The observations of seabed sediment erosion and resuspension processes in the Jiaozhou Bay in China

In estuarine and coastal areas, the seabed is in a constant process of dynamic change under marine conditions.Seabed sediment erosion and resuspension are important processes that safely control the geological environment. Field tripod observations conducted in the Jiaozhou Bay in China are reported, to investigate the effects of hydrodynamic conditions on the erosion and resuspension processes of the seabed. The observational results show that the maximum shear stress created by tidal currents can reach 0.35 N/m2, which is higher than the wave-induced shear stress during fair weather conditions. A seabed erosion frequently occurs during the flood tide, whereas a seabed deposition occurs during ebb tide. Waves can produce a bottom shear stress approximately equivalent to that induced by currents when the local wind reaches Force 4 with a speed of 5 m/s.When the wind reaches 7 m/s and the significant wave height reaches 26 cm, waves play a more significant role than currents in the dynamic processes of the seabed sediment resuspension and lead to a high value of turbidity that is approximately two to eight times higher than that in fair weather. These analyses clearly illustrate that periodic current-induced sediment erosion and resuspension are dominant in fair weather, whereas episodic high waves are responsible for significant sediment resuspension. Additional work is needed to establish a more thorough understanding of the mechanisms of sediment dynamics in the Jiaozhou Bay.

Seabed deposition and erosion change and influence factors in the Yangshan Deepwater Port over the years

The seabed scouring and silting are very important to the construction of port and waterway engineering. Seabed deposition and erosion change is complicated due to the influence of sediment supply, human activities and other factors. The Yangshan Deepwater Port is the new deep water harbor, which is an important part of the Shanghai International Shipping Service Center. Its construction has received much attention. At present, the water depth from the 1 st to the 3 rd harbor district is currently suitable under regular dredging and tidal current action. The fourth harbor district will be built in the world’s largest fully-automated deep water wharf. In the study, bathymetry change of the entire sea area of the Yangshan Deepwater Port and the 4 th harbor district(i.e.,Phase IV project) waters were analyzed quantitatively using multiyear bathymetric, hydrological and sediment data. The results show that from 1998 to 2010, seabed changes are characterized by large volumes of erosion and sedimentation, which the southern part was deposited and the northern part was eroded in the inner harbor waters, but the seabed of the Kezhushan inlet was eroded. Seabed changes of Phase IV project waters generally show a scour tendency in recent few years with the annual scour rate about 0.7 m. Among the many factors, the existence of Kezhushan inlet and its influence of the western water flow play an important positive role in water depth changes under the ebb tide action.

Second sea－entering approach of Changjiang River： Tongl Canal－planning of control dimensions， analysis of erosion and siltation and selection of outlet

Assume that the Tonglu Canal would be widened and deepened in which a water lock is constructed atthe river side, and made open to the sea side. The canal's planned control dimensions are determined, and the erosionand siltation characteristics along the river (totally 81. 8 km) are analyzed by the numerical calculation of one-dimen-sional unsteady flow and the relative standards. According to the data of the evolution, hydrology and sediment inthe Xiaomiaohong Waterway, it is found reasonable to select the channel near the Xingang Gate as the second sea-entering approach. This paper is helpful in planning and designing the approach.

Integrated Evaluation of Soil Erosion Hazard and Risk Management in the Oued Beht Watershed Using Remote Sensing and GIS Techniques: Impacts on El Kansra Dam Siltation (Morocco)

The initial state of the Oued Beht watershed (430,728 ha) is characterized by a socio-ecological vulnerability associated to the water erosion risk. Especially, the consequences are chained and the soil loss alters its hydrological behavior and its ability to protect functional and structural challenges (good land, El Kansra dam, agricultural activities). In this perspective, this study suggests a methodology, reproducible and generalizable, to assess the natural water erosion risk (R). The approach used is based on spatial processing technology of information to develop a spatial database and geographic information system (GIS) concerning biophysical and?topoclimatic parameters in the Oued Beht watershed. Thus, the risk analysis is obtained by combining thematic maps of Susceptibility (S) and potential Consequences (C). Although, the spatial analysis of maps obtained reveals the extent of susceptibility involving land degradation, with the potential risks, which generated a decrease in the storage capacity of El Kansra dam (?3.03 Mm3/year). The results show that erosion is active on more than three quarters (3/4) of the watershed, and a considerable loss of land with 8.36 Million tonnes per year. In this way, flood analysis and study of?hydrometeorological events identified the vulnerability of flood sites (hot-spot) contributing at 77%?of El Kansra siltation dam. Therefore, the consequence assessment is obtained by identifying risk elements and estimating potential damage coefficient, which represents the financial gap flow affecting the socio-economic context due to the erosion impacts.

Sediment movement characteristics of coast and analysis of seabed evolution

The rotary ring flume is used to study the silty sand movement in a periodic alternating current.Characteristics of sediment movement of different coasts in the tidal current are summarized.More detailed analysis of erosion-sedimentation function in a numerical simulation is made.The equilibrium sediment concentration is advanced.Based on the equilibrium sediment concentration,the seabed erosion-sedimentation index is derived and the seabed erosion-sedimentation calculation is analyzed.The seabed erosion-sedimentation index is used to calculate the seabed evolution of Yangshan sea area and a good agreement with field measurements is obtained.

1300—2019年江苏沿海风暴潮灾害时空分布特征

历史上江苏沿海曾频发2类风暴潮灾害,给当地带来了巨大损失。建立该地区长时间尺度的风暴潮灾害序列对了解过去与预测未来意义重大。以历史文献、地方志、海洋灾害公报等记载的风暴潮资料为基础,建立了风暴潮灾害识别体系,重建了1300—2019年江苏沿海风暴潮灾害序列,分析了风暴潮灾害时空变化规律,探究了其与气候异常和黄河、长江入海口变迁之间的关系。结果表明:江苏沿海地区主要受台风风暴潮灾害的影响,1300—2019年间共发生246次风暴潮灾害,平均周期为2.9年,且近100年来发生频率有增大的趋势;小波分析结果显示,风暴潮灾害年际变化存在17年、61年和115年的时间尺度周期,其中115年周期最为明显。海气相互作用影响下,厄尔尼诺活跃年江苏沿海台风风暴潮灾害偏少;气温与台风风暴潮灾害频次有一定的正相关性,但其影响机制尚不明确。盐城、南通和苏州为风暴潮灾害高发地区,常州和无锡发生频率较小。在气候变暖与江苏海岸冲淤变化的作用下,1855年后盐城和南通地区风暴潮灾害发生频率增加,连云港地区明显增加;随着海岸线的变迁与长江河口的演变,镇江、扬州、泰州与苏锡常地区受风暴潮灾害影响减少。

六垛南闸闸下淤积加重原因及防淤减淤策略分析

江苏灌溉总渠六垛南闸近年来闸下河道淤积明显加重,通过实测资料分析近年来灌溉总渠水沙条件变化特征及闸下淤积加重的原因,认为潮波变形引起的河口不平衡输沙是闸下淤积的根本成因,近年来上游来水减少及河口侵蚀加剧是闸下淤积加重的主要原因。进而总结了潮汐河口闸下淤积的机理和关键控制因素,并结合挡潮闸冲淤调度实践,提出了六垛南闸闸下清淤的策略和措施,认为下泄流量对闸下河道冲淤平衡起着决定性作用,水力冲淤辅助机械扰动可以大幅提升清淤效率,可作为六垛南闸清淤的常规措施。

考虑清淤策略的桩基时变可靠度分析

为发展淤积岸坡-高桩码头相互作用体系结构可靠性分析方法,基于Fick第二定律推导了能考虑氯离子侵蚀效应的二维扩散模型,并采用时间离散法提出了一种综合考虑结构抗力衰减、淤积作用量化和预测,以及桩基受力变形分析的高桩码头桩基时变可靠度数值计算方法。并结合以目标可靠度为导向的清淤策略,编写了淤积岸坡-高桩码头体系时变可靠度外挂求解程序DPRP。在此基础上,开展了多工况计算分析,探讨了高桩码头桩基时变可靠度的演化规律。计算分析结果表明:码头近海侧桩基可靠度更易低于目标可靠度,在实际工程中需重点养护与修复;泥沙淤积作用会降低多数桩基时变可靠度,而对于近海侧及近岸侧且向岸倾斜的斜桩,其时变可靠度则会因泥沙淤积作用而增大。该高桩码头桩基时变可靠度数值求解流程框架及对应外挂子程序DPRP,可为高桩码头-岸坡相互作用体系的相关工程设计与可靠性评价提供参考。

钢圆筒防护装置周围海床冲淤试验研究

通航区内水下油气生产系统需安装在海床下的钢圆筒防护装置内,以避免往来船舶抛锚、渔业活动等对油气开发设备产生破坏。为揭示海床下钢圆筒防护装置局部冲淤特性,同时验证工程设计方案的可靠性,基于通航区海床下水下生产系统钢圆筒防护装置,对周围土体冲淤特性开展试验研究。根据工程区域现场土样的级配资料配制现场土样,并对不同回填土质的水动力特性进行敏感性分析,得到不同回填土质临界起动流速,为工程回填材料选择提供参考。同时针对平整海床、凸出式和齐平式防护装置类型,开展模型试验研究。结果表明,基于工程场址土壤条件,在安装钢圆筒防护装置、设置回填材料等各种情况下冲淤量很小,均不会发生明显的冲淤现象。现场实测验证了设计方案冲淤试验结果的可靠性。研究结果可为海床下防护结构的设计提供参考。

入海水沙变化背景下黄河三角洲岸线冲淤研究

受黄河入海流路变迁和入海泥沙锐减的影响,近年来黄河三角洲岸线冲淤变化复杂。本研究基于Landsat遥感影像,提取2000—2020年黄河三角洲的年平均岸线,分析其岸线冲淤变化。结果显示,北部岸段和原清水沟入海水道岸段岸线呈现蚀退作用,现清八汊入海水道岸线呈现淤积作用。

基于多源数据融合的河道冲淤监测技术

开展河道陆上和水下地形测量时,单一的测量方法和孤岛数据已经满足不了河道数字化发展。提出了基于多无人智能系统协同采集河道数据,融合构建三维模型,计算分析冲淤量的监测技术方案,并开展了荆州长江大桥冲淤监测项目和公安河弯段河道地形观测项目试验。结果表明:该技术方案精度能够满足大比例尺河道冲淤监测项目要求,构建的三维模型能提升监测数据整体质量;三维模型平面精度高,在陆上三维模型高程精度方面,低密度植被覆盖的区域有94.2%的点误差在0.25 m以内,高密度植被覆盖的区域有82.91%的点误差在0.25 m以内;项目监测效率整体提升20%以上。该技术方案与传统作业方式相比,数据产品形式更加丰富,监测质量和效率明显提高,在大部分河道测区具有较高的可行性。

Mapping of Soil Erosion Zones of Meghadrigedda Catchment, Visakhapatnam, India for Conservation <br/>—A Geospatial Approach

Meghadrigedda, a non-perennial drainage system is one of the major water resources of Vishakhapatnam city located in the northern coastal region of Andhra Pradesh, India. It traverses through the hilly terrain of Eastern GhatMobile Belt (EGMB) characterized by khondalitic rock formations. Excessive siltation scenario aggravated due to soil erosion in its catchment is threatening the very existence of Meghadrigedda reservoir. In order to assess the intensity of soil erosion as well as silt deposition in the reservoir, an integrated study has been undertaken which takes into consideration various topographic, morphological, soil, and land use/land cover characteristics of the basin. The study aims at identification and mapping of erosion prone zones with respect to silt deposition using remote sensing and GIS techniques.Alteration in human induced land use practices in its catchment due to rapid growth in population, urbanization and industrialization are found to be of prime reasons for various forms of erosion. The study has noticed that various forms of erosion like sheet, gully and stream erosion are responsible for the siltation at large scale which is causing reduction of its designed storage capacity by 40%. Various sub-watersheds of the basin have been prioritized on the basis of erosion intensity for suggesting various mitigation measures like check-dam construction, afforestation etc. to protect the reservoir from the silting problem.

汊道汇流段通道建设条件及防洪河势影响研究

针对南京仙新路过江通道复杂水动力及河床冲淤变化的问题,采用定、动床河工模型试验,对八卦洲汊道下游汇流段过江通道建设条件以及工程方案防洪及河势影响进行了研究分析,为工程建设提供技术支撑。

1985年以来黄河三角洲东营港工程变化与海床冲淤演变响应关系

河口三角洲区域地质环境脆弱,对环境变化响应敏感,三角洲港口冲淤演变受工程结构影响较大。黄河三角洲的东营港区域以粉砂质海岸为主,区域内泥沙运移活跃,此类区域港口建设的关键问题在于工程结构导致的海床冲淤变化。通过东营港建港以来实测水深数据构建水下地形数字高程模型(DEM),并结合水动力数值模拟,探讨了东营港冲淤演变过程和工程影响。结果表明,由于波浪和潮流导致的海底地形变化,东营港近岸海域的冲淤演变形势已从单一侵蚀转变到近岸侵蚀、离岸淤积的新情势;工程结构影响局地潮流流速和流向,口门处出现高速横流,最大流速可达0.7 m/s;高流速导致北防波堤的堤头位置出现直径约1 km的冲刷坑;工程结构的遮蔽区有促淤效应,遮蔽区大小与潮流流向、工程结构-岸线夹角有关,但在波浪、余流的作用下,2007-2015年工程结构遮蔽区依旧存在0.5 m以上的侵蚀。持续的侵蚀作用使海域防波堤和海堤的不稳定性加剧,迫切需要加强检测与防护。

日照北部重点海滩侵蚀现状与保护对策研究

分析了日照海滨国家森林公园海滩和日照万平口海水浴场海滩剖面在“温比亚”“利奇马”两场台风过境前后的监测数据,认为台风是引起海滩侵蚀淤积的一个重要因素。海滨国家森林公园海滩2个探槽均表现出浅部样品的分选性优于深部的特点,南部探槽样品的分选性优于北部探槽;万平口海水浴场海滩3个探槽均表现出中部样品的分选性优于浅部和深部的特点,中部和南部探槽样品的分选性优于北部探槽。这些数据可为滩肩抛沙提供粒径依据。海滨国家森林公园海滩北部和万平口海水浴场海滩宜采用人工养滩和离岸潜堤相结合的方法,以达到海滩保护修复的目的,可实现生态环境影响较少,无损于视觉景观的效果。

1980年以来山东文登张家埠港冲淤演变分析

山东文登张家埠港位于山东半岛南部的靖海湾,属于潮汐汊道-溺谷型海湾,研究其冲淤演变特征,对于认识这类海湾的动力地貌演变以及人类活动对海湾的影响具有一定参考价值。本文基于1980、1997、2009和2021年4年份的海图水深资料,采用GIS技术进行等深线叠加分析和数字化定量冲淤计算,分析1980年以来张家埠港航道地区的等深线变化、平面冲淤变化及固定剖面的地形变化。结果表明:1980−2021年,张家埠港整体处于淤积态势,平均淤积厚度为1.08 m;0 m等深线整体向航道中心淤进,5 m等深线淤积变浅面积减少了67.01%;航道在塘子咀至长会口咀岸段西侧的淤积厚度远大于东侧。自1980年以来,张家埠港两侧养殖池的修建改变了当地的潮流状况,导致航道内由淤积转为侵蚀状态,长会口外的拦门沙被迫下移,张家埠港的地貌发生了深刻变化。

渤海湾曹妃甸深槽断面监测研究进展

通过研究曹妃甸海区2021年实测水深和浅地层剖面资料,结合2004、2008和2013年历史资料,在区域和深度上对曹妃甸深槽海底地形进行动态对比。研究发现,深槽南侧海底冲刷作用较强烈,局部冲-淤速率最大可达-65 cm/a,这种现状有利于维持深槽水深,深槽轴线移动不明显,但35和40 m等深线均有南移趋势,最大外移距离约1 000 m。深槽地貌形成是海洋水体潮流水动力、古滦河三角洲演变和地质构造等内外营力综合作用的结果,结合浅地层剖面对比分析发现,深槽底部缺失全新世晚期海相沉积层,海底出现新的滑塌和侵蚀洼地等海洋地质灾害,对曹妃甸港带来一定的安全隐患,应加强深槽监测工作。

长江口拦门沙段滩涂形态调整及冲淤响应机制

为研究长江口拦门沙段重要滩涂对水沙条件改变及人类活动的响应机制,以横沙浅滩、九段沙及南汇东滩为例,分析了拦门沙段重要滩涂的平面形态调整特点及其对环境因素变化的响应过程,并建立了代表滩涂面积与汛期水沙条件间的经验关系。结果表明,横沙浅滩、九段沙及南汇东滩近年来滩涂平面形态呈萎缩态势、沙尾总体滞涨,且横沙浅滩及九段沙有不同程度的串沟发育现象;横沙浅滩面积与前7年平均的汛期水流冲刷强度具有良好的幂函数关系,反映了浅滩面积随水沙条件变化的滞后响应过程;河口治理工程对滩涂局部的守护能较快抑制水沙条件改变所引起的冲刷,但其对周边区域可能产生缓慢、长期的累积影响。

三维水下黏质斜坡海床变形冲蚀特征试验研究

以舟山某海域的某三维斜坡海床为原型,开展一系列大型波浪港池试验,探究波浪作用下三维黏质斜坡海床的孔压响应、变形及冲蚀破坏特征。研究结果表明:当波高较小时,黏质斜坡海床内部的超孔压累积不明显,多表现为振荡孔压;当波高逐渐增大时,黏质斜坡发生由坡顶到坡脚的浅层破坏,在靠近坡脚处出现明显的黏土碎屑状堆积,海床内超孔压表现为先累积后消散,其变化规律与海床冲蚀失稳特征密切相关。

大鱼山填海工程对海床冲淤变化影响分析

根据舟山大鱼山海域1960—2021年间5个年份的水深地形资料,基于GIS(地理信息系统)技术采用数字化定量冲淤计算和特征等深线叠加方法,对工程附近典型水下地形的平面冲淤和平面形态变化规律进行研究,探讨大鱼山填海工程对周边海床冲淤变化的影响。结果表明:自然状态下,研究区整体处于轻微冲刷状态;填海后,南侧深槽近岸淤积,外侧和北侧深槽继续冲刷,东西两侧浅滩呈现大幅度淤积。大鱼山填海工程极大地改变了原本岸线分布以及周边水动力泥沙环境,最终导致填海区附近海床冲淤变化,但整体仍维持海底的潮滩分布格局。