七弓岭弯道颈口裁弯条件及其对城陵矶水位影响
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摘要
下荆江与东洞庭湖交汇段的七弓岭弯道,其颈口宽度已远小于河道宽度,而且三峡水库蓄水后清水冲刷河岸,加速颈口河道缩窄,存在漫滩冲刷或崩岸贯穿作用下颈口裁弯的可能性,故研究七弓岭弯道的颈口裁弯临界条件较为迫切。采用水文资料、地形数据和MIKE21水动力模型,建立七弓岭弯道上下游(监利-螺山)的二维水动力学模型,在不同流量和颈口设置不同深度的浅槽条件下,开展颈口裁弯前后的河道水动力数值模拟,分析七弓岭弯道颈口裁弯条件和预测七弓岭裁弯对城陵矶水位的影响。研究表明,七弓岭颈口可能在高水位条件下发生冲切型裁弯和较窄颈口宽度条件下发生崩岸型裁弯,裁弯将导致城陵矶水位至少增加0.3m,这主要是七弓岭下游的洞庭湖入汇长江对七弓岭弯道水位的顶托作用,而且在不同强弱顶托作用下裁弯后新河道与老河道的分流量差值小于上游来流量的1%。
The neck of Qigongling bend, located in the section of lower Jingjiang River connecting the East Dongting Lake, is much narrower than the average mainstream channel width, and its narrowing is speeded up together with a riverbank scour under the existing conditions of this special location in combination with the effect of Three Gorges Reservoir. Hence the occurrence of its cutoff to be triggered by overbank flooding or bank collapse is quite possible, and the threshold of this event must be understood. In this work, we develop a two-dimensional hydrodynamic model of the upper and lower reaches of the bend(i.e. Jianli-Luoshan reach) based on the hydrological data, topographic data, and MIKE21 hydrodynamic model, and conduct simulations and analysis for different inflow conditions and different flow depths in the cutoff channel to reveal the influence of the cutoff event on the mainstream stage at Chenglingji. Results show that being triggered by overbank flooding and bank collapse, the possibility of the neck cutoff is very high as a result of either a high flood discharge or neck narrowing. Chenglingji stage tends to be raised by at least 0.3 m by the event under the lake's top-off effect on the confluence. However, the difference between the discharges through the new cutoff channel and old main channel will keep less than 1% of the inflow, though this top-off produces quite different effects on the mainstream stage.
The neck of Qigongling bend, located in the section of lower Jingjiang River connecting the East Dongting Lake, is much narrower than the average mainstream channel width, and its narrowing is speeded up together with a riverbank scour under the existing conditions of this special location in combination with the effect of Three Gorges Reservoir. Hence the occurrence of its cutoff to be triggered by overbank flooding or bank collapse is quite possible, and the threshold of this event must be understood. In this work, we develop a two-dimensional hydrodynamic model of the upper and lower reaches of the bend(i.e. Jianli-Luoshan reach) based on the hydrological data, topographic data, and MIKE21 hydrodynamic model, and conduct simulations and analysis for different inflow conditions and different flow depths in the cutoff channel to reveal the influence of the cutoff event on the mainstream stage at Chenglingji. Results show that being triggered by overbank flooding and bank collapse, the possibility of the neck cutoff is very high as a result of either a high flood discharge or neck narrowing. Chenglingji stage tends to be raised by at least 0.3 m by the event under the lake's top-off effect on the confluence. However, the difference between the discharges through the new cutoff channel and old main channel will keep less than 1% of the inflow, though this top-off produces quite different effects on the mainstream stage.
引文
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[4]许全喜,袁晶,伍文俊,等.三峡工程蓄水运用后长江中游河道演变初步研究[J].泥沙研究,2011(2):38-46.XU Quanxi,YUAN Jing,WU Wenjun,et al.Fluvial processes in Middle Yangtze River after impoundment of Three Gorges Project[J].Journal of Sediment Research,2011(2):38-46.(in Chinese)
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[6]XIA J Q,ZONG Q L,ZHANG Y,et al.Prediction of recent bank retreat processes at typical sections in the Jingjiang Reach[J].Science China:Technological Sciences,2014,57(8):1490-1499.
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[8]XIA J Q,DENG S,ZHOU M,et al.Geomorphic response of the Jingjiang Reach to the Three Gorges Project operation[J].Earth Surface Processes&Landforms,2017,42(6):866-876.
[9]夏军强,宗全利,邓珊珊,等.三峡工程运用后荆江河段平滩河槽形态调整特点[J].浙江大学学报(工学版),2015,49(2):238-245.XIA Junqiang,ZONG Quanli,DENG Shanshan,et al.Adjustments in reach-scale bankfull channel geometry of Jingjiang reach after operation of Three Gorges Project[J].Journal of Zhejiang University(Engineering Science),2015,49(2):238-245.(in Chinese)
[10]余文畴.长江中下游河道崩岸机理中的河床边界条件[J].长江科学院院报,2008,25(1):8-11.YU Wenchou.River boundary conditions of mechanism of bank failure in middle and lower reaches of Changjiang River[J].Journal of Yangtze River Scientific Research Institute,2008,25(1):8-11.(in Chinese)
[11]MICHELI E R,LARSEN E W.River channel cutoff dynamics,Sacramento River,California,USA[J].River Research and Applications,2011,27(3):328-344.
[12]LI Z W,YU G A,BRIERLEY G,et al.Migration and cutoff of meanders in the hyperarid environment of the middle Tarim River,northwestern China[J].Geomorphology,2017,276:116-124.
[13]ERSKINE W,MELVILLE M,PAGE K J,et al.Cutoff and oxbow lake[J].Australian Geographer,1981,15(3):174-180.
[14]GAY G R,GAY H H,GAY W H,et al.Evolution of cutoffs across meander necks in Power River,Montana,USA[J].Earth Surface Processes and Landforms,2015,23(7):651-662.
[15]HOOKE J M.Cutoffs galore!:Occurrence and causes of multiple cutoffs on a meandering river[J].Geomorphology,2004,61(3):225-238.
[16]HOOKE J M.River channel adjustment to meander cutoffs on the River Bollin and River Dane,northwest England[J].Geomorphology,1995,14(3):235-253.
[17]CONSTANTINE J A,MCLEAN S R,DUNNE T.Amechanism of chute cutoff along large meandering rivers with uniform floodplain topography[J].GSABulletin,2010,122(5/6):855-869.
[18]GAUTIER E,BRUNSTEIN D,VAUCHEL P,et al.Temporal relations between meander deformation,water discharge and sediment fluxes in the floodplain of the Rio Beni(Bolivian Amazonia)[J].Earth Surface Processes&Landforms,2007,32(2):230-248.
[19]THOMPSON D M.A geomorphic explanation for a meander cutoff following channel relocation of a coarse-bedded river[J].Environmental Management,2003,31(3):385-400.
[20]LEOPOLD L B,LANGBEIN W B.River meanders[J].Scientific American,1960,71(6):769-793.
[21]CAMPOREALE C,PERUCCA E,RIDOLFII L.Significance of cutoff in meandering river dynamics[J].Journal of Geophysical Research,2008,113:F01001.Doi:10.1029/2006JF000694.
[22]唐日长.下荆江裁弯对荆江洞庭湖影响分析[J].人民长江,1999,30(4):20-23.TANG Richang.Impact of river bend cut-off of lower Jingjiang River on the river and Dongting Lake[J].Yangtze River,1999,30(4):20-23.(in Chinese)
[23]许全喜,胡功宇,袁晶.近50年来荆江三口分流分沙变化研究[J].泥沙研究,2009(5):1-8.XU Quanxi,HU Gongyu,YUAN Jing.Research on the flow and sediment diversion in the three outlets along Jingjiang River in recent 50 years[J].Journal of Sediment Research,2009(5):1-8.(in Chinese)
[24]石国钰,许全喜,陈泽方.长江中下游河道冲淤与河床自动调整作用分析[J].山地学报,2002,20(3):257-265.SHI Guoyu,XU Quanxi,CHEN Zefang.Analysis on channel scouring and silting and self-adjusting in midstream and downstream reaches of Changjiang River[J].Mountain Research,2002,20(3):257-265.(in Chinese)
[25]余文畴,卢金友.长江河道崩岸与护岸[M].北京:中国水利水电出版社,2008.YU Wenchou,LU Jinyou.Bank collapse and revetment of Yangtze River channel[M].Beijing:China Water&Power Press,2008.(in Chinese)
[26]夏军强,宗全利,许全喜,等.下荆江二元结构河岸土体特性及崩岸机理[J].水科学进展,2013,24(6):810-820.XIA Junqiang,ZONG Quanli,XU Quanxi,et al.Soil properties and erosion mechanisms of composite riverbanks in Lower Jingjiang Reach[J].Advances in Water Science,2013,24(6):810-820.(in Chinese)
[27]方春明,胡春宏,陈绪坚.三峡水库运用对荆江三口分流及洞庭湖的影响[J].水利学报,2014,45(1):36-41.FANG Chunming,HU Chunhong,CHEN Xujian.Impacts of Three Georges Reservoir’s operation on outflow of the three outlets of Jingjiang River and Dongting Lake[J].Journal of Hydraulic Engineering,2014,45(1):36-41.(in Chinese)
[28]何广水,姚仕明,金中武.长江荆江河段弯道凸岸边滩非典型冲刷研究[J].人民长江,2011,42(17):1-3.HE Guangshui,YAO Shiming,JIN Zhongwu.Study of atypical erosion of convex bank of river bend in Jingjiang Reach of Yangtze River[J].Yangtze River,2011,42(17):1-3.(in Chinese)
[29]李志威,王兆印,徐梦珍,等.弯曲河流颈口裁弯模式与机理[J].清华大学学报(自然科学版),2013,53(5):618-624.LI Zhiwei,WANG Zhaoyin,XU Mengzhen,et al.Patterns and mechanisms of neck cutoffs on meandering rivers[J].Journal of Tsinghua University(Science and Technology),2013,53(5):618-624.(in Chinese)
[2]李志威,袁帅,朱玲玲,等.荆江河段4次裁弯后干流河道调整研究[J].长江流域资源与环境,2018,27(4):882-890.LI Zhiwei,YUAN Shuai,ZHU Lingling,et al.Channel adjustments induced by four meander cutoffs in the middle Yangtze River(Jinjiang reach)[J].Resources and Environment in the Yangtze Basin,2018,27(4):882-890.(in Chinese)
[3]韩其为.江湖关系变化的内在机理[J].长江科学院院报,2014,31(6):104-112.HAN Qiwei.Variation mechanism of the relation between Jingjiang River and Dongting Lake[J].Journal of Yangtze River Scientific Research Institute,2014,31(6):104-112.(in Chinese)
[4]许全喜,袁晶,伍文俊,等.三峡工程蓄水运用后长江中游河道演变初步研究[J].泥沙研究,2011(2):38-46.XU Quanxi,YUAN Jing,WU Wenjun,et al.Fluvial processes in Middle Yangtze River after impoundment of Three Gorges Project[J].Journal of Sediment Research,2011(2):38-46.(in Chinese)
[5]朱玲玲,许全喜,熊明.三峡水库蓄水后下荆江急弯河道凸冲凹淤成因[J].水科学进展,2017,28(2):193-202.ZHU Lingling,XU Quanxi,XIONG Ming.Fluvial processes of meandering channels in the Lower Jingjiang River reach after the impoundment of Three Gorges Reservior[J].Advances in Water Science,2017,28(2):193-202.(in Chinese)
[6]XIA J Q,ZONG Q L,ZHANG Y,et al.Prediction of recent bank retreat processes at typical sections in the Jingjiang Reach[J].Science China:Technological Sciences,2014,57(8):1490-1499.
[7]XIA J Q,DENG S,LU J,et al.Dynamic channel adjustments in the Jingjiang Reach of the Middle Yangtze River[J].Scientific Reports,2016,6:22802.
[8]XIA J Q,DENG S,ZHOU M,et al.Geomorphic response of the Jingjiang Reach to the Three Gorges Project operation[J].Earth Surface Processes&Landforms,2017,42(6):866-876.
[9]夏军强,宗全利,邓珊珊,等.三峡工程运用后荆江河段平滩河槽形态调整特点[J].浙江大学学报(工学版),2015,49(2):238-245.XIA Junqiang,ZONG Quanli,DENG Shanshan,et al.Adjustments in reach-scale bankfull channel geometry of Jingjiang reach after operation of Three Gorges Project[J].Journal of Zhejiang University(Engineering Science),2015,49(2):238-245.(in Chinese)
[10]余文畴.长江中下游河道崩岸机理中的河床边界条件[J].长江科学院院报,2008,25(1):8-11.YU Wenchou.River boundary conditions of mechanism of bank failure in middle and lower reaches of Changjiang River[J].Journal of Yangtze River Scientific Research Institute,2008,25(1):8-11.(in Chinese)
[11]MICHELI E R,LARSEN E W.River channel cutoff dynamics,Sacramento River,California,USA[J].River Research and Applications,2011,27(3):328-344.
[12]LI Z W,YU G A,BRIERLEY G,et al.Migration and cutoff of meanders in the hyperarid environment of the middle Tarim River,northwestern China[J].Geomorphology,2017,276:116-124.
[13]ERSKINE W,MELVILLE M,PAGE K J,et al.Cutoff and oxbow lake[J].Australian Geographer,1981,15(3):174-180.
[14]GAY G R,GAY H H,GAY W H,et al.Evolution of cutoffs across meander necks in Power River,Montana,USA[J].Earth Surface Processes and Landforms,2015,23(7):651-662.
[15]HOOKE J M.Cutoffs galore!:Occurrence and causes of multiple cutoffs on a meandering river[J].Geomorphology,2004,61(3):225-238.
[16]HOOKE J M.River channel adjustment to meander cutoffs on the River Bollin and River Dane,northwest England[J].Geomorphology,1995,14(3):235-253.
[17]CONSTANTINE J A,MCLEAN S R,DUNNE T.Amechanism of chute cutoff along large meandering rivers with uniform floodplain topography[J].GSABulletin,2010,122(5/6):855-869.
[18]GAUTIER E,BRUNSTEIN D,VAUCHEL P,et al.Temporal relations between meander deformation,water discharge and sediment fluxes in the floodplain of the Rio Beni(Bolivian Amazonia)[J].Earth Surface Processes&Landforms,2007,32(2):230-248.
[19]THOMPSON D M.A geomorphic explanation for a meander cutoff following channel relocation of a coarse-bedded river[J].Environmental Management,2003,31(3):385-400.
[20]LEOPOLD L B,LANGBEIN W B.River meanders[J].Scientific American,1960,71(6):769-793.
[21]CAMPOREALE C,PERUCCA E,RIDOLFII L.Significance of cutoff in meandering river dynamics[J].Journal of Geophysical Research,2008,113:F01001.Doi:10.1029/2006JF000694.
[22]唐日长.下荆江裁弯对荆江洞庭湖影响分析[J].人民长江,1999,30(4):20-23.TANG Richang.Impact of river bend cut-off of lower Jingjiang River on the river and Dongting Lake[J].Yangtze River,1999,30(4):20-23.(in Chinese)
[23]许全喜,胡功宇,袁晶.近50年来荆江三口分流分沙变化研究[J].泥沙研究,2009(5):1-8.XU Quanxi,HU Gongyu,YUAN Jing.Research on the flow and sediment diversion in the three outlets along Jingjiang River in recent 50 years[J].Journal of Sediment Research,2009(5):1-8.(in Chinese)
[24]石国钰,许全喜,陈泽方.长江中下游河道冲淤与河床自动调整作用分析[J].山地学报,2002,20(3):257-265.SHI Guoyu,XU Quanxi,CHEN Zefang.Analysis on channel scouring and silting and self-adjusting in midstream and downstream reaches of Changjiang River[J].Mountain Research,2002,20(3):257-265.(in Chinese)
[25]余文畴,卢金友.长江河道崩岸与护岸[M].北京:中国水利水电出版社,2008.YU Wenchou,LU Jinyou.Bank collapse and revetment of Yangtze River channel[M].Beijing:China Water&Power Press,2008.(in Chinese)
[26]夏军强,宗全利,许全喜,等.下荆江二元结构河岸土体特性及崩岸机理[J].水科学进展,2013,24(6):810-820.XIA Junqiang,ZONG Quanli,XU Quanxi,et al.Soil properties and erosion mechanisms of composite riverbanks in Lower Jingjiang Reach[J].Advances in Water Science,2013,24(6):810-820.(in Chinese)
[27]方春明,胡春宏,陈绪坚.三峡水库运用对荆江三口分流及洞庭湖的影响[J].水利学报,2014,45(1):36-41.FANG Chunming,HU Chunhong,CHEN Xujian.Impacts of Three Georges Reservoir’s operation on outflow of the three outlets of Jingjiang River and Dongting Lake[J].Journal of Hydraulic Engineering,2014,45(1):36-41.(in Chinese)
[28]何广水,姚仕明,金中武.长江荆江河段弯道凸岸边滩非典型冲刷研究[J].人民长江,2011,42(17):1-3.HE Guangshui,YAO Shiming,JIN Zhongwu.Study of atypical erosion of convex bank of river bend in Jingjiang Reach of Yangtze River[J].Yangtze River,2011,42(17):1-3.(in Chinese)
[29]李志威,王兆印,徐梦珍,等.弯曲河流颈口裁弯模式与机理[J].清华大学学报(自然科学版),2013,53(5):618-624.LI Zhiwei,WANG Zhaoyin,XU Mengzhen,et al.Patterns and mechanisms of neck cutoffs on meandering rivers[J].Journal of Tsinghua University(Science and Technology),2013,53(5):618-624.(in Chinese)