下荆江河槽形态及过流能力调整对上下游边界条件的响应
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摘要
受三峡工程运用与洞庭湖出流顶托影响,下荆江河段的进口水沙条件及其出口侵蚀基准面发生改变,河床冲淤调整剧烈,平滩河槽形态及过流能力变化显著,威胁到两岸的防洪安全。首先采用一维水动力学模型及河段平均的河床演变分析方法,计算了下荆江2002—2016年河段尺度的平滩特征值(平滩宽度■、水深■、面积■及流量■),以及石首与监利两站相应警戒水位下的过流流量(Q_(wn)~(SS)、Q_(wn)~(JL))。其次分析了上述参数对上下游边界条件的响应,并建立了这些参数与前5年汛期平均水流冲刷强度■(上边界)、当年上下游汛期平均水位差■(下边界)之间的单因素及多因素响应关系,并对综合关系式进行了率定与验证。结果表明:(1)受大规模护岸工程控制,下荆江河床调整以河段平滩水深增加为主,增幅为8.8%,相应宽深比减小8%,河床趋于窄深;(2)河道过流能力年际间变化较大,无明显单向增加或减少趋势,其中河段平滩流量介于27 401～34 548 m~3/s之间,多年平均值为31 335 m~3/s,而石首及监利两站警戒水位下过流流量的多年平均值分别为36 976、34 381 m~3/s;(3)在综合关系式中,对于河段平滩面积■而言,上边界■占比的平均值约为96%,且■随■的增加而增大;对于河道过流能力(■、Q_(wn)~(SS)、Q_(wn)~(JL))而言,下边界■占比的平均值约为86%,且■、QwnSS和QwnL均随■的增加而增大。故下荆江河段平滩河槽形态调整主要与进口水沙条件有关,而过流能力调整主要受出口侵蚀基准面条件(洞庭湖出流顶托)控制。
The Lower Jingjiang Reach(LJR)underwent remarkable morphodynamic evolution owing to the combined effects of the altered flow-sediment regimes caused by the upstream operation of the Three Gorges Project(TGP),and the local base-level changes because of the downstream confluence from the Dongting Lake.Variations in bankfull channel geometry and flood-discharge capacity of this reach were investigated by a one-dimensional hydrodynamic model and a reach-averaged method,covering the changes in reach-scale bankfull geometry(width ■,depth ■ and area ■)and discharge(■),as well as thespecified discharge under the warning levels at the water gauge stations of Shishou(Q_(wn)~(SS))and Jianli(Q_(wn)~(JL))during the period 2002-2016.Furthermore,these variables were represented by empirical functions of two key hydrodynamic parameters,covering the previous five-year average fluvial erosion intensity during floodseasons at Jianli(upstream boundary ■),and the corresponding difference between the average water stages at Xinchang and Lianhuatang(downstream boundary ■).Calculated results indicate that:(i)owing to the impacts of various river regulation engineering,channel evolution in the LJR was mainly characterised by the variation in bankfull depth,with an increase of 8.8%and 9.9%in the reach-scale bankfull depthand area from 2002 to 2016,respectively;(ii)the flood-discharge capacity of this reach varied greatly in different years after the TGP operation,showing no monotone increasing or decreasing trend,with the average values of ■,Q_(wn)~(SS),Q_(wn)~(JL) being 31 335,36 976 and 34 381 m~3/s,respectively;and(iii)the adjustments in the channel geometry were mainly controlled by the upstream boundary condition,with the value of ■ increasing with a larger value of ■,but the variation in the flood-discharge capacity was mainly influenced by the downstream boundary condition,with the values of ■,Q_(wn)~(SS) and Q_(wn)~(JL) increasing with a larger value of ■.
The Lower Jingjiang Reach(LJR)underwent remarkable morphodynamic evolution owing to the combined effects of the altered flow-sediment regimes caused by the upstream operation of the Three Gorges Project(TGP),and the local base-level changes because of the downstream confluence from the Dongting Lake.Variations in bankfull channel geometry and flood-discharge capacity of this reach were investigated by a one-dimensional hydrodynamic model and a reach-averaged method,covering the changes in reach-scale bankfull geometry(width ■,depth ■ and area ■)and discharge(■),as well as thespecified discharge under the warning levels at the water gauge stations of Shishou(Q_(wn)~(SS))and Jianli(Q_(wn)~(JL))during the period 2002-2016.Furthermore,these variables were represented by empirical functions of two key hydrodynamic parameters,covering the previous five-year average fluvial erosion intensity during floodseasons at Jianli(upstream boundary ■),and the corresponding difference between the average water stages at Xinchang and Lianhuatang(downstream boundary ■).Calculated results indicate that:(i)owing to the impacts of various river regulation engineering,channel evolution in the LJR was mainly characterised by the variation in bankfull depth,with an increase of 8.8%and 9.9%in the reach-scale bankfull depthand area from 2002 to 2016,respectively;(ii)the flood-discharge capacity of this reach varied greatly in different years after the TGP operation,showing no monotone increasing or decreasing trend,with the average values of ■,Q_(wn)~(SS),Q_(wn)~(JL) being 31 335,36 976 and 34 381 m~3/s,respectively;and(iii)the adjustments in the channel geometry were mainly controlled by the upstream boundary condition,with the value of ■ increasing with a larger value of ■,but the variation in the flood-discharge capacity was mainly influenced by the downstream boundary condition,with the values of ■,Q_(wn)~(SS) and Q_(wn)~(JL) increasing with a larger value of ■.
引文
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[17]王之晗,夏叶,于合理,等.侵蚀基准面对石亭江双盛段河床演变的影响[J].工程科学与技术,2017(S2):67-73.
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[21]夏军强,吴保生,王艳平,等.黄河下游河段平滩流量计算及变化过程分析[J].泥沙研究,2010(2):6-14.
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[23]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.
[24] WU B S,ZHENG S,THORNE C R. A general framework for using the rate law to simulate morphological response to disturbance in the fluvial system[J]. Progress in Physical Geography,2012,36(5):575-597.
[2] SCHUMM S A. River response to base-level change:implications for sequence stratigraphy[J]. Journal of Geology,1993,101(2):279-294.
[3] WU B S,XIA J Q,FU X D,et al. Effect of altered flow regime on bankfull area of the Lower Yellow River,China[J]. Earth Surface Processes and Landforms,2008,33(10):1585-1601.
[4] WU B S,WANG G Q,XIA J Q,et al. Response of bankfull discharge to discharge and sediment load in the Lower Yellow River[J]. Geomorphology,2008,100(3):366-376.
[5] XIA J Q,ZHOU M R,LIN F F,et al. Variation in reach-scale bankfull discharge of the Jingjiang Reach undergoing upstream and downstream boundary controls[J]. Journal of Hydrology,2017,547:534-543.
[6] XIA J Q,DENG S S,ZHOU M R,et al. Geomorphic response of the Jingjiang Reach to the Three Gorges Project operation[J]. Earth Surface Processes and Landforms,2017,42:866-876.
[7]王兆印,李昌志,王费新.潼关高程对渭河河床演变的影响[J].水利学报,2004(9):1-8.
[8] WEATHERLY H,JAKOB M. Geomorphic response of Lillooet River,British Columbia,to meander cutoffs and base level lowering[J]. Geomorphology,2014,217:48-60.
[9] EDWARDS B L,KEIM R F,JOHNSON E L,et al. Geomorphic adjustment to hydrologic modifications along a meandering river:Implications for surface flooding on a floodplain[J]. Geomorphology,2016,269:149-159.
[10] XIA J Q,LI X J,LI T,et al. Response of reach-scale bankfull channel geometry to the altered flow and sediment regime in the lower Yellow River[J]. Geomorphology,2014,213:255-265.
[11] XIA J Q,LI X J,ZHANG X L,et al. Recent variation in reach-scale bankfull discharge in the Lower Yellow River[J]. Earth Surface Processes and Landforms,2014,39(6):723-734.
[12]胡春宏,张治昊.黄河口尾闾河道横断面形态调整及其与水沙过程的响应关系[J].应用基础与工程科学学报,2011,19(4):543-553.
[13]申红彬,吴保生,郑珊,等.黄河内蒙古河段平滩流量与有效输沙流量关系[J].水科学进展,2013,24(4):477-482.
[14] SHIBATA K,ITO M. Relationships of bankfull channel width and discharge parameters for modern fluvial systems in the Japanese Islands[J]. Geomorphology,2014,214:97-113.
[15]郑珊,吴保生.黄河小北干流和渭河下游淤积过程模拟[J].水利学报,2014,45(2):150-162.
[16]郑珊,谈广鸣,吴保生,等.利津水位对河口演变响应的计算方法[J].水利学报,2015,46(3):315-325.
[17]王之晗,夏叶,于合理,等.侵蚀基准面对石亭江双盛段河床演变的影响[J].工程科学与技术,2017(S2):67-73.
[18]潘庆燊.长江中下游河道近50年变迁研究[J].长江科学院院报,2001,18(5):18-22.
[19]毛北平,吴忠明,梅军亚,等.三峡工程蓄水以来长江与洞庭湖汇流关系变化[J].水力发电学报,2013,32(5):48-57.
[20]荆州市长江河道管理局.防汛手册[Z]. 2005.
[21]夏军强,吴保生,王艳平,等.黄河下游河段平滩流量计算及变化过程分析[J].泥沙研究,2010(2):6-14.
[22]曹广晶,王俊.长江三峡工程水文泥沙观测与研究[M].北京:科学出版社,2015.
[23]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.
[24] WU B S,ZHENG S,THORNE C R. A general framework for using the rate law to simulate morphological response to disturbance in the fluvial system[J]. Progress in Physical Geography,2012,36(5):575-597.