长江口南汇边滩冲淤变化规律与机制
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摘要
根据1842—2004年海图资料分析发现,南汇边滩存在近百年尺度的强烈冲刷—淤积旋回。长江主泓走南港或北港是造成冲刷期"北滩、东滩淤积,南滩、过渡带冲刷"或淤积期冲淤态势反相的主要原因;冲刷期内风暴强度和频数明显多于淤积期,造成冲刷期滩面叠置记忆的是暴风浪成因的"高滩冲刷、低滩淤积"的冲淤态势,而淤积期保存的是弱风浪成因的"高滩淤积、低滩冲刷"叠置增强的剖面特征。尽管三角洲整体冲淤态势的转变主要受流域来沙量的控制,但不同岸段受河口河势分水分沙作用、潮流和波浪等共同作用,明显存在此冲彼淤、冲淤动态调整等特征。已有的入海泥沙含量阈值研究以点代面或以局部代整体,这是造成阈值估算偏高的主要原因。2003年三峡水库开始蓄水后平均年输沙量154 Mt/a已低于低阈值184 Mt/a,但三角洲尚未如预测那样发生由净淤积向净侵蚀的转变。已有的河口水文观察资料显示,水体含沙量也未发生明显下降,这可能是潮控型三角洲潮流对泥沙在河口的再分配起主导作用,并可能由此延长三角洲冲淤转变对入海泥沙量减少的滞后。今后需进一步加强潮控型河口复杂过程的综合研究,提高对泥沙含量阈值估算和应对可能面临的海岸侵蚀及其相关的环境地质灾害的能力。
Nanhui muddy bank shows its cyclic geomorphic evolution at different time scales.The nearly-a-centennial alternations of serious erosion and deposition are obvious from the bathymetrical data analyses of the longest time series(1842—2004) of charts available in the Changjiang Estuary.The erosion phase is characterized by "accretion on the northern and eastern flats,and erosion on the southern flat and the transition belt",while the deposition/erosion pattern is generally reversal during the deposition phase.The changing phases from erosion to deposition are inferred to highly relate to the shifting of the Changjiang main channel from the South Channel to the North Channel.There are much more and stronger storms in the erosion phases than the deposition phases.It is presumed that the pattern of"the higher flat erosion and the lower flat accretion" results from the iterative recording of bank erosion profiles by larger storms in the erosion phases;while the pattern of "the higher flat deposition and the lower flat erosion" is ascribed to the enhanced preservation of normal bank accretion landforms under weak wave conditions in the deposition phases.Net accretion/erosion regimes of the river delta are highly related to sediment discharge,but the morphodynamics is far from unification with the different delta sections undergoing dynamic erosion/deposition cycles at different tempo-spatial scales,which is jointly controlled by tides,waves,and river distributary processes through diverting riverine sediment toward/away from the study sections.There are at least three scenarios having been proposed for the critical sediment discharge(CSD) turning the delta from net accretion into net erosion.The higher and medium CSD values are considered to overestimate due to their deduction from segments instead of the entirety.The average annual sediment discharge has declined to 154 Mt/a since 2003 when the Three-Gorges Dam started its first phase operation,much lower than the lower CSD value of 184 Mt/a,but the Changjiang Delta is not observed to undergo the presumed change from net accretion into net erosion till now.Recent hydrologic data did not show the decrease of suspended sediment content in the estuary,either.It is partially due to the Changjiang Delta of tidal dominated type where tides play an important role in redistributing sediment within the estuary,resulting in lag response of delta to the sediment decrease.Synthetical studies are therefore proposed to improve complex processes in tide-dominated estuaries,and to elevate the accuracy for CSD scenario construction and the adaptability to potential disasters related to coastal erosion.
Nanhui muddy bank shows its cyclic geomorphic evolution at different time scales.The nearly-a-centennial alternations of serious erosion and deposition are obvious from the bathymetrical data analyses of the longest time series(1842—2004) of charts available in the Changjiang Estuary.The erosion phase is characterized by "accretion on the northern and eastern flats,and erosion on the southern flat and the transition belt",while the deposition/erosion pattern is generally reversal during the deposition phase.The changing phases from erosion to deposition are inferred to highly relate to the shifting of the Changjiang main channel from the South Channel to the North Channel.There are much more and stronger storms in the erosion phases than the deposition phases.It is presumed that the pattern of"the higher flat erosion and the lower flat accretion" results from the iterative recording of bank erosion profiles by larger storms in the erosion phases;while the pattern of "the higher flat deposition and the lower flat erosion" is ascribed to the enhanced preservation of normal bank accretion landforms under weak wave conditions in the deposition phases.Net accretion/erosion regimes of the river delta are highly related to sediment discharge,but the morphodynamics is far from unification with the different delta sections undergoing dynamic erosion/deposition cycles at different tempo-spatial scales,which is jointly controlled by tides,waves,and river distributary processes through diverting riverine sediment toward/away from the study sections.There are at least three scenarios having been proposed for the critical sediment discharge(CSD) turning the delta from net accretion into net erosion.The higher and medium CSD values are considered to overestimate due to their deduction from segments instead of the entirety.The average annual sediment discharge has declined to 154 Mt/a since 2003 when the Three-Gorges Dam started its first phase operation,much lower than the lower CSD value of 184 Mt/a,but the Changjiang Delta is not observed to undergo the presumed change from net accretion into net erosion till now.Recent hydrologic data did not show the decrease of suspended sediment content in the estuary,either.It is partially due to the Changjiang Delta of tidal dominated type where tides play an important role in redistributing sediment within the estuary,resulting in lag response of delta to the sediment decrease.Synthetical studies are therefore proposed to improve complex processes in tide-dominated estuaries,and to elevate the accuracy for CSD scenario construction and the adaptability to potential disasters related to coastal erosion.
引文
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[4]STANLEY DJ.Nile Delta:extreme case of sedi ment entrapment on a delta plain and consequent coastal land loss[J].Marine Geology,1996,129:189—195.
[5]CARRI QUIRYJ D,S NCHEZ A.Sedi mentationin the Colorado River Delta and Upper Gulf of California after nearly a century of dis-charge loss[J].Marine Geology,1999,158:125—145.
[6]KENNISH MJ.Coastal salt marsh systems in the U.S.:a review of anthropogenic i mpacts[J].Journal of Coastal Research,2001,17:731—748.
[7]STONE R.Three Gorges Dam:into the unknown[J].Science,2008,321:628—632.
[8]陈吉余,徐海根.三峡工程对长江河口的影响[J].长江流域资源与环境,1995,4(3):242—246.
[9]李从先,杨守业,范代读,等.三峡大坝建成后长江输沙量的减少及其对长江三角洲的影响[J].第四纪研究,2004,24(5):495—500.
[10]YANG Z,WANG H,SAITO Y,et al.Dami mpacts on the Changjiang(Yangtze)River sedi ment discharge to the sea:the past 55 yearsand after the Three Gorges Dam[J].Water Resources Research,2006,42:w04407,doi:10.1029/2005 WR003970.
[11]JI AO N,YAO Z,ZENG Y,et al.Ecological anomalies in the East China Sea:i mpacts of the Three Gorges Dam?[J].Water Research,2007,41:1287—1293.
[12]YANG S L,ZHANGJ,XU X J.Influence of the Three Gorges Dam on downstream delivery of sedi ment and its environment i mplica-tions,Yangtze River[J].Geophysical Research Letter,2007,34:L10401,doi:10.1029/2007GL029472.
[13]宋晓红,石学法,蔡德陵,等.三峡截流后长江口秋季TSM,POC和PN的分布特征[J].海洋科学进展,2007,25(2):168—177.
[14]GAO S,WANG Y P.Changes in material fluxes fromthe Changjiang River and their i mplications on the adjoining continental shelf eco-system[J].Continental Shelf Research,2008,28:1490—1500.
[15]中华人民共和国水利部.中国河流泥沙公报2007[Z].北京:中国水利水电出版社,2008:60.
[16]CHEN X.Changjiang(Yangtze)River Delta,China[J].Journal of Coastal Research,1998,14(3):838—858.
[17]CHEN X,ZONG Y.Coastal erosion along the Changjiang deltaic shoreline,China:history and prospective[J].Estuarine,Coastal andShelf Science,1998,46:733—742.
[18]YANG S L,BELKI NI M,BELKI NA AI,et al.Delta response to declinein sedi ment supply fromthe Yangtze River:evidence of the re-cent four decades and expectations for the next half-century[J].Estuarine,Coastal and Shelf Science,2003,57:689—699.
[19]杨世伦,朱骏,李鹏.长江口前沿潮滩对来沙锐减和海平面上升的响应[J].海洋科学进展,2005,23(2):152—158.
[20]范代读.潮坪韵律沉积的形成和保存及沉积间断的定量分析[M].上海:同济大学出版社,2007:110.
[21]陈吉余,程和琴,戴志军.河口过程中第三驱动力的作用和响应——以长江河口为例[J].自然科学进展,2008,18(9):994—1000.
[22]时钟,陈吉余,虞志英.中国淤泥质潮滩沉积研究的进展[J].地球科学进展,1996,11(6):555—562.
[23]陈吉余,陈沈良,丁平兴,等.长江口南汇咀近岸水域泥沙输移途径[J].长江流域资源与环境,2001,10(2):166—172.
[24]陈沈良,谷国传,虞志英.长江口南汇东滩淤涨演变分析[J].长江流域资源与环境,2002,11(3):239—243.
[25]李九发,戴志军,应铭,等.上海市沿海滩涂土地资源圈围与潮滩发育演变分析[J].自然资源学报,2007,22(3):361—371.
[26]付桂,李九发,戴志军,等.长江口南汇咀岸滩围垦工程潮流数值模拟研究[J].海洋湖沼通报,2007(4):47—54.
[27]吴华林,沈焕庭,吴加学.长江口海图深度基准面换算关系研究[J].海洋工程,2002,20(1):69—74.
[28]恽才兴.长江河口潮滩冲淤和滩槽泥沙交换[J].泥沙研究,1983,4:43—521.
[29]李九发.长江河口南汇潮滩泥沙输移规律探讨[J].海洋学报,1990,12(1):75—82.
[30]陈卫跃.潮滩泥沙输移及沉积动力环境——以杭州湾北岸、长江口南岸部分潮滩为例[J].海洋学报,1991,13(6):813—821.
[31]FAN D D,GUO Y X,WANG P,et al.Cross-shore variationsin morphodynamic processes of an open-coast mudflat inthe Changjiang Del-ta:with an emphasis on stormi mpacts[J].Continental Shelf Research,2006,26:517—538.
[32]徐钢,陈吉余.长江河口海岸演变长周期波动的初步研究[J].华东师范大学学报:自然科学版,1997(4):64—71.
[33]刘苍字,虞志英.杭州湾北岸的侵蚀/淤积波及形成机制[J].福建地理,2000,15(3):12—15.
[34]刘苍字,吴立成,曹敏.长江三角洲南部古沙堤(冈身)的沉积特征、成因及年代[J].海洋学报,1985,7(1):55—66.
[35]恽才兴,时伟荣,何青.长江口通海航道泥沙场动态分析[J].华东师范大学学报:长江口深水航道治理与港口建设专辑,1995,50—79.
[36]陈吉余,徐海根.长江河口南支河段的河槽演变[C]∥陈吉余,沈焕庭,恽才兴.长江河口动力过程和地貌演变.上海:上海科学技术出版社,1988.375—389.
[37]陈吉余,潘定安,苏法崇,等.长江口北港河槽演变分析[C]∥陈吉余,沈焕庭,恽才兴.长江河口动力过程和地貌演变.上海:上海科学技术出版社,1988.390—403.
[38]火恩杰,刘昌森.上海地区自然灾害史料汇编[G].北京:地震出版社,2002:294.
[39]刘曙光,李从先,丁坚,等.黄河三角洲整体冲淤平衡及其地质意义[J].海洋地质与第四纪地质,2001,21(4):13—17.
[40]许炯心.黄河三角洲造陆过程中的陆域水沙临界条件研究[J].地理研究,2002,21(2):163—170.
[41]GAO S.Modeling the growthli mit of the Changjiang Delta[J].Geomorphology,2007,85:225—236.
[42]李九发,季中.长江来水来沙对河口南槽边滩冲淤变化的统计分析[J].泥沙研究,1988(4):76—82.
[43]高抒.潮滩沉积记录正演模拟初探[J].第四纪研究,2007,27(5):750—755.
[44]MILLI MANJ D,SHEN H,YANGZ,et al.Transport and deposition of river sedi ment inthe Changjiang Estuary and adjacent continentalshelf[J].Continental Shelf Research,1985,4:37—45.
[45]沈焕庭.长江河口物质能量[M].北京:海洋出版社,2001:176.
[46]LI B H,LI C X,SHEN H T.Apreli minary study on sedi ment fluxin the Changjiang Delta during the postglacial period[J].Science inChina:Series D Earth Sciences,2003,46(7):743—752.
[2]HAY W W.Detrital sedi ment fluxes fromcontinents to oceans[J].Chemical Geology,1998,145:287—323.
[3]SYVITSKI J P M.Supply and flux of sedi ment along hydrological pathways:research for the 21st century[J].Global and PlanetaryChange,2003,39:1—11.
[4]STANLEY DJ.Nile Delta:extreme case of sedi ment entrapment on a delta plain and consequent coastal land loss[J].Marine Geology,1996,129:189—195.
[5]CARRI QUIRYJ D,S NCHEZ A.Sedi mentationin the Colorado River Delta and Upper Gulf of California after nearly a century of dis-charge loss[J].Marine Geology,1999,158:125—145.
[6]KENNISH MJ.Coastal salt marsh systems in the U.S.:a review of anthropogenic i mpacts[J].Journal of Coastal Research,2001,17:731—748.
[7]STONE R.Three Gorges Dam:into the unknown[J].Science,2008,321:628—632.
[8]陈吉余,徐海根.三峡工程对长江河口的影响[J].长江流域资源与环境,1995,4(3):242—246.
[9]李从先,杨守业,范代读,等.三峡大坝建成后长江输沙量的减少及其对长江三角洲的影响[J].第四纪研究,2004,24(5):495—500.
[10]YANG Z,WANG H,SAITO Y,et al.Dami mpacts on the Changjiang(Yangtze)River sedi ment discharge to the sea:the past 55 yearsand after the Three Gorges Dam[J].Water Resources Research,2006,42:w04407,doi:10.1029/2005 WR003970.
[11]JI AO N,YAO Z,ZENG Y,et al.Ecological anomalies in the East China Sea:i mpacts of the Three Gorges Dam?[J].Water Research,2007,41:1287—1293.
[12]YANG S L,ZHANGJ,XU X J.Influence of the Three Gorges Dam on downstream delivery of sedi ment and its environment i mplica-tions,Yangtze River[J].Geophysical Research Letter,2007,34:L10401,doi:10.1029/2007GL029472.
[13]宋晓红,石学法,蔡德陵,等.三峡截流后长江口秋季TSM,POC和PN的分布特征[J].海洋科学进展,2007,25(2):168—177.
[14]GAO S,WANG Y P.Changes in material fluxes fromthe Changjiang River and their i mplications on the adjoining continental shelf eco-system[J].Continental Shelf Research,2008,28:1490—1500.
[15]中华人民共和国水利部.中国河流泥沙公报2007[Z].北京:中国水利水电出版社,2008:60.
[16]CHEN X.Changjiang(Yangtze)River Delta,China[J].Journal of Coastal Research,1998,14(3):838—858.
[17]CHEN X,ZONG Y.Coastal erosion along the Changjiang deltaic shoreline,China:history and prospective[J].Estuarine,Coastal andShelf Science,1998,46:733—742.
[18]YANG S L,BELKI NI M,BELKI NA AI,et al.Delta response to declinein sedi ment supply fromthe Yangtze River:evidence of the re-cent four decades and expectations for the next half-century[J].Estuarine,Coastal and Shelf Science,2003,57:689—699.
[19]杨世伦,朱骏,李鹏.长江口前沿潮滩对来沙锐减和海平面上升的响应[J].海洋科学进展,2005,23(2):152—158.
[20]范代读.潮坪韵律沉积的形成和保存及沉积间断的定量分析[M].上海:同济大学出版社,2007:110.
[21]陈吉余,程和琴,戴志军.河口过程中第三驱动力的作用和响应——以长江河口为例[J].自然科学进展,2008,18(9):994—1000.
[22]时钟,陈吉余,虞志英.中国淤泥质潮滩沉积研究的进展[J].地球科学进展,1996,11(6):555—562.
[23]陈吉余,陈沈良,丁平兴,等.长江口南汇咀近岸水域泥沙输移途径[J].长江流域资源与环境,2001,10(2):166—172.
[24]陈沈良,谷国传,虞志英.长江口南汇东滩淤涨演变分析[J].长江流域资源与环境,2002,11(3):239—243.
[25]李九发,戴志军,应铭,等.上海市沿海滩涂土地资源圈围与潮滩发育演变分析[J].自然资源学报,2007,22(3):361—371.
[26]付桂,李九发,戴志军,等.长江口南汇咀岸滩围垦工程潮流数值模拟研究[J].海洋湖沼通报,2007(4):47—54.
[27]吴华林,沈焕庭,吴加学.长江口海图深度基准面换算关系研究[J].海洋工程,2002,20(1):69—74.
[28]恽才兴.长江河口潮滩冲淤和滩槽泥沙交换[J].泥沙研究,1983,4:43—521.
[29]李九发.长江河口南汇潮滩泥沙输移规律探讨[J].海洋学报,1990,12(1):75—82.
[30]陈卫跃.潮滩泥沙输移及沉积动力环境——以杭州湾北岸、长江口南岸部分潮滩为例[J].海洋学报,1991,13(6):813—821.
[31]FAN D D,GUO Y X,WANG P,et al.Cross-shore variationsin morphodynamic processes of an open-coast mudflat inthe Changjiang Del-ta:with an emphasis on stormi mpacts[J].Continental Shelf Research,2006,26:517—538.
[32]徐钢,陈吉余.长江河口海岸演变长周期波动的初步研究[J].华东师范大学学报:自然科学版,1997(4):64—71.
[33]刘苍字,虞志英.杭州湾北岸的侵蚀/淤积波及形成机制[J].福建地理,2000,15(3):12—15.
[34]刘苍字,吴立成,曹敏.长江三角洲南部古沙堤(冈身)的沉积特征、成因及年代[J].海洋学报,1985,7(1):55—66.
[35]恽才兴,时伟荣,何青.长江口通海航道泥沙场动态分析[J].华东师范大学学报:长江口深水航道治理与港口建设专辑,1995,50—79.
[36]陈吉余,徐海根.长江河口南支河段的河槽演变[C]∥陈吉余,沈焕庭,恽才兴.长江河口动力过程和地貌演变.上海:上海科学技术出版社,1988.375—389.
[37]陈吉余,潘定安,苏法崇,等.长江口北港河槽演变分析[C]∥陈吉余,沈焕庭,恽才兴.长江河口动力过程和地貌演变.上海:上海科学技术出版社,1988.390—403.
[38]火恩杰,刘昌森.上海地区自然灾害史料汇编[G].北京:地震出版社,2002:294.
[39]刘曙光,李从先,丁坚,等.黄河三角洲整体冲淤平衡及其地质意义[J].海洋地质与第四纪地质,2001,21(4):13—17.
[40]许炯心.黄河三角洲造陆过程中的陆域水沙临界条件研究[J].地理研究,2002,21(2):163—170.
[41]GAO S.Modeling the growthli mit of the Changjiang Delta[J].Geomorphology,2007,85:225—236.
[42]李九发,季中.长江来水来沙对河口南槽边滩冲淤变化的统计分析[J].泥沙研究,1988(4):76—82.
[43]高抒.潮滩沉积记录正演模拟初探[J].第四纪研究,2007,27(5):750—755.
[44]MILLI MANJ D,SHEN H,YANGZ,et al.Transport and deposition of river sedi ment inthe Changjiang Estuary and adjacent continentalshelf[J].Continental Shelf Research,1985,4:37—45.
[45]沈焕庭.长江河口物质能量[M].北京:海洋出版社,2001:176.
[46]LI B H,LI C X,SHEN H T.Apreli minary study on sedi ment fluxin the Changjiang Delta during the postglacial period[J].Science inChina:Series D Earth Sciences,2003,46(7):743—752.
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