Upstream-downstream relationships of annual streamflow discharges and severity and frequency of stream-flow drought events are critical in understanding how streamflow droughts propagate over time and space. Such info...Upstream-downstream relationships of annual streamflow discharges and severity and frequency of stream-flow drought events are critical in understanding how streamflow droughts propagate over time and space. Such information can be used to resolve water disputes, trigger mitigation strategies, and understand how streamflow changes due to changes in the environment. During drought years, such information is even more critical as water resources are contested. The objective of this research is to study the upstream-downstream relationships of streamflow in Nebraska along four major river systems with diverse hydrologic characteris-tics and human activities: North Platte, Big Blue, Republican, and Niobrara. The relationships among the upstream and downstream stations along the four rivers are investigated by comparing several statistics de-rived from the annual flow discharge and on drought events. Trend analysis and coefficient of variation are applied to annual flow discharge values, and a host of drought-related parameters (e.g., annual maximum drought duration, annual accumulated drought duration, number of drought events) are also computed with respect to five different levels of streamflow drought events: water shortage, mild drought, moderate drought, significant drought, and extreme drought. The paired-t test and ANOVA with MIXED procedure are subse-quently applied to the statistics to observe whether there is a significant difference between upstream and downstream stations along a river. The analysis allows us to characterize the upstream-downstream relation-ships of the four river systems, laying the groundwork for further investigations to identify the reasons for some of the trends and observations. These findings will be essential in water resources management during or prior to hydrological droughts.展开更多
This study compared three approaches,regional averaging,nearest neighbor,and donor techniques,to regionalize parameters in the Soil and Water Assessment Tool(SWAT)on eleven watersheds located in the Dissected Plains,P...This study compared three approaches,regional averaging,nearest neighbor,and donor techniques,to regionalize parameters in the Soil and Water Assessment Tool(SWAT)on eleven watersheds located in the Dissected Plains,Plains,and Rolling Hills Landforms in the eastern portion of the State of Nebraska,USA.Within the Rolling Hills Landform,three watersheds were randomly selected as calibration watersheds while two were randomly selected as validation watersheds.Two watersheds were randomly selected as calibration watersheds while one was randomly selected as a validation watershed within each of the Dissected Plains and Plains Landforms.The seven calibration watersheds were used to provide the necessary calibrated parameter sets to execute each of the regional approaches,while the four validation watersheds were used to assess the impact of applying each of these approaches to an uncalibrated watershed.Percent Bias(PBIAS)and the Nash Sutcliffe Coefficient of Efficiency(NSE)were used to assess model performance.Test results of this study show that all three methods performed poorly,since the majority of watersheds among each method tested exhibited PBIAS values greater than ±25% and/or NSE values less than 0.50,which were considered to be unsatisfactory in terms of model performance.The average regionalization,nearest neighbor and donor methods resulted in only four(two calibration and two validation),zero and one satisfactory set of simulated watershed results,respectively.The findings from this study indicate that although each watershed was successfully calibrated with NSE values ranging from 0.51 to 0.84,none of the three regionalization methods provided suitable calibration data sets to define parameter values for performing satisfactory simulations on ungaged watersheds across the eastern Nebraska landscape.展开更多
The U.S.federal government’s requirements and guidance for wetland conservation are reflected in a series of federal laws,regulations,and policies.However,the degree to which these requirements are reflected in local...The U.S.federal government’s requirements and guidance for wetland conservation are reflected in a series of federal laws,regulations,and policies.However,the degree to which these requirements are reflected in local planning efforts is unclear.This study using five components with 56 indicators evaluates how well wetland conservation efforts are integrated into 112 local comprehensive plans in Nebraska,USA.The results show that the majority of local comprehensive plans pay little direct attention to wetland conservation,although many conservation efforts are conducted under the umbrella of environmental protection frameworks.The indicators include water resource protection received the highest score and was the descriptor of natural or environmental resources and resulted in the highest level of local awareness on natural assets.The indicator of setting goals for no net loss of wetlands received the lowest score among all indicators,demonstrating a clear gap between the national vision and the local reality of wetland conservation.Findings suggest local governments need more direct and proactive inputs to improve wetland conservation.Further findings from this research provide a practical roadmap for planners globally,particularly for the developing countries,to integrate wetland conservation into the local planning systems.展开更多
The backdrop of Willa Cather's works is usually set on the prairie of West Nebraska.She focuses on the depiction of the life style and spirit of the farmers working in the harsh environment of the west,and her wor...The backdrop of Willa Cather's works is usually set on the prairie of West Nebraska.She focuses on the depiction of the life style and spirit of the farmers working in the harsh environment of the west,and her work is a loving tribute to the tough and pioneering spirit of its people.She also depicts the spiritual alienation of the various immigrants who move away from home to settle down in the west,exploring their hardship and disillusionment.My Antonia is just this kind of work,which features Jim Burden and his quest of an Antonianized prairie,pregnant with touching nostalgia for a rural past in the west threatened by the multiple complications of an overdeveloping modern world.The thesis aims to dissect the state of spiritual belongingness of the novel's several characters,and analyze their respective implication.展开更多
根据对美国内布拉斯加大学研究生的教学方法和教学效果的调查结果,并结合笔者旁听"Geochemistry of Natural Waters"这门课程的体会,对如何提高研究生的教学质量提出了几点建议:加强教学资源建设,增强教师在教学方面及学生在...根据对美国内布拉斯加大学研究生的教学方法和教学效果的调查结果,并结合笔者旁听"Geochemistry of Natural Waters"这门课程的体会,对如何提高研究生的教学质量提出了几点建议:加强教学资源建设,增强教师在教学方面及学生在课程学习方面的投入,注重教学效果,切实提高学生的学习积极性。展开更多
文摘Upstream-downstream relationships of annual streamflow discharges and severity and frequency of stream-flow drought events are critical in understanding how streamflow droughts propagate over time and space. Such information can be used to resolve water disputes, trigger mitigation strategies, and understand how streamflow changes due to changes in the environment. During drought years, such information is even more critical as water resources are contested. The objective of this research is to study the upstream-downstream relationships of streamflow in Nebraska along four major river systems with diverse hydrologic characteris-tics and human activities: North Platte, Big Blue, Republican, and Niobrara. The relationships among the upstream and downstream stations along the four rivers are investigated by comparing several statistics de-rived from the annual flow discharge and on drought events. Trend analysis and coefficient of variation are applied to annual flow discharge values, and a host of drought-related parameters (e.g., annual maximum drought duration, annual accumulated drought duration, number of drought events) are also computed with respect to five different levels of streamflow drought events: water shortage, mild drought, moderate drought, significant drought, and extreme drought. The paired-t test and ANOVA with MIXED procedure are subse-quently applied to the statistics to observe whether there is a significant difference between upstream and downstream stations along a river. The analysis allows us to characterize the upstream-downstream relation-ships of the four river systems, laying the groundwork for further investigations to identify the reasons for some of the trends and observations. These findings will be essential in water resources management during or prior to hydrological droughts.
文摘This study compared three approaches,regional averaging,nearest neighbor,and donor techniques,to regionalize parameters in the Soil and Water Assessment Tool(SWAT)on eleven watersheds located in the Dissected Plains,Plains,and Rolling Hills Landforms in the eastern portion of the State of Nebraska,USA.Within the Rolling Hills Landform,three watersheds were randomly selected as calibration watersheds while two were randomly selected as validation watersheds.Two watersheds were randomly selected as calibration watersheds while one was randomly selected as a validation watershed within each of the Dissected Plains and Plains Landforms.The seven calibration watersheds were used to provide the necessary calibrated parameter sets to execute each of the regional approaches,while the four validation watersheds were used to assess the impact of applying each of these approaches to an uncalibrated watershed.Percent Bias(PBIAS)and the Nash Sutcliffe Coefficient of Efficiency(NSE)were used to assess model performance.Test results of this study show that all three methods performed poorly,since the majority of watersheds among each method tested exhibited PBIAS values greater than ±25% and/or NSE values less than 0.50,which were considered to be unsatisfactory in terms of model performance.The average regionalization,nearest neighbor and donor methods resulted in only four(two calibration and two validation),zero and one satisfactory set of simulated watershed results,respectively.The findings from this study indicate that although each watershed was successfully calibrated with NSE values ranging from 0.51 to 0.84,none of the three regionalization methods provided suitable calibration data sets to define parameter values for performing satisfactory simulations on ungaged watersheds across the eastern Nebraska landscape.
基金This work was supported by the U.S.Environmental Protection Agency[CD97790401]and[CD 97763501].
文摘The U.S.federal government’s requirements and guidance for wetland conservation are reflected in a series of federal laws,regulations,and policies.However,the degree to which these requirements are reflected in local planning efforts is unclear.This study using five components with 56 indicators evaluates how well wetland conservation efforts are integrated into 112 local comprehensive plans in Nebraska,USA.The results show that the majority of local comprehensive plans pay little direct attention to wetland conservation,although many conservation efforts are conducted under the umbrella of environmental protection frameworks.The indicators include water resource protection received the highest score and was the descriptor of natural or environmental resources and resulted in the highest level of local awareness on natural assets.The indicator of setting goals for no net loss of wetlands received the lowest score among all indicators,demonstrating a clear gap between the national vision and the local reality of wetland conservation.Findings suggest local governments need more direct and proactive inputs to improve wetland conservation.Further findings from this research provide a practical roadmap for planners globally,particularly for the developing countries,to integrate wetland conservation into the local planning systems.
文摘The backdrop of Willa Cather's works is usually set on the prairie of West Nebraska.She focuses on the depiction of the life style and spirit of the farmers working in the harsh environment of the west,and her work is a loving tribute to the tough and pioneering spirit of its people.She also depicts the spiritual alienation of the various immigrants who move away from home to settle down in the west,exploring their hardship and disillusionment.My Antonia is just this kind of work,which features Jim Burden and his quest of an Antonianized prairie,pregnant with touching nostalgia for a rural past in the west threatened by the multiple complications of an overdeveloping modern world.The thesis aims to dissect the state of spiritual belongingness of the novel's several characters,and analyze their respective implication.
文摘根据对美国内布拉斯加大学研究生的教学方法和教学效果的调查结果,并结合笔者旁听"Geochemistry of Natural Waters"这门课程的体会,对如何提高研究生的教学质量提出了几点建议:加强教学资源建设,增强教师在教学方面及学生在课程学习方面的投入,注重教学效果,切实提高学生的学习积极性。
