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
In the Elkhorn River,burrows,tubes,and sediment mounds created by invertebrate bioturbation were observed in the exposed streambed and commonly concentrated on the fine-sediment patches,which consist of silt,clay,and ...In the Elkhorn River,burrows,tubes,and sediment mounds created by invertebrate bioturbation were observed in the exposed streambed and commonly concentrated on the fine-sediment patches,which consist of silt,clay,and organic matter.These invertebrate activities could loosen the thin layer of clogging sediments and result in an increase of pore size in the sediments,leading to greater vertical hydraulic conductivity of the streambed(Kv).The measurements of the vertical hydraulic gradient across the submerged streambed show that vertical flux in the hyporheic zone can alter directions(upward versus downward)for two locations only a few meters apart.In situ permeameter tests show that streambed Kv in the upper sediment layer is much higher than that in the lower sediment layer,and the calculated Kv in the submerged streambed is consistently greater than that in the clogged sediments around the shorelines of the sand bars.Moreover,a phenomenon of gas bubble release at the water-sediment interface from the subsurface sediments was observed in the groundwater seepage zone where flow velocity is extremely small.The bursting of gas bubbles can potentially break the thin clogging layer of sediments and enhance the vertical hydraulic conductivity of the streambed.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.
基金the Program for Changjiang Scholars and Innovative Research Team of China Ministry of Education(No.IRT0811).
文摘In the Elkhorn River,burrows,tubes,and sediment mounds created by invertebrate bioturbation were observed in the exposed streambed and commonly concentrated on the fine-sediment patches,which consist of silt,clay,and organic matter.These invertebrate activities could loosen the thin layer of clogging sediments and result in an increase of pore size in the sediments,leading to greater vertical hydraulic conductivity of the streambed(Kv).The measurements of the vertical hydraulic gradient across the submerged streambed show that vertical flux in the hyporheic zone can alter directions(upward versus downward)for two locations only a few meters apart.In situ permeameter tests show that streambed Kv in the upper sediment layer is much higher than that in the lower sediment layer,and the calculated Kv in the submerged streambed is consistently greater than that in the clogged sediments around the shorelines of the sand bars.Moreover,a phenomenon of gas bubble release at the water-sediment interface from the subsurface sediments was observed in the groundwater seepage zone where flow velocity is extremely small.The bursting of gas bubbles can potentially break the thin clogging layer of sediments and enhance the vertical hydraulic conductivity of the streambed.
