The Experts below are selected from a list of 181935 Experts worldwide ranked by ideXlab platform
Chiyuan Miao - One of the best experts on this subject based on the ideXlab platform.
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a preliminary estimate of human and natural contributions to the changes in Water Discharge and sediment load in the yellow river
Global and Planetary Change, 2011Co-Authors: Chiyuan Miao, Alistair G L Borthwick, Lin YangAbstract:Water Discharge and sediment load have changed continuously during the last half century in the Yellow River basin, China. In the present paper, data from 7 river gauging stations and 175 meteorological stations are analyzed in order to estimate quantitatively the contributions of human activities and climate change to hydrological response. Coefficients of Water Discharge (C(w)) and sediment load (C(s)) are calculated for the baseline period of 1950s-1960s according to the correlations between the respective hydrological series and regional precipitation. Consequently, the natural Water Discharge and natural sediment load time series are reconstructed from 1960s-2008. Inter-annual impacts are then separated from the impacts of human activities and climate change on the hydrological response of different regions of the Yellow River basin. It is found that human activities have the greatest influence on changes to the hydrological series of Water Discharge and sediment load, no matter whether the effect is negative or positive. Moreover, the impact of human activities is considerably greater on Water Discharge than sediment load. During 1970-2008. climate change and human activities respectively contribute 17% and 83% to the reduction in Water Discharge, and 14% and 86% to the reduction in sediment yield in the Upper reaches of Yellow River basin; The corresponding relative contributions in the Middle reaches are 71% and 29% to reductions in Water Discharge. and 48% and 52% to reductions in sediment load. Moreover, it is observed that the impacts of human activities on the whole basin are enhanced with time. In the 2000s. the impact of human activities exceeds that of climate change in the 2000s, with human activities directly responsible for 55% and 54% of the reductions in Water Discharge and sediment load in the whole basin. (C) 2011 Elsevier B.V. All rights reserved.
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recent changes of Water Discharge and sediment load in the yellow river basin china
Progress in Physical Geography, 2010Co-Authors: Chiyuan Miao, Alistair G L BorthwickAbstract:The Yellow River basin contributes approximately 6% of the sediment load from all river systems globally, and the annual runoff directly supports 12% of the Chinese population. As a result, describing and understanding recent variations of Water Discharge and sediment load under global change scenarios are of considerable importance. The present study considers the annual hydrologic series of the Water Discharge and sediment load of the Yellow River basin obtained from 15 gauging stations (10 mainstream, 5 tributaries). The Mann-Kendall test method was adopted to detect both gradual and abrupt change of hydrological series since the 1950s. With the exception of the area draining to the Upper Tangnaihai station, results indicate that both Water Discharge and sediment load have decreased significantly (p<0.05). The declining trend is greater with distance downstream, and drainage area has a significant positive effect on the rate of decline. It is suggested that the abrupt change of the Water Discharge from...
Alistair G L Borthwick - One of the best experts on this subject based on the ideXlab platform.
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a preliminary estimate of human and natural contributions to the changes in Water Discharge and sediment load in the yellow river
Global and Planetary Change, 2011Co-Authors: Chiyuan Miao, Alistair G L Borthwick, Lin YangAbstract:Water Discharge and sediment load have changed continuously during the last half century in the Yellow River basin, China. In the present paper, data from 7 river gauging stations and 175 meteorological stations are analyzed in order to estimate quantitatively the contributions of human activities and climate change to hydrological response. Coefficients of Water Discharge (C(w)) and sediment load (C(s)) are calculated for the baseline period of 1950s-1960s according to the correlations between the respective hydrological series and regional precipitation. Consequently, the natural Water Discharge and natural sediment load time series are reconstructed from 1960s-2008. Inter-annual impacts are then separated from the impacts of human activities and climate change on the hydrological response of different regions of the Yellow River basin. It is found that human activities have the greatest influence on changes to the hydrological series of Water Discharge and sediment load, no matter whether the effect is negative or positive. Moreover, the impact of human activities is considerably greater on Water Discharge than sediment load. During 1970-2008. climate change and human activities respectively contribute 17% and 83% to the reduction in Water Discharge, and 14% and 86% to the reduction in sediment yield in the Upper reaches of Yellow River basin; The corresponding relative contributions in the Middle reaches are 71% and 29% to reductions in Water Discharge. and 48% and 52% to reductions in sediment load. Moreover, it is observed that the impacts of human activities on the whole basin are enhanced with time. In the 2000s. the impact of human activities exceeds that of climate change in the 2000s, with human activities directly responsible for 55% and 54% of the reductions in Water Discharge and sediment load in the whole basin. (C) 2011 Elsevier B.V. All rights reserved.
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recent changes of Water Discharge and sediment load in the yellow river basin china
Progress in Physical Geography, 2010Co-Authors: Chiyuan Miao, Alistair G L BorthwickAbstract:The Yellow River basin contributes approximately 6% of the sediment load from all river systems globally, and the annual runoff directly supports 12% of the Chinese population. As a result, describing and understanding recent variations of Water Discharge and sediment load under global change scenarios are of considerable importance. The present study considers the annual hydrologic series of the Water Discharge and sediment load of the Yellow River basin obtained from 15 gauging stations (10 mainstream, 5 tributaries). The Mann-Kendall test method was adopted to detect both gradual and abrupt change of hydrological series since the 1950s. With the exception of the area draining to the Upper Tangnaihai station, results indicate that both Water Discharge and sediment load have decreased significantly (p<0.05). The declining trend is greater with distance downstream, and drainage area has a significant positive effect on the rate of decline. It is suggested that the abrupt change of the Water Discharge from...
Sigurd Einum - One of the best experts on this subject based on the ideXlab platform.
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seasonal effects of hydropeaking on growth energetics and movement of juvenile atlantic salmon salmo salar
River Research and Applications, 2015Co-Authors: Michael Puffer, Ole Kristian Berg, Ari Huusko, Teppo Vehanen, Torbjorn Forseth, Sigurd EinumAbstract:The performance and movements of juvenile Atlantic salmon Salmo salar exposed to variable Water Discharge (simulating hydropeaking) but with a stable Water-covered area were studied in six experimental stream channels, both during the winter and summer. Thirty fish were stocked into each channel, and the growth, body fat and movements of the fish were followed for about 2.5 months in each season. During the winter, no effect of hydropeaking was documented on performance or movement. In the summer, fish experiencing hydropeaking had lower body mass, lower body fat, and higher movement rates than the control fish. In general, effect sizes were small, and the rapid and frequent changes in Water Discharge and Water level in the present study had small effects on the performance of juvenile Atlantic salmon. The cumulative long-term effect at the population level is unknown, but a reduced growth rate of 10% and a reduction in body fat of 16% in the hydropeaking experiments in the summer might to some extent translate into increased smolt age and lower overwintering survival. Copyright © 2014 John Wiley & Sons, Ltd.
Jeffrey A Nittrouer - One of the best experts on this subject based on the ideXlab platform.
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spatial and temporal trends for Water flow velocity and bed material sediment transport in the lower mississippi river
Geological Society of America Bulletin, 2012Co-Authors: Jeffrey A Nittrouer, John B Shaw, Michael P Lamb, David MohrigAbstract:Where rivers near the coastline, the receiving basin begins to influence flow, and gradually varied, nonuniform flow conditions arise. The section of the river affected by nonuniform flow is typically referred to as the backWater segment, and for large lowland rivers, this portion of the river can extend many hundreds of kilometers above the outlet. River morphology and kinematics vary in the backWater segment; however, these channel properties have not been explicitly related to properties of the flow and sediment-transport fields. This study examines the influence of spatially and temporally varying flow velocity and sediment transport on channel properties for the lower 800 km of the Mississippi River, a section of the river that includes the backWater segment. Survey transects (n = 2650) were used to constrain the cross-sectional area of Water flow every ∼312 m along the Mississippi River channel for eight successive intervals of Water Discharge. Assuming conservation of Water Discharge, the local flow velocity was calculated at each transect by dividing Water Discharge by the local measurement of cross-sectional flow area. Calculated flow velocity was converted to total bed stress using a dimensionless friction coefficient that was determined by optimizing the match between a predicted and a measured Water-surface profile. Estimates for the skin-friction component of the total bed stress were produced from the values for total shear stress using a form-drag correction. These skin-friction bed-stress values were then used to model bed-material transport. Results demonstrate that in the lower Mississippi River, cross-sectional flow area increases downstream during low- and moderate-Water Discharge. This generates a decrease in calculated Water-flow velocity and bed-material transport. During high-Water Discharge, the trend is reversed: Cross-sectional flow area decreases downstream, producing an increase in calculated Water-flow velocity and bed-material transport. An important contribution of this work is the identification of a downstream reversal in the trend for channel cross-sectional area due to variable Water Discharge. By accounting for the spatial divergences in sediment transport predicted over an average annual hydrograph, we demonstrate the tendency for channel-bed aggradation in much of the backWater reach of the Mississippi River (150–600 km above the outlet); however, a region of channel-bed erosion is calculated for the final 150 km. These results help to explain the spatial variability of channel morphology and kinematics for the lower Mississippi River, and they can be extended to other lowland river systems near the coastline.
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punctuated sand transport in the lowermost mississippi river
Journal of Geophysical Research, 2011Co-Authors: Jeffrey A Nittrouer, David Mohrig, Mead A AllisonAbstract:[1] Measurements of sand flux and Water flow in the Mississippi River are presented for a portion of the system 35–50 km upstream from the head of its subaerial delta. These data are used to provide insight into how nonuniform flow conditions, present in the lower reaches of large alluvial rivers, affect the timing and magnitude of sand transport near the river outlet. Field surveys during both low and high Water Discharge include (1) sequential digital bathymetric maps defining mobile river bottom topography which were used to estimate bed material flux, (2) multiple Water velocity profiles, and (3) multiple suspended sediment profiles collected using a point-integrated sampler. These data show that total sand transport increases by two orders of magnitude over the measured range in Water Discharge (11,300 to 38,400 m3 s−1). During low Water Discharge no sand is measured in suspension, and sand Discharge via bed form migration is minimal. During high Water Discharge 54% of the sand Discharge is measured in suspension while 46% of the sand Discharge is part of bed form migration. The component of boundary shear stress associated with moving this sediment is estimated using a set of established sediment transport algorithms, and values for the total boundary shear stress are predicted by fitting logarithmic velocity functions to the measured profiles. The estimates of boundary shear stress, using measurements of suspended sand transport, bed form transport, and downstream oriented velocity profiles are internally consistent; moreover, the analyses show that boundary shear stress increases by nearly 10-fold over the measured Water Discharge range. We show how this increase in shear stress is consistent with backWater flow arising where the river approaches its outlet. The hydrodynamic properties of backWater flow affect the timing and magnitude of sand flux and produce punctuated sand transport through the lowermost Mississippi River. Our field data are used to evaluate the influence of this sand transport style on development of the mixed bedrock alluvial channel for the lowermost Mississippi River.
J. Némery - One of the best experts on this subject based on the ideXlab platform.
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Monitoring Discharge in a tidal river using Water level observations: Application to the Saigon River, Vietnam
Science of the Total Environment, 2021Co-Authors: B. Camenen, N. Gratiot, J.-a. Cohard, F. Gard, V.q. Tran, A.-t. Nguyen, G. Dramais, T. Van Emmerik, J. NémeryAbstract:The hydrological dynamics of the Saigon River is ruled by a complex combination of factors, which need to be disentangled to prevent and limit risks of flooding and salt intrusion. In particular, the Saigon Water Discharge is highly influenced by tidal cycles with a relatively low net Discharge. This study proposes a low-cost technique to estimate river Discharge at high frequency (every 10 min in this study). It is based on a stage-fall-Discharge (SFD) rating curve adapted from the general Manning Strickler law, and calibrated thanks to two ADCP campaigns. Two pressure sensors were placed at different locations of the river in September 2016: one at the centre of Ho Chi Minh City and one in Phu Cuong, 40 km upstream approximately. The instantaneous Water Discharge data were used to evaluate the net residual Discharge and to highlight seasonal and inter-annual trends. Both Water level and Water Discharge show a seasonal behaviour. Rainfall, including during the Usagi typhoon that hit the megalopolis in November 2018, has no clear and direct impact on Water level and Water Discharge due to the delta flat morphology and complex response between main channel and side channel network and ground Water in this estuarine system under tidal influence. However, we found some evidences of interactions between precipitation, groundWater, the river network and possibly coastal Waters. This paper can be seen as a proof of concept to (1) present a low-cost Discharge method that can be applied to other tidal rivers, and (2) demonstrate how the high-frequency Discharge data obtained with this method can be used to evaluate Discharge dynamics in tidal river systems.
