The backwater effect caused by tributary inflow can significantly elevate the water level profile upstream of a confluence point.However,the influence of mainstream and confluence discharges on the backwater effect in...The backwater effect caused by tributary inflow can significantly elevate the water level profile upstream of a confluence point.However,the influence of mainstream and confluence discharges on the backwater effect in a river reach remains unclear.In this study,various hydrological data collected from the Jingjiang Reach of the Yangtze River in China were statistically analyzed to determine the backwater degree and range with three representative mainstream discharges.The results indicated that the backwater degree increased with mainstream discharge,and a positive relationship was observed between the runoff ratio and backwater degree at specific representative mainstream discharges.Following the operation of the Three Gorges Project,the backwater effect in the Jingjiang Reach diminished.For instance,mean backwater degrees for low,moderate,and high mainstream discharges were recorded as 0.83 m,1.61 m,and 2.41 m during the period from 1990 to 2002,whereas these values decreased to 0.30 m,0.95 m,and 2.08 m from 2009 to 2020.The backwater range extended upstream as mainstream discharge increased from 7000 m3/s to 30000 m3/s.Moreover,a random forest-based machine learning model was used to quantify the backwater effect with varying mainstream and confluence discharges,accounting for the impacts of mainstream discharge,confluence discharge,and channel degradation in the Jingjiang Reach.At the Jianli Hydrological Station,a decrease in mainstream discharge during flood seasons resulted in a 7%–15%increase in monthly mean backwater degree,while an increase in mainstream discharge during dry seasons led to a 1%–15%decrease in monthly mean backwater degree.Furthermore,increasing confluence discharge from Dongting Lake during June to July and September to November resulted in an 11%–42%increase in monthly mean backwater degree.Continuous channel degradation in the Jingjiang Reach contributed to a 6%–19%decrease in monthly mean backwater degree.Under the influence of these factors,the monthly mean backwater degree in 2017 varied from a decrease of 53%to an increase of 37%compared to corresponding values in 1991.展开更多
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
By introducing a water depth connecting formula, the hydraulic equations in the dividing channel system were coupled and the relation of discharge distribution between the branches of the dividing channels can be yiel...By introducing a water depth connecting formula, the hydraulic equations in the dividing channel system were coupled and the relation of discharge distribution between the branches of the dividing channels can be yielded. In this manner, a numerical model for the confluent channels was established to study the variation of backwater effects with the parameters in the channel junction. The meeting of flood peaks in the mainstream and tributary can be analyzed with this model.The flood peak meeting is found to be a major factor for the extremely high water level in the mainstream during the 1998 Yangtze River flood. Subsequently the variations of discharge distribution and water level with channel parameters between each branch in this system were studied as well. As a result, flood evolution caused by Jingjiang River shortcut and sediment deposition in the entrance of dividing channels of the Yangtze River may be qualitatively elucidated.It is suggested to be an effective measure for flood mitigation to enhance regulation capability of reservoirs available upstream of the tributaries and harness branch entrance channels.展开更多
River-dominated lacustrine deltas typically consist of multiple lobes due to autogenic lobe switching that occurs over short time scales.However,the switching patterns of multiple lobes in these deltas remain poorly u...River-dominated lacustrine deltas typically consist of multiple lobes due to autogenic lobe switching that occurs over short time scales.However,the switching patterns of multiple lobes in these deltas remain poorly understood,and the architectural features attributed to lobe switching are also lacking.By integrating Delft3D simulations,flume experiments,and modern deposit analysis,we proposed that autogenic lobe switching follows a cyclic pattern.Autocyclicity begins with the formation of an offshore lobe and concludes after a series of longshore lobe growth events,marked by longshore avulsions occurring along the sides of offshore distributary channels.Longshore avulsions follow a sequence that usually occurs earlier distally than proximally and subsequently occurs on one longshore side and then on the other side.Each lobe begins with rapid growth,which gradually slows and then stops once a channel avulsion is influenced by the backwater effect that triggers lobe switching.Three signals indicate lobe switching:a decrease in progradation rate,foreset slope steepening coupled with topset slope gentling,and the deposition of mud-dominated sediments.The number of autocyclic events never exceeds seven.The first two autocyclicities contribute to more than 55%of delta length and 70%of delta area.The lobes are separated by 1-6 stages of mud-dominated accretion beds that exhibit a downstream-inclined shape and convexup or lateral overlapping pattern.This study conducts a coupled growth-geometric assessment to establish an architectural pattern for river-dominated lacustrine deltas.This architectural pattern offers valuable insights into predicting sandy lobe distribution in river-dominated lacustrine delta reservoirs,and the architecture of muddy accretion beds aids in predicting the rule of oil-water movement and distribution of remaining oil.展开更多
基金supported by the National Key Research and Development Program of China(Grant No.2023YFC3209504)the National Natural Science Foundation of China(Grants No.U2040215 and 52479075)the Natural Science Foundation of Hubei Province(Grant No.2021CFA029).
文摘The backwater effect caused by tributary inflow can significantly elevate the water level profile upstream of a confluence point.However,the influence of mainstream and confluence discharges on the backwater effect in a river reach remains unclear.In this study,various hydrological data collected from the Jingjiang Reach of the Yangtze River in China were statistically analyzed to determine the backwater degree and range with three representative mainstream discharges.The results indicated that the backwater degree increased with mainstream discharge,and a positive relationship was observed between the runoff ratio and backwater degree at specific representative mainstream discharges.Following the operation of the Three Gorges Project,the backwater effect in the Jingjiang Reach diminished.For instance,mean backwater degrees for low,moderate,and high mainstream discharges were recorded as 0.83 m,1.61 m,and 2.41 m during the period from 1990 to 2002,whereas these values decreased to 0.30 m,0.95 m,and 2.08 m from 2009 to 2020.The backwater range extended upstream as mainstream discharge increased from 7000 m3/s to 30000 m3/s.Moreover,a random forest-based machine learning model was used to quantify the backwater effect with varying mainstream and confluence discharges,accounting for the impacts of mainstream discharge,confluence discharge,and channel degradation in the Jingjiang Reach.At the Jianli Hydrological Station,a decrease in mainstream discharge during flood seasons resulted in a 7%–15%increase in monthly mean backwater degree,while an increase in mainstream discharge during dry seasons led to a 1%–15%decrease in monthly mean backwater degree.Furthermore,increasing confluence discharge from Dongting Lake during June to July and September to November resulted in an 11%–42%increase in monthly mean backwater degree.Continuous channel degradation in the Jingjiang Reach contributed to a 6%–19%decrease in monthly mean backwater degree.Under the influence of these factors,the monthly mean backwater degree in 2017 varied from a decrease of 53%to an increase of 37%compared to corresponding values in 1991.
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.
文摘By introducing a water depth connecting formula, the hydraulic equations in the dividing channel system were coupled and the relation of discharge distribution between the branches of the dividing channels can be yielded. In this manner, a numerical model for the confluent channels was established to study the variation of backwater effects with the parameters in the channel junction. The meeting of flood peaks in the mainstream and tributary can be analyzed with this model.The flood peak meeting is found to be a major factor for the extremely high water level in the mainstream during the 1998 Yangtze River flood. Subsequently the variations of discharge distribution and water level with channel parameters between each branch in this system were studied as well. As a result, flood evolution caused by Jingjiang River shortcut and sediment deposition in the entrance of dividing channels of the Yangtze River may be qualitatively elucidated.It is suggested to be an effective measure for flood mitigation to enhance regulation capability of reservoirs available upstream of the tributaries and harness branch entrance channels.
基金supported by the National Natural Science Foundation of China(No.42202178)Science Foundation of China University of Petroleum(Beijing)(No.2462023YJRC034).
文摘River-dominated lacustrine deltas typically consist of multiple lobes due to autogenic lobe switching that occurs over short time scales.However,the switching patterns of multiple lobes in these deltas remain poorly understood,and the architectural features attributed to lobe switching are also lacking.By integrating Delft3D simulations,flume experiments,and modern deposit analysis,we proposed that autogenic lobe switching follows a cyclic pattern.Autocyclicity begins with the formation of an offshore lobe and concludes after a series of longshore lobe growth events,marked by longshore avulsions occurring along the sides of offshore distributary channels.Longshore avulsions follow a sequence that usually occurs earlier distally than proximally and subsequently occurs on one longshore side and then on the other side.Each lobe begins with rapid growth,which gradually slows and then stops once a channel avulsion is influenced by the backwater effect that triggers lobe switching.Three signals indicate lobe switching:a decrease in progradation rate,foreset slope steepening coupled with topset slope gentling,and the deposition of mud-dominated sediments.The number of autocyclic events never exceeds seven.The first two autocyclicities contribute to more than 55%of delta length and 70%of delta area.The lobes are separated by 1-6 stages of mud-dominated accretion beds that exhibit a downstream-inclined shape and convexup or lateral overlapping pattern.This study conducts a coupled growth-geometric assessment to establish an architectural pattern for river-dominated lacustrine deltas.This architectural pattern offers valuable insights into predicting sandy lobe distribution in river-dominated lacustrine delta reservoirs,and the architecture of muddy accretion beds aids in predicting the rule of oil-water movement and distribution of remaining oil.
