Floodplain lakes are important water storage areas in lowland regions that often undergo geomorphologic evolution,and timely topographic data are generally unavailable.In this study,to assess the impacts of lakebed de...Floodplain lakes are important water storage areas in lowland regions that often undergo geomorphologic evolution,and timely topographic data are generally unavailable.In this study,to assess the impacts of lakebed deformation on hydraulic performance in Dongting Lake,a set of semi-empirical methods was proposed to establish performance graphs(PGs)using only hydrological data.These methods were used to evaluate the changes in water level,storage capacity,and flood detention ability in Dongting Lake caused by topographic adjustment after the Three Gorges Reservoir impoundment.These methods showed that PGs can effectively simulate the water level and outflow processes of Dongting Lake with Nash-Sutcliffe efficiency coefficients(NSEs)above 0.9.A comparison of the estimated water level and discharge using PGs from different periods suggested that bed erosion in Dongting Lake caused water level decreases of 0.18 m and 0.32 m during the flood and dry seasons,respectively.Because the magnitude of erosion at high elevations in the lake is small,the impacts of bed adjustment on the storage capacity and flood detention ability are not currently significant.This study showed that the hydraulic performance of a floodplain lake can be evaluated independently of topographic data under the condition of no reverse flows or negative watersurface slopes.展开更多
Saltwater intrusion in the estuary area threatens the use of freshwater resources.If river discharge increases to a critical value,then saltwater intrusion frequency and salinity level decreases.In this study,long-ter...Saltwater intrusion in the estuary area threatens the use of freshwater resources.If river discharge increases to a critical value,then saltwater intrusion frequency and salinity level decreases.In this study,long-term river discharge and tidal range data in the Yangtze River Estuary(YRE)and salinity data obtained in the upper South Branch of the YRE were used to analyze the characteristics of different variables and the basic law of their interactions.Two methods,namely,the material analysis method and empirical models,were applied to determine the critical river discharge for saltwater intrusion control.Results are as follows:(1)the salinity might exceed the drinking water standard of China when the river discharge was less than 30,000 m^3/s.Approximately 69%of salinity excessive days occurred when the river discharge was less than 15,000 m^3/s;(2)the tidal range in the YRE roughly varied in sinusoidal pattern with a 15-day cycle length.Exponential relationship existed between daily salinity(chlorinity)and daily mean tidal range.Combining these two features with the cumulative frequency statistics of tidal ranges,it was showed that notable saltwater intrusion occurred when the tidal range was more than 2.7 m at Qinglonggang station.Moreover,the critical discharge was found to be slightly higher than 11,000 m^3/s;(3)various of empirical models for salinity prediction could be chosen to calculate the critical discharge.The values obtained by different models were in the range of 11,000–12,000 m^3/s;(4)the proposed critical discharge to reduce notable saltwater intrusion was 11,500 m^3/s.After the Three Gorges Reservoir operation,the minimum river discharge into the YRE in 2008–2017 was below the critical discharge,thereby suggesting an increase in the minimum river discharge by reservoir regulation in drought periods.展开更多
基金National Natural Science Foundation of China,No.51879198The Follow-up Research Program for the Three Gorges Project from the Ministry of Water Resources of China,No.12630100100020J005。
文摘Floodplain lakes are important water storage areas in lowland regions that often undergo geomorphologic evolution,and timely topographic data are generally unavailable.In this study,to assess the impacts of lakebed deformation on hydraulic performance in Dongting Lake,a set of semi-empirical methods was proposed to establish performance graphs(PGs)using only hydrological data.These methods were used to evaluate the changes in water level,storage capacity,and flood detention ability in Dongting Lake caused by topographic adjustment after the Three Gorges Reservoir impoundment.These methods showed that PGs can effectively simulate the water level and outflow processes of Dongting Lake with Nash-Sutcliffe efficiency coefficients(NSEs)above 0.9.A comparison of the estimated water level and discharge using PGs from different periods suggested that bed erosion in Dongting Lake caused water level decreases of 0.18 m and 0.32 m during the flood and dry seasons,respectively.Because the magnitude of erosion at high elevations in the lake is small,the impacts of bed adjustment on the storage capacity and flood detention ability are not currently significant.This study showed that the hydraulic performance of a floodplain lake can be evaluated independently of topographic data under the condition of no reverse flows or negative watersurface slopes.
基金National Key Research and Development Program of China,No.2018YFC0407802National Major Scientific and Technological Program for Water Pollution Control and Treatment,No.2014ZX07104-005。
文摘Saltwater intrusion in the estuary area threatens the use of freshwater resources.If river discharge increases to a critical value,then saltwater intrusion frequency and salinity level decreases.In this study,long-term river discharge and tidal range data in the Yangtze River Estuary(YRE)and salinity data obtained in the upper South Branch of the YRE were used to analyze the characteristics of different variables and the basic law of their interactions.Two methods,namely,the material analysis method and empirical models,were applied to determine the critical river discharge for saltwater intrusion control.Results are as follows:(1)the salinity might exceed the drinking water standard of China when the river discharge was less than 30,000 m^3/s.Approximately 69%of salinity excessive days occurred when the river discharge was less than 15,000 m^3/s;(2)the tidal range in the YRE roughly varied in sinusoidal pattern with a 15-day cycle length.Exponential relationship existed between daily salinity(chlorinity)and daily mean tidal range.Combining these two features with the cumulative frequency statistics of tidal ranges,it was showed that notable saltwater intrusion occurred when the tidal range was more than 2.7 m at Qinglonggang station.Moreover,the critical discharge was found to be slightly higher than 11,000 m^3/s;(3)various of empirical models for salinity prediction could be chosen to calculate the critical discharge.The values obtained by different models were in the range of 11,000–12,000 m^3/s;(4)the proposed critical discharge to reduce notable saltwater intrusion was 11,500 m^3/s.After the Three Gorges Reservoir operation,the minimum river discharge into the YRE in 2008–2017 was below the critical discharge,thereby suggesting an increase in the minimum river discharge by reservoir regulation in drought periods.
