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A numerical study based on FVCOM model was carried out to investigate the storm surge behavior induced by Typhoon Mangkhut in and around Lingdingyang Bay, Pearl River Estuary. Through elaborate calibration, the simulation results matched well with the measurements on the tidal-gauge stations. The validated Typhoon Mangkhut simulation was used as a case to study temporal–spatial behavior of the storm surge. Specifically, hourly spatial distribution of surge evolvement before the landfall of Typhoon Mangkhut and the time series of the surge from the twelve points in and around Lingdingyang Bay were analyzed. Beyond that, a series of artificial typhoons were designed through revising some parameters of the original typhoon including the landfall time, central pressure deficit, landfall location and moving direction, to study the influence caused by typhoon uncertainties. Results show that the influence of landfall time is dominated by the rule of tide–surge interaction, namely the lowest surge on the high tidal level and vice versa. The results also illustrate that the response of the surge to the same shift of the pressure deficit for a typhoon is uneven in space. The response of surge is more sensitive near shallow coastal regions than that in deep sea. Through investigating the surge in response to the track for the original typhoon, we find that a west shift of the track makes the ascending surge advanced and an east shift of the track makes the receding surge delayed in Lingdingyang Bay. A decrease of the angle between the coast and the direction of movement enlarges the maximum surge and an increase of the angle induces the opposite result. This study could improve our understanding about how uncertainties of a northwesterly moving typhoon would induce the storm surge response along the coastal regions such like Lingdingyang Bay, in Pearl River Estuary.

A high-resolution Finite-Volume Coastal Ocean Model (FVCOM) inundation model has been developed for Dartmouth Town near Apponagansett Bay and Clarks Cove. Series of modeling experiments were conducted for the purpose of: (1) Assess the potential impacts of the climate-induced Sea Level Rise (SLR) on the storm-induced coastal inundation in Dartmouth Town; (2) Compare the current patterns, wave fields and surge distributions under different dynamic forces including winds in different directions and wave-current interaction; (3) Evaluate the impact of the bank on the flooding protection. Results show that under the hundred-year nor’easter storm condition, the climate-induced SLR could significantly enlarge possible flooding areas with the percent area enlargement of approximately 60% per foot of SLR. The directions of wind essentially determine the feature of the current patterns, wave and surge distributions. The northeasterly and easterly winds mainly threaten the western coast of the bay and the estuarine areas, and the southerly and southeasterly winds endanger the regions around the inner part of the bay. Wave-current interaction can change the current pattern nearshore, including formation of eddies and narrow alongshore currents, greatly enhancing the strength and complexity of the currents near the mouth of the bay. In addition, wave-induced surge tends to accumulate in the bay and near the estuary and coastal regions. The bank blocks a large amount of flooding current and waves into the bay and improves the local current and wave condition effectively near the mouth and in the bay.

Both the river network and the regions outside the estuary mouths in the Pearl River Delta (PRD) of China experienced significant changes from 1999 to 2014. A validated hydrodynamic model across the entire PRD and adjacent regions outside the estuary mouths is employed to simulate both present (circa 2014) and past conditions (circa 1999). The total net water flux of the PRD decreased. The flow division of the West River is increasing, with values of 3.63% and 4.66% for the Makou and Denglongshan sections, respectively. The flood flow division of the North River is correspondingly decreasing. The value of the flood levels significantly decreased (more than 2 m) in the upper portion of the PRD, moderately decreased in the middle of the PRD (more than 1.1 m) and slightly decreased in the bottom part of the PRD (less than 0.22 m). In addition, the effects of morphodynamic evolution in different regions (i.e., the river network, coastline and bathymetry changes outside the estuary mouth) on floods are quantified. The results indicate that the decreased net water flux was caused by the increased channel’s capacity and the gentler water-level profile from the downcutting riverbed of the river network. The uneven morphodynamic evolution of the riverbed of the river network was primarily responsible for changes in the flood flow division in the PRD, and morphological evolution outside the estuary mouth was primarily responsible for reallocation within the outlets. The downcutting riverbed in the river network was primarily responsible for the lower flood levels in the upper and middle portion of the PRD. Reclamation seemed to have barely affected the flood level. The deepening bathymetry outside the estuary mouth was mainly responsible for the decrease in the flood level in the bottom portion of the PRD. The downcutting riverbed may decrease the stability of the riverbank, increasing the flood risk. The morphodynamic evolution of both the river network and the regions outside the estuary mouth should be considered to avoid unwanted side effects when designing local projects and flood mitigation strategies for the PRD.

Urban flooding poses serious threats to human life. In China, many cities have recently experienced flooding during every rainy season. Several years ago, policies, scientific methods, and engineering measures were applied to address this systematic problem. However, flooding disasters remain frequent in urban areas in China. Therefore, this article discusses the human-earth relationship from a philosophical perspective to analyse the causes of urban water problems. This article mainly illustrates the value of the what-if analysis concept and how to use this concept to address urban flooding issues and improve the management of urban overland flow. However, the existing simulation models and software do not effectively support what-if analyses. In particular, most existing urban hydrological simulation models and software do not sufficiently consider the heterogeneity of geographical objects on urban surfaces and lack interactions to support what-if analyses. These limitations hinder effective implementation of what-if analysis. This article introduces three key technologies that allow an urban overland flow simulation system to effectively support what-if analyses: 1) urban spatial automatic discretization and topo-adjacency, which reflect the heterogeneity of an urban area; 2) hydrological models for the simulation of the hydrologicalprocesses of the main geographical objects in the urban area; and 3) key strategies for a visual analytic platform to support what-if analyses in well-perceived way. The experiment was conducted using a community in Chongqing as a case study. The results demonstrate that the designed key technologies and functions of the proposed system can support what-if analysis and that what-if analysis is an important and useful concept for urban water management.

This study presents an incorporation and application of a two-dimensional, unstructured-grid hydrodynamic model with a suspended sediment transport module in Daishan, China. The model is verified with field measurement data from 2017: water level, flow velocities and suspended sediment concentration (SSC). In the application on the Daishan, the performance of the hydrodynamic model has been satisfactorily validated against observed variations of available measurement stations. Coupled with the hydrodynamic model, a sediment transport model has been developed and tested. The simulations agreed quantitatively with the observations. The validated model was applied to the construction of breakwaters and docks under a different plan. The model can calculate the flow field and siltation situation under different breakwater settings. After we have analyzed the impact of existing breakwater layout schemes and sediment transport, a reasonable plan will be selected. The results show that the sea area near the north of Yanwo Shan and Dongken Shan has a large flow velocity exceeding 2.0 m/s and the flow velocity within the isobath of 5 m is small, within 0.6 m/s. According to the sediment calculation, the dock project is feasible. However, the designed width of the fairway should be increased to ensure the navigation safety of the ship according to variation characteristics of cross flow velocity in channel.

Parlange and Brutsaert (1987) derived a modified Boussinesq equation to account for the capillary effect on water table dynamics in unconfined aquifers. Barry et al. (1996) solved this equation subject to a periodic boundary condition. Their solution shows significant influence of capillarity on water table fluctuations, which evolve to finite-amplitude standing waves at the high frequency limit. Here we propose a new governing equation for the water table, which considers both horizontal and vertical flows in an unsaturated zone of finite thickness. An approximate analytical solution for periodic water table fluctuations based on the new equation was derived. In agreement with previous results, the analytical solution shows that the unsaturated zone's storage capacity permits water table fluctuations to propagate more readily than predicted by the Boussinesq equation. Furthermore, the new solution reveals a capping effect of the unsaturated zone on both the amplitude and phase of the water table fluctuations as well as the water table overheight. Due to the finite thickness of the unsaturated zone, the capillary effect on water table fluctuations is modified mainly with reduced amplitude damping and phase shift.

Deriving analytical solutions for tide-induced groundwater fluctuations in unconfined aquifers confronts two problems: (1) As the Boussinesq equation itself contains nonlinear terms, the “secular term” would be generated in derivation, thus making perturbation solution unable to be deduced to higher order; (2) for aquifers with sloping beaches, the perturbation parameter in existing analytical solution integrating the beach slope and hydrogeological property would be sometimes larger than 1. So the application of perturbation solutions is relatively limited. Furthermore, as the beach slope decreases, the error of analytical solution would gradually increase. Given that water table over-height would increase the aquifer thickness and speed up wave propagation, this paper integrates over-height into the perturbation parameter and adjusts boundary conditions to settle the problem of “secular term” and to derive a new high-order analytical solution for nonlinear Boussinesq equation in terms of sloping beaches. Results show that the new analytical solution is more reasonable, and the analytical accuracy is obviously improved in comparison with the existing analytical solution for a gentle slope. The new analytical solution provides a theoretical basis for analyzing the propagation characteristics (e.g., wave length and over-height variation) of tide-induced groundwater wave in unconfined aquifers, particularly those with sloping beaches.

Organized spatial distribution of plants (plant zonation) in salt marshes has been linked to the soil aeration condition in the rhizosphere through simplistic tidal inundation parameters. Here, a soil saturation index (ratio of saturation period to tidal period at a soil depth) is introduced to describe the soil aeration condition. This new index captures the effects of not only the tidal inundation period and frequency but also the flow dynamics of groundwater in the marsh soil. One-dimensional numerical models based on saturated flow with the Boussinesq approximations and a two-dimensional variably saturated flow model were developed to explore the behaviour of this new soil aeration variable under the influence of spring-neap tides. Simulations revealed two characteristic zones of soil aeration across the salt marsh: a relatively well aerated near-creek zone and a poorly aerated interior zone. In the near-creek zone, soils undergo periodic wetting and drying as the groundwater table fluctuates throughout the spring-neap cycle. In the interior, the soil remains largely water saturated except for neap tide periods when limited drainage occurs. Although such a change of soil aeration condition has been observed in previous numerical simulations, the soil saturation index provides a clear delineation of the zones that are separated by an 'inflexion point' on the averaged index curve. The results show how the saturation index represents the effects of soil properties, tidal parameters and marsh platform elevation on marsh soil aeration. Simulations of these combined effects have not been possible with traditional tidal inundation parameters. The saturation index can be easily derived using relatively simple models based on five non-dimensional variables. Copyright (C) 2010 John Wiley & Sons, Ltd.

This paper presents a new perturbation solution of the non-linear Boussinesq equation for one-dimensional tidal groundwater-flow in a coastal unconfined aquifer. Built upon the work of Parlange et at. [Parlange, J.-Y., Stagnitti, F., Starr, J. L., Braddock, R. D., 1984. Free-surface flow in porous media and periodic solution of the shallow-flow approximation, J. Hydrol., 70, 251-263], the solution adopts a new perturbation parameter that is by definition less than unit, and thus is applicable to a wider range of physical conditions within the constraint of the Boussinesq approximation. This approach avoids a secular term in the third-order perturbation equation of Parlange et at. (1984), enabling the derivation of the third- and higher-order solutions. In comparison with a numerical ("exact") solution, the new perturbation solution is shown to be slightly more accurate than that of Parlange et at. (1984) with the second-order approximation. The obtained third-order solution exhibits considerable improvement in accuracy. In relatively simple analytical forms, the present perturbation solution will help to understand better the non-linear characteristics of tidal water table fluctuations as modeled by the non-linear Boussinesq equation in coastal unconfined aquifers. (C) 2007 Elsevier B.V. All rights reserved.

Tidal watertable fluctuations in a coastal aquifer are driven by tides on a moving boundary that varies with the beach slope. Based on a linearised one-dimensional Boussinesq model, tidal signals in the aquifer are analysed, focusing on the watertable overheight induced by the moving-boundary condition. The watertable overheight is an important parameter related to the estimation of submarine groundwater discharge (SGD). This note presents a new analytical approach to solving the Boussinesq equation with the Fourier-series expansion. Moreover, it is proved that the asymptote of watertable overheight normalised by the tidal amplitude is unit as a controlling parameter (( \(\varepsilon_0\))), combining the aquifer properties and tidal frequency, approaches infinity. Physically, this condition represents beaches of very low drainage capacity.

Ye, R.; Song, Z.; Zhang, C.; He, Y.; Yu, S.; Kong, J., and Li, L., 2017. Analytical model for surface saltwater intrusion in estuaries. Based on the laterally averaged salt transport equation, a physically based surface saltwater intrusion model is presented for estimating the spatial distribution of salinity near the surface of the river along the estuary over high-water slack, low-water slack, and tidal-average conditions. The model is applied to simulate steady-state salinity profiles on the water surface of the Modaomen Estuary of the Pearl River delta in China. The results indicate that this model describes the surface salt profiles reasonably well and is capable of forecasting surface saltwater intrusion.

This article describes systematic research on the tide dynamic system under the support of the Geographic Information System and ocean fluid dynamics model. Through the high-resolution numerical simulation, we found some previously unreported phenomena, such as a low tide amplitude zone of the M2 constituent near Zhoushan isles, a low tide amplitude zone of the K1 constituent near Taiwan island, and a circular flow point band. The results of this research also show that the formation of the tide system is affected by sea-bottom friction coefficient, topography under water, and shoreline morphology. The change of shoreline morphology and significant change of topography under water play important roles in the tide system. Under specified conditions on input tide waves, shoreline morphology has a dominant impact on the formation of the tide system. With the systematically reconstructed sea level and the coastal change of 30 periods since the Pleni Glacier, the evolution process of the tide system of the Eas...

Many scholars at home and abroad have studied tidal velocity profile in estuarine and coastal waters. The results show that velocity profile of tidal current often deviated obviously from the traditional logarithmic profile, due to the flow including wind-driven current, wave-driven current, salinity and so on. In estuarine waters, runoff should be included as a component. In this paper, two patters of vertical velocity profile of tidal current are firstly divided, that are monotone increasing I-velocity profile (during flood tide and ebb tide stage) and non-monotone increasing II -velocity profile (during slack tide stage). Then, by use of variable fractal dimension to obtain the law of II-velocity profile, the results show that: (1)The II -velocity vertical profile does express a first-order accumulated variable-dimensional fractal phenomenon. (2) Through of the fractal dimension, the various formula fitting II-velocity profile were compared, and the results showed that, in practical applications of engineering, cubic function formula is the best fit as the measured data have been verified. Finally, the cubic function formula is applied to flow separation of II -velocity measured in Yangtze River. By the easily separation of the measured flow, we can not only get a reasonable surface flow velocity, such as wind-driven current, runoff, salinity, as well as their driving force weight in the hydrodynamic of estuarine and coastal waters, but also gain the data of bed roughness length and sea surface wind speed, providing reasonable border conditions of the seabed and sea surface for the hydrodynamic numerical simulation in estuarine and coastal waters.Copyright © 2009 by ASME

In estuary and coastal areas the storm surge will usually occur in typhoon season. When simulating the storm surge by numerical model, the wind speed at the height of 10m above the mean sea level will be usually used. Determining the wind drag stress on free surface reasonably plays an important role to simulate the storm surge accurately. In the past numerical models, the wind drag stress on free surface was calculated only considering the relative wind speed. There are many formulas about wind stress can be used, whereas these formulas are usually got in laboratory, where the water surface fluctuates in a small range, and the water elevation itself has not been considered in formula. Actually in some place, the astronomical tidal range is large, such as Yangtze estuary and Hangzhou bay in China, and during typhoon season, the water fluctuation range is much larger than ever there. In conventional method the wind stress will be underestimate in flood tide and be over-valuated in ebb tide without considering the fluctuation of water, so it is obviously unsuitable to take no account of the influence of tidal level on wind stress. Therefore in the intensive tide coastal area, the relationship of the relative wind speed, tidal level should be considered together. A new kind of wind stress formula has been established in this paper and been adopted in simulating the storm surge of typhoon Winnie in Yangtze estuary, and the results are better and satisfying.Copyright © 2007 by ASME

Previous studies pointed out that due to the acceleration or deceleration action of tide current, the flow structure deviates from traditional logarithmic law in estuary, coast or other near shore water. The tidal velocity distribution model was derived and compared with the traditional logarithmic model. It should be pointed out that the velocity data adopted have four layers within one meter above the bed, and the roughness length z0 is different in the two models even in the same velocity profile. Because the fluctuation of roughness length z0 is remarkable when determining by single velocity profile, some studies thought that the variation of roughness length was small between adjacent time when the change of topography was less obviously. Therefore, the measured data is divided into several sections by one day or a tidal cycle to fit the velocity profile of every section to obtain a roughness length z0 , i.e., the roughness length z0 varies only after a day or a tidal cycle. The purpose of the paper is to expand the log-linear model to full depth by adding the surface boundary condition ∂u∂zz=D = 0 (D is water depth) and to discuss the difference when 6 points (bottom layer, 0.2D, 0.4D, 0.6D, 0.8D, surface layer) velocity profile are fitted by logarithmic model, log-linear model, and extended log-linear model with the same roughness length z0 in different time section, respectively. The calculated friction velocity and friction coefficient and their correlation are discussed. The results show that the log-linear model and the log-linear extend model are closer to the measure velocity profile than that of the logarithmic model.Copyright © 2006 by ASME

Based on a liberalized one-dimensional Boussinesq model and the previous study results, this paper provides two experience solutions to quantify the tidal groundwater overheight behind arbitrary sloping beaches. One solution is obtained with an asymptotic matching method advanced by Guo, and the other solution is origined by the analytical solution as perturbation parameter less than unity, the errors of both solutions compared with numerical solution are small and acceptive for the application.