Investigation and comparison of one-dimensional (1-D) analytical models prediction for salt intrusion condition in two selected estuaries

Abstract

In this paper, two analytical models used worldwide to assess salinity variation in alluvial estuaries are applied to the Ashtamudi estuary, a Ramsar site, southwest coast of India; and Bouregreg estuary, in northwest part of Morocco. The estuaries’ bathymetry is described by an exponential function. Both models are quite similar and use a predictive equation for the dispersion in the estuary mouth (D₀). The major difference between the two models is the use of the constant value of K?=?0.5 for the Van der Burgh coefficient (K) and the introduction of the correction factor ζ, which is a function of damping (δ) and shape (γ). The performance of these two models was evaluated by comparing their results with field measurements; this revealed that both analytical models apply well to both the estimation of salinity distribution and the prediction of salt intrusion in the Ashtamudi and Bouregreg estuaries (Ashtamudi: RMSE = 0.60–1.22 ppt; Bouregreg: RMSE = 0.92–2.71 ppt). One model agrees more with the field measurements of salinity distribution along the estuaries axis; the second underestimate and overestimate some values of salinity distribution along the estuaries. Possibly, the constant value of K?=?0.5 for the Van der Burgh coefficient (K) has applicability limits for the estuaries under tidal conditions. The specifying of the parameterization may be a field of research.     

Comment on “A note on salt intrusion in funnel-shaped estuaries: Application to the Incomati estuary, Mozambique” by

A comment is provided on the paper by Brockway et al. (2006. A note on salt intrusion in funnel-shaped estuaries: application to the Incomati estuary, Mozambique. Estuarine, Coastal and Shelf Science 66, 1–5) on a simple method to determine the salt intrusion in the Incomati estuary. Although this method is able to describe the salt intrusion in the Incomati reasonably well with only limited information, it is demonstrated that with the same data, but a more up-to-date methodology, a better and generally applicable equation could have been obtained.     

Prediction of salinity intrusion in the sheltered estuary of Terengganu River in Malaysia using 1-D empirical intrusion model

Generally one dimensional(1-D) empirical salinity intrusion model is limited to natural alluvial estuary. However,this study attempts to investigate its ability to model a sheltered alluvial estuary of the Terengganu River in Malaysia. The constructed breakwater at the mouth of the river shelters the estuary from direct influence of the open sea. The salinity density along the estuary was collected during the wet and dry seasons for scenarios before and after the constructed breakwater. Moreover, the freshwater discharges, tidal elevations and bathymetry data were also measured as model inputs. A good fit was demonstrated between simulated and observed variables,namely salinity distribution and intrusion length for both scenarios. Thus, the results show that 1-D empirical salinity model can be utilized for sheltered estuarine condition at the Terengganu Estuary, but with an appropriate determination of an initial point. Furthermore, it was observed that the salinity intrusion in the study area is largely dependent on the freshwater discharge rather than tidal elevation fluctuations. The scale of the salinity intrusion length in the study area is proportional to the river discharge of the –1/2 power. It was appeared that the two lines of the 1-D empirical salinity model and discharge power based equation fitted well to each other, with the average predicted minimum freshwater discharge of 150 m3/s is going to be required to maintain acceptable salinity levels during high water slack(HWS) near the water intake station, which is located at 10.63 km from river mouth.     

台风路径对磨刀门水道咸潮上溯动力过程的影响机制

随着全球气候变暖加剧, 台风强度和强台风数量不断增加, 加剧了磨刀门水道咸潮灾害的变化形势。本文采用SCHISM(semi-implicit cross-scale hydroscience integrated system model)模型建立磨刀门水道三维水流盐度数值模型, 分析台风路径对磨刀门水道盐水入侵的影响。选取以“纳沙”为代表的西径型台风和以“天兔”为代表的东径型台风, 发现二者对盐度输运和层化过程的动力响应具有差异性。东径型台风导致外海减水, 平流通量向海增大; 而西径型台风引起外海增水, 逆转了原本向口外输出盐度的平流通量, 会引起严重的盐水入侵。台风不仅引起外海的增减水效应, 还带来强劲的局地风作用, 对水道流速和盐度分布产生重要影响。在西径型台风下, 顺河口向上游的风会减弱盐淡水分层, 并加强平流项的向海输出; 而在东径型台风下, 一定强度顺河口向下游的风加强盐淡水分层, 但当风速过强时, 则会削弱盐淡水分层。     

长江口深水航道三维泥沙数值模型相关问题探讨

基于近年来长江口三维水沙盐数值模型及水沙运动机理的研究进展,系统梳理了在长江口实际应用中面临的若干理论和技术难题,其中包括长江口物质输运模拟计算格式的守恒性和稳定性、河口区域河床切应力的准确计算、拦门沙区域近底高浓度泥沙形成机理及数值模型模拟、长江口近底高浓度泥沙横向入槽模式等问题,通过对于上述问题的梳理和总结,表明在长江口这类巨型河口进行三维水沙盐数值模型和水沙机理研究的复杂性,并针对此类区域的模型技术研发和水沙运动理论研究,提出了有科学意义和研究价值的方向和思路。     

Sorption model for dissolved and particulate aluminium in the Conway estuary, UK

Dissolved Al carried in river water apparently undergoes a fractional removal at the early stages of mixing in the Conway estuary. On the other hand, dissolved Al behaves almost conservatively in high salinity (>13) estuarine waters. In order to understand the geochemistry of Al in these estuarine waters, simple empirical sorption models have been used. Partitioning of Al occurs between solid and solution phases with a distribution coefficient, K_d, which varies from 0.67 × 10⁵ to 3.38 × 10⁶ ml g⁻¹ for suspended particle concentrations of 2–64 mg l⁻¹. The K_d values in general decrease with increasing suspended particulate matter and this tendency termed the “particle concentration effect” is quite pronounced in these waters. The sorption model derived by previous workers for predicting concentrations of dissolved Al with changing suspended sediment loads has been applied to these data. Reasonable fits are obtained for K_d values of 10⁵, 10⁶ and 10⁷ ml g⁻¹ with various values of α. Further, a sorption model is proposed for particulate Al concentrations in these waters that fits the data extremely well defined by a zone with K_d value 10⁷ ml g⁻¹ and C₀ values 16 × 10⁻⁶ mg ml⁻¹ and 92 × 10⁻⁶ mg ml⁻¹. These observations provide strong evidence of sorption processes as key mechanisms influencing the distribution of dissolved and particulate Al in the Conway estuary and present new insight into Al geochemistry in estuaries.     

整治工程影响下分汊河口水动力变化研究

本文针对分汊河口一侧河道整治工程对工程汊及非工程汊水动力的影响问题,采用数学模型试验方法,建立了潮汐分汊河口概化数学模型,计算了整治工程(双导堤与丁坝)前后水动力变化,分析了主要分潮M2、M4的潮位、流速沿程变化规律以及工程后丁坝局部流速流向特征,讨论了潮波的变形及不对称性。结果显示,整治工程导致工程汊分流比减小,工程区域内流速增加,工程区外流速减小,非工程汊整体流速增加。工程汊的潮流变形及不对称性均较工程前有所增强,导致外海泥沙盐水通过航槽向上游上溯的距离更长,坝田区内流速明显小于航槽流速,并呈明显的旋转流态势,导致坝田淤积。     

A study of the mixed layer of the South China Sea based on the multiple linear regression

Multiple linear regression(MLR) method was applied to quantify the effects of the net heat flux(NHF),the net freshwater flux(NFF) and the wind stress on the mixed layer depth(MLD) of the South China Sea(SCS) based on the simple ocean data assimilation(SODA) dataset.The spatio-temporal distributions of the MLD,the buoyancy flux(combining the NHF and the NFF) and the wind stress of the SCS were presented.Then using an oceanic vertical mixing model,the MLD after a certain time under the same initial conditions but various pairs of boundary conditions(the three factors) was simulated.Applying the MLR method to the results,regression equations which modeling the relationship between the simulated MLD and the three factors were calculated.The equations indicate that when the NHF was negative,it was the primary driver of the mixed layer deepening;and when the NHF was positive,the wind stress played a more important role than that of the NHF while the NFF had the least effect.When the NHF was positive,the relative quantitative effects of the wind stress,the NHF,and the NFF were about 10,6 and 2.The above conclusions were applied to explaining the spatio-temporal distributions of the MLD in the SCS and thus proved to be valid.     

长江口海水盐度和悬浮体对中肋骨条藻生长的影响

2001年5月通过实验室培养的方法研究了长江口优势赤潮浮游植物种类——中肋骨条藻(Skeletonema costatum)在长江口海水中的生长情况。实验结果显示,在实验光强范围内该藻相对生长速率常数随光强的减小而减小,表明光照的可得性是影响其生长的重要因素;悬浮体的遮光效应会限制其生长。海水盐度超出其适宜生长的范围也会对其的生长产生不利影响。两个相互对比的实验说明在泥沙含量很高的长江口咸淡混合水中光照的可得性和盐度均影响中肋骨条藻的生长,综合这两个因素,在实验盐度范围内最适宜中肋骨条藻生长的盐度是约为19．2的咸淡水。适于中肋骨条藻适宜生长的盐度为14～23。     

Economic base model for the Guadiana estuary,Portugal an application for Integrated Coastal Zone Management

The concept of base-multiplier analysis is that export activities constitute the economic base of a region, whereas the other economic activities that sell their goods and services to the local residents grow or shrink depending on the performance of the base activities. These concepts, with origins extending at least as far back as the early 1900s, have reached maturity and are widely applied. The attractiveness of an economic base model (EBM) draws in its simplicity in expressing the power of demand in regional income determination. Extensive literature has grown up around the economic base theory, however, systematic publications concerning empirical application are scarce and focus mostly on the socio-economic dimension of the analyzed system. Such territorially oriented economic models are useful in a variety of decision making procedures; preparation of annual budgets, short-run market demand forecasting, longer-term growth strategies. The purpose of this article is to present a practical application of EBM to the geographical area of the Guadiana Estuary, on the south coast of Portugal. The interest of the EBM application in this case study includes its integration in a broader project that applies a Systems Approach Framework (SAF) towards Integrated Coastal Zone Management (ICZM). There are three pillars of sustainability considered here: social, ecological and economic, hence, the article not only describes EBM application but also how it has been use to demonstrate a chain of events resulting from the interaction between the ecological and the socio-economic sub systems of the area. The results obtained will probably raise the usual criticism to which the economic base model has been exposed previously; however it provides unequivocal evidence that a truly interdisciplinary approach to a given territorial target can be successfully shared with end users and the research community.     

Sedimentary processes on an intertidal mudflat in the upper macrotidal Seine estuary, France

In order to understand the hydrodynamic parameters that control the fluvial sediment dynamics on an intertidal mudflat located in a sheltered zone in the upper part (fluvial part) of the macrotidal Seine estuary (France), a two-year field study of high-frequency field measurements was carried out. The bed-level evolution of the mudflat surface was measured from the semi-diurnal period to annual time scales using a high-resolution altimeter. The data showed that the sedimentary patterns on the mudflat were mainly controlled by river flows and tides. During high river flows in winter, sedimentation dominated; suspended particulate matter concentrations were higher, submersion was constant and at semi-diurnal scale, sedimentation duration was more important than erosion due to an asymmetrical tide. By contrast during low river flows in summer, erosion dominated mainly as a result of immersion/emersion of tidal flats during semi-diurnal cycle. From this annual sedimentation–erosion cycle we identify a temporary storage of 10–30% of the fine-grained (<63 μm) river-borne particles on mudflats in the upper section of the fluvial Seine estuary during high river flows.River-related sediment fluxes were estimated from the measurement of fine-grained sedimentation zones in the fluvial part of the estuary. The erosion/sedimentation processes were perennial, and the amounts of contributing sediments were directly related to the solid river load. Our results indicate that mudflats in the fluvial part of the Seine estuary play an important role in the downstream transfer of fine-grained suspended particulate matter (SPM) towards the turbidity maximum and the Rouen docks particularly during low river flows, when roughly 30–50% of the SPM originates from the eroded intertidal flats.     

滦河三角洲及其周边海岸土地利用/覆被变化的遥感研究

基于1987年和2000年LandSat卫星影像的分类结果,结合常规调查资料,得到了滦河三角洲及其邻近海岸地带近13年来土地利用/土地覆被变化的动态信息。通过对地类变化的细致分析,得出本区研究时段内自然与人类活动情况的地面指示。     

长江口海域表层沉积物重金属元素的潜在生态风险评价

根据三峡水库一期蓄水3 a后(2006年)长江口海域表层沉积物样品中元素(Cd,Cr,Cu,Pb,Zn,Al,As,Ca和Sr等)质量比和黏土组分百分含量,采用Hakanson潜在生态风险指数法,分析了长江口海域表层沉积物中重金属元素(Cd,Cr,Cu,Pb,Zn和As)的污染程度,评价了长江口海域表层沉积物的环境质量现状,定量分析了长江口海域表层沉积物的潜在生态风险程度,并结合2003年的资料,讨论了三峡水库一期蓄水3 a后长江口海域的环境变化。结果表明,长江口海域表层沉积物环境质量状况良好,6种重金属元素的污染程度排序为:AsCrCdZnCuPb;表层沉积物的潜在生态风险程度为轻度,6种重金属元素的潜在生态风险程度排序为:CdAsCuCrPbZn。从区域差异来看,杭州湾口外泥质区和长江口外东北偏北海域表层沉积物中重金属元素(As,Cr,Zn,Cu和Pb)的污染指数和潜在生态风险指数均出现相对高值。从元素差异来看,Cd的污染指数和潜在生态风险指数高值区的分布明显异于其他重金属元素,说明Cd存在与其他重金属元素不同的富集机制,很可能是因为Cd更易受悬浮体浓度、有机质含量以及水体盐度的影响。与2003年的资料相比,三峡水库一期蓄水3 a后(2006年)表层沉积物总体潜在生态风险程度和重金属元素(除Cd之外)潜在生态风险指数的高值区均未发生显著变化。     

Numerical and Experimental Study on Hydrodynamic Performance of A Novel Semi-Submersible Concept

The Multiple Column Platform (MCP) semi-submersible is a newly proposed concept, which differs from the conventional semi-submersibles, featuring centre column and middle pontoon. It is paramount to ensure its structural reliability and safe operation at sea, and a rigorous investigation is conducted to examine the hydrodynamic and structural performance for the novel structure concept. In this paper, the numerical and experimental studies on the hydrodynamic performance of MCP are performed. Numerical simulations are conducted in both the frequency and time domains based on 3D potential theory. The numerical models are validated by experimental measurements obtained from extensive sets of model tests under both regular wave and irregular wave conditions. Moreover, a comparative study on MCP and two conventional semi-submersibles are carried out using numerical simulation. Specifically, the hydrodynamic characteristics, including hydrodynamic coefficients, natural periods and motion response amplitude operators (RAOs), mooring line tension are fully examined. The present study proves the feasibility of the novel MCP and demonstrates the potential possibility of optimization in the future study.     

渤海莱州湾南岸平原浅埋古河道带及其与海(咸)水入侵关系研究

根据2100余个钻孔资料,并结合大比例尺地形图、航片、卫片判读分析,以及野外实地考察和沉积物样品的粒度分析、岩相分析、14C测年,研究了莱州湾南岸平原浅埋古河道带的分布规律、埋藏和沉积特征、古河道的分期断代以及与海(咸)水入侵关系。该区在埋深60m内的浅埋古河道带,可分成弥河、潍河和白浪河3个系统,它们大都呈掌状、放射状分布,并与其所属河流的冲洪积扇范围相吻合。该区古河道的形成和发育与古气候和海平面变化密切相关。自晚更新世晚期以来,该区有4期古河道发育,其中玉木旱冰期古河道和玉术主冰期古河道的砂层沉积粒度粗、连通性好、分布广,既是富水性强、水质好的淡水含水层,又是该区海(咸)水入侵的主要通道。控制在浅埋古河道带超采地下淡水,并在丰水季节利用其进行地下水回灌,是治理该区海(咸)水入侵灾害的重要措施之一。     

Reproductive cycle and minimal length at sexual maturity of Engraulis encrasicolus (L.) in the Zrmanja River estuary (Adriatic Sea, Croatia)

The reproductive cycle of anchovy, Engraulis encrasicolus (L.), was studied from monthly random samples of purse seine catches. A total of 1477 anchovy specimens were collected from January to December 2003 in the Zrmanja River estuary (Novigrad Sea). The analysis was based on the temporal evolution of gonadosomatic index, mass and stage of gonads. The total length of anchovy ranged from 4.5 to 14.5 cm and mass from 0.56 to 19.80 g. Sex ratio was slightly different from 1:1; the females were insignificantly predominated (♂/♀ = 0.99). The period of reproductive activity was from April to September coinciding with the most developed stages of gonads as well as with the highest gonad weights, and gonadosomatic indices. To estimate the length at maturity, a sub sample of 454 anchovy was taken from May to July (peak of anchovy spawning period). The length at which 50% of anchovy were mature (L₅₀) was calculated to be 8.2 cm. The length–weight relationship of anchovy was described by the expression: W = 3.51 × 10⁻³ L_T^3.211 (r² = 0.998). The relationships between total length–standard length and total length–fork length are L_T = 1.1405L_S + 0.2420 and L_T = 1.0425 L_F + 0.3944, respectively.     

Perturbed solution of sea-air oscillator for the El Niño/La Niña-Southern Oscillation mechanism

A class of coupled system of the El Niño/La Niña-Southern Oscillation (ENSO) mechanism is studied. Using the perturbed theory, the asymptotic expansions of the solution for ENSO model are obtained and the asymptotic behavior of solution for corresponding problem is considered.