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
Present study raises a serious issue of wetland loss and transformation due to damming and water di-version.At present study,it is noticed that overall rainfall trend(-0.006)of the study period(1978-2015)remains uncha...Present study raises a serious issue of wetland loss and transformation due to damming and water di-version.At present study,it is noticed that overall rainfall trend(-0.006)of the study period(1978-2015)remains unchanged but riparian wetland area is attenuated after damming both pre monsoon(March to May)and post monsoon season(October to December).Total wetland area in pre-and post-monsoon seasons is respectively reduced from 42.2 km^(2) to 27.87 km^(2),and from 277.85 km^(2) to 220.90 km^(2) in post dam period.Transformation of frequently inundated wetland area into sparsely inundated wetland is mainly triggered by flow modification due to installation of Komardanga dam and Barrage over Punarbhaba and its major tributary Tangon river.Sparsely inundated seasonal wetland area is rapidly reclaimed for agricultural practice.This extreme issue will invite instability in socio-ecological setup of the neighbouring region.展开更多
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Present study raises a serious issue of wetland loss and transformation due to damming and water di-version.At present study,it is noticed that overall rainfall trend(-0.006)of the study period(1978-2015)remains unchanged but riparian wetland area is attenuated after damming both pre monsoon(March to May)and post monsoon season(October to December).Total wetland area in pre-and post-monsoon seasons is respectively reduced from 42.2 km^(2) to 27.87 km^(2),and from 277.85 km^(2) to 220.90 km^(2) in post dam period.Transformation of frequently inundated wetland area into sparsely inundated wetland is mainly triggered by flow modification due to installation of Komardanga dam and Barrage over Punarbhaba and its major tributary Tangon river.Sparsely inundated seasonal wetland area is rapidly reclaimed for agricultural practice.This extreme issue will invite instability in socio-ecological setup of the neighbouring region.
