, 张明进The relationship between water level change and river channel geometry adjustment in the downstream of the Three Gorges Dam (TGD)
YANGYunping, ZHANGMingjin收稿日期:2016-12-26
修回日期:2017-02-7
网络出版日期:2017-07-12
版权声明:2017《地理学报》编辑部本文是开放获取期刊文献，在以下情况下可以自由使用：学术研究、学术交流、科研教学等，但不允许用于商业目的.
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1 引言
三峡工程是当今世界上最大的综合性水利枢纽工程,具有防洪、发电、航运、供水和节能减排等巨大的综合效益[1],其建设和运行期对坝下游河道冲淤、洪枯水位等产生的影响,一直备受全球研究人员关注。河道冲淤：1950-1988年宜昌—汉口河段以淤积为主,2003-2007年转为冲刷[2];2009-2010年与1998-2002年比较,坝下游100 km内深泓单向下切,下游为冲淤交替变化[3-4],冲淤河槽分布逐渐由蓄水前“冲槽淤滩”转为“滩槽均冲”[5-7],且冲刷集中在宜昌—城陵矶河段[6],并集中在枯水河槽[8];2012年与2002年相比较,长江中下游河道冲刷以下切为主,断面趋于窄深化发展[9]。已有河道形态演变研究主要是基于蓄水后某一时段的比较,未全面反映不同蓄水阶段、河段单元尺度调整的差异。枯水位变化：三峡大坝下游枯水位为下降趋势[10],与预测结果一致[11-12],也与全球大型水库下游枯水位下降规律一致[13]。洪水位变化：在全球大型水库下游,洪水位表现出略有上升或变化不大的规律[13];三峡水库蓄水后,同流量洪水位变化的认识尚未统一,争议的焦点在洪水位下降[14]、变化不大或无明显上升[15]、上升趋势[16-17]等3个方面。部分研究成果表明：三峡大坝下游河道在清水下泄的条件下,没有降低洪水位,反而荆江向洞庭湖分洪减小,河道泄洪能力萎缩[17];2003-2013年期间,汉口站流量为50000 m3/s流量对应水位有抬高趋势[17]。洪枯水位变化成因：河道的大幅冲刷,是引起同流量枯水位下降的主因;滩地淤积、洪水河宽缩窄、床面粗化及岸滩植被等变化是洪水位抬高的控制要素[18-19]。三峡水库蓄水后,坝下游河道形态发生调整,与蓄水前相比,河床粗化、水流漫滩天数减少、人类活动增加等要素对洪水位变化的影响缺乏关注。2016年6-8月长江中下游发生区域性洪水,螺山及以下河段超出警戒水位,但出现警戒水位对应的流量均小于1998年、2010年,其原因也是本文关注的内容。综上,已有研究关注了三峡大坝下游河道整体冲淤,而对于洪、枯水位变化成因及河道形态调整的阶段性特征有待深入研究。本文以1955-2016年水位、河道地形等资料为分析对象,在洪枯水位、河道形态调整研究基础上,明确单元河段尺度上河道形态调整过程,结合河道综合阻力、坝下游人类活动等要素,明晰洪、枯水位变化成因,并分析水位变化与长江防洪情势和航道水深关系。
2 研究区域及水沙条件
2.1 研究区域
三峡大坝下游宜昌—大通河段长度1183 km,宜昌—杨家脑为砂卵石河段,长度约116.4 km,杨家脑以下为沙质河段,长度为1066.6 km（图1）。研究河段内干流有宜昌、枝城、沙市、监利、螺山、汉口、九江及大通站等水文站;洞庭湖分流口为松滋口、太平口和藕池口,习称洞庭湖三口,湖区有湘江、资水、沅江和澧水入汇,习称洞庭湖四水,入江水文控制站为城陵矶站;汉江入江水文控制站为皇庄站;鄱阳湖入江水文控制站为湖口站,湖区有修水、赣江、抚河、信江及饶河入湖,习称鄱阳湖五河。
显示原图|下载原图ZIP|生成PPT图1三峡水库坝下游河段概略图
-->Fig. 1Schematic of the river sections in the downstream of the Three Gorges Reservoir (TGR)
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2.2 资料来源说明
本文涉及的水文站为宜昌、枝城、沙市、监利、螺山、汉口、九江、大通站,洞庭湖三口和城陵矶站,鄱阳湖湖口站。收集了1955-2016年大坝下游各水文站径流量、流量、输沙量和水位资料,1987-2014年宜昌—湖口河段的河道冲淤量和断面资料,1981-2016年宜昌—汉口河段沿程水尺资料,数据收集时间长度不一致,其截至年份为近3年,可充分体现近期的变化规律。各项数据来源如表1所示。Tab. 1
表1
表1三峡大坝下游水文泥沙观测数据来源
Tab. 1Sediment source and hydrological data of the downstream of the Three Gorges Dam (TGD)
| 序号 | 水文站及河段 | 资料内容 | 资料长度 | 数据来源 |
|---|---|---|---|---|
| 1 | 宜昌、枝城、沙市、监利、螺山、汉口、大通 | 水量、输沙量、流量、水位 | 1955-2016年 | 长江泥沙公报 长江水利委员会水文局 |
| 2 | 洞庭湖三口、城陵矶 鄱阳湖湖口 | 水量、沙量、流量 | ||
| 3 | 宜昌—湖口河段 | 冲淤量 | 1987-2015年 | 长江水利委员会水文局 |
| 4 | 宜昌—汉口水尺 | 水位 | 1981-2014年 | 长江航道规划设计研究院 |
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2.3 水文泥沙变化
径流量和输沙量变化：1955-2015年宜昌站和大通站径流量无趋势性增加或减少,2003-2015年较1955-2002年分别减少7.7%和5.5%（图2a）,主要是气候变化的影响[20];输沙量均呈现阶梯型减少趋势,2003-2015年减幅增加,大通站减幅小于宜昌站（图2b）,这一现象与全球大型水坝下游泥沙输移规律一致[21]。径流量和输沙量构成：三峡水库蓄水前后大通站径流量来自宜昌站、洞庭湖分汇、汉江入汇、鄱阳湖入汇及区间产汇流的比例相对稳定（图2c）;三峡水库蓄水前的3个时期大通站输沙量主要来自宜昌站,洞庭湖分沙淤积态势减缓,汉江来沙比例减小,鄱阳湖汇沙比例变化不大,干线河道呈淤积态势。三峡水库蓄水后大通站输沙量来自宜昌站比例为29.2%,较蓄水前各时期比例大幅减小;洞庭湖分汇关系由分沙转变为汇沙,比例约占6.8%;汉江汇沙比例约占4.4%,与1955-2002年期间相比变化不大;鄱阳湖汇沙比例约10.2%,较蓄水前3个时期均增加;干线河道由淤积转为冲刷,冲刷沙量占大通站输沙量的49.5%。
显示原图|下载原图ZIP|生成PPT图2三峡大坝下游水、沙通量变化
-->Fig. 2Changes of discharge and flux in the downstream of the TGD
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3 三峡大坝下游河道洪、枯水位变化
3.1 同流量水位变化
选取2003年、2012年和2016年为研究代表年份,随着流量增加,宜昌、枝城、沙市、监利、螺山、汉口和九江站同流量—水位均为先减小后增大,存在增加和减少的转换临界流量,与水文站所在河段的平滩流量接近（图3）。在洪水时期,同流量洪水位均为增大趋势,并未出现逾期的减少趋势。2016年、2012年分别与2003年比较,枯水和洪水增减趋势转换流量为减小趋势,表明大流量高洪水位逐渐向中洪水流量高水位转变。
显示原图|下载原图ZIP|生成PPT图3三峡大坝下游水文站流量—水位关系
-->Fig. 3Relationship between the water flow and water level in the lower reaches of the TGD
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3.2 最高、最低水位变化
最低水位变化（图4）：三峡水库蓄水前,宜昌、枝城、沙市站年最低水位呈波动下降,蓄水后为上升趋势,螺山站和汉口站蓄水前后整体为上升趋势。最高水位变化（图4）：三峡水库蓄水前,宜昌、枝城、沙市站年最高水位呈波动下降,蓄水后无明显趋势性,其蓄水后的最大值低于蓄水前;三峡水库蓄水前螺山、汉口站最高水位略有抬高,蓄水后趋势性不明显。
显示原图|下载原图ZIP|生成PPT图4三峡大坝下游水文站最高水位及最低水位变化
-->Fig. 4Highest and lowest water levels in the downstream hydrologic stations of the TGD
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4 三峡大坝下游河道冲淤调整过程
4.1 三峡水库蓄水前后河槽冲淤变化
1981-2002年期间,宜昌—湖口河段枯水河槽冲刷,宜昌—枝城及上荆江河段冲刷集中在枯水河槽,枯水—平滩河槽之间略有淤积;下荆江、城陵矶—汉口及汉口—湖口河段为淤积趋势,表现出“冲槽淤滩”的演变特点[6-7, 9]。2003-2015年期间,宜昌—枝城、上荆江、下荆江、城陵矶—汉口、汉口—湖口河段总冲刷量分别为-1.44亿m3、-4.11亿m3、-2.80亿m3、-2.18亿m3、-3.89亿m3（图5,其中宜昌—枝城、汉口—湖口缺少2014年10月-2015年10月期间数据）。对应三峡水库不同的蓄水位阶段,划分为2003-2006年、2006-2008年及2008-2015年比较单位河长枯水河槽、基本河槽和平滩河槽冲刷强度变化规律（图5）：宜昌—枝城河段各河槽冲刷强度减弱;上荆江枯水河槽和基本河槽冲刷强度增强,平滩河槽为先减弱后增强;下荆江各河槽单冲刷强度先减弱后增强;城陵矶—汉口河段枯水河槽和基本河槽冲刷强度呈增强趋势,平滩河槽先减弱后增强;汉口—湖口河段枯水河槽冲刷强度增强,基本河槽和平滩河槽先减弱后增强。单位河长冲刷强度沿程变化特点：2003-2006年期间宜昌—枝城河段最大,下荆江河段次之,城陵矶—湖口河段最小;2006-2008年期间最大区域在宜昌—枝城河段,上荆江河段次之,下荆江河段最小;2008-2015年期间最大区域在上荆江河段,汉口—湖口河段次之。2008-2015年期间单位河长冲刷强度最大区域已由2003-2008年期间的宜昌—枝城河段下移至上荆江,同时下荆江及其下游河段冲刷强度增加,受清水下泄的影响程度逐渐增强。
显示原图|下载原图ZIP|生成PPT图5宜昌—湖口河段单位河长河床冲淤过程变化
-->Fig. 5Erosion and deposition changes in the channels of the Yichang-Hukou Section
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4.2 河道冲淤分布变化
枯水河槽定义为深槽,枯水—基本河槽之间为低滩,基本—平滩河槽之间为高滩。表2统计了枯水河槽、低滩和高滩冲淤量占平滩河槽冲淤量的比例,分析表明：（1）三峡水库蓄水前宜昌—枝城、上荆江河段枯水河槽冲刷,高、低滩小幅淤积;下荆江、城陵矶—湖口河段枯水河槽冲刷,高、低滩大幅淤积,表现出“冲槽淤滩”的演变特点。
（2）2003-2008年宜昌—枝城、上荆江和下荆江河段枯水河槽、高、低滩均为冲刷趋势;城陵矶—汉口河段与三峡水库蓄水前一致,表现出“冲槽淤滩”的演变特点,且淤积集中在高滩;汉口—湖口河段为枯水河槽和低滩冲刷,高滩略有淤积。
（3）2008-2015年与2003-2008年相比,宜昌—枝城、荆江河段冲刷更集中在枯水河槽,滩地冲刷比例减小;城陵矶—汉口河段冲刷集中在枯水河槽,低滩由淤积转为冲刷,高滩淤积减缓;汉口—湖口河段冲刷集中在枯水河槽,低滩由冲刷转为淤积,高滩持续淤积,表现出“冲槽淤滩”的演变特点。
Tab. 2
表2
表2宜昌—湖口河段河槽冲淤比例变化
Tab. 2Erosion and deposition proportion changes in the Yichang-Hukou Section
| 时间段 | 河段名称 | 宜昌—枝城 | 上荆江 | 下荆江 | 城陵矶—汉口 | 汉口—湖口 |
|---|---|---|---|---|---|---|
| 河长(km) | 60.8 | 171.7 | 175.5 | 251.0 | 295.4 | |
| 三峡水库蓄水前 （1981-2002年） | 枯水河槽(%) | 102.0 | 100.6 | 9.2 | 17.5 | 69.6 |
| 低滩(%) | -2.0 | -0.6 | -109.2 | -117.5 | -169.6 | |
| 高滩(%) | ||||||
| 2003-2008年 (2002年10月-2008年10月) | 枯水河槽(%) | 88.6 | 89.6 | 73.2 | 301.8 | 60.4 |
| 低滩(%) | 1.7 | 2.2 | 11.6 | -30.7 | 48.3 | |
| 高滩(%) | 9.6 | 8.2 | 15.2 | -171.1 | -8.7 | |
| 2009-2014年 (2008年10月-2015年11月) | 枯水河槽(%) | 96.4 | 94.0 | 95.4 | 95.3 | 115.0 |
| 低滩(%) | 4.8 | 3.1 | -0.4 | 5.8 | -11.4 | |
| 高滩(%) | -1.1 | 2.9 | 5.0 | -1.1 | -3.6 |
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5 枯水位变化的成因及其对航道水深的影响分析
5.1 枯水位变化与河道冲淤关系
2014年10月与2002年10月相比较,坝下游410 km河段内深泓为平均下切约1.50 m,其下游为冲淤交替变化（图6）。2003-2014年航行基准面水位与1981-2002年进行比较,在近坝段240 km内平均下降1.10 m,其下游为增加趋势。其中深泓下切集中在宜昌—枝城、上荆江和下荆江河段,水位下降主要在宜昌—枝城、上荆江河段（图6）,在未来一段时期,应防控下荆江河段河床下切引起的枯水位下降。
显示原图|下载原图ZIP|生成PPT图6三峡大坝下游河道深泓与枯水位关系
-->Fig. 6Relationship between the thawed and dry TGR
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以2003年、2008年和2014年枯水期（宜昌站流量为5600 m3/s）为代表时间（图7）,分析表明：2008-2014年与2003-2008年宜昌—磨盘溪、陈二口—汉口河段之间水位降幅增大,云池—枝城河段降幅减小。在沿程上,以枝城水尺分界,上、下游水位降幅均为先增大后减小,表明枝城河段对上下游水位的维持起到卡口或节点控制作用。枝城以下水位降幅有所增加,并有向上游传递趋势,应关注枝城以下河段因枯水河槽冲刷引起水位下降的溯源传递作用。
显示原图|下载原图ZIP|生成PPT图7宜昌—汉口河段水位下降过程
-->Fig. 7Process of water level decline in Yichang-Hankou Section
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绘制各河段冲淤量与水位降幅的关系曲线（图8）,两者表现出较好的相关性,随着河道累积冲刷量增加枯水位为下降趋势。宜昌—枝城、上荆江河段枯水位随累积冲淤量增大其水位降幅有所减缓,下荆江、城陵矶—汉口、汉口—湖口河段为增加趋势,随着下荆江以下至湖口河段冲刷强度增强,同流量枯水位仍存在进一步下降的可能。
显示原图|下载原图ZIP|生成PPT图8河床冲淤量与枯水位关系
-->Fig. 8Erosion and siltation amount of dry riverbed and its relationship with low water level
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5.2 枯水位变化与航道水深关系
三峡水库蓄水后,坝下游河槽冲刷是航道水深提升的基础,为了防控岸线崩退、边心滩萎缩、通航主汊道枯水期分流减少等不利变化,2003-2015年期间长江航道管理部门对中下游航道实施了系统的整治工程。工程实施后,宜昌—城陵矶、城陵矶—武汉、武汉—安庆河段航道水深由2003年的2.9 m、3.2 m和4.0 m,提升至2015年的3.5 m、3.7 m和4.5 m,航深提高了0.50~0.60 m,同时航宽也增加。2015年航道尺度与长江干线2020年规划目标对比[21-22],提前5年实现了规划目标。6 洪水位变化成因及对防洪情势的影响分析
6.1 河湖关系及干线河道冲淤对洪水位变化的影响
从泥沙冲淤平衡角度分析（图9）：1960-2006年洞庭湖湖区泥沙淤积,2007-2015年湖区为冲刷趋势;1960-1999年鄱阳湖湖区泥沙为冲淤交替,2000-2015年为冲刷趋势。实际上洞庭湖和鄱阳湖湖区均存在河道采砂[23],三峡水库蓄水后湖区冲刷量可能更大。三峡水库蓄水后,洞庭湖和鄱阳湖湖区冲刷趋势,一定程度增加了湖区调蓄容积,可减少湖泊对干线洪水组成的贡献,可降低干线防洪压力。两湖对干线洪水的影响在入江径流量上,决定是上游洪水还是湖泊洪水叠加造成的干流洪水,但对于同流量洪水位抬高的贡献不是主要的。
显示原图|下载原图ZIP|生成PPT图9洞庭湖和鄱阳湖湖区的泥沙淤积情况
-->Fig. 9Sedimentation in the Dongting and Poyang lakes
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在河道形态特征上,下游河道边界的卡口对洪水排泄具有阻碍作用[24],武汉—九江河段在Q ≥ 50000 m3/s以上时,田家镇卡口阻滞上游洪水下泄时间约2~3天[25],也会造成上游洪水位的壅高。三峡水库蓄水前,长江中下游干线河道整体淤积[26-27],是长江干流同流量洪水位抬高的主要原因。三峡水库蓄水后,坝下游河道平滩河槽均冲刷,尤其是枯水河槽（图6,表2）,在理论上不仅可以降低枯水位,也可以降低洪水位,但河槽冲刷趋势与洪水位抬高不一致,在同流量洪水位抬高的原因的研究中,应从河道冲刷过程中的河道形态、床面阻力及人类活动影响等方面展开。
6.2 三峡水库蓄水后洪水位变化原因分析
三峡水库蓄水后,河床大幅度冲刷下切,但洪水位并出现预期中的下降趋势,但由于水库调蓄作用使得最大流量减小,防洪安全得到保障。未来一段时间,三峡水库实行汛期削峰调度[28],中洪水流量时期水位增加是关注的重点,其形成原因也是关注的重点。本节从河床粗化、岸滩植被、港口及航道整治工程等人类活动直接或间接的影响出发,同时考虑河道形态调整因素,分析三峡水库蓄水后各要素变化与中洪水流量水位升高的关系。6.2.1 河床粗化的影响 河床表层泥沙粗化,床面阻力增大,相应的壅高河道水位。三峡水库蓄水后,坝下游河道床面表层泥沙为粗化趋势[29-30],宜昌—枝城河段床沙D50由2003年11月的0.638 mm增大到2010年10月的30.4 mm,增大达48倍;枝城至大埠街（杨家脑）河段床沙D50比蓄水前增大20倍左右。文献[31]与文献[29-30]计算数据相同,计算三峡蓄水前后河床的糙率数值（表3）,坝下游61 km（宜昌—枝城）、61~111 km、111~319 km、319~865 km河段内的糙率分别增大91%、65%、3%和2%。数学模型计算表明[31]：在宜昌—杨家脑的砂卵石河段,河床在糙率增大后,宜昌站5000 m3/s、10000 m3/s、23000 m3/s、35000 m3/s的水位平均增加1.57 m、2.04 m、2.7 m、3.3 m,大于各流量下的水位实际降幅,充分说明床沙粗化有效抑制砂卵石河段枯水位下降;杨家脑以下的沙质河段,在宜昌流量为5000 m3/s、10000 m3/s、23000 m3/s、35000 m3/s时,水位平均增大值分别0.13 m、0.11 m、0.16 m、0.16 m,相对于深泓下切值,水位增幅有限。
Tab. 3
表3
表3河床粗化引起的糙率变化[
Tab. 3Roughness change due to riverbed coarsening [
| 河床组成类型 | 砂卵石河段 | 砂卵石~沙质过渡段 | 沙质河段 | |
|---|---|---|---|---|
| 河段 | 宜昌—枝城(61 km) | 枝城—大埠街(50 km) | 荆江沙质段(208 km) | 城陵矶—湖口(546 km) |
| 增加倍数 | 1.91 | 1.65 | 1.03 | 1.02 |
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6.2.2 岸滩植被对洪水位变化的影响 岸滩植被能防止水流侵蚀河岸,维持河床稳定[32],同时也会增加水流行进阻力,流速减小,水位抬高,一定程度上影响河道防洪能力[33]。2011年美国密西西比河发生大洪水,其流量小于1927年和1973年大洪水[34],由于高海拔区（对应高滩区域）植被茂盛产生的壅水作用进一步增加洪水位抬高[35],发生了中水流量—高水位的区域性洪水。三峡水库蓄水后,2009-2016年与2003-2008年比较,漫滩以上流量天数略有缩短（图10）。以2016年为分析对象,螺山以下河段平滩流量天数大幅增加,水流漫滩时间长（图10）。2016年长江中游螺山以下河段发生洪水,且水流漫滩天数增加,在前期的中枯水年份漫滩天数少,滩地植被相对茂盛,会加大对洪水位的壅高程度,影响河道行洪能力。在宜昌—城陵矶河段,在三峡水库削峰和洞庭湖三口分流等综合作用下,漫滩天数几乎未出现,荆江河段的防洪安全得到保障。以武汉河段为例,2016年该河段的洪水更多地是由该河段内倒水、举水、巴水、浠水等支流来流量偏大,顶托干线水位作用增加所致,其最大流量可达24800 m3/s（出现时间为2016年6月30日,数值为九江站与汉口站流量的差值）,也是2016年武汉河段洪水位偏高的原因之一。
显示原图|下载原图ZIP|生成PPT图10三峡水库调节作用及平滩以上流量天数变化
-->Fig. 10The regulation effect of the Three Gorges Reservoir and the change of the flow days
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6.2.3 坝下游人类活动对洪水位变化的影响 长江中游荆江河段是防洪重点区域,素有“万里长江,险在荆江”的说法。长江中下游两侧岸线分布有大量的港区、码头、桥梁及景观工程等,占用部分的长江防洪水域,缩窄了洪水河宽。其中单体工程建设对防洪影响较小,而桥梁群和码头群等工程共同作用后引起河道洪水位和流场的叠加影响,对河道行洪与河势稳定不利[36]。自1998年长江大洪水过后,长江水利委员会对整个中下游岸线堤防进行了加固和提高,降低了同流量—洪水位抬高对堤防安全的风险。
长江中下游素有“黄金水道”的美誉,2003-2015年期间,长江航道局对碍航滩段实施了针对性的航道整治工程：砂卵石河段工程形式为护底,目的是稳定河槽,防控河床进一步冲刷引起的航道水位下降;沙市以下沙质河段对边滩和心滩进行守护,在江心洲头实施守护和调整型工程;同时为提高边界的稳定性,实施了岸线加固或守护工程,维持航道边界稳定的同时也增加阻水程度。在2015年6月论证阶段,《长江宜昌—安庆段提高航道标准对河势控制与防洪影响研究》报告显示[37],29个碍航滩段整治工程实施后,10个滩段最大阻水率在5%~12.2%,19个滩段阻水率介于0~5%,其中7个滩段洪水位最大壅高5~12.4 cm,22个滩段洪水位最大壅高1~5 cm。航道整治工程主要是枯水河槽的整治,对洪水位的影响有限,在工程设计过程中通过优化实施方案和相应补偿措施,降低对洪水位的影响程度。
6.3 洪水位变化对长江中游防洪情势的影响
武汉市是长江中游防洪的重点城市,以汉口站为例,2003-2016年期间,汉口站超过警戒水位的年份有2010年和2016年,其中2010年最高水位仅超过警戒水位1 cm,2016年7月7日超警戒水位107 cm,最高水位为1870年以来的第5位。计算不同年份警戒水位对应的流量（图11）：宜昌站、螺山站和汉口站达到防洪警戒水位的流量逐渐减小,2016年较1998年分别减小10600 m3/s、10700 m3/s 、8500 m3/s,2016年与2003年相比较,也为减小趋势。在近坝段的宜昌站,因三峡水库削峰作用,大幅减小了下泄流量,超过警戒水位天数大幅减少,多数年份未超过警戒水位,防洪情势大幅缓解。三峡水库蓄水前,螺山河段淤积是造成该区域洪水位抬高的主要原因 [28],蓄水后螺山—汉口河段冲刷,由于河道综合阻力,引起的壅水作用较为明显,是螺山站洪水位抬高在三峡水库蓄水前后差异的原因所在。2016年7月,长江中下游发生区域性大洪水,通过三峡水库及上游梯级水库联合调度,拦蓄洪水227亿m3,分别降低荆江河段、城陵矶附近区域、武汉以下河段水位0.8~1.7 m、0.7~1.3 m、0.2~0.4 m,减少超警戒堤段长度250 km,有效减轻了长江中游城陵矶河段和洞庭湖区域防洪压力,避免了荆江河段超警和城陵矶地区分洪,确保了荆江河段人民群众生命安全,确保了长江干堤和重要基础设施安全。
显示原图|下载原图ZIP|生成PPT图11长江中下游防洪损失流量变化
-->Fig. 11Flood control losses in the middle and lower reaches of the Yangtze River
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依据三峡水库调度规则,三峡水库拟实行中小洪水调度,进一步增加流量调平幅度[29],将有效缓解宜昌—城陵矶河段防洪情势,在荆江大堤防洪标准提升后,该河段防洪压力大幅缓解。螺山以下河段受湖泊和支流洪水的影响较大,在干流、湖泊、支流洪水及降雨的综合作用下,螺山以下河段仍是防洪的重点区域。可以预见,三峡水库拦蓄中小洪水后,一旦遭遇特大洪水,有效防洪能力必然进一步降低[15]。针对目前长江中下游出现的中洪水流量高水位现象,尚难判别这一现象是否是趋势性变化还是过程性调整,主要是研究过程中未滤除水位、流量变化的随机因素。在三峡水库蓄水后,长江中下游虽未发生类同于1954年、1998年的流域大洪水,但防洪警戒水位对应流量减小,大流量高洪水位逐渐向中洪水流量高水位转变,应引起足够的重视。
7 结论
三峡水库蓄水利用已有13年,175 m试验性蓄水至今也有7年,对坝下游水位及河道形态调整产生了深刻影响。本文通过60余年实测水位、河道形态调整资料的分析和研究,得出的主要结论为：（1）三峡大坝下游同流量枯水位下降趋势,中洪水位相对抬高,因枯季水库下泄流量增加,坝下游最低水位升高,洪季削减洪峰作用,最高水位下降。
（2）伴随河道冲刷与深泓下切,同流量枯水位下降,在航道整治叠加作用下,同流量枯水位降幅小于枯水河槽河床高程下切值,航道水深增加,是三峡水库蓄水后坝下游航道水深提升的基础,
（3）枯水河槽冲刷是枯水位下降的主要原因,上荆江及以上河段枯水位下降趋势减缓,下荆江及以下河段下降速率存在增加趋势,需引起航道管理部门重视。
（4）三峡水库蓄水后,河床粗化、岸滩植被、人类活动等作用使得同流量洪水位提升;宜昌—监利河段同流量洪水位虽有一定的升高,由于三峡水库汛期削峰调度,下泄流量大幅减少,超过防洪警戒水位的天数减少或未出现,该段的防洪情势大幅缓解;螺山及以下河段出现了中洪水流量高水位的现象,应引起足够重视,三峡水库可有效提升中下游洪水防御能力,但不排除遭遇支流洪水叠加效应,中下游洪水压力仍然较大。
The authors have declared that no competing interests exist.
参考文献 原文顺序
文献年度倒序
文中引用次数倒序
被引期刊影响因子
| [1] | |
| [2] | ABSTRACT The impacts of a dam on the river downstream in terms of hydrology and morphology are determined by a complex mix of variables that includes the patterns of release of water through the dam and the characteristics of the downstream channel. Scour of the downstream channel is a common response because large dams cause a significant interruption to sediment continuity. Here we show that in the case of China's Three Gorges Dam on the Yangtze River the outcome is complicated, as is commonly the case in large rivers. The downstream channel and floodplain system compose an area of long-term sediment accumulation and unstable channels with seasonally contrasting erosion and deposition patterns related to the migrating seasonal monsoon rainfall zones. In achieving one of the main purposes of this dam, that of flood control in the middle and lower basins, the pattern of flows released from the dam will closely resemble those seasonal flows that are responsible for channel instability in the middle catchment, thus effectively making erosive conditions the most common during a year. There is obviously concern about the ultimate impact of sediment storage in the dam on the dynamics of the delta and adjacent coast, and we show that this depends on the trajectory and duration of the erosive responses in the middle Yangtze basin. In this particular case, the outcome is of great significance to the well being of the densely populated riparian areas of the river. |
| [3] | |
| [4] | Under the influence of climate and human activities, fluvial systems have natural ability to make adjustments so that the river hydrology, sediment movement, and channel morphology are in dynamic equilibrium. Taking the Changjiang (Yangtze River) for example. In the early stages after the Three Gorges Dam (TGD) began operational ten years ago, the suspended sediment content (SSC) and fluxes in the middle and lower reaches of the river decreased noticeably. At present, they appear to be in a stable state on the decadal scale. Although the river runoff has not shown any trends, the water level in the river decreased appreciably in time. In the meantime, channel down cutting along the thalweg almost existed throughout the river course. The riverbed has turned from depositional before the dam construction to erosional afterwards. In other words, the riverbed had turned from being sediment sinks to sediment sources. In the main channel of the Changjiang between Yichang and Nanjing, a distance of 1300 km, the riverbed sedimentation mode displays strong, intermediate, and weak erosion depending on the closeness to the TGD. |
| [5] | Extensive research into the changing sediment load throughout the Yangtze River (Changjiang) basin has been completed over recent years, and it provides an ongoing example of how to evaluate the consequences of natural and anthropogenic impacts on sediment processing in a very large fluvial system. This paper reviews these recent studies and critically assesses their findings regarding changes in sediment yield, load (both spatial and temporal variations), grain size, and rating curves, as well as the morphodynamic response of the channel and delta. We also discuss the factors driving these changes, including climate change, soil and water conservation measures, dam construction, and sand extraction, and consider the likely future trends in sediment load. Based on a consideration of the major outcomes of, and discrepancies between, recent studies, we conclude that sediment supply, transport, mobilization, and deposition in this large river system are complicated by the heterogeneous nature of its morphology and climate, as well as the progressive intensification of human activities. Therefore, the identification and interpretation of hydrological and sedimentological changes in the Yangtze basin can be difficult, and an in-depth study of the causal mechanisms of variations in sediment load and the impacts on the Yangtze River system is urgently required. |
| [6] | . . |
| [7] | 为了分析三峡工程对库区及坝下长江中游河势的影响,基于实测资料,较为系统地研究了三峡水库蓄水运用以来水库泥沙淤积和坝下游河床冲刷特性。研究表明,1991年以来长江干流各站径流量变化不大,输沙量明显减小;三峡水库蓄水运用后的2003～2011年入库沙量继续大幅减少,仅为原设计值的40%,水库年均淤积泥沙1.40亿t,也仅为论证阶段的40%左右,且绝大部分淤积在常年回水区和死库容内;受上游来沙减小和三峡水库蓄水拦沙影响,坝下游输沙量大幅减小,悬移质泥沙颗粒也明显变粗,长江中游原有的冲淤相对平衡状态被打破,河床发生沿程冲刷,2002年10月至2010年10月,宜昌至湖口河段总冲刷量为9.79亿m3,河床冲淤形态转变为＂滩、槽均冲＂,主要冲刷发生在宜昌至城陵矶河段。 . 为了分析三峡工程对库区及坝下长江中游河势的影响,基于实测资料,较为系统地研究了三峡水库蓄水运用以来水库泥沙淤积和坝下游河床冲刷特性。研究表明,1991年以来长江干流各站径流量变化不大,输沙量明显减小;三峡水库蓄水运用后的2003～2011年入库沙量继续大幅减少,仅为原设计值的40%,水库年均淤积泥沙1.40亿t,也仅为论证阶段的40%左右,且绝大部分淤积在常年回水区和死库容内;受上游来沙减小和三峡水库蓄水拦沙影响,坝下游输沙量大幅减小,悬移质泥沙颗粒也明显变粗,长江中游原有的冲淤相对平衡状态被打破,河床发生沿程冲刷,2002年10月至2010年10月,宜昌至湖口河段总冲刷量为9.79亿m3,河床冲淤形态转变为＂滩、槽均冲＂,主要冲刷发生在宜昌至城陵矶河段。 |
| [8] | 根据实测水沙、地形资料,分析 了荆江沙质河段内洪枯河槽、宽窄河段等不同部位的冲淤幅度差异,并结合观测资料讨论了河道形态调整对水沙过程的响应关系。结果表明:荆江河道泥沙冲淤强度 平面分布不均,泥沙冲刷主要集中于枯水河槽,断面形态趋向窄深;宽浅河段冲刷强度大于束窄河段,河道形态沿程趋于均一化。蓄水前河道形态与水沙过程相适 应,河床在不同流量下以造床流量为界发生冲淤交替,长时期水沙过程作用下河道整体冲淤平衡。蓄水后含沙量大幅减小、大洪水消减而中洪水持续时间增长是荆江 沙质河段冲淤分布特征形成的主要原因。 . 根据实测水沙、地形资料,分析 了荆江沙质河段内洪枯河槽、宽窄河段等不同部位的冲淤幅度差异,并结合观测资料讨论了河道形态调整对水沙过程的响应关系。结果表明:荆江河道泥沙冲淤强度 平面分布不均,泥沙冲刷主要集中于枯水河槽,断面形态趋向窄深;宽浅河段冲刷强度大于束窄河段,河道形态沿程趋于均一化。蓄水前河道形态与水沙过程相适 应,河床在不同流量下以造床流量为界发生冲淤交替,长时期水沙过程作用下河道整体冲淤平衡。蓄水后含沙量大幅减小、大洪水消减而中洪水持续时间增长是荆江 沙质河段冲淤分布特征形成的主要原因。 |
| [9] | 利用长江干、支流水文和河道地形实测资料,研究了三峡工程运用前 后坝下游水沙输移特性与河湖泥沙冲淤的时空格局和变化特征.结果表明:①三峡工程建成运行后,长江中游洪峰流量减小,中水时间延长,汛后退水时间缩短,干 流输沙量大幅减少,泥沙来源发生新变化,荆江三口分流分沙量继续减少;②长江中游干流河势总体稳定,但河床沿程纵向冲刷强度与三峡水库运用前相比明显增 大,且冲刷强度和发展速度均大于原预测值;③荆江三口洪道由蓄水前的淤积转为冲刷;④洞庭湖淤积速度大为减缓,鄱阳湖受河道采砂等影响,总体由淤积转为冲 刷;⑤长江中游河、湖泥沙冲淤格局发生调整,三峡水库蓄水前长江中游河、湖呈淤积状态,蓄水后则呈冲刷状态. . 利用长江干、支流水文和河道地形实测资料,研究了三峡工程运用前 后坝下游水沙输移特性与河湖泥沙冲淤的时空格局和变化特征.结果表明:①三峡工程建成运行后,长江中游洪峰流量减小,中水时间延长,汛后退水时间缩短,干 流输沙量大幅减少,泥沙来源发生新变化,荆江三口分流分沙量继续减少;②长江中游干流河势总体稳定,但河床沿程纵向冲刷强度与三峡水库运用前相比明显增 大,且冲刷强度和发展速度均大于原预测值;③荆江三口洪道由蓄水前的淤积转为冲刷;④洞庭湖淤积速度大为减缓,鄱阳湖受河道采砂等影响,总体由淤积转为冲 刷;⑤长江中游河、湖泥沙冲淤格局发生调整,三峡水库蓄水前长江中游河、湖呈淤积状态,蓄水后则呈冲刷状态. |
| [10] | 以宜昌至江口河段内布置的十余个枯水位监测点近十年来的观测值、历年河床地形资料以及数学模型相结合,归纳了河段内枯水位降幅的时空分布规律,分区间讨论了地貌、河型、河床组成、前期人类行为等因素对河床和枯水位调整过程的影响.分析结果表明：三峡水库蓄水后河床调整是特殊环境下河道对悬移质来沙量减少的综合响应,各区间之间调整方式具有明显的空间差异,不同时期调整幅度具有非线性发展特征.宜都以上区间内枯水位降幅在2008年附近发生突变,是由床面粗化进程逐渐趋缓所致;宜都附近枯水位降幅最大、枝城至陈二口附近枯水位降幅最小,枝城上下游水位流量关系变化存在明显差异,均是由深蚀和侧蚀两种变形分别在枝城上下游河段居主导地位所致.河段内枯水位下降规律和成因的分区间差异性,是由河道的固有属性决定,在趋势预测和河道治理中均需重视. . 以宜昌至江口河段内布置的十余个枯水位监测点近十年来的观测值、历年河床地形资料以及数学模型相结合,归纳了河段内枯水位降幅的时空分布规律,分区间讨论了地貌、河型、河床组成、前期人类行为等因素对河床和枯水位调整过程的影响.分析结果表明：三峡水库蓄水后河床调整是特殊环境下河道对悬移质来沙量减少的综合响应,各区间之间调整方式具有明显的空间差异,不同时期调整幅度具有非线性发展特征.宜都以上区间内枯水位降幅在2008年附近发生突变,是由床面粗化进程逐渐趋缓所致;宜都附近枯水位降幅最大、枝城至陈二口附近枯水位降幅最小,枝城上下游水位流量关系变化存在明显差异,均是由深蚀和侧蚀两种变形分别在枝城上下游河段居主导地位所致.河段内枯水位下降规律和成因的分区间差异性,是由河道的固有属性决定,在趋势预测和河道治理中均需重视. |
| [11] | . |
| [12] | |
| [13] | Climate change, land-use change and in-stream river engineering affect trends in river discharges and river stages, and distinguishing such overlapping contributions is a major challenge in hydrologic time-series analysis. In this study, a systematic investigation of river stages and discharges was carried out for 78 stream gauges of rivers in Germany. We analysed the available times series for trends in flood stages, flood discharges, flood frequency and in stage-discharge relationships over time. With respect to annual maximum discharges and flood frequencies, no significant trends could be identified consistently throughout the study area. Significant discharge trends were identified at a number of stations, however, and tended to be catchment-specific. In contrast, trends in flood stages tended to be gauge-dependent, as stages over time are influenced by changes in local rating curves and thus by local and reach-scale channel modifications. Specific gauge analysis is a suitable tool for analysing such changes. No significant trends in specific stages over time were identified at most of the investigated gauges, generally paralleling the trend-based stage results at the same sites. Nevertheless, we could identify several river gauges with significant decreasing specific-gauge trends (e.g., Danube at Ingolstadt, Elbe at Magdeburg, Weser at Intschede) and others with significant increasing trends (e.g., Elbe at Dresden, Ems at Greven, Fulda at Grebenau, Leine at Herrenhausen). The identified trends were small compared with trends identified on heavily engineered rivers in the US driven by local changes in the channel (e.g., incision or wing dike groyne construction) or changes on the floodplain (e.g., dike displacement or changing land use in the flood plain). The trends in discharges and stages documented here have contributed to past changes in flood frequency and intensity on German rivers. |
| [14] | . . |
| [15] | The effects of the sediment regime on the flood level in the middle reach of the Yangtze River before and after the construction of the Three Gorges Dam (TGD) are investigated. Before the dam construction, the sediment regime has driven the flood level higher and higher over recent decades in the middle reach of the Yangtze River, which has reflected changes in the location and amount of sediment deposition. After dam completion, the magnitude and rate of channel degradation determines the process of flood stage lowering but they are difficult to estimate owing to insufficient understanding of the sediment discharge recovery process. To make a rational prediction of channel degradation of the Yangtze River downstream from the TGD, the sediment transport rate during channel degradation downstream from other dams is examined. It is found that, for any grain size, postdam sediment transport rates cannot exceed the predam level at any location along the downstream channel. Erosion amounts predicted for the reach downstream from the TGD before its closure are too high. In light of this, a numerical simulation of the channel degradation process is carried out. The results indicate that, although degradation takes place immediately after the TGD closure, the flood level in the middle reach of the Yangtze River will still remain at its predam condition in the following 20 years. This is determined not only by the regional characteristics of the middle reach of the Yangtze River but also by the common law of sediment transportation downstream from dams. |
| [16] | 三峡工程的首要任务是防洪，防洪的重点是保荆江安全。在此背景下分析长江中游当前防洪形势和三峡工程存在的问题，认为相对于长江中游洪水形势和防洪要求，三峡水库防洪库容远小于长江中游超额洪水，动态防洪库容小于设计静态防洪库容，有效防洪库容更小；长期河道演变使城陵矶等地同流量水位显著升高；中游蓄滞洪区建设规模严重偏小，而建设进度严重滞后，已有蓄滞洪区使用困难；当前大规模清水冲刷没有降低洪水位，反而荆江向洞庭湖分洪减小、河道泄洪能力进一步萎缩；三峡水库2008年按正常水位运行以来，连年拦中小洪水和超汛限水位运行，大量占据防洪库容和压低下泄洪水流量，使下游河道长期得不到洪水塑造，行洪能力和堤防得不到检验和考验。考虑到气候变化等不确定性影响，现在长江中游防洪形势仍然严峻。建议：切实维护三峡工程规划确定目标和防洪调度方式，严格控制汛限水位，积极采取优化调度增加水库防洪能力；尽快完成三峡工程规划要求的城陵矶附近蓄滞洪区建设，采取政策措施保证分洪与发展兼顾；改变和优化金沙江下游4大梯级水库汛期运行方式；加强三峡库区岸坡治理、提高水库防洪调度灵活性；采取积极措施维护长江中游江湖关系稳定。 . 三峡工程的首要任务是防洪，防洪的重点是保荆江安全。在此背景下分析长江中游当前防洪形势和三峡工程存在的问题，认为相对于长江中游洪水形势和防洪要求，三峡水库防洪库容远小于长江中游超额洪水，动态防洪库容小于设计静态防洪库容，有效防洪库容更小；长期河道演变使城陵矶等地同流量水位显著升高；中游蓄滞洪区建设规模严重偏小，而建设进度严重滞后，已有蓄滞洪区使用困难；当前大规模清水冲刷没有降低洪水位，反而荆江向洞庭湖分洪减小、河道泄洪能力进一步萎缩；三峡水库2008年按正常水位运行以来，连年拦中小洪水和超汛限水位运行，大量占据防洪库容和压低下泄洪水流量，使下游河道长期得不到洪水塑造，行洪能力和堤防得不到检验和考验。考虑到气候变化等不确定性影响，现在长江中游防洪形势仍然严峻。建议：切实维护三峡工程规划确定目标和防洪调度方式，严格控制汛限水位，积极采取优化调度增加水库防洪能力；尽快完成三峡工程规划要求的城陵矶附近蓄滞洪区建设，采取政策措施保证分洪与发展兼顾；改变和优化金沙江下游4大梯级水库汛期运行方式；加强三峡库区岸坡治理、提高水库防洪调度灵活性；采取积极措施维护长江中游江湖关系稳定。 |
| [17] | Abstract The magnitude of anthropogenic influence, especially dam regulation, on hydrological system is of scientific and practical value for large river management. As the largest dam in the world by far, Three Gorges Dam (TGD) is expected to be a strong evidence on dam impacts on downstream hydrological regime. In this study, statistical methods are performed on the pre- and post-TGD daily hydrological data at Yichang, Hankou, and Datong stations to detect the daily, monthly, yearly, and spatial fluctuations in river hydrology along the Yangtze River during the period of 20002013. It is found that TGD makes a significant hydrological variation along the Yangtze River following the dam operation since 2003. Specifically, the daily discharge and water level are gathered to normal event ranges with less extreme events than before 2003. Both maximum and minimum daily water levels at the study stations have decreased due to TGD-induced riverbed incision. The operation of TGD shifts the maximum monthly discharge and water level from August to July at Yichang station. The significance of TGD effect on discharge and water level relationship presents spatial variation. The rating curves at upstream reach experience the most significant effects with a substantial upward shift, while those at lower reach only suggest slight modification. Of the potential drivers considered in this study, dam regulation is responsible for the changes in downstream river hydrology. Moreover, the tributary and adjoining riparian lakes of the Yangtze River contribute to weaken the effect of TGD on downstream hydrological behavior. |
| [18] | The maximum at-station total incision observed at each of the studied channels was significantly less then the total lake level drop and varied in response to both drainage area and lake bathymetry. The model applied predicted degradation rates and the pattern of degradation with high accuracy. This suggests that sediment flux in the modeled channels is indeed linearly dependent on slope. Further support for this linear dependency is provided by a linear correlation between the diffusion coefficient and the mean annual rain volume over each basin (a proxy for discharge). The model presented could be a valuable tool for planning in rapid base level fall environments where incision may risk infrastructure. |
| [19] | Floods increase fluvial complexity by eroding established surfaces and creating new alluvial surfaces. As dams regulate channel flow, fluvial complexity often decreases and the hydro-eco-geomorphology of the riparian habitat changes. Along the Missouri River, flow regulation resulted in channel incision of 13 m within the study area and disconnected the pre-dam floodplain from the channel. Evidence of fluvial complexity along the pre-dam Missouri River floodplain can be observed through the diverse depositional environments represented by areas of varying soil texture. This study evaluates the role of flow regulation and depositional environment along the Missouri River in the riparian invasion of red cedar downstream of Gavins Point dam, the final dam on the Missouri River. We determine whether invasion began before or after flow regulation, determine patterns of invasion using Bayesian t -tests, and construct a Bayesian multivariate linear model of invaded surfaces. We surveyed 59 plots from 14 riparian cottonwood stands for tree age, plot composition, plot stem density, and soil texture. Red cedars existed along the floodplain prior to regulation, but at a much lower density than today. We found 2 out of 565 red cedars established prior to regulation. Our interpretation of depositional environments shows that the coarser, sandy soils reflect higher energy depositional pre-dam surfaces that were geomorphically active islands and point bars prior to flow regulation and channel incision. The finer, clayey soils represent lower energy depositional pre-dam surfaces, such as swales or oxbow depressions. When determining patterns of invasion for use in a predictive statistical model, we found that red cedar primarily establishes on the higher energy depositional pre-dam surfaces. In addition, as cottonwood age and density decrease, red cedar density tends to increase. Our findings indicate that flow regulation caused hydrogeomorphic changes within the study area that permitted red cedar invasion of the riparian habitat and that the type of depositional environment partially determines where along the riparian landscape red cedar invades. |
| [20] | The increasing impact of both climatic change and human activities on global river systems necessitates an increasing need to identify and quantify the various drivers and their impacts on fluvial water and sediment discharge. Here we show that mean Yangtze River water discharge of the first decade after the closing of the Three Gorges Dam (TGD) (2003-2012) was 67塳m(3)/yr (7%) lower than that of the previous 50 years (1950-2002), and 126 m(3)/yr less compared to the relatively wet period of pre-TGD decade (1993-2002). Most (60-70%) of the decline can be attributed to decreased precipitation, the remainder resulting from construction of reservoirs, improved water-soil conservation and increased water consumption. Mean sediment flux decreased by 71% between 1950-1968 and the post-TGD decade, about half of which occurred prior to the pre-TGD decade. Approximately 30% of the total decline and 65% of the decline since 2003 can be attributed to the TGD, 5% and 14% of these declines to precipitation change, and the remaining to other dams and soil conservation within the drainage basin. These findings highlight the degree to which changes in riverine water and sediment discharge can be related with multiple environmental and anthropogenic factors. |
| [21] | The sediment load of the Yangtze River (China) is decreasing because of construction of dams, of which the Three Gorges Dam (TGD) is the best known example. The rate of the decline in sediment load is well known, but changes in the sediment grain size distribution have not been given much attention. The TGD mostly traps sand and silt while clay is flushed through the reservoir. A large amount of sand is available in the Yangtze River downstream of the reservoir, and therefore the pre-dam sand concentration is not substantially reduced. The availability of silt on the Yangtze River bed is limited, and it is expected that most silt will be removed from the riverbed within one to two decades. In order to evaluate the impact of the change in grain size distribution on the tidal flats of the Yangtze Estuary, a highly schematized tidal flat model is setup. This model broadly reveals that the observed deposition rates are exceptionally large because of the high sediment concentration, the abundance of silt, the seasonal dominance of waves (shaping a concave profile), and the offshore tidal asymmetry. The model further suggests that deposition rates will be limitedly influenced by reductions in clay or fine silt but strongly impacted by reductions in median to coarse silt. The response of the downstream morphology to reservoir sedimentation therefore strongly depends on the type of trapped sediment. As a consequence, silt-dominated rivers, such as the Yangtze River and the Yellow River may be more strongly impacted than sand-dominated systems. |
| [22] | Abstract The 6380 km long Yangtze River is the longest in China and third longest in the world. With more than 3600 branches it provides a total of 65 000 km of waterways, over half of the country's inland navigation network. This paper describes China's 'golden waterway' and its huge national and regional economic benefits. It reports on the recent channel improvement projects on the trunk line, including the Three Gorges dam and major estuary works, which have significantly increased both reliability and capacity and resulted in a direct stimulus to economic growth. A further 4 pound billion of improvements are now planned. |
| [23] | . |
| [24] | 由使用装轮船的声学的 Doppler 基于测量水文学数据当前的剖析程序(ADCP ) 仪器，我们分析了中间的长江盆的河十字节的形状(主要集中于 Makou 和 Tianjiazhen 河活动范围) 。Hydrodynami |
| [25] | The Tianjiazhen reach of the middle Yangtze is about 802km long, and characterized by a narrow river width of 65002m and local water depth of > 9002m in deep inner troughs, of which about 6002m is below the mean sea level. The troughs in the channel of such a large river are associated with regional tectonics and local lithology. The channel configuration plays a critical role in modifying the height and duration of river floods and erosion of the riverbed. The formation of the troughs in the bed of the Yangtze is considered to be controlled by sets of NW–SE-oriented neotectonic fault zones, in which some segments consist of highly folded thick Triassic limestone crossed by the Yangtze River. Several limestone hills, currently located next to the river channel, serve as nodes that create large vortices in the river, thereby accelerating downcutting on the riverbed composed of limestone highly susceptible to physical corrosion and chemical dissolution. Hydrological records indicate that the nodal hills and channel configuration at Tianjiazhen do not impact on normal flow discharges but discharges > 50,00002m 3s 61 1 are slowed down for 2–302days. Catastrophic floods are held up for even longer periods. These inevitably result in elevated flood stages upstream of prolonged duration, affecting large cities such as Wuhan and a very large number of people. |
| [26] | 依据大量的实测资料,详细分析了长江中下游近50年来的洪水位变化与河床冲淤及其分布关系, 发现部分水文断面洪水位抬升明显、高洪水位持续时间加长的现象,与河段河床演变及河道形态变化以及沿江湖泊的淤积密切相关,并阐述了二者的理论关系,为长 江中下游洪水抬升机理分析提供了重要的依据. . 依据大量的实测资料,详细分析了长江中下游近50年来的洪水位变化与河床冲淤及其分布关系, 发现部分水文断面洪水位抬升明显、高洪水位持续时间加长的现象,与河段河床演变及河道形态变化以及沿江湖泊的淤积密切相关,并阐述了二者的理论关系,为长 江中下游洪水抬升机理分析提供了重要的依据. |
| [27] | 近50年实测水沙资料分析表明,城陵矶水位变化取决于螺山—汉口河段冲淤量.三峡蓄水后,螺山—汉口河段冲淤量又取决于宜昌下泄和宜昌—城陵矶河段冲起的粗沙量(d0.085mm)及汉口(扣除汉江)粗沙输沙量.通过估算三峡蓄水后宜昌—城陵矶河段粗沙冲刷量和汉口(扣除汉江)粗沙输沙量,表明螺山—汉口河段最大冲刷约9.5×108t,螺山流量为10000—60000m3/s时,城陵矶水位下降约1.26—0.32m,并且随着螺山流量的增大,城陵矶水位下降幅度减小. . 近50年实测水沙资料分析表明,城陵矶水位变化取决于螺山—汉口河段冲淤量.三峡蓄水后,螺山—汉口河段冲淤量又取决于宜昌下泄和宜昌—城陵矶河段冲起的粗沙量(d0.085mm)及汉口(扣除汉江)粗沙输沙量.通过估算三峡蓄水后宜昌—城陵矶河段粗沙冲刷量和汉口(扣除汉江)粗沙输沙量,表明螺山—汉口河段最大冲刷约9.5×108t,螺山流量为10000—60000m3/s时,城陵矶水位下降约1.26—0.32m,并且随着螺山流量的增大,城陵矶水位下降幅度减小. |
| [28] | . |
| [29] | . |
| [30] | |
| [31] | . |
| [32] | This study experimentally investigated the effects of submerged vegetation on the characteristics of flow and the formation of a scour hole. The submerged vegetations were modeled by bundled plastic fibers. Experiments were performed for various spacings of the plastic fibers, resulting in vegetation density ranging from 0.21 to 0.65. The vegetation models were aligned with the approaching flow in a rectangular channel. Vertical distributions of time-averaged velocity and turbulence intensity at various streamwise distances were evaluated using an acoustic Doppler velocimeter (ADV). The characteristic lengths of the scour hole, including scour depth, dune height, the length of the scour hole, the horizontal distance of the maximal scour depth, and the horizontal distance of the dune crest, were determined from the bed profiles. Velocity and turbulence intensity plots indicated that the deflected flow over the vegetation was promoted with the decrease in spanwise spacing. Downstream of the vegetation zone, two shear layers developed from the vegetation zone. As the spanwise plant spacing increased, the turbulence intensity of the upper shear layer decreased because of the strong flow through the vegetation. Vegetation densities were used to examine the effects of vegetation on the characteristic lengths of the scour hole. Scour depth, dune height, length of the scour hole, horizontal distance of the maximal scour depth, and horizontal distance of the dune crest increased linearly with a decrease in vegetation density. |
| [33] | |
| [34] | During the 1927 Mississippi flood, the levee was dynamited downstream of New Orleans creating a 2 km wide crevasse that inundated the Breton Sound estuary and deposited a crevasse splay of about 130 km. We measured sediment deposition in the splay that consisted of a silty-clay layer bounded by aged peat below and living roots above. Based on coring, we developed a map of the crevasse splay. The clay layer ranged from 2 to 42 cm thick and occurred 24 to 55 cm below the surface. Bulk density of the clay layer decreased and soil organic matter increased with distance from the river. Pband Cs dating an age of ~1926-1929 for the top of the layer. During the flood event, deposition was at least 22 mm month-10 times the annual post-1927 deposition. The crevasse splay captured from 55% to 75% of suspended sediments that flowed in from the river. The 1927 crevasse deposition shows how pulsed flooding can enhance sediment capture efficiency and deposition and serves as an example for large planned diversions for Mississippi delta restoration. |
| [35] | During the 2011 Mississippi River flood, discharge to the lower river exceeded that of the 1927 and 1937 floods and the lower river remained above flood stage for nearly 2 months. A combination of WorldView-2 and Land Satellite 5 Thematic Mapper (Landsat 5 TM) imagery was used to assess the impact of this flood event on the Wax Lake Delta, one of few areas where the river is building new land. Vegetation community change was mapped from 2010 to 2011 and related to elevation change using plant species elevation distributions calculated from light detection and ranging (LIDAR) data. Changes in the land area in the delta were also assessed by regressing land area against water level for a series of preand postflood Landsat 5 TM images. The results indicate a net growth of 6.5 km at mean water level and 4.90 km at mean sea level. Areal gains were greatest at high water levels, indicating substantial vertical accretion across the subaerial delta. At least 8.7 km , or 31.8%, of the area studied converted to a higher-elevation species. The most change occurred at low elevations with conversion from fully submerged aquatic vegetation to Potamoget n nodosus and Nelumbo lutea. Conversion to lower-elevation species occurred across 3.4 km , or 12.8% of the study area, while 55.5% remained unchanged. The results highlight the importance of infrequent, large flood events in the maintenance of river deltas and provide a reference for estimating the impact of proposed large-scale river diversions on the Mississippi River Delta. |
| [36] | <p>在分析长江中下游岸线开发利用现状及存在问题基础上，分别选取武汉河段和扬中河段作为代表性河段，针对桥梁群和码头群两类主要岸线开发利用形式，开展了涉河工程群对河道洪水位及流场累积影响的数学模型计算分析。计算结果表明，群体工程共同作用后将引起河道洪水位和流场的叠加影响，其影响值及影响范围远大于单个工程，当群体工程的影响积累到一定程度，可能对河道的行洪与河势稳定带来不利影响。建议桥梁群应保持合理的密度，码头群应合理控制港区规模，上下游港区间应保持合理的距离，在岸线开发过程中应制定岸线利用规划，规范涉河工程设计，以尽可能减小对防洪的累积影响</p> . <p>在分析长江中下游岸线开发利用现状及存在问题基础上，分别选取武汉河段和扬中河段作为代表性河段，针对桥梁群和码头群两类主要岸线开发利用形式，开展了涉河工程群对河道洪水位及流场累积影响的数学模型计算分析。计算结果表明，群体工程共同作用后将引起河道洪水位和流场的叠加影响，其影响值及影响范围远大于单个工程，当群体工程的影响积累到一定程度，可能对河道的行洪与河势稳定带来不利影响。建议桥梁群应保持合理的密度，码头群应合理控制港区规模，上下游港区间应保持合理的距离，在岸线开发过程中应制定岸线利用规划，规范涉河工程设计，以尽可能减小对防洪的累积影响</p> |
| [37] |
