入湖三角洲形成过程与淤积形态变化的实验研究
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摘要
入湖三角洲的形成和发展过程是冲积河流演变的重要组成部分,三角洲尾闾水道生成、地貌演变机理更是河流动力学研究中的重点问题。利用自然模型法对入湖三角洲形成与形态发展过程进行模型试验,通过改变上游来沙和下游水位探究不同边界条件对三角洲平面形态、纵向推进、横向展宽及垂向抬高的影响。三角洲堆积体先呈舌状推进,随后随朵体的生长而变化,其长宽比先迅速增大后逐渐减小。上游来沙量越大,三角洲长宽比越小,下游水位越高对三角洲尺寸抑制越明显。三角洲纵向推进和横向展宽都呈现先迅速增长,后进入相对平稳期,并出现"台阶式"增长的趋势。来沙越多,横纵推进速度越快,越早出现突变式的增长。水位越高,三角洲越早以较小尺寸进入平稳期,突变周期越长,增长值越小。泥沙主要落淤在三角洲中下游,但较多来沙量会促使泥沙淤积在上游,并使上游河槽深度减小,中下游横截面坡度增大,三角洲整体纵向坡度也增大。
Formation and evolution of shallow lake deltas are an important alluvial process of a river system, and research on the waterway and morphology over such deltas has become a key issue of river dynamics. In this study, a tank experiment based on the natural model method is conducted to simulate the formation and evolution of a shallow lake delta, focusing on the influence of boundary conditions, i.e. different sediment inflows and different lake stages, on its plane shape and stretching in longitudinal, vertical and horizontal directions. Results reveal that the delta first stretches forward like a tongue and then evolve as a developing lobe. Its aspect ratio of length to width increases rapidly first but approaches a relatively stable stage; the more the sediment inflow, the smaller the aspect ratio; a higher lake stage suppresses more the size of the delta. Both its longitudinal stretching and lateral broadening manifest a rapid growth at the initial stage, and then it enters a relatively stable mode of stepped growth. Higher sediment concentration leads to faster advancing longitudinally and laterally, resulting in an earlier start of the stepped growth mode; a higher lake stage leads to a similar earlier start with a smaller delta size, a longer mutation period, and a smaller delta size increment in one step. Sediment often silts over the lower delta. However, more incoming sediment will cause silting over the upper part. This brings about a decrease in the upper channel depth, an increase in the lateral bed slope of the middle and lower reaches, and an increase in the delta's overall longitudinal slope.
Formation and evolution of shallow lake deltas are an important alluvial process of a river system, and research on the waterway and morphology over such deltas has become a key issue of river dynamics. In this study, a tank experiment based on the natural model method is conducted to simulate the formation and evolution of a shallow lake delta, focusing on the influence of boundary conditions, i.e. different sediment inflows and different lake stages, on its plane shape and stretching in longitudinal, vertical and horizontal directions. Results reveal that the delta first stretches forward like a tongue and then evolve as a developing lobe. Its aspect ratio of length to width increases rapidly first but approaches a relatively stable stage; the more the sediment inflow, the smaller the aspect ratio; a higher lake stage suppresses more the size of the delta. Both its longitudinal stretching and lateral broadening manifest a rapid growth at the initial stage, and then it enters a relatively stable mode of stepped growth. Higher sediment concentration leads to faster advancing longitudinally and laterally, resulting in an earlier start of the stepped growth mode; a higher lake stage leads to a similar earlier start with a smaller delta size, a longer mutation period, and a smaller delta size increment in one step. Sediment often silts over the lower delta. However, more incoming sediment will cause silting over the upper part. This brings about a decrease in the upper channel depth, an increase in the lateral bed slope of the middle and lower reaches, and an increase in the delta's overall longitudinal slope.
引文
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[16]刘飞,张小峰,邓安军,等.入湖河流三角洲形成发展规律[J].应用基础与工程科学学报,2016(5):943-954.LIU Fei,ZHANG Xiaofeng,DENG Anjun,et al.The law of formation and development of lacustrine delta[J].Journal of Basic Science and Engineering,2016(5):943-954.(in Chinese)
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[18]REITZ M D,JEROLMACK D J,SWENSON J B.Flooding and flow path selection on alluvial fans and deltas[J].Geophysical Research Letters,2010,37(6):L06401.
[19]NICHOLAS A P,CLARKE L,QUINE T A.A numerical modelling and experimental study of flow width dynamics on alluvial fans[J].Earth Surface Processes&Landforms,2010,34(15):1985-1993.
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[21]HOOKE R L.Model geology:Prototype and laboratory streams:Discussion[J].Geological Society of America Bulletin,1968,79(3):391-393.
[22]SWENSON J B,VOLLER V R,PAOLA C,et al.Fluviodeltaic sedimentation:A generalized Stefan problem[J].European Journal of Applied Mathematics,2000,11:433-452.
[2]谢鉴衡.江河演变与治理研究[M].武汉:武汉大学出版社,2004.XIE Jianheng.Research on the evolution and governance of rivers[M].Wuhan:Wuhan University Press,2004.(in Chinese)
[3]MCCARTHY T S,CADLE A B,BLAIR T C,et al.Alluvial fans and their natural distinction from rivers based on morphology,hydraulic processes,sedimentary processes,and facies assemblages[J].Journal of Sedimentary Research-Section A,1994,65(51):3088-3095.
[4]姜在兴.沉积体系及层序地层学研究现状及发展趋势[J].石油与天然气地质,2010,31(5):535-541.JIANG Zaixing.Research status and development trend of sedimentary system and sequence stratigraphy[J].Petroleum and Natural Gas Geology,2010,31(5):535-541.(in Chinese)
[5]裘亦楠,肖敬修,薛培华.湖盆三角洲分类的探讨[J].石油勘探与开发,1982(1):1-11.QIU Yinan,XIAO Jingxiu,XUE Peihua.A study on the classification of lacustrine delta[J].Petroleum Exploration and Development,1982(1):1-11.(in Chinese)
[6]张哲源,徐海珏,白玉川,等.基于卫星遥感技术的赣江尾闾河势演变分析[J].水利水电技术,2017,48(7):20-27.ZHANG Zheyuan,XU Haijue,BAI Yuchuan,et al.Evolution of river regime of Ganjiang River based on satellite remote sensing technology[J].Water Conservancy and Hydropower Technology,2017,48(7):20-27.(in Chinese)
[7]金振奎,李燕,高白水,等.现代缓坡三角洲沉积模式:以鄱阳湖赣江三角洲为例[J].沉积学报,2014,32(4):710-723.JIN Zhenkui,LI Yan,GAO Baibing,et al.Depositional model of modern gentle slope delta:A case study from Ganjiang Delta in Poyang Lake[J].Acta Sedimentologica Sinica,2014,32(4):710-723.(in Chinese)
[8]王军,杨勇,张阳,等.水位变化对鄱阳湖三角洲分流河道沉积特征的影响[J].中国石油大学学报(自然科学版),2017,41(1):1-10.WANG Jun,YANG Yong,ZHANG Yang,et al.Influence of water level change on sedimentary characteristics of distributary channel in Poyang Lake Delta[J].Journal of China University of Petroleum(Edition of Natural Science),2017,41(1):1-10.(in Chinese)
[9]POSTMA G,KLEINHANS M G,MEIJER P,et al.Sediment transport in analogue flume models compared with real-world sedimentary systems:A new look at scaling evolution of sedimentary systems in a flume[J].Sedimentology,2008,55(6):1541-1557.
[10]GUERIT L,MéTIVIER F,DEVAUCHELLE O,et al.Laboratory alluvial fans in one dimension[J].Physical Review E Statistical Nonlinear&Soft Matter Physics,2014,90(2):022203.
[11]WICKERT A D,MARTIN J M,TAL M,et al.River channel lateral mobility:Metrics,time scales,and controls[J].Journal of Geophysical Research:Earth Surface,2013,118(2):396-412.
[12]VAN DIJK M,KLEINHANS M G,POSTMA G,et al.Contrasting morphodynamics in alluvial fans and fan deltas:Effect of the downstream boundary[J].Sedimentology,2012,59(7):2125-2145.
[13]CLARKE L,QUINE T A,NICHOLAS A.An experimental investigation of autogenic behaviour during alluvial fan evolution[J].Geomorphology,2010,115(3):278-285.
[14]HOYAL D C J D,SHEETS B A.Morphodynamic evolution of experimental cohesive deltas[J].Journal of Geophysical Research Atmospheres,2009,114(F2):134-150.
[15]POWELL E J,KIM W,MUTO T.Varying discharge controls on timescales of autogenic storage and release processes in fluvio-deltaic environments:Tank experiments[J].Journal of Geophysical Research:Earth Surface,2012,117:F02011.
[16]刘飞,张小峰,邓安军,等.入湖河流三角洲形成发展规律[J].应用基础与工程科学学报,2016(5):943-954.LIU Fei,ZHANG Xiaofeng,DENG Anjun,et al.The law of formation and development of lacustrine delta[J].Journal of Basic Science and Engineering,2016(5):943-954.(in Chinese)
[17]ZHANG X F,WANG S Q,WU X,et al.The development of a laterally confined laboratory fan delta under sediment supply reduction[J].Geomorphology,2016,257:120-133.
[18]REITZ M D,JEROLMACK D J,SWENSON J B.Flooding and flow path selection on alluvial fans and deltas[J].Geophysical Research Letters,2010,37(6):L06401.
[19]NICHOLAS A P,CLARKE L,QUINE T A.A numerical modelling and experimental study of flow width dynamics on alluvial fans[J].Earth Surface Processes&Landforms,2010,34(15):1985-1993.
[20]许栋,白玉川,谭艳.无黏性沙质床面上冲积河湾形成和演变规律自然模型试验研究[J].水利学报,2011,42(8):918-927.XU Dong,BAI Yuchuan,TAN Yan.Natural model test study on formation and evolution of alluvial river meanders on cohesive sandy bed[J].Journal of Hydraulic Engineering,2011,42(8):918-927.(in Chinese)
[21]HOOKE R L.Model geology:Prototype and laboratory streams:Discussion[J].Geological Society of America Bulletin,1968,79(3):391-393.
[22]SWENSON J B,VOLLER V R,PAOLA C,et al.Fluviodeltaic sedimentation:A generalized Stefan problem[J].European Journal of Applied Mathematics,2000,11:433-452.