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Rice production in the Mekong River Delta of Vietnam (MRD) is endangered by sea-level rise and an associated increase in the incidence of salinity intrusion. This paper examines the diffusion of salt tolerant rice varieties in the MRD that were promoted through Consortium for Unfavorable Rice Environments (CURE) activities. Factors associated with adoption of CURE-related varieties are estimated using a random utilty model and a dataset of 800 farm households with rice fields in salinity prone areas of the MRD. Results suggest that there has been widespread adoption of CURE-related varieties in salinity-prone areas. Further, multivariate analysis reveals that environment and location characteristics, rather than household characteristics, are the most important determinants of adoption. In particular, CURE-related varieties are more likely to be adopted in high-salinity-risk areas that are not protected by salinity barrier gates. Neighbhors' adoption decisions also strongly influence household decisions to adopt CURE-related varieties. The contracting of mechanization, particularly for land preparation and harvest, requires the coordination of village households in timing of planting, harvest and varietal duration. This coordination appears to extend to choice of CURE-related varieties. Finally, CURE-related varieties and other varieties generate similar net revenues in a year with low salinity exposure, suggesting that CURE-related varieties are a low-cost insurance policy against salinity inundation in high risk areas. Combined, these results highlight the need to address complex factors beyond current economic profits, like environment, community choices, and risk mitigation, when designing technologies and policies that support farmer adaptation to climatic change. BM -1 International Fund for Agricultural Development Published version BM -1 International Fund for Agricultural Development https://www.ifad.org/en/The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript

River delta degradation has been caused by extraction of natural resources, sediment retention by reservoirs, and sea-level rise. Despite global concerns about these issues, human activity in the world’s largest deltas intensifies. Harbour development, construction of flood defences, sand mining and land reclamation emerge as key contemporary factors that exert an impact on delta morphology. Tides interacting with river discharge can play a crucial role in the morphodynamic development of deltas under pressure. Emerging insights into tidal controls on river delta morphology suggest that—despite the active morphodynamics in tidal channels and mouth bar regions—tidal motion acts to stabilize delta morphology at the landscape scale under the condition that sediment import during low flows largely balances sediment export during high flows. Distributary channels subject to tides show lower migration rates and are less easily flooded by the river because of opposing non-linear interactions between river discharge and the tide. These interactions lead to flow changes within channels, and a more uniform distribution of discharge across channels. Sediment depletion and rigorous human interventions in deltas, including storm surge defence works, disrupt the dynamic morphological equilibrium and can lead to erosion and severe scour at the channel bed, even decades after an intervention. River deltas are shaped by interactions between fluvial and tidal processes. Tides act to stabilize delta morphology, but sediment depletion due to human activities disrupts the balance and leads to erosion and scour.

Due to accelerated anthropogenic activity, a significant amount of pollutants has been directly or indirectly discharged into coastal estuaries of Kampar. Nutrient pollution along the river to the estuary that adversely affects coastal and estuary ecosystem mainly originates from inland such as industrial effluent, household, and agricultural waste as well as a naturally derived pollutant from biogeochemical cycle, which is controlled by the propagation of undular bore ( Bono ) . The purpose of this study is to determine the environmental impact of distribution of nutrients caused by the mechanism of Bono. This research employed a purposive quantitative method, the concentration of dissolved phosphate, nitrate, nitrite and ammonia was analyzed using a spectrophotometer, tidal data retrieval was measured for 30 days’ near the estuarine area, while, current flow was measured for 24 hours’ measurement. Phosphate concentrations ranged from 0.02-0.1 mg.L -1 , nitrate concentrations ranged from 0.76-5.73 mg.L -1 , ammonia concentrations ranged from 0.2-0.41 mg.L -1 , nitrate concentrations ranged from 0.001-0.03 mg.L -1 . The tidal type is mixed tide prevailing semidiurnal with tidal range reach 4.2 m during spring tide condition. At the time of Bono propagate, drastically enhance the surface elevation and directly increase the drift of velocity with the flow direction from estuary into the river upstream, that mechanism affects the nutrient distribution in Kampar river. Keywords : Bono, Fluid dynamics, Nutrient distribution, Tidal bore, Water quality

Tidal rivers are a vital and little studied nexus between physical oceanography and hydrology. It is only in the last few decades that substantial research efforts have been focused on the interactions of river discharge with tidal waves and storm surges into regions beyond the limit of salinity intrusion, a realm that can extend inland hundreds of kilometers. One key phenomenon resulting from this interaction is the emergence of large fortnightly tides, which are forced long waves with amplitudes that may increase beyond the point where astronomical tides have become extinct. These can be larger than the linear tide itself at more landward locations, and they greatly influence tidal river water levels and wetland inundation. Exploration of the spectral redistribution and attenuation of tidal energy in rivers has led to new appreciation of a wide range of consequences for fluvial and coastal sedimentology, delta evolution, wetland conservation, and salinity intrusion under the influence of sea level rise and delta subsidence. Modern research aims at unifying traditional harmonic tidal analysis, nonparametric regression techniques, and the existing understanding of tidal hydrodynamics to better predict and model tidal river dynamics both in single-thread channels and in branching channel networks. In this context, this review summarizes results from field observations and modeling studies set in tidal river environments as diverse as the Amazon in Brazil, the Columbia, Fraser and Saint Lawrence in North America, the Yangtze and Pearl in China, and the Berau and Mahakam in Indonesia. A description of state-of-the-art methods for a comprehensive analysis of water levels, wave propagation, discharges, and inundation extent in tidal rivers is provided. Implications for lowland river deltas are also discussed in terms of sedimentary deposits, channel bifurcation, avulsion, and salinity intrusion, addressing contemporary research challenges.

In this paper, we analyse the behaviour of fine sediments in the hyper-turbid Lower Ems River, with focus on the river’s upper reaches, a stretch of about 25 km up-estuary of Terborg. Our analysis is based on long records of suspended particulate matter (SPM) from optical backscatter (OBS) measurements close to the bed at seven stations along the river, records of salinity and water level measurements at these stations, acoustic measurements on the vertical mud structure just up-estuary of Terborg and oxygen profiles in the lower 3 m of the water column close to Leerort and Terborg. Further, we use cross-sectionally averaged velocities computed with a calibrated numerical model. Distinction is made between four timescales, i.e. the semi-diurnal tidal timescale, the spring–neap tidal timescale, a timescale around an isolated peak in river flow (i.e. about 3 weeks) and a seasonal timescale. Thedata suggest that a pool of fluid/soft mud is present in these upper reaches, from up-estuary of Papenburg to a bit downestuaryof Terborg. Between Terborg and Gandersum, SPM values drop rapidly but remain high at a few gram per litre. The pool of fluid/soft mud is entrained/mobilized at the onset of flood, yielding SPM values of many tens gram per litre. This suspension is transported up-estuary with the flood. Around high water slack, part of the suspension settles, being remixed during ebb, while migrating down-estuary, but likely not much further than Terborg. Around low water slack, a large fraction of the sediment settles, reforming the pool of fluid mud. The rapid entrainment from the fluid mud layer after low water slack is only possible when the peak flood velocity exceeds a critical value of around 1 m/s, i.e. when the stratified water column seems to become internally supercritical. If the peak flood velocity does not reach this critical value, f.i. during neap tide, fluid mud is not entrained up to the OBS sensors. Thus, it is not classical tidal asymmetry, but the peak flood velocity itself which governs the hyper-turbid statein the Lower Ems River. The crucial role of river flow and river floods is in reducing these peak flood velocities. During elongated periods of high river flow, in e.g. wintertime, SPM concentrations reduce, and the soft mud deposits consolidate and possibly become locally armoured aswell by sand washed in from the river. We have no observations that sediments are washed out of the hyper-turbid zone. Down-estuary of Terborg, where SPM values do not reach hyper-turbid conditions, the SPMdynamics are governed by classical tidal asymmetry and estuarine circulation. Hence, nowhere in the river, sediments are flushed from the upper reaches of the river into the Ems-Dollard estuary during high river flow events. However, exchange of sediment between river and estuary should occur because of tide-induced dispersion.

Estuarine navigation channels have long been recognized as conduits for saltwater intrusion into coastal wetlands. Salt flux decomposition and time series measurements of velocity and salinity were used to examine salt flux components and drivers of baroclinic and barotropic exchange in the Houma Navigation Channel, an estuarine channel located in the Mississippi River delta plain that receives substantial freshwater inputs from the Mississippi-Atchafalaya River system at its inland extent. Two modes of vertical current structure were identified from the time series data. The first mode, accounting for 90% of the total flow field variability, strongly resembled a barotropic current structure and was coherent with alongshelf wind stress over the coastal Gulf of Mexico. The second mode was indicative of gravitational circulation and was linked to variability in tidal stirring and the horizontal salinity gradient along the channel’s length. Tidal oscillatory salt flux was more important than gravitational circulation in transporting salt upestuary, except over equatorial phases of the fortnightly tidal cycle during times when river inflows were minimal. During all tidal cycles sampled, the advective flux, driven by a combination of freshwater discharge and wind-driven changes in storage, was the dominant transport term, and net flux of salt was always out of the estuary. These findings indicate that although human-made channels can effectively facilitate inland intrusion of saline water, this intrusion can be minimized or even reversed when they are subject to significant freshwater inputs.

Tidal flats play a critical role in supporting biodiversity and in providing ecosystem services but are rapidly disappearing because of human activities. The Yangtze Estuary is one of the world’s largest alluvial estuaries and is adjacent to the most developed economic zone in China. Using the Yangtze Estuary as a study region, we developed an automatic algorithm to estimate tidal flat areas based on the Land Surface Water Index and the Normalized Difference Vegetation Index. The total area of tidal flats in the Yangtze Estuary has decreased by 36% over the past three decades, including a 38% reduction in saltmarshes and a 31% reduction in barren mudflats. Meanwhile, land claim has accumulated to 1077 km2, a value that exceeds the area of the remaining tidal flats. We divided the Yangtze Estuary into Shanghai and Jiangsu areas, which differ in riverine sediment supply and tidal flat management patterns. Although land claim has accelerated in both areas, the decline in tidal flat area has been much greater in Jiangsu than in Shanghai because of abundant supplies of sediment and artificial siltation in the latter area. The results highlight the need for better coastal planning and management based on tidal flat dynamics.

Estuaries and tidal embayments are partly enclosed coastal bodies of water with a free connection to the open sea at their tidal inlet and with minimal (tidal embayments) or substantial fluvial input (estuaries). Their tidal inlets can only remain open over multiple centuries to millennia when (1) the formation of accommodation space exceeds infilling or (2) the inlet system is in dynamic equilibrium (i.e., sediment input equals output). Numerical modeling studies often suggest that estuaries and tidal embayments can develop toward a dynamic equilibrium under constant boundary conditions and consequently remain open over centuries to millennia, whereas in the Holocene sedimentary record many estuaries and tidal embayments are observed to have filled up and closed off. This raises the questions whether and how tidal inlets can remain open over long timescales (centuries to millennia), and what the effects are of river inflow and sediment supply. Here we compare the long-term evolution of contrasting tidal systems along the Dutch coastal plain to empirically identify the most important factors that control their long-term evolution. We study tidal systems along the Dutch coast because of (1) high data density, (2) abundant well-preserved and well-described estuaries and tidal embayments with contrasting boundary conditions and morphodynamic evolution and (3) their low-sloping setting with soft boundaries. This makes contrasting estuarine dimensions and development largely dependent on initial conditions, boundary conditions and internal biogeomorphological processes. In the Middle Holocene, Dutch estuaries and tidal embayments were mainly formed by rapid relative sea-level rise. In the late Holocene, they were predominantly the result of natural and human-induced subsidence in coastal plain peatlands. Tidal inlets connected to rivers (estuaries) persisted and attained dynamic large-scale equilibrium while tidal embayments without or with a marginal fluvial inflow were unstable and closed off under abundant sediment supply. Estuaries probably attained a quasi-stable configuration wherein sediment input equaled export due to river-enhanced ebb flow, until fluvial influx was cut off by upstream avulsion causing transition to an embayment and system closure. Long-term net import of sediment from the sea into Dutch tidal embayments is favored by strong, flood-dominated, tidal asymmetry along the Dutch coast, the shallow sand-rich floor of the North Sea, erosion of inherited coastal promontories, and the abundance of mud in the coastal area supplied by the Rhine and Meuse rivers. While sandy tidal embayments without fluvial feeders and with fixed boundaries may obtain dynamic equilibrium and remain open over long timescales, we hypothesize that an abundance of mud and eco-engineering species often culminates in continuous embayment filling with fine sediment and the growth of intertidal and supratidal areas, eventually resulting in closure of the embayment.

INTRODUCTION Understanding the hydrological dynamics of brackish water bodies is considered important for the effective conservation and management of the natural environment of tidal estuaries. Especially, fresh water inflows and residence times have a marked effect on the salinity within an estuary. Residence time, which refers to the mean time required to transport dissolved or suspended matter out of a water body, can be one of the limiting factors affecting phytoplankton abundance within a system (Monbet, 1992). Howarth et al. (2000) reported that a decrease in river inflows results in increased residence times and primary production in estuaries. Moreover, since the settlement and deposition of suspended matter is dependent on residence time, short residence times are considered to improve the water quality of estuarine water. A box model using salt as a conservative tracer is often applied to estimate both fresh water inflows and residence time within a system, both of which are considered important indicators of the physical condition of the estuarine environment. However, while the box model is simple in principle, the cases to which it can be applied are relatively limited, particularly in tidal estuaries because of its non-steady flow. Tidal flats along the periphery of tidal estuaries are important habitats for a variety of coastal organisms, particularly as nurseries for fish. The tidal flats of Ota River Estuary support numerous benthic fauna (16 Eucrustacea spp., 14 Pelecypoda spp. and Gastropoda spp., and 6 Polychaeta spp.) (Hibino et al., 2006). The salinity and dissolved oxygen concentration of the pore water in these areas and the particle size of the bed material has been shown to restrict the habitat preference of these species (Lalli and Persons, 1993). Submarine groundwater discharge is also important for material circulation in coastal region (Simmons, 1992; Moore, 1996; Burnett, 2003). Nonetheless, the groundwater environment of tidal flats is relatively poorly understood.

In recent decades major water developments have led to an agricultural transformation of the Senegal delta both in Senegal and Mauritania. This otherwise, semi-arid region of the Sahel band now has an abundant supply of freshwater all year round mostly used for irrigation and urban water supply, including for the capital cities of the two countries. Archives from the Landsat satellites and in-situ hydrographs were used in this paper to retrace and analyse the hydrological changes that have taken place in the region since the middle of the 20th century. The satellite archives indicate that the area covered by irrigation increased by one order of magnitude from 73 km(2) in 1973 to similar to 770 km(2) in 2010. The observed hydrological changes are complex, multi-faceted and often of great magnitude. If the water cycle was representative of natural conditions in the early 1980s, it is now representative of a heavily modified system controlled and impacted by human activities. The first hydraulic infrastructure was installed in 1947 to enable the Lake of Guiers to become the main water supply for Dakar. Two large dams were built on the Senegal River in the mid-1980s that modified the hydrological regime of the river by 1) preventing seawater intrusion, 2) raising the stage of the river and-of Lake of Guiers and 3) moderating floods. Another recent hydrological change in the delta was the opening of river mouth in 2003, which has led to a reduction of the average water level while increasing the semi-diurnal tidal wave between the river mouth and Diama. Each phase of these river regime changes and each step of the irrigation expansion are expressed in localised changes in the physical groundwater system. Increasingly, the retroaction from the shallow aquifer systems is observed as a rise of the saline water table. This poses a threat to the environmental and agricultural value of the region, and the salinization of the soils. Mitigating actions for this threat are currently being envisaged by the authorities.

Humans have played an important role in fluvial systems because of the impact of their land-use activities, frequently leading to degradation of environmental conditions. Rivers, which are the primary agents in sediment transport, have thus been subject to changes in sediment fluxes. The Suriname River has been affected by anthropogenic activities since colonial times, and has experienced strong discharge and sediment-load changes since the construction of the Afobaka Dam in 1964. The river's estuary sediments largely consist of fine-grained sediments, originating, ultimately, from the Amazon River and transported by the strong tidal current. The influence of this tidal current is diminished at the head of the estuary, allowing the river flow to become dominant. Also remarkable is the interaction of the Suriname River and the westward-migrating mudbanks which is evident in the changing magnitude and volume of Braamspunt, a mudcape located at the mouth of the estuary. The regulated discharge of the river results in a change of the river's morphology, resulting, among other things, in the growth of river bars.

Bangladesh is the biggest delta of the world. Construction of numbers of polders is one of the flood resilient approach. But the presence of coastal polders de-linked the flood plain. The siltation in river causes riverbeds to become higher than the adjacent crop lands, and vast area under the polders became permanently water logged rendering large tract of land uncultivable. The current practice is temporarily de-poldering by cutting embankment. This is a natural water management process with very little human interventions but it needs strong participation and consensus with a great deal of sacrifice by the stakeholders for a specific period (3 to 5 years or even more)[1]. An attempt has been made to study the phenomena of tidal basin management reviewing some secondary data and processes involved in successfully operated tidal basins of Bangladesh. And preliminary laboratory experiments are carried out to precisely look into the suspended sediment transport. With varying outflow discharge and sediment supply, the transport processes are investigated. 3D sediment transport model developed using openFOAM has good agreement with experimental result and can be used to better understand effectiveness of tidal basin management.

Tidal sand bars and tidal sand ridges are extensively developed in the macrotidal Gulf of Khambhat, offshore western India. The inner and outer regions of the gulf are characterised by the development distinct tidal sand bodies with discrete geometries and dimensions. The outer gulf ridges are long, narrow, curvilinear and several metres high (similar to 20 m). They are asymmetric in cross-section and migratory in nature, forming 'ribbon' like sand bodies separated by tidal channels. Active dunes on these ridges indicate the presence of sand and their orientation parallel to palaeo-shorelines supports a tidal origin. In contrast to the outer gulf tidal sand ridges, sand bars associated with macrotidal estuaries flanking the Gulf of Khambhat typically have an elongate to diamond shape and are only hundreds of metres in width and a few kilometres length. These tidal sand bars occur in the estuary mouths and within the tidally influenced fluvial reaches of the rivers flowing into the gulf. The height of these sand bars is in the range similar to 1-3 m. Due to high tidal ranges and bi-directional flow the sand bars do not develop significant height and are formed between the mutually evasive ebb and flow channels. Their bi-directional foresets and the presence of abundant mud drapes associated with the dunes within in-channel sand bars indicate a tidal origin. The Gulf of Khambhat acquired the present configuration in the last few thousand years since the Pleistocene sea-level lowstand (last glacial maximum, similar to 18 Ka) when the entire continental shelf was subaerially exposed and rivers down-cut into the coastal plain. With increasing sea-level rise, the exposed shelf was drowned, flooding parts of the Modern western Indian peninsula, and large tidal sand ridges formed in the outer gulf. After the fall of sea-level at 2 ka the gulf acquired the Modern configuration with multiple estuaries on both coastlines, rivers supplied the embayment with sandy sediment, and tidal sand bars formed in the Modern estuaries. Quantitative data gathered from the Modern Gulf of Khambhat indicates that for the P50 case, a vertical drill hole will encounter tidal sand bodies (ridges and bars combined) of approximate dimensions 1700 m long, 470 m wide and 1.5 m high, with a spacing of 400 m. In subsurface hydrocarbon reservoirs, where data is sparse and only limited amount of core is available, this quantitative dataset can be useful to constrain subsurface geocellular models. Also, the overall geometry, distribution and aspect ratio of the tidal sand ridges and tidal sand bars can be used to identify ancient counterparts through seismic geomorphology or in core. (C) 2016 Elsevier Ltd. All rights reserved.

International audience; Estuaries are coastal areas controlled by hydrodynamic factors such as sea-level changes, waves and tidal currents, and river discharge. This study focuses on the Vilaine Estuary which is strongly impacted by human activity after construction of Arzal dam in 1970. The purpose of this research is to differentiate the role of natural from anthropogenic factors on sediment dynamics within the Vilaine Estuary. We are proposing a hypothetical model based on the hydrodynamic modification and morpho-sedimentary development by analyzing the natural estuarine evolution and the impact of human alteration to the natural system by utilizing datasets including river discharge, tidal currents, winds and wave activities to further combine with photographic, bathymetric, topographic and sedimentary surveys. Results show that waves carry sediment from the sea and rework local sediments. The river damming is reducing the tidal prims and leads to the fall of tidal currents. This new situation supports the sediment deposition and reduces at the same time the accommodation space which decrease tidal currents in feed-back. The Vilaine Estuary is therefore coming close to a bay-type functioning which leads to a channel narrowing, a drastic increase of the tidal flat zone, an acceleration of erosional processes affecting the main channel, salt marsh and all associated depositional systems. We propose a hypothetical model showing that this evolution took place in two steps and we show that the dam has an effect to accelerate a natural infilling of the estuary.

Dynamic equilibrium of short tidal systems with ebb deltas, inlets, and basins is poorly understood. Observations suggest the possibility of equilibrium with sediment import balancing export, while individual channels and shoals at the local scale remain dynamic. Our objectives are to ascertain (1) whether tidal systems under entirely steady forcing can attain this state and (2) under what conditions cyclic channel-shoal migration occurs. We present experiments of tidal systems developing from an initial breach in the coast. We periodically tilted the entire flume to obtain reversing tidal currents and sediment transports. The surface area of the back-barrier basin with an inlet channel with erodible boundaries continued to enlarge while sediment mobility decreased. Experiments with fixed inlet boundaries remained smaller and much more dynamic and had cyclically migrating ebb and flood channels. The same cyclicity with a period of about 80 tides is observed in shifting dominance of the two channels of the inlet and in the shifting channels in the basin. Experiments with stepwise sea level rises resulted in more rapid channel and bar shifting, increased channel dimensions and basin size. We conclude that cyclic migration of channels is coupled between inlet and basin but the ebb delta did not show such cyclicity. Furthermore, tidal basins with erodible boundaries slowly enlarge by margin erosion toward a system where sediment mobility is at the threshold for motion, as in braided gravel-bed rivers. Consequently, in nature dimensions of tidal systems are partly determined by naturally formed cohesive and vegetated margins and geological context.

Changes in tidal regime in the heavily modified Venice Lagoon, Italy, are investigated using long-term observations and numerical modelling. The amplitudes of the major tidal constituents exhibit a significant increase over the last century. Analysis of tide gauge data in the adjacent Adriatic Sea reveals that these changes could be only partially attributed to the rise of the mean sea level. Numerical experiments confirm that natural and anthropogenic morphological changes are responsible for the alteration of tidal regime inside the lagoon. Temporal and spatial changes in tidal asymmetry highlight the complex impacts of human interventions on tidal changes and long-term morphodynamics. Our results suggest that over time the lagoon became more and more an ebb-dominant system. Moreover, in Venice the tidal modulations are significantly impacting the frequency with which high water level thresholds are exceeded. Occurrence of flooding events is therefore influenced by sea level rise and secondarily by the increase in amplitude of principal tidal waves.

Vegetation is increasingly recognized as an important control on flow and landform patterns in many landscape types. Field studies on the landscape-scale effect of vegetation in fluvial and tidal floodplains are relatively scarce while insights are especially based on flume and numerical models. Large-scale flow patterns and landforms were measured on a vegetated tidal marsh and unvegetated tidal flat, in particular dynamic changes in two-dimensional water surface slopes, flow velocities and directions on an extensive network of locations. It was found that during flooding and drainage of the vegetated tidal marsh, the flow was concentrated in and routed through bare tidal channels, whereas on the unvegetated tidal flat more homogeneous sheet flow occurred. On the marsh the peak flow velocities were lower on the vegetated platform (< 0.1 m/s) compared to their adjacent tidal channels (0.3− 1 m/s), while on the bare tidal flat the channel and platform flow velocities were not significantly different from each other (0.1 − 0.4 m/s). These differences in flow patterns have important implications for the landform differences between vegetated and bare tidal floodplains: (1) for tidal channels with channel widths smaller than 10 m, width-to-depth ratios (= β) were smaller for the tidal marsh channels (β ~ 3) than for the tidal flat channels (β ~ 9) (due to flow concentration towards the channels in the marsh); and (2) the vegetated marsh platform exhibits a clear levee-basin topography (due to vegetation-induced platform flooding from the channels), while there is no levee-basin topography on the bare flat (due to sheet flow). This study not only emphasizes previous findings on the direct effect of vegetation, acting as frictional constraints on flow in tidal marshes, it also suggests that the indirect effect of vegetation, namely its induced micro-topography, influences the flooding and drainage behavior of marsh systems potentially altering feedbacks caused by direct vegetation effects.

We use a one-dimensional morphodynamic model to analyze the long-term evolution of the lower reaches of the Fly River, Papua New Guinea, from the Everill Junction to the delta mouth. The model shows how the break in the exponential trend of river width triggers deposition, thus producing a tidal region characterized by a higher bed elevation with respect to the river-dominated one. Numerical simulations indicate that the river attains a dynamic equilibrium configuration in which the amount of sediment entering upstream is flushed seaward. A sensitivity analysis is performed, in which the effect of varying solid discharge, tidal harmonics, and initial conditions is discussed. The model shows that an equilibrium configuration results from a delicate balance between the aggrading effect associated with channel divergence (acting mainly during neap tide and at slack water) and the opposite effect of tidal flushing driven by residual water discharge. A physically meaningful morphodynamic equilibrium occurs only for a small range of values of sediment discharge prescribed at the upstream boundary. In particular, an increase in sediment discharge leads to aggradation, while a decrease triggers extensive scour and a deepening of the estuary.

Tidal influence and local morphology on circulation and salt transport are investigated in the Caeté river estuary, a well-mixed estuary along the north coast of Brazil. Velocity, temperature, and salinity data were collected in three different locations along the estuary’s main channel, over three single, 13 h tidal cycles. The aim of this study was to investigate the relationship between tidal distortion and salinity by using classical methods of comparison of three cross-channel circulation characteristics, as well as computation of salt flux and vertical mixing. Findings indicate a flood-ebb asymmetry in currents, due to the distinct funneling morphology of the estuary, with shallow marginal areas being dominant towards the estuary head, while both stratification and shear dominate near the estuary mouth. The tidal currents enhanced vertical diffusion in the mid- and lower reaches, explaining the prevailing weakly stratified conditions, while the dominant well-mixed conditions in the upper estuary are a result of a combination of stronger flood currents and negligible vertical saline gradient. The predominant downstream salt transport supports the conclusion that there is little accumulation of salt in the Caeté river estuary. In addition, findings indicate that tidal correlation and Stokes drift are important components in the upper estuary, while tidal correlation played an important role in the middle estuary, with fluvial discharge most important in the lower estuary.

Tidal propagation in, and division of net water transport over different channels in an estuarine network are analyzed using a newly developed idealized model. The water motion in this model is governed by the cross-sectionally averaged shallow water equations and is forced by tides at the seaward boundaries and by river discharge. Approximate analytical solutions are constructed by means of a harmonic truncation and a perturbation expansion in a small parameter, being the ratio of tidal amplitude and depth. The net water transport results from an imposed river discharge and from residual water transport generated by nonlinear tidal rectification. Two new drivers are identified that contribute to the net water transport in tidal estuarine networks, viz. the generation of residual water transport due to gradients in dynamic pressure and due to a coupling between the tidally averaged and quarter diurnal currents through the quadratic bottom stress. The model is applied in a case study on the Yangtze Estuary, to investigate tides and division of net water transport over its multiple channels during the wet and dry season, as well as before and after the construction of the Deepwater Navigation Channel. Model results agree fairly well with observations. Process analysis reveals that the decrease in tides from dry to wet season is due to enhanced bottom stress generated by river-tide interactions. Also, the seasonal variations in net water transport are explained. It is furthermore shown and explained that due to the Deepwater Navigation Channel tidal currents have increased and net water transport has decreased in the North Passage. These changes have profound implications for net sediment transport and salinity intrusion.

Bifurcations in tidally influenced deltas distribute river discharge over downstream channels, asserting a strong control over terrestrial runoff to the coastal ocean. Whereas the mechanics of river bifurcations is well-understood, junctions in tidal channels have received comparatively little attention in the literature. This paper aims to quantify the tidal impact on subtidal discharge distribution at the bifurcations in the Mahakam Delta, East Kalimantan, Indonesia. The Mahakam Delta is a regular fan-shaped delta, composed of a quasi-symmetric network of rectilinear distributaries and sinuous tidal channels. A depth-averaged version of the unstructured-mesh, finite-element model second-generation Louvain-la-Neuve Ice-ocean Model has been used to simulate the hydrodynamics driven by river discharge and tides in the delta channel network. The model was forced with tides at open sea boundaries and with measured and modeled river discharge at upstream locations. Calibration was performed with water level time series and flow measurements, both spanning a simulation period. Validation was performed by comparing the model results with discharge measurements at the two principal bifurcations in the delta. Results indicate that within 10 to 15 km from the delta apex, the tides alter the river discharge division by about 10% in all bifurcations. The tidal impact increases seaward, with a maximum value of the order of 30%. In general, the effect of tides is to hamper the discharge division that would occur in the case without tides.

Although rising global sea levels will affect the estuarine flooded areas over the coming decades, the local and regional-scale processes will also induce important changes in these coastal systems. The main aim of this work is to investigate possible tidal changes in estuarine systems induced by local geomorphologic modifications, analysing the particular case of Ria de Aveiro which is in risk of inundation. Located in the Portuguese west coast, this tidally driven lagoon has a large area of mostly abandoned salt pans, which are in progressive degradation caused by the lack of maintenance and by the strong currents which erode their protective walls. To explore possible tidal changes the hydrodynamic model ELCIRC was applied to Ria de Aveiro to simulate and analyse the impact in the lagoon hydrodynamics of this degradation which results in the enlargement of the lagoon flooded area. A high-resolution grid (grid spacing of the order of 1 m) was developed in order to represent the narrow channels adjacent to the salt pans. The hydrodynamic model was then successfully calibrated and assessed for skill for the Aveiro lagoon through comparison between measurements and model results and quantification of the numerical accuracy. The model was subsequently used to investigate the effect of the flooded lagoon area enlargement on tidal propagation in Ria de Aveiro. Simulations were performed for three geomorphologic configurations, representing the reference or present situation and two flooded scenarios. Results were compared through the analysis of tidal currents, tidal asymmetry and tidal prism. The increase of the lagoon flooded area results in an intensification of the tidal currents, tidal prism and tidal asymmetry. Results also indicate that the tidal prism further increases when the flooding depth increases. Otherwise, changes in tidal currents and in tidal asymmetry pattern are negligible with the increase of the flooded area depth. These results indicate that modifications of the flooded area of estuarine systems will result in tidal changes, with an intensification of the actual tidal patterns induced by the enlargement of inundation areas.

The physical influence of sea tides on the lower reaches of the Amazon River can be identified more than 1000 km upstream from the sea. Analysis of upstream tidal wave propagation on the Amazon River contributes to the understanding of the hydrodynamics of the lower reaches and to the quantification of the influence of sea level on sedimentation rates. Continuous over-the-year recording of water levels has been undertaken at eight locations along the lower reaches of the Amazon River and flow measurement campaigns have been organized for different river discharge rates (100 000 m3 s−1, 190 000 m3 s−1 and 250 000 m3 s−1) and sea-tide amplitudes (2–3·5 m). Damping, time-delay and deformation of the tidal wave signals, depending on water regimes and distances from the sea, have been analyzed. The physical processes of wave propagation and cyclic water storage and release have been investigated both through data analysis and the application of mathematical hydrodynamic models. The impact of tidal pulses on sediment transport to the sea has been assessed. Copyright © 2009 John Wiley & Sons, Ltd.

Made available in DSpace on 2016-10-10T03:51:47Z (GMT). No. of bitstreams: 5 Water demand and flows in the São Francisco River Basin (Brazil) with increased irrigation.pdf: 671626 bytes, checksum: 02e646fd3fc0f8c9c45ed49f814916da (MD5) license_url: 52 bytes, checksum: 3d480ae6c91e310daba2020f8787d6f9 (MD5) license_text: 23738 bytes, checksum: 1a64b812a61c51c296c1ad647d0096a6 (MD5) license_rdf: 23930 bytes, checksum: 6b71892b27c4389434057b8b0e86b43e (MD5) license.txt: 1887 bytes, checksum: 445d1980f282ec865917de35a4c622f6 (MD5) Previous issue date: 2009 Most activities that support economic growth in the Sa˜o Francisco River Basin (Brazil) need water. Allocation of the water resources to each competing use needs quantification in order to develop an integrated water management plan. Irrigation agriculture is the largest water consuming activity in the basin. It has produced large economic and social advancements in the region and has potential for further development. The local development agency in the Sa˜o Francisco River has projected an increase ofmore than 500,000 ha in irrigation developments distributed within the basin. Water requirements of the projected irrigation expansions and their effects on river flow were quantified. A semi-distributed model was constructed to simulate the water balance in 16 watersheds within the basin. The watersheds were hydrologically characterized by the average precipitation, atmospheric demand and runoff as well as their variability. Water requirements for increased irrigated agriculture were calculated using an agronomic mass balance. A Monte Carlo procedure generated the variability of irrigation requirements and resulting decreased river flows from the multidimensional probability distribution of the hydrologic variables of each watershed. Irrigation requirements were found to be more variable during the wet season because of weather variability. In contrast to what might be expected, in drier years, irrigation requirements were often larger during the wet season than in the dry season because the cropped area is largest in the wet months and variability of precipitation is greater. Increased irrigation shifted downward the distribution of river flows but not enough to affect other strategic water uses such as hydropower. Further irrigation expansion may be limited by wet season flows. Sim Publicado

OBJECTIVES: Patients with knee osteoarthritis (OA) often suffer pain that is not fully controlled by analgesics and often require intra-articular therapies. The aim of this study was to compare the benefits of intra-articular corticosteroid injections (CSIs) and tidal irrigation (TI) in patients with OA of the knee. METHODS: We performed a dual-centre, single blind, randomised, parallel group trial comparing TI and CSI. Patients with knee OA were randomised to either irrigation using a 3.2mm arthroscope under local anaesthesia or an intra-articular injection of 40 mg triamcinolone acetonide and 1% lidocaine. Patients were followed for 6 months. The primary outcome measure was the Western Ontario and McMaster Universities OA Index total pain score (visual analogue scale, VAS). RESULTS: One hundred and fifty patients were recruited of whom 71 received TI and 79 CSI. In both treatment groups, over 80% of patients reported improvement at 2 and 4 weeks. After this time, the benefit of CSI decreased whereas that of TI was maintained: at 26 weeks the pain relief afforded by TI was significantly greater than that of CSI. At 26 weeks 29% of the CSI group reported improvement vs 64% of the TI group (P

[1] Shallow tidal basins such as the Venice Lagoon, Italy, are often characterized by extensive tidal flats and salt marshes that lie within specific ranges of elevation. Tidal flats lie just below the mean sea level, approximately between −0.6 and −2.0 meters above the mean sea level (m a.m.s.l.), whereas salt marshes lie at an average elevation higher than mean sea level (i.e., between +0.1 and +0.5 m a.m.s.l.). Only a small fraction of the tidal basin area has elevations between −0.6 and +0.1 m a.m.s.l. This occurrence suggests that the morphodynamic processes responsible for sediment deposition and erosion produce either tidal flats or salt marshes but no landforms located in the above intermediate range of elevations. A conceptual model describing this evolutionary trend has recently been proposed. The model assumes that the bimodal distribution of bottom elevations stems from the characteristics of wave induced sediment resuspension and demonstrates that areas at intermediate elevations are inherently unstable and tend to become either tidal flats or salt marshes. In this work, the conceptual model is validated through comparison with numerical results obtained with a two-dimensional wind wave-tidal model applied to the Lagoon of Venice, Italy. Both the present and the 1901 bathymetries of the Venice Lagoon are used in the simulations and the obtained numerical results confirm the validity of the conceptual model. A new framework that explains the long-term evolution of shallow tidal basins based on the results presented herein is finally proposed and discussed.

There is a well-tested theory for the computation of salt intrusion in alluvial estuaries that is fully analytical and predictive. The theory uses analytical equations to predict the mixing behaviour of the estuary based on measurable quantities, such as channel topography, river discharge and tidal characteristics. It applies to single-channel topographies and estuaries that demonstrate moderate tidal damping. The Mekong delta is a multi-channel estuary where the tide is damped due to a relatively strong river discharge (in the order of 2000 m3/s), even during the dry season. As a result the Mekong is a strongly riverine estuary. This paper aims to test if the theory can be applied to such a riverine multi-channel estuary, and to see if possible adjustments or generalisations need to be made. The paper presents salt intrusion measurements that were done by moving boat in 2005, to which the salt intrusion model was calibrated. The theory has been expanded to cater for tidal damping. Subsequently the model has been validated with observations made at fixed locations over the years 1998 and 1999. Finally it has been tested whether the Mekong calibration fits the overall predictive equations derived in other estuaries. The test has been successful and led to a slight adjustment of the predictive equation to cater for estuaries that experience a sloping bottom.

Tidal inlet characteristics are controlled by wave energy, tidal range, tidal prism, sediment supply and direction and rates of sand delivered to the inlet. This paper deals with the relations between inlet and lagoon evolutions, linked by the tidal prism. Our study is focused on the Maumusson Inlet and the Marennes-Oleron Bay (first oyster farming area in Europe), located on the western coast of France. The tidal range (2–6 m) and wave climate (mean height: 1.5 m) place this tidal inlet system in the mixed energy (tide, waves), tide-dominated category. The availability of high-resolution bathymetric data since 1824 permits to characterise and quantify accurately morphological changes of both the inlet and the tidal bay. Since 1824, sediment filling of the tidal bay has led to a 20% decrease in its water volume, and a 35% reduction of the inlet throat section. Furthermore, the bay is subjected to a very high anthropic pressure, mainly related to oyster farming. Thus, both natural and human-related processes seem relevant to explain high sedimentation rates. Current measurements, hydrodynamic modelling and cross-sectional area of the inlet throat are used in order to quantify tidal prism changes since 1824. Both flood and ebb tidal prism decreased by 35%. Decrease in the Marennes-Oleron Bay water volume is inferred to be responsible for a part of tidal prism decrease at the inlet. Tidal prisms decrease may also be explained by an increase in frictional resistance to tidal wave propagation, due to a general shoaling and oyster farms in the bay. A conceptual model is proposed, taking into account natural and human-related sedimentation processes, and explaining tidal inlet response to tidal bay evolutions.

Bahía Blanca Estuary is a complex network of tidal channels, extensive tidal flats, low marshes areas and islands. The lack of a large source of sediments either from river or the shelf results in that the tidal channels of this estuary controlling the dispersal of sediment into the system. A 3-year study of morphodynamic equilibrium has been carried out in the tidal channels of Bahía Blanca Estuary with the aim to investigate the evolution of the system. Detailed changes in the spatial bathymetry linked to the observed flow and sediment processes give a clearer indication of the tidal circulation in the channels. This paper discusses morphologic variability and processes of the erosion, deposition and transport of sediment, which determines the morphological evolution of the system. Current measurements showed that channels appeared to be ebb-dominated with peak speeds of up to 1.2 m/s. Examination of current durations suggests that flood-time dominance is about 7 hr, while ebb period is 5 hr. The cross section bathymetry is usually bimodal with two channels separated by a shallow area. The deeper channel experiences ebb-directed net, while the shallower channel could be influenced by the net flood current. The net sediment transport into of these systems is shown to be governed more by the degree of tidal velocity asymmetry (ebb flow). In change the degree of time asymmetry (flood flow) governs the trends of erosion by the longer duration of tidal flood. Channel migration causes a shift from degradation in the north sector to aggradation in the south side, during adjustment. As a consequence, the estimated rate of migration is on the order of 25 m yr−1. Comparing the migration pattern between tidal and fluvial channel, we can to say that in rivers, where the water flows only one way, all morphologic features tend to migrate downstream. In tidal channels, by contrast, the erosive features appear to migrate in opposed directions to the dominant sediment transport direction. It is the erosive processes at tidal channels, which are mainly associated with flood currents dominance. El estuario de Bahía Blanca esta formado por una compleja red de canales de marea mesomareales, extensas llanuras de marea, marismas e islas. La escasa cantidad de sedimento aportado por los ríos y el introducido desde la plataforma, hacen que los canales de marea controlen la dispersión de los mismos dentro del sistema. Un estudio de tres años sobre el equilibrio morfodinámco, fue realizado en los canales de marea del Estuario de Bahía Blanca con el propósito de investigar la evolución del sistema. Sobre la base de análisis de relevamientos batimétricos espaciados 3 años, observaciones del flujo y procesos sedimentarios, se determinó la circulación en los canales. Por lo tanto, este trabajo discute los cambios morfológicos y los procesos de erosión, sedimentación y transporte de sedimento en los canales de marea del Estuario de Bahía Blanca, los cuales determinan la evolución morfológica del sistema. Las corrientes de marea muestran que los canales son dominados por el reflujo con velocidades máximas de 1.2 m/s, alcanzando el flujo velocidades máximas de 0.80 m/s. Exámenes de la duración de las corrientes sugieren que el flujo demora 7 hr mientras el reflujo dura 5 hr. Las secciones batimétricas transversales a los canales son bimodales, con dos canales separados por un área mas somera. El canal más profundo experimenta una corriente neta en dirección al reflujo mientras que el canal mas somero la corriente neta es en dirección al flujo. Nosotros consideramos que el transporte neto de sedimento dentro del sistema es gobernado por el grado de asimetría en velocidad, el cual es en dirección del reflujo. En cambio la duración de las corrientes de flujo/reflujo gobierna la erosión en el sistema de los canales, siendo dicha asimetría en dirección al flujo. Esta provocaría la migración de los canales hacia el sector norte con una velocidad de erosión de 25 m/año. Comparando el modelo de migración de los canales de marea con el de los ríos podemos observar que estos últimos migran corriente abajo, en dirección al transporte de sedimento. En cambio, los canales de marea migran en dirección opuesta al transporte de sedimento. Por lo tanto, consideramos que los procesos erosivos en los canales de marea están relacionados con las corrientes de flujo. Fil: Ginsberg, Silvia Susana. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Bahía Blanca. Instituto Argentino de Oceanografía. Universidad Nacional del Sur. Instituto Argentino de Oceanografía; Argentina Fil: Perillo, Gerardo Miguel E.. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Bahía Blanca. Instituto Argentino de Oceanografía. Universidad Nacional del Sur. Instituto Argentino de Oceanografía; Argentina. Universidad Nacional del Sur; Argentina

Water quality of the Calabar River Estuary was measured during November, February and May representing the major climatic conditions and during high tide, low tide and mid-tide representing the most important tidally forced hydrodynamic conditions in the estuary. The lowest water quality ( Key Words: Water quality, Tidal regimes, Seasonality, Calabar River Estuary, Nigeria. [Global Jnl Environ Sci Vol.2(2) 2003: 106-111]

An idealized morphodynamic model is used to gain further understanding about the formation and characteristics of shoreface-connected sand ridges and tidal sand banks on the continental shelf. The model consists of the 2D shallow water equations, supplemented with a sediment transport formulation and describes the initial feedback between currents and small amplitude bed forms. The behaviour of bed forms during both storm and fair weather conditions is analyzed. This is relevant in case of coastal seas characterized by tidal motion, where the latter causes continuous transport of sediment as bed load. The new aspects of this work are the incorporation of both steady and tidal currents (represented by an M2 and M4 component) in the external forcing, in combination with dominant suspended sediment transport during storms. The results indicate that the dynamics during storms and fair weather strongly differ, causing different types of bed forms to develop. Shoreface-connected sand ridges mainly form during storm conditions, whereas if fair weather conditions prevail the more offshore located tidal sand banks develop. Including the M4 tide changes the properties of the bed forms, such as growth rates and migration speeds, due to tidal asymmetry. Finally a probabilistic formulation of the storm and fair weather realization of the model is used to find conditions for which both types of large-scale bed forms occur simultaneously. These conditions turn out to be a low storm fraction and the presence strong tidal currents in combination with strong steady currents during storms.

The time-course evolution of ammonium concentration has been examined in the flood water during the first 25 min of tidal inundation. The way this transport fluctuates with the tidal ranges and wind conditions was investigated. Flood water was collected at three sites, located along a transect from the lower to the upper intertidal area of the Tagus estuary. At spring and intermediate tides, the periods of air exposure vary slightly along the transect due to the high tidal amplitude and the flatness of the area, but the upper site remains uncovered at neap tide over the entire tidal cycle. At each site, sampling was performed at different tidal ranges covering the neap-spring tidal cycle and wind conditions. Ammonium was determined in the flood water at short time intervals: 1, 2, 3, 4, 5, 10, 15, 20 and 25 min. A clear pattern was observed along the transect: considerable quantities of ammonium were exported from the sediment to the water column at the beginning of the inundation, ranging from 0.2 to 4.8 mmol m(-2) d(-1). The highest transport was recorded at the lower intertidal site under spring tide conditions, which corresponds to the higher energetic situation and shorter emersion period. The lowest transport was observed at the upper intertidal site during the first inundation that followed three days of neap tide and continuous exposure of the sediment to the air. The value rates (0.2-4.8 mmol m(-2) d(-1)) were one order of magnitude higher than those calculated from molecular diffusion (0.07-0.16 mmol m(-2) d(-1)). This study points to the importance of the tidal flushing of ammonium from the intertidal sediments, and its spatial and tidal fluctuation., La concentration en ammonium des eaux a été étudiée dans la zone intertidale de l'estuaire du Tage : évolution pendant les vingt-cinq premières minutes du courant de flot et intensité du largage en fonction des marées et des conditions de vent. L'eau a été prélevée en trois stations, du plus bas au plus haut de la zone intertidale. En eaux vives et par marées intermédiaires, les durées d'exposition à l'air varient légèrement le long de la section étudiée en raison des marées plus fortes et de la déclivité du sol mais, en eaux mortes, la station haute reste découverte pendant tout le cycle des marées. À chaque station, les prélèvements ont été effectués pour différentes marées couvrant le cycle eau morte/eau vive, avec différentes conditions de vent, lors de séquences de 1, 2, 3, 4, 5, 10, 15, 20 et 25 min. Le schéma suivant a été observé : des quantités considérables d'ammonium sont transférées (0,2 à 4,8 mmol m−2 j−1) du sédiment vers la colonne d'eau à l'arrivée du courant de flot. La plus forte valeur du transfert est enregistrée à la station basse pendant les eaux vives, correspondant à l'énergie maximale et à la plus courte période d'émersion. La plus faible valeur du transfert est observée à la station la plus haute pendant le flot faisant suite à 3 j d'eaux mortes et d'exposition à l'air. Les valeurs mesurées dépassent d'un ordre de grandeur celles calculées à partir de la diffusion moléculaire (0,07 à 0,16 mmol m−2 j−1). Ces résultats mettent en évidence le rôle de la marée dans l'extraction de l'ammonium des sédiments intertidaux et les variations du largage en fonction de l'espace et des fluctuations de la marée.

The freshwater discharge of the Colorado River into the Gulf of California has been reduced to negligible quantities since the construction of the Hoover Dam in 1935. These radical anthropogenic changes in the hydrography of the Colorado River Delta had striking repercussions on both physical and biological processes. Using historical river discharge data, the changes in the flow dynamics and hydrographic patterns before and after the drastic freshwater reduction are studied numerically, using a three-dimensional nonlinear shelf model. The results are applied to assess the environmental impact of the reduction of river discharge on the area. Satellite imagery is also used to compare our results with observed fronts.

The effects of large-scale interventions in the North Passage of the Yangtze Estuary (the Deep Waterway Project, DWP) on the along-channel flow structure, suspended sediment distribution and its transport along the main channel of this passage are investigated. The focus is explaining the changes in net sediment transport in terms of physical mechanisms. For this, data of flow and suspended sediment concentration (SSC), which were collected simultaneously at several locations and at different depths along the main channel of the North Passage prior to and after the engineering works, were harmonically analyzed to assess the relative importance of the transport components related to residual (time-mean) flow and various tidal pumping mechanisms. Expressions for main residual flow components were derived using theoretical principles. The SSC revealed that the estuarine turbidity maximum (ETM) was intensified due to the interventions, especially in wet seasons, and an upstream shift and extension of the ETM zone occurred. The amplitude of the M 2 tidal current considerably increased, and the residual flow structure was significantly altered by engineering works. Prior to the DWP, the residual flow structure was that of a gravitational circulation in both seasons, while after the DWP, there was seaward flow throughout the channel during the wet season. The analysis of net sediment transport reveals that during wet seasons and prior to the DWP, the sediment trapping was due to asymmetric tidal mixing, gravitational circulation, tidal rectification, and M 2 tidal pumping, while after the DWP, the trapping was primarily due to seaward transport caused by Stokes return flow and fresh water discharge and landward transport due to M 2 tidal pumping and asymmetric tidal mixing. During dry seasons, prior to the DWP, trapping of sediment at the bottom relied on landward transports due to Stokes transport, M 4 tidal pumping, asymmetric tidal mixing, and gravitational circulation, while after the DWP the sediment trapping was caused by M 2 tidal pumping, Stokes transport, asymmetric tidal mixing, tidal rectification, and gravitational circulation.

The Han River Estuary (HRE), located on the west coast of South Korea, is well known for its macro tidal characteristics with a tidal range more than 8.5 m. This estuary has a distinctive salinity distribution because its system consists of 3 main channels and 3 rivers, through which major tidal flow and river discharge meet each other. To determine the effect of change in external forcing (e.g., river discharge and tidal variation) on the salinity, a numerical model is established and verified with observation. Based on previous observation, the main channel of HRE shows well- and/or partially-mixed estuary during spring and neap periods, respectively. The vertical stratification during the neap period is stronger than that during the spring due to decreasing turbulent mixing. The numerical results show that the salinity distribution during high river flow condition can be temporally and spatially characterized by river discharge. The asymmetries of the salinity distribution response to increasing and decreasing river discharge are indicated in this estuary. During high river flow conditions, the front of Incheon Harbor is within the region of the freshwater influence.