Stability of the Stratification of Water Bodies in the North Passage of the Yangtze River Estuary Based on the EFDC Model

To study the stratified stability of a water column in the North Passage of the Yangtze River Estuary,a numerical model of the hydrodynamics of this estuary is established using the EFDC model.On the basis of EFDC results,this paper derives and pro-vides the discriminative index of water body stability caused by salinity and analyzes the along-range variation in water body strati-fication stability in the North Passage of the Yangtze River Estuary and the periodic variation at a key location(bend area)based on the simulation results of the numerical model.This work shows that the water body in the bend area varies between mixed and strati-fied types,and the vertical average flow velocity has a good negative correlation with the differential velocity between the surface and bottom layers of the water body.The model simulation results validate the formulae for the stratified stability discriminant during spring tides.

In-Situ Observation of Fluid Mud in the North Passage of Yangtze Estuary, China

Observations of fluid mud were made in the lower North Passage of the Yangtze Estuary in February 2000, on 10～11 August 2000, on 30～31 August 2000 (after two strong typhoons), on 21～24 August 2000 (neap tide) and on 3～6 September 2000 (mean tide) respectively. In situ data show that the fluid mud in this area consists of fine cohesive sediment (median size 7.23 μm). The formation and movement of fluid mud varied during the neap-spring and flood-ebb tidal cycle. Observations suggest that fluid mud phenomena in this area may be categorised in a three-fold manner as slack water, storm and saltwedge features. The thickness of the fluid mud layer of slack water during the neap tide ranged from 0.2 to 0.96 m, whereas during the mean tide, the thickness ranged from 0.17 to 0.73 m, and the thickness of the fluid mud layer was larger during slack water than at the flood peak. Shoals cover an area of 800 km2 with a water depth smaller than 5 m. Erosion of these extensive intertidal mudflats due to storm action provides an abundant sediment source. This is particularly significant in this estuary when the tidal level is lower than 5 m. The lower North Passage is a typical zone of saltwater wedging, so the saltwedge fluid mud has the most extensive spatial range in the estuary.

Relationship between the Late Spring NAO and Summer Extreme Precipitation Frequency in the Middle and Lower Reaches of the Yangtze River

The relationship between the late spring North Atlantic Oscillation (NAO) and the summer extreme precipitation frequency (EPF) in the middle and lower reaches of the Yangtze River Valley (MLYRV) is examined using an NECP/NCAR reanalysis dataset and daily precipitation data from 74 stations in the MLYRV. The results show a significant negative correlation between the May NAO index and the EPF over the MLYRV in the subsequent summer. In positive EPF index years, the East Asian westerly jet shifts farther southward, and two blocking high positive anomalies appear over the Sea of Okhotsk and the Ural Mountains. These anomalies are favorable to the cold air from the mid-high latitudes invading the Yangtze River Valley (YRV). The moisture convergence and the ascending motion dominate the MLYRV. The above patterns are reversed in negative EPF index years. A wave train pattern that originates from the North Atlantic extends eastward to the Mediterranean and then moves to the Tibetan Plateau and from there to the YRV, which is an important link in the May NAO and the summer extreme precipitation in the MLYRV. The wave train may be aroused by the tripole pattern of the SST, which can explain why the May NAO affects the summer EPF in the MLYRV.

Morphological Evolution and Its Response to the Navigational Improvements in the North Passage,Yangtze Estuary

By use of bathymetric chart, recent change of the riverbed in the North Passage of the Yangtze Estuary has been studied in this paper. The main channel of the upper, middle and lower （section） in the North Passage has been successively eroded and its groin field significantly deposited. At the same time, sediment has been deposited on the entrance region. Erosion and deposition had responded rapidly to the construction of the regulation engineering. There was about one year duration of lagging between erosion in the deep channel and the construction of the regulation engineering. The siltation lag of time in the groin field varied with the initial depth, but the average deposited thickness was about 0.5 m per year. Volumetric analysis demonstrates that there is a increasing trend of siltation in the North Passage after 2002, because of the difference in duration and quantity between erosion in the deep channel and deposition in the groin field. The water volume of the North Passage was reduced by =9% （280 million m^3） between 2002 and 2006. Sediment budget reveals that the main sediment deposited in the North Passage takes its source from the river and the ocean. The decreasing water volume was attributable to shoaling in the groin field. Its triggering factors for increased sedimentation are the navigational improvements（jetties and groins） after 1998, which altered the passage boundary and destroyed the equilibrium state on the average ebb and flood sediment fluxes. The establishment of a stable estuary is attributed to a reduction in depth of the groin field. The forecast on the sediment deposition quantity and continuous infilling time in the groin system is about 325 × 10^6m^3 and 6 - 7 years, respectively.

The Rock Paintings of the Helan Mountains

THE HelanMountains sit ina corner of theNingxia Hui Autonom-ous Region of north-western China in a widearc running for 250 kmfrom north to south.Insome places the range is20 to 30 km across;the individual moun-tain peaks are on aver-age 1,400 m above sealevel and the high-est peak Shaguozhou,reaches 3,556 m intothe sky.When the YellowRiver enters

长江安徽段江湖连通性及生物通道恢复研究

江湖阻隔是导致长江中下游江湖复合生态系统衰退的最主要原因,江湖连通和生物通道恢复是流域生态修复的重要措施之一。通过现场调查等方法研究了华阳河湖群、菜子湖、升金湖和安庆西江古道等与长江干流的阻隔现状及连通性特征,在此基础上探讨了技术和管理层面存在的问题并提出对策建议。结果发现:依托涉水工程建设开展恢复河湖生物通道的做法可以有效缓解江湖复合生态系统的衰退,尤其是以“过鱼设施建设、季节性灌江纳苗、生态水网建设”相结合的生物通道恢复方案具有技术可行性。相关成果可为长江中下游江湖连通性及生物通道恢复、国家水网建设提供有益的参考。

黄河北干流水沙时空变化特征及协调性分析

为了解黄河北干流河段径流和输沙的时空变化规律及趋势,基于2002—2021年黄河北干流水沙数据,采用Mann-Kendall检验、突变点检验、小波分析、水沙关系协调性分析等方法,对黄河北干流河段的头道拐、龙门、潼关3个水文站2002—2021年的水沙时空变化特征进行了分析。结果表明:黄河北干流河段的输沙年内不均匀程度和集中度均大于径流,并且年内特征变化更加显著;各站径流集中期主要出现在9月,而输沙集中期主要在8月和9月;流域内水沙变化的显著突变年份多发生在2005年和2017年,可能与近年大型水利工程的调控影响相关;3个水文站水沙序列主要时间尺度对应的周期分别为13、10、9 a;黄河北干流的水沙不协调性在2008年之前主要表现为水少沙多,而在2008年之后则表现为水多沙少,其中头道拐的来沙系数始终小于0.009,一直处于水多沙少的状态。总体上,研究期内黄河北干流河段径流量在不断上升,而输沙量明显减少,且随着时间的推移水多沙少的趋势愈发显著。

1997—2019年长江口北槽地形演化特征及驱动机制

河口拦门沙位于河流和海洋的交界,具有弱动力、易沉积、水深浅的环境特征。打通拦门沙,建设深水航道一直是海洋学和工程学的一个难题,目前深水航道工程已经深刻地改变了拦门沙河槽的演化格局。本文根据北槽三期航道工程建设时间节点,收集了1997年、2002年、2007年和2019年北槽航道水下地形数据分析工程前后的地形演变特征,并结合航道工程建设、人为疏浚和外部环境变化等因素对北槽地形演变的驱动效应进行分析。结果表明:深水航道建设后长江口北槽主要出现了“槽冲滩淤”的河槽地形演化特征;空间上,北槽上段主要发生了北侧滩涂淤积,南侧航道侵蚀,而下段主要发生了南侧滩涂淤积,北侧航道侵蚀的演变格局。导堤和丁坝的建设是引起河槽“槽冲滩淤”的主要因素,而科氏力引起的涨、落潮流路变化也增加了河槽上下段的差异演化;深水航道工程建设是引起1997—2007年北槽淤积的主要驱动因素,而人为疏浚则是2007—2019年北槽侵蚀的主要影响因素;尽管人类活动已经成为北槽河槽演化的主要原因,但周围环境变化如流域来沙减少和海平面上升也加剧了近期的北槽侵蚀。

长江口北槽最大浑浊带形态影响因素数值模拟研究

为了探明层化、絮凝沉降和可悬浮泥沙量对长江口北槽最大浑浊带形态的影响,基于长江口三维水流、盐度、泥沙耦合模型对三种影响因素开展数值模拟研究。研究结果表明:悬沙制紊可以在盐度制紊基础上进一步加强水体层化作用,促进形成近底高浓度泥沙分布形态。北槽上段受盐水入侵影响小于中下段,层化制紊作用相应较弱,这也是北槽上段悬沙垂向分布较为均匀的重要原因;泥沙絮凝沉速在北槽断面呈现显著的垂向和纵向变化,对最大浑浊带悬沙垂向分布形态影响也具有较明显的沿航道变化特征;悬浮泥沙量沿北槽不均匀分布是造成最大浑浊带含沙量与沿程流速没有良好对应关系的原因,可悬浮泥沙量增加不仅可以提高最大浑浊带整体含沙量,并且可以通过影响层化以及絮凝沉降加强泥沙垂向捕集作用,促进近底高浓度泥沙分布形态。

南水北调中线供水区水域面积变化遥感分析

为更好地研究调水对供水区域水域面积的影响,利用遥感技术研究了南水北调中线工程调水前后供水区及其下游四季的水域面积变化情况及其动因。研究表明:在调水工程实施之后,汉江中下游区域出现了水域面积大幅度下降的情况,汉江流域水域面积从2011年到2015年整体减少,尤其是春夏季水域面积减少最多,春季减少52.6km^(2),夏季减少65.8km^(2),减少比例达到17.3%,秋季和冬季水域面积减少幅度较小,秋季水域面积减少23.4km^(2),冬季水域面积减少最少,为4.2km^(2)。

地铁暗挖施工深孔注浆试验段试验研究

针对北京地铁12号线四季青站C出入口横通道垂直下穿南水北调暗涵的工程问题,提出可行的施工方法。采用试验段试验的方法进行研究,试验段主要开展洞内深孔注浆试验,包括试验方案确定与实施、试验效果分析和综合对比分析。通过试验段研究,获得能够指导施工的洞内深孔注浆要素:注浆方式与工艺、机械设备、孔位布设、浆液类型、注浆加固与开挖长度、注浆相关具体参数等。四季青站C出入口横通道垂直下穿南水北调暗涵工程,用试验段总结的施工方法施工,工程安全顺利完成。

Formation of the Anomalous Summer Precipitation in East China in 2010 and 1998: A Comparison of the Impacts of Two Kinds of El Nio

In the summers of 1998 and 2010, severe floods occurred in the middle and lower reaches of the Yangtze River. Although an El Nifio event took place preceding each of the summer floods, significant differences between the two summer floods and the two E1 Nifio events were identified. The 1997/98 E1 Nifio is a conventional one with strongest warming in the central-eastern Pacific, whereas the 2009/10 event is an E1 Nifio Modoki with strongest warming in the central Pacific. In this study, summer rainfall anomalies （SRA） in the two years were first compared based on the rainfall data at 160 stations in China's Mainland, and a significant difference in SRA was found. To understand the underlying mechanism for the difference, the atmospheric circulation systems, particularly the western North Pacific anticyclone （WNPAC）, the western Pacific subtropical high （WPSH）, and the low-level air flows, were compared in the two years by using the NCEP/NCAR reanalysis data. The results display that the WNPAC was stronger in 2010 than in 1998, along with a northwestward shift, causing weakened southwesterly from the Bay of BengM to the South China Sea but intensified southerly in eastern China. This resulted in less water vapor transport from the tropical Indian Ocean and the South China Sea but more from the subtropical western Pacific to East Asia. Subsequently, the rainband in 2010 shifted northward. The difference in the WNPAC was causedby the anomalous ascending motion associated with the warming location in the two E1 Nifio events. ~rthermore, the role of tropical sea surface temperature （SST） in modulating these differences was investigated by conducting sensitivity experiments using GFDL AM2.1 （Geophysical Fluid Dynamics Laboratory Atmospheric Model）. Two experiments were performed, one with the observed monthly SST and the other with June SST persisting through the whole summer. The results suggest that the model well reproduced the primary differences in the atmospheric circulation systems in the two years. It is found that the difference in E1 Nifio events has shaped the rainfall patterns in the two years of 1998 and 2010. At last, the case of 2010 was compared with the composite of historical E1 Nifio Modoki events, and the results indicate that the impact of E1 Nifio Modoki varies from case to case and is more complicated than previously revealed.

长江口规划生态航道建设方向研究

针对长江口北港、南槽生态航道的建设问题,通过分析区域环境特点和航道发展需求,梳理已建的长江口深水航道生态化建设情况,提出长江口生态航道建设的核心和模式。结果显示:1)南槽和北港生态航道的建设需以确保河势格局稳定为基础;2)需与滩涂保护、生态功能区域保护形成联动布局;3)需积极研发和应用生态结构,构筑“人工生态礁体”群,优化河口综合环境;4)需结合滩涂泥沙资源需求和航道建设自身筑堤用沙需求,实现航道疏浚土的资源化、生态化利用;5)需强化建设运营中科学的管控体系、生态补偿体系等。

Using Moving North Pacific Index to Improve Rainy Season Rainfall Forecast over the Yangtze River Basin by Analog Error Correction

A new analog error correction （AEC） scheme based on the moving North Pacific index （MNPI） is designed in this study. This scheme shows obvious improvement in the prediction skill of the operational coupled general circulation model （CGCM） of the National Climate Center of China for the rainy season rainfall （RSR） anomaly pattern correlation coefficient （ACC） over the mid-to-lower reaches of the Yangtze River （MLRYR）. A comparative analysis indicates that the effectiveness of the new scheme using the MNPI is better than the system error correction scheme using the North Pacific index （NPI）. A Euclidean distance- weighted mean rather than a traditional arithmetic mean, is applied to the integration of the analog year＇s prediction error fields. By using the MNPI AEC scheme, independent sample hindcasts of RSR during the period 2003-2009 are then evaluated. The results show that the new scheme exhibited a higher forecast skill during 2003-2009, with an average ACC of 0.47; while the ACC for the NPI case was only 0.19. Furthermore, the forecast skill of the RSR over the MLRYR is examined. In the MNPI case, empirical orthogonal function （EOF） was used in the degree compression of the prediction error fields from the CCCM, whereas the AEC scheme was applied only to its first several EOF components for which the accumulative explained variance accounted for 80% of the total variance. This further improved the ACC of the independent sample hindcasts to 0.55 during the 7-yr period.

长江口深水航道治理工程实施后南北槽分汊段河床演变

利用1998-2006年的水深测图和南北槽分流、分沙比测量资料,研究了长江口深水航道治理工程实施后南、北槽分流比的变化过程、原因及其与分汊口河床冲淤演变的关系。结果表明,随着长江口深水航道治理工程的实施,北槽落潮分流比总体呈减小的趋势,南槽落潮分流比呈增加的趋势。伴随着南、北槽落潮分流比的南增、北减,南槽进口段(长约18 km)的主槽发生了冲刷,北槽进口段(长约12 km)的主槽发生了淤积,南、北槽进口段河槽总过水断面面积呈下降趋势。北槽落潮分流比与北槽河槽总容积、南北槽落潮分流比与各自进口段的河槽断面平均水深之间均具有较好的相关性,据此,预测了未来南、北槽的落潮分流比和进口段河槽冲淤的平衡量值。

长江口深水航道治理一期工程前后泥沙运动特性初步分析

利用长江口徐六泾、横沙和佘山三站三年逐日表层含沙量、盐度和气象观测资料 ,以及北槽河段沿线含沙量洪、枯季准同步观测资料 ,对长江口深水航道治理一期工程实施前后北槽河段含沙量沿程分布规律和垂向变化特征 ,以及滩槽泥沙交换的机理进行了分析。结果表明 :北槽河段高含沙区分布位置在一期工程后适量下移 ;风浪对浅滩泥沙的掀动作用和滩槽间泥沙交换是造成工程区河段含沙量增加的主要动力因素 ;滩槽泥沙交换及输移途径取决于滩槽间流场变化 ,南北导堤在二期工程继续下延后 ,将进一步削弱滩槽泥沙交换量 。

南水北调中线工程与汉江中下游地区可持续发展

汉江是长江最大的支流,汉江中下游地区是湖北省经济基础最强的地区。同时汉江流域也存在着洪涝灾害威胁大、水资源开发利用水平不高、环境建设和生态保护力度不够、传统的工农业生产方式和产业结构加重环境的恶化、管理体制不顺等问题。南水北调中线工程以及配套工程的实施,对汉江流域的经济发展将起推动作用,同时从汉江的丹江口水库调水,将改变汉江中下游的水资源分配,社会经济发展与生态环境的协调将会出现新的矛盾。要解决好流域经济发展问题,必须把握好建设南水北调中线工程的机遇,更新观念,加强前期研究和规划,注重生态环境的保护和示范工程的建设,建立相应的政策法规和流域管理体制,全面保证汉江中下游地区的可持续发展。

长江口九段沙的形成演变及其与南北槽发育的关系

根据１８４２～１９９５年的地形图和１９９６、１９９７年的野外观测，探讨了九段沙和南北槽的形成历史及形成后的演变过程。研究表明：九段沙是原铜沙浅滩南沿经涨、落潮槽对切贯通后形成的，北槽和北港一样最初原形是涨潮槽；南槽的前身是南港下段。九段沙形成以来具有趋势性和非趋势性两种冲淤变化。前者表现为扩大、淤高和位置向下游移动，后者反映在南北两侧的频繁冲淤。九段沙和南北槽在冲淤上存在相互制约关系。目前，南北槽河势已进入相对稳定时期。

长江口深水航道治理一期工程实施后北槽冲淤分析

对长江口深水航道治理一期工程实施后北槽的地形资料进行分析计算 ,论述了北槽河床冲淤变化。结果表明 :一期工程实施后 ,整治工程段北槽河床普遍冲刷 ,平均水深增幅达 1 2m ,断面平均水深最大增幅超过2m ,坝田明显淤积 ,河床断面比较对称 ,航槽回淤减少。北槽进口段和北槽中段的深槽发生较为明显的淤积 ,北槽纵向河床断面面积和平均水深趋于均匀 ,形成了一条上、下段平顺衔接的微弯深泓线。工程实施后北槽的河床总容积基本保持不变。整治建筑物完成一年后河床基本达到冲淤平衡 ,工程引起河床大幅度冲淤调整完成后 ,北槽仍具有明显的洪淤枯冲规律 ,主槽季节性冲淤幅度平均在 30cm～ 5 0cm之间。

长江口深水航道整治工程影响下北槽河床冲淤变化分析

根据长江口深水航道整治工程前后(1998年1月与2008年2月)的地形测图,定量分析工程影响下的北槽河床冲淤变化,结果表明:1)10年间,研究区域内泥沙淤积总量高达3.37亿方,平均淤积厚度1.03m,其中入口段、上段、中段及下段的淤积量分别占淤积总量的16.5%、32.1%、29.6%与21.8%,淤积厚度分别为1.23m、1.12m、1.39m与0.65m;2)坝田泥沙淤积总量3.50亿方,其中航道北侧淤积量占58.3%,淤积分布特征为上段淤积厚度最大,下段次之,中段最小,分别为3.94m、2.44m和0.92m,航道南侧从上游向下淤积厚度逐渐减小,分别为3.32m、3.10m与1.87m;3)主槽整体净冲刷,泥沙冲刷总量0.68亿方,其中航道北侧冲刷量占87.9%,主槽上段冲刷深度最大,平均1.40m,下段次之(南侧0.10m北侧0.79m),中段淤积(南侧1.28m北侧0.59m)。此外,还发现北槽河床冲淤分布,主要受整治工程影响,疏浚抛泥仅影响贮泥坑和抛泥区附近的局部区域,流域来沙量变化对北槽淤积量变化影响很小。