of dams on annual peak flows were more related to latitude than longitude. Compared with dams built for other purposes, the dam exclusively used for flood management cut off more flood peaks. Increases in the ratios of C/R and C/D increased the degree of modification of annual maximum discharge.
文摘Semi-arid and arid areas exhibit great temporal variability in water availability. In some of these regions, a one- or two-day rainfall is followed by intervening dry periods of variable length. In recent decades, many rivers of the semi-arid portion of the Jequitinhonha Basin have been undergoing a progressive discharge reduction, mainly of their base flow, the Aracuai River is one of them. In order to understand this transformation, a long-term analysis of the annual water balance of the Aracuai River Basin was performed, the results of which are presented herein. Satellite images, hydrometeorological and river discharge data were analyzed; mean and variance tests were conducted to determine temporal homogeneity. Historical pluviometric data analysis shows no corresponding precipitation reduction and temperature undergoes only a slight increase in the same period. On the other hand, evaporation is extremely high, higher than precipitation during most of the year, leaving almost no water for infiltration （aquifer recharge） and runoff. Furthermore, the Aracuai head- waters of its tributaries are now occupied by a monoculture, Eucaliptus sp., used for paper production. Because of the decreased fluvial discharges, its lowlands, usually used for agriculture and pasture, are abandoned and partially eroded.
文摘A 2-D vertical dynamic near-field numerical model is developed for the simulation of a vertical jet discharging into tidal flows. This model is a k-εturbulent model. The semi-implicit method for pressure-linked equations is used to solve all the governing equations, which are discretized by control volume method. The model has been tested by water channel experiments. On this basis, the designed hydrological condition for one plan of wastewater of the Dachang district discharging into the Changjiang River has been obtained by this model.
文摘Rapid development and urbanization in recent years have contributed to a reduction in freshwater discharge and intensified saltwater intrusion in the Pearl River Delta. This comprises a significant threat to potable water supplies and overall estuary ecosystem health. In this study, the environmental flows of the Modaomen Estuary, one of the estuaries of the Pear/River Delta in China, were determined based on the salinity demand of keystone species and the linear relationship between river discharge and estuarine salinity. The estimated minimum and optimal annual environmental flows in the Modaomen Estuary were 116.8 ~ I09m3 and 273.8 ~ 109m3, respectively, representing 59.3% and 139.0% of the natural runoff. Water quality assessments in recent years indicate that the environmental flows have not been satisfied most of the time, particularly the optimal environmental flow, despite implementation of various water regulations since 2005. Therefore, water regulations and wetland network recov- eries based on rational environmental flows should be implemented to alleviate saltwater intrusion and for the creation of an ideal estuarine habitat.
