Extreme Events Assessment Methodology Coupling Debris Flow,Flooding and Tidal Levels in the Coastal Floodplain of the Sao Paulo North Coast(Brazil)

The North Coastal Region of the State of S?o Paulo, which comprises the Municipalities of Caraguatatuba, S?o Sebasti?o, Ilhabela and Ubatuba, is one of the most prone to flooding and debris flow deposition Brazilian areas, owing to hydrological extreme rainfall events usually coupled with extreme tidal levels. This risk is also high due to human lives and material assets, with increasing population rates and the establishment of large companies such as the Oil industry, with reduced defense/prevention measures and works.The catastrophic scenario of the city of Caraguatatuba, in March 1967, resulting from one of the most serious natural disasters in Brazil, fosters discussions about probabilities of heavy rainfall-caused events and rise in the sea level in coastal areas. Hence, this research is a consequence of this reality. The research is founded on an innovative methodology based on the analysis of past data of rainfall and tidal stations, complemented with debris flow registers in the region of the north coastal zone of the State of S?o Paulo (Brazil). The anaysis developed involved the meteorological, hydraulic, geotechnical and statistical knowledge areas.Practical results are intended to be used for urban planning, designs of macro-drainage, fluvial, maritime projects and debris flow retention structures. These practical applications will then associate the probability of occurrence of certain types of heavy rainfall-caused events such as flooding or debris flow coupled with a corresponding increase in tidal levels.

Tidal Level Response to Sea-Level Rise in the Yangtze Estuary

The rise of tidal level in tidal reaches induced by sea-level rise has a large impact on flood control and water supply for the regions around the estuary. This paper focuses on the variations of tidal level response along the tidal reaches in the Yangtze Estuary, as well as the impacts of upstream discharge on tidal level response, due to the sea-level rise of the East China Sea. Based on the Topex/Poseidon altimeter data obtained during the period 1993-2005, a stochastic dynamic analysis was performed and a forecast model was run to predict the sea-level rise of the East China Sea. Two- dimensional hydrodynamic numerical models downscaling from the East China Sea to estuarine areas were implemented to analyze the rise of tidal level along the tidal reaches. In response to the sea-level rise, the tidal wave characteristics change slightly in nearshore areas outside the estuaries, involving the tidal range and the duration of flood and ebb tide. The results show that the rise of tidal level in the tidal reaches due to the sea-level rise has upstream decreasing trends. The step between the stations of Zhangjiagang and Shiyiwei divides the tidal reaches into two parts, in which the tidal level response declines slightly. The rise of tidal level is 1-2.5 mm/a in the upper part, and 4-6 mm/a in the lower part. The stations of Jiangyin and Yanglin, as an example of the upper part and the lower part respectively, are extracted to analyze the impacts of upstream discharge on tidal level response to the sea-level rise. The relation between the rise of tidal level and the upstream discharge can be fitted well with a quadratic fimction in the upper part. However, the relation is too complicated to be fitted in the lower part because of the tide dominance. For comparison purposes, hourly tidal level observations at the stations of Xuliujing and Yanglin during the period 1993-2009 are adopted. In order to uniform the influence of upstream discharge on tidal level for a certain day each year, the hourly tidal level observations are corrected by the correlation between the increment of tidal level and the increment of daily mean upstream discharge. The rise of annual mean tidal level is evaluated. The resulting rise of tidal level at the stations of Xuliujing and Yanglin is 3.0 mm/a and 6.6 mm/a respectively, close to the rise of 5 mm/a according to the proposed relation between the rise of tidal level and the upstream discharge.

Mean water level setup/setdown in the inlet-lagoon system induced by tidal action—a case study of Xincun Inlet,Hainan Island in China

With the tides propagating from the open sea to the lagoon, the mean water level （MWL） in the inlet and lagoon becomes different from that at the open sea, and a setup/setdown is generated. The change of MWL （setup/setdown） in the system imposes a great impact on regulating the development of tidal marshes, on determining the long-term water level for harbor maintenance, on the planning for the water front development with the flood control for the possible inundation, and on the interpretation of the historical sea level change when using tidal marsh peat deposits in the lagoon as the indicator for open sea＇ s sea level. In this case study on the mechanisms which control the setup/setdown in Xincun Inlet, Hainan in China, the 2-D barotropic mode of Eulerian - Lagrangian CIRCulation （ELCIRC） model was utilized. After model calibration and verification, a series of numerical experiments were conducted to examine the effects of bottom friction and advection terms, wetting and drying of intertidal areas, bathymetry and boundary conditions on the setup/setdown in the system. The modeling results show that setup occurs over the inlet and lagoon areas with an order of one tenth of the tide range at the entrance. The larger the bottom friction is, a larger setup is generated. Without the advection term, the setup is reduced clue to a decrease of water level gradient to compensate for the disappearance of the advection term. Even without overtides, a setup can still be developed in the system. Sea level rise and dredging in the inlet and tidal channel can cause a decrease of setup in the system, whereas shoaling of the system can increase the setup. The uniqueness of the Xincun Inlet with respect to MWL change is that there is no evident setdown in the inlet, which can be attributed to the complex geometry and bathymetry associated with the inlet system.

Effect of Sea Level Variation on Tidal Characteristic Values for the East China Sea

Tidal waves in the East China Sea are simulated numerically with POM(Princeton Ocean Model) model for normal mean sea level, 30 cm higher, 60 cm higher, and 100 cm higher, respectively, and the simulated result is compared with the harmonic analysis result of hourly sea level data from 19 tide gauges for more than 19 years. It is indicated that the long-term mean sea level variation affects notably tidal waves in this region. Generally, the tidal amplitude increases when the mean sea level rises, but this relationship may be inverse for some sea areas. The maximal variation of tidal amplitude takes place in the zones near the Fujian coast and the Zhejiang coast, rather than the shallowest Bohai Sea. The maximum increase of M2 amplitude can exceed about 15 cm corresponding to the 60 cm rise of the mean sea level along the Fujian coast. The other regions with large variations of tidal amplitude are those along the Jiangsu coast, the south-east coast of Shandong, and the south-east coast of Dalian. The propagation of tidal waves is also related to mean sea level variation, and the tidal phase-lag decreases generally when the mean sea level rises. Almost all the regions where the tidal phase-lag increases with rising mean sea level are close to amphidromic points, meanwhile the spatial area of such regions is very small. Because the influence of mean sea level variation upon tidal waves is spatially marked, such spatial effect should be considered in calculation of the tidal characteristic value and engineering water level. In the region where the amplitudes of the major tidal constituents increase, the probable maximum high water level becomes higher, the probable maximum low water level becomes lower, and both design water level andcheck water level increase obviously. For example, the design water level at Xiamen increases by 13.5 cm due to the variation of tidal waves when the mean sea level rises 60 cm, the total increase of design water level being 73.5 cm.

The impact of coastal reclamation on tidal and storm surge level in Sanmen Bay, China

In recent years,fast economic development demands for more land use and thus many reclamation projects are initiated around the Sanmen Bay,Zhejiang,SE China in the East China Sea,for which tidal and storm surge levels are reassessed.A two-dimensional numerical model based on an advanced circulation model(ADCIRC)was applied to evaluate the impact of reclamation projects on tidal and storm surge levels in the bay.The results show that the shoreline relocation and topographic change had opposite effects on tidal heights.Shoreline relocation decreased the tidal amplitude,while siltation caused topographic change and increased the amplitude.Such variations of the amplitude were significant in the top areas of Sanmen Bay.Three types of typhoon paths were selected for a case study to investigate the impacts of shoreline relocation and topographic change on storm surge level.Results show that the maximum increase in storm surge level due to shoreline relocation was less than 0.06 m.The rise of peak surge level due to the change of topography was significant and the peak surge level rose when siltation increased.The maximum surge level rise occurred in the path of northwest landing typhoons,which exceeded 0.24 m at the top of the bay.The rise in peak surge level can potentially lead to severe damages and losses in Sanmen Bay and more attention needs to be paid to this problem of shoreline change in the future.

A method to calculate design tide levels on the basis of numerical model of tidal current and its application

In order to determine the design tide levels in the areas without measured tide level data, especially in the areas where it is difficult to measure tidal levels, a calculation method based on a numerical model of tidal current is proposed. The essentials of the method are described, and its application is illustrated with an example. The results of the application show that the design tide levels calculated by the method are close to those determined by long-time measured tide level data, and its calculation precision is high, so it is feasible to use the method to determine the design tide levels in the areas.

Tidal Response Characteristics of the Well Water Level in the Sichuan-Yunnan Region

In this paper,the long time series data of the well water-level data of 12 wells in the Sichuan and Yunnan area is analyzed by the Baytap-G tidal analysis software,and well water level tidal response characteristic parameters( amplitude ratio and phase change)are extracted. We analyzed the features of the shape and stage change,and characteristic parameters of the tidal response of well water level before and after the earthquakes,which can provide a new method and approach to analyzing the response relationships between well water level and earth tide and barometric pressure. The results show that Luguhu Well and 9 other wells are affected by earth tides,and their well water level amplitude ratios and phases are relatively stable; the Nanxi Well and Dayao Well water level changes are affected by the barometric pressure combined with tide force,and their well water level amplitude ratios and phases are more discrete. The water level amplitude ratios and phases of Jiangyou Well,Luguhu Well and Dongchuan Well are significant to large earthquakes,and the relationship between seismic energy density and water level amplitude ratios and phases of M_2 wave of the three wells are presented.

杭州湾北岸现代潮滩沉积物粒度特征及其对古海平面的指示意义

对杭州湾北岸3处现代潮滩沉积物进行高精度粒度分析,查找研究区潮滩不同微相的粒度特征和差异,提取基于粒度分析的潮滩微相识别敏感指标,并将其应用到该区域的全新世钻孔潮滩沉积物中,识别钻孔潮滩沉积微相,据此建立研究区全新世早期的海平面曲线。研究表明:杭州湾北岸现代高潮滩盐沼沉积物粘土含量明显高于高潮滩下部和中潮滩,而砂含量与之相反;高潮滩盐沼平均粒径等粒度参数明显小于中、高潮滩的粒度参数;盐沼沉积物粒度频率曲线峰态宽缓,明显区别于高潮滩下部和中潮滩。上述现代潮滩微相粒度敏感指标可成功应用到钻孔潮滩沉积微相划分中,并建立了该区域全新世早期海平面曲线。曲线显示,9700~8700 cal a BP期间海平面上升约11.6 m,海平面上升速率可达1.2 cm/a。现代潮滩不同位置沉积物粒度参数的规律性差异可作为潮滩微相识别的有效指标,为古潮滩沉积微相识别和古海平面重建提供参考依据。

2023年2月6日土耳其两次7.8级地震引起的井水位同震响应对比分析

2023年2月6日,土耳其发生的两次7.8级地震引起了新疆乌鲁木齐地区新04井、新10井和新11井的同震响应,但同震变化形态各有不同。本文对比分析了这三口观测井水位的同震响应特征,探讨了地震引起的井水位同震响应机理。结果显示,本研究中的三口观测井水位的同震响应类型有振荡、同震下降和同震上升三种。其中,新10井表现为振荡,而新04井和新11井则分别表现为同震下降和上升,表明井水位同震变化机理的复杂性。两次地震在同一观测井的同震响应形态一致,不同观测井水位同震变化与井孔所在位置的渗透性结构改变有关。

合理确定排涝泵站规模的感潮河道模型试验研究

合理确定泵站规模一直是感潮河道排涝工程设计中的关键问题。通过建立物理模型,在选定的水文边界条件和相应工程运行要求下,对某感潮水系两座涌口泵站规模进行试验研究。试验发现,受限于河涌过流能力,泵站规模存在临界值,超过该值后,即使再进一步增加泵站规模,水位也不会继续下降;泵站抽排对某位置水位的降低效应与泵站和该位置之间的距离密切相关,距离越近,水位降低越明显。基于上述认识,通过试验确定了满足水位管控要求的两座泵站规模的合理组合:距离相对较远的温涌泵站为80 m3/s,较近的金紫涌泵站为130 m~3/s。试验方法和主要成果可为工程方案比选及优化提供重要依据,对类似河涌整治工程也具有一定的借鉴意义。

江苏沿海台风风暴潮特征分析

收集了1950—2022年影响江苏沿海的历史台风风暴潮过程资料,对引起江苏沿海台风风暴潮的台风路径进行了分类和分析,开展了江苏沿海台风风暴潮的月际分布和年际变化研究,提出了不同路径台风风暴潮的预报要点。结果表明:引起江苏沿海台风风暴潮次数最多的是外海转向型台风,占比高达44.3%,而正面登陆型台风最少,占比只有5.4%,但引起的增水量值最大;江苏沿海台风风暴潮在6—10月均有出现,8月出现次数最多;风暴潮强度等级为Ⅴ级(增水50~100 cm)的过程占比最多,为42.7%,而高潮位超警戒程度等级为Ⅳ级(超警戒30 cm之内或达到黄色警戒潮位值)的占比最多,为45.0%;风暴潮发生次数在近几年呈上升趋势,尤其是增水为50~100 cm的过程,高潮位超警戒或达到黄色警戒潮位值以上的过程在近20年只出现3次;在江苏沿海台风风暴潮的预报和应对中,需要重视可能正面登陆的和9—10月的外海转向型台风;8月和9月是江苏沿海出现风暴潮灾害可能性较高的月份,若这两个月的天文高潮与风暴增水叠加合适,极有可能出现达到黄色警戒潮位以上的高潮位。

PPK技术在海洋倾倒区潮位测量中的方法研究

在分析传统潮位测量和RTK潮位测量缺陷的基础上,基于PPK技术开展海洋倾倒区潮位测量方法研究。系统介绍了PPK技术原理及PPK潮位测量体系,对数据进行后处理,利用姿态参数修正天线高,采用小波分析、拟合平滑的方法滤除波浪,提取大地高潮位信息,并基于EGM2008重力场模型结合水准控制点进行基准转换,得到85基准下的PPK潮位数据。试验结果表明,PPK潮位精度与验潮站潮位基本一致,可靠性高,能够广泛应用于海洋倾倒区潮位测量中。

六垛南闸下游引河泥沙淤积特性数值分析

为了明确六垛南闸下游引河的淤积特性,基于Mike软件数值计算求解了该闸下游引河的水沙运动,对闸下引河冲淤进行了预测分析,并通过闸下实测水位和预测水位进行对比验证了计算模型的正确性。结果表明:各泄流量时下游引河的水流均为顺岸流动,流速分布规律相同;相同流量时沿程流速整体呈增大趋势。闸下引河的冲淤特性呈现出潮位越低,冲淤量越大的特点。建议六垛南闸开闸冲淤应尽量选择入海口潮位<0.3m时进行,同时可按照10d一个周期进行开闸冲淤。研究成果可为江苏省同类沿海挡潮闸防淤减淤提供参考。

台风风暴潮与上游洪水耦合作用下温州飞云江感潮河段潮水位模拟研究

在全球气候急剧变化的背景下,沿海地区风暴潮发生的频率与受灾程度逐渐增加,特别是受风暴潮与上游流域洪水共同影响下的河口感潮河段区域。尽管现有风暴潮模型也引入多种不同的边界设置,但提供的边界条件有限,且无法满足当前国内复杂水工程的概化需求。为此,文章以飞云江流域为研究对象,通过耦合上游流域水动力模型IFMS与海洋风暴潮模型ADCIRC模式,充分发挥二者各自的优势,构建河口感潮河段洪水演进模型,实现飞云江感潮河段潮水位时空模拟。该模型不仅有效地考虑了河口海洋处风暴潮上溯对感潮河段区域洪水演进的影响,也考虑了流域上游洪水对该区域的影响。首先,采用2016年台风“鲇鱼”对模型进行验证,模拟结果与实测系列吻合度较高,误差满足基本要求。然后,对台风“杜苏芮”和“卡奴”影响下的瑞安、马屿、碧山六桥及洞头4个潮位站的洪水过程进行模拟,结果显示4个站点的洪峰误差值均低于0.30m,纳什系数大于0.80,表明该模型能较好地反映高低潮位变化,可应用于河口感潮河段防灾减灾中。最后,还分析了上、下游边界的驱动作用对感潮河段3个站点(瑞安、马屿、碧山六桥)潮水位预测的影响,证明了下边界对3个站点的潮水位预报影响比上边界的影响大。研究成果不仅为河口感潮河段洪水模拟提供了一种新方法,而且通过分析给出提升模型模拟精度的方向。

A precise tidal prediction mechanism based on the combination of harmonic analysis and adaptive network-based fuzzy inference system model

An efficient and accurate prediction of a precise tidal level in estuaries and coastal areas is indispensable for the management and decision-making of human activity in the field wok of marine engineering. The variation of the tidal level is a time-varying process. The time-varying factors including interference from the external environment that cause the change of tides are fairly complicated. Furthermore, tidal variations are affected not only by periodic movement of celestial bodies but also by time-varying interference from the external environment. Consequently, for the efficient and precise tidal level prediction, a neuro-fuzzy hybrid technology based on the combination of harmonic analysis and adaptive network-based fuzzy inference system（ANFIS）model is utilized to construct a precise tidal level prediction system, which takes both advantages of the harmonic analysis method and the ANFIS network. The proposed prediction model is composed of two modules： the astronomical tide module caused by celestial bodies’ movement and the non-astronomical tide module caused by various meteorological and other environmental factors. To generate a fuzzy inference system（FIS） structure,three approaches which include grid partition（GP）, fuzzy c-means（FCM） and sub-clustering（SC） are used in the ANFIS network constructing process. Furthermore, to obtain the optimal ANFIS based prediction model, large numbers of simulation experiments are implemented for each FIS generating approach. In this tidal prediction study, the optimal ANFIS model is used to predict the non-astronomical tide module, while the conventional harmonic analysis model is used to predict the astronomical tide module. The final prediction result is performed by combining the estimation outputs of the harmonious analysis model and the optimal ANFIS model. To demonstrate the applicability and capability of the proposed novel prediction model, measured tidal level samples of Fort Pulaski tidal station are selected as the testing database. Simulation and experimental results confirm that the proposed prediction approach can achieve precise predictions for the tidal level with high accuracy, satisfactory convergence and stability.

围填海工程对九龙江河口纳潮量影响研究

纳潮量是海湾可以接纳的潮水体积,对维护海湾良好的生态环境至关重要。文章首先针对围填海工程所在厦门九龙江河口的自然条件进行了分析。其次,分别采用传统计算方法、实测水文资料统计以及经充分验证的二维潮流数值模型对九龙江河口现状条件下的纳潮量进行了统计计算。最后,采用数值模拟手段对厦门港海沧港区围填海工程建成后九龙江河口水流特征、潮位变化和纳潮量变化进行了模拟计算,并采用传统计算与数值模拟相结合的方法对其进行了合理性分析。研究结果表明:海沧港区围填海工程面积约为2.95 km^(2),工程实施后九龙江河口纳潮量减少率约为4.3%。

长江下游感潮河段水闸引排水能力的计算模型应用——以新孟河界牌水利枢纽为例

针对长江下游感潮河段水闸引排水调度的精细化需求,以新孟河界牌水利枢纽为研究对象,构建潮位预报与引排水流量计算模型。采用多元线性回归分析潮汐特性,结合镇江站与新孟河闸的水位实测资料,建立镇江站潮位动态预报方案。在此基础上,推求新孟河闸的过程水位,并构建闸下水位与引排水流量的函数关系,实现潮周期内引排水流量的精细化计算以满足水利枢纽调度需求。研究成果可为长江下游感潮河段水闸引排水调度提供理论方法和技术支撑。

沉积成因Sr/Ba指示的福建潮控海湾全新世沉积环境及海平面意义

福建沿海多发育潮控型海湾,潮滩平坦宽广,海湾水深较浅,有孔虫等微体生物较为匮乏,且其化石在地层中保存相对较差,致使沉积微相辨识存在一定难度,从而限制了深入理解该区全新世海平面变化过程及沉积环境响应。本研究拟利用不受保存环境限制的沉积成因Sr/Ba指标,探索其在福建宁德三沙湾地区沉积微相的辨识潜力,并结合AMS 14C年龄,探讨该区全新世以来的沉积环境演化及区域海平面变化。结果表明:①沉积成因Sr/Ba在三沙湾潮滩和海湾表层沉积物中平均值分别为9.06和20.43,具有显著差异。潮滩沉积物中的Sr/Ba明显高于长江等大河口地区(1~3),这是该区淡水输入量较少、潮滩盐度较高所致,这说明该指标辨识海陆过渡沉积相时需要考虑区域水文特点。②晚第四纪NDGK2钻孔沉积物Sr/Ba自下而上可分为3层(Ⅰ—Ⅲ):层Ⅰ为杂色硬黏土,Sr/Ba比值全孔最低(均值5.29),但也高于淡水环境,推测为前期海相沉积物的暴露改造;层Ⅱ—Ⅲ均为深灰色黏土,其中层Ⅱ均值为10.77,接近潮滩相;层Ⅲ均值为全孔最高(13.44),接近海湾相。结合AMS 14C年龄可知,NDGK2钻孔的河漫滩-潮滩-海湾沉积相演化受控于全新世海平面上升过程,潮滩相形成于约8.9 cal.kaBP,当时该区海平面大约在−21.0±2.5 m,最大海泛面出现于约8.2 cal.kaBP,之后出现了长达6 ka的低沉积速率时期,直至约2.2 cal.kaBP海湾内加速沉积。③该区15个钻孔全新统底部Sr/Ba均显现出明显的潮滩相特征,这为重建区域全新世相对海平面提供了可行性。

结合潮位与DEM的红树林遥感识别研究

以广西北部湾为研究区,针对潮位周期性变化导致稀疏低矮红树林难以被准确提取的问题,基于多潮位Landsat8 OLI图像和数字高程模型(DEM)数据,通过构建红树林识别决策树模型,并以支持向量机(SVM)为对照,评价结合潮位和DEM信息的决策树法提取红树林信息的可行性.研究结果表明:1)不同高度、不同密度以及不同潮位红树林之间光谱差异均较大,稀疏低矮红树林也与阴坡林地、水体-陆生植被混合像元光谱存在严重“异物同谱”效应;2)无论是基于低潮位、高潮位图像,还是多潮位图像,相比未区分高度和密度,在SVM中将细分为高密红树林和稀矮红树林,其总体精度(分为红树林和非红树林两类)可分别提高4.65、4.41和7.22个百分点;3)基于多潮位图像及DEM的决策树模型识别的总体精度和Kappa系数分别为98.80%和0.973,比SVM中最佳值分别高出1.62个百分点和0.035.因此,通过同时考虑红树林高度、密度、潮位和DEM等特征,可明显提高红树林遥感识别的精度.

黄浦江感潮河段潮位预报精度提升研究

黄浦江感潮河段水位波动以天文潮影响为主,同时也受上游径流、区间降雨和风暴潮等因素的影响,传统的调和分析方法难以考虑径流等非天文潮因素,在对黄浦江感潮河段进行潮位预报时总体精度偏低。本文在对传统调和分析方法预报误差频谱分析的基础上,提出了将传统调和分析模型和自回归模型相结合的预报方法,并将该方法应用于黄浦江感潮河段3个代表性站点(吴淞口、黄浦公园、米市渡)的潮位逐时预报中。结果表明:24 h潮位预报的均方根误差由原来的0.20 m左右降至0.10~0.14 m,预报精度显著提升。