Search

To solve the difficulty of Chinese scientific examiner eating fresh vegetables in Antarctica station, a greenhouse in the research station was built. It is the first natural light greenhouse in Antarctic land. Running in the severe environment, the greenhouse has the problem of unattended operation and no professional cultivation, and thus demands high reliability. An automatic control system for the Antarctic greenhouse was developed to create a good environment for crop growth. The system is composed of a computer, an environment controller, a data collector, sensors, actuators, and so on. In the greenhouse, environmental parameters are collected and sent to computer for processing and displaying by an environment controller connecting to the data collector for acquisition. In extremely cold area, temperature is the primary factor for a greenhouse, which is heated by water pipes. The fuzzy logic was used to automatically adjust the heating pipe opening according to the measured ambient temperature for temperature control. Sodium lamp and LED were used to supplement light in greenhouse according to Photosynthetic effective value. With controlling the greenhouse’s top cover, side cover, and the natural light supplement, it could simulate the diurnal variation and the seasons change to facilitate plant growth. The greenhouse is irrigated in the tidal irrigation way. For different plants, it is convenient to adjust the irrigation time and duration for greenhouse workers. According to the control strategy, the main factors such as temperature, illumination, and fertilizer of the greenhouse environment are automatically adjusted. Since it was installed in the Antarctica Great Wall Station, the system has proved to run stably with long time monitoring data, providing a guarantee for fresh vegetables supply for resident scientific examiner.

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

Due to channel sedimentation, water deficits and flood still becomes problems in Katingan tidal irrigation system, while the stakeholder plans to reclaim new area in the presence of pyrite soil. This research aims to overcome these problems through four water management scenarios simulated using HEC-RAS to meet the needs of water supply, flushing and drainage. The result shows that water leaching requirement for existing area is 2.48 million m3 and could only be fulfilled by canal normalization. Moreover, extended network with narrow intake canal supplies less than 4.3 million m3 water leaching, so that wide canal connected to the river is required to facilitate more water flowing into the system. Related to flushing, installing pumps in the middle intake could increase canal circulation with one-way outflow during ebb tide, while the inflow depends on flap gates at the same position. Furthermore, the volume of rainwater is generally able to be discharged for every rainy day by all scenario designs. However, existing condition and network expansion with narrow intake canal have less rainwater deficit duration. In conclusion, leaching and drainage aspects require more water storage and wide canal intake, where flushing criterion need the use of pumps and gates.

Marsh restoration projects are nowadays being implemented as ecosystem-based strategies to reduce flood risks and to restore intertidal habitat along estuaries. Changes in estuarine tidal hydrodynamics are expected along with such intertidal area changes. A validated hydrodynamic model of the Scheldt Estuary is used to gain fundamental insights in the role of intertidal area characteristics on tidal hydrodynamics and tidal asymmetry in particular through several geomorphological scenarios in which intertidal area elevation and location along the estuary is varied. Model results indicate that the location of intertidal areas and their storage volume relative to the local tidal prism determine the intensity and reach along the estuary over which tidal hydrodynamics are affected. Our model results also suggest that intertidal storage areas that are located within the main estuarine channel system, and hence are part of the flow-carrying part of the estuary, may affect tidal hydrodynamics differently than intertidal areas that are side-basins of the main estuarine channel, and hence only contribute little to the flow-carrying cross-section of the estuary. If tidal flats contribute to the channel cross-section and exert frictional effects on the tidal propagation, the elevation of intertidal flats influences the magnitude and direction of tidal asymmetry along estuarine channels. Ebb-dominance is most strongly enhanced if tidal flats are around mean sea level or slightly above. Conversely, flood-dominance is enhanced if the tidal flats are situated low in the tidal frame. For intertidal storage areas at specific locations besides the main channel, flood-dominance in the estuary channel peaks in the vicinity of those areas and generally reduces upstream and downstream compared to a reference scenario. Finally, the model results indicate an along estuary varying impact on the tidal prism as a result of adding intertidal storage at a specific location. In addition to known effects of tidal prism decrease upstream and tidal prism increase downstream of additional storage areas, our model results indicate a reduction in tidal prism far downstream of intertidal storage areas as a result of a decreasing tidal range. This study may assist estuarine managers in assessing the impact of marsh restoration and managed shoreline realignment projects, as well as with the morphological management of estuaries through dredging and disposal of sediment on intertidal areas. (C) 2017 Elsevier Ltd. All rights reserved.

Xiangshan Bay is a semi-enclosed bay in China, in which tidal flats have been substantially reclaimed to support the development of local economies and society over previous decades. The loss of tidal flats has led to changes of tides and locally suspended sediment in the bay. The effects of tidal flat reduction on locally suspended sediment dynamics was investigated using a numerical model forced by tidal data and calibrated by observed tidal elevation and currents. The model satisfactorily reproduces observed water levels, currents, and suspended sediment concentration in the estuary, and therefore is subsequently applied to analyze the impact of tidal flat reclamation on locally suspended sediment transport. After the loss of the tidal flats from 1963 to 2010, the suspended sediment concentrations (SSC) at the bottom boundary layer were reduced/increased in the outer bay/tidal flat areas due to weakened tidal currents. In the inner bay, the SSC values near the bottom level increased from 1963 to 2003 due to the narrowed bathymetry, and then decreased from 2003 to 2010 because of the reduced tidal prism. The model scenarios suggest that: (1) a reduction of tidal flat areas appears to be the main factor for enhancing the transport of sediments up-estuary, due to the increased Eulerian velocity and tidal pumping; (2) A reduction of tidal flat areas impacts on spatial and temporal SSC distribution: reducing the SSC values in the water areas due to the reduced current; and (3) a tidal flat reduction influences the net sediment fluxes: lessening the erosion and inducing higher/lower landward/seaward sediment transportation.

Many studies around the world have found that tidal dynamics control the transport of suspended sediments in estuaries, as well as their relationship with runoff discharges and bathymetry morphology. This manuscript examines tidal impact on suspended sediments in the Macuse estuary in Mozambique, southern Africa. Data was collected at 42 stations, including tidal current measurements with an Acoustic Doppler Current Profiler (ADCP), tide elevation with a tidal gauge and suspended sediments with a Niskin bottle. A 14-month model simulation was implemented beginning in November 2013, forced by tides, wind regime and runoff discharges. The results indicated a tidal elevation of 4 m that generated tidal currents of 120 cm s − 1 . These currents combined with the runoff of 500 m3 s − 1 and bathymetry configuration, drove the suspended sediments during the ebb and flood tides. Suspended sediment concentrations suggested the occurrence of sedimentation where water flow was less than 0.10 cm s − 1 for silt and less than 10 cm s − 1 for fine sand. Results of silt concentrations was about ∼ 300 mg l − 1 while fine sand was found to be 0.2 mg l − 1 in both tidal periods in ebb and flood tides during the rainy and dry seasons. The model accuracy of about R2 = 0.88 between the observed and simulated results demonstrated the ability to predict the impact of tides and runoff discharges in the Macuse estuary and may be extended to other estuaries. The model matches in reproducing the sediment transport mechanism will help making political decisions about the estuary sustainability and local coastal management.

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.

This study aims to provide further understanding about the effects that tidal turbines arranged in block farms could have over the water levels when they are deployed in estuaries with shallow bathymetry. As an application of the methodology presented for this purpose, a real case study, the Solway Firth estuary in the UK, has been modelled by means of MIKE21. An idealised model of the estuary has been used to identify the trends in extractable energy and impacts on tidal range for different farm densities and contrasted with a fully detailed model. A spring tide and a coastal flooding scenario have been considered for the detailed model as well as different densities and configurations of the tidal farms. For the densest arrays the extractable energy tends to a limit and the impacts on tidal range become relevant, although they are still lower than the ones resulting from tidal range schemes with similar installed capacities. It has been found that the effects on water levels are not linearly proportional to the increase of the farm density but they seem more closely related to the energy dissipated by the farms. The results of the changes on high and low tide levels over the estuary and time-series at specific locations have been analysed for the detailed models. When comparing between different layouts, changes during low tide levels are slightly higher for the parallel arrays. It can also be concluded that flood risk levels could be potentially reduced in the shoreline whereas some of the intertidal areas and their habitats could disappear as a consequence of significant water level rise at low tides.

River gauging stations are often located upriver of tidal propagation where sediment transport processes and storage are impacted by widely varying ratios of marine to freshwater influence. These impacts are not yet thoroughly understood. Therefore, sediment fluxes measured at these stations may not be suitable for predicting changes to coastal morphology. To characterize sediment transport dynamics in this understudied zone, flow velocity, salinity, and suspended-sediment properties (concentration, size, and settling velocity) were measured within the tidal Song Hậu distributary of the lower Mekong River, Vietnam. Fine-sediment aggregation, settling, and trapping rates were promoted by seasonal and tidal fluctuations in near-bed shear stress as well as the intermittent presence of a salt wedge and estuary turbidity maximum. Beginning in the tidal river, fine-grained particles were aggregated in freshwater. Then, in the interface zone between the tidal river and estuary, impeded near-bed shear stress and particle flux convergence promoted settling and trapping. Finally, in the estuary, sediment retention was further encouraged by stratification and estuarine circulation which protected the bed against particle resuspension and enhanced particle aggregation. These patterns promote mud export (~1.7 t s−1) from the entire study area in the high-discharge season when fluvial processes dominate and mud import (~0.25 t s−1) into the estuary and interface zone in the low-discharge season when estuarine processes dominate. Within the lower region of the distributaries, morphological change in the form of channel abandonment was found to be promoted within minor distributaries by feedbacks between channel depth, vertical mixing, and aggregate trapping. In effect, this field study sheds light on the sediment trapping capabilities of the tidal river – estuary interface zone, a relatively understudied region upstream of where traditional concepts place sites of deposition, and predicts how fine-sediment dynamics and morphology of large tropical deltas such as the Mekong will respond to changing fluvial and marine influences in the future.

Hydrodynamics and sediment dynamics vary greatly in tide-dominated estuaries worldwide, but there is a paucity of data of large tide-dominated estuary systems due to difficulties of observation in a large spatial scale. In this study, we investigate sediment dynamic transitions in a 660-km long section between the tidal limit and mouth of the Yangtze River. We found that tidal effects are almost undetectable in the uppermost 100-km section, but the mean tidal range gradually increases downstream to nearly 3 m at the river mouth. Flow is generally unidirectional in the uppermost 400-km section, although its velocity changes in response to flood/ebb tidal dynamics; in the lowest 250-km section, flow is bidirectional, and ebb flow durations decrease towards the sea. In the lowermost 100 km, the ebb flow durations decreases to below 60%, and the flow is dominated by tidal currents. Salinity is only detectable in the lowest 100-km section due to the dominance of Yangtze River water discharge. Bed sediments mainly include sand in the uppermost 500-km section, whereas mud dominates in the remaining areas. In contrast, the median grain size of the suspended sediments was found to be greater in the lowest 100-km section (8–13 μm) than in the upper sections (5–6 μm) due to strong exchanges between suspended and near bed sediments. The suspended sediment concentration (SSC) was found to be low ( 1 g/L and both surface-bottom and intratidal variabilities occurred. The rates of sediment parameter changes were rapid in the river-sea transitional zone, and this zone may shift upstream and downstream in response to the relative contributions of the river, tides and waves. A conceptual model of the river-sea transition of sediment dynamics for the Yangtze estuary was established, and this model shed light on quantitative studies of sediment dynamics in other large tide-impacted estuaries worldwide.

Flow division at bifurcations in the Yangtze Estuary has received ample attention, since it may control the pathways of terrestrial sediments over downstream river branches including the 12.5 m Deepwater Navigation channel. While some efforts have been made to interpret flow division at the bifurcations of the Yangtze Estuary, little attention has been paid to the role of tides. Flow division at estuarine bifurcations is made complicated by tides that propagate from the outlet of the tidal channels into the delta. To quantify the tidal influence on the distribution of river discharge, and more generally, to understand the mechanisms governing the subtidal flow division at the tidally affected bifurcation in the Yangtze River Delta, a two-dimensional hydrodynamic model is employed. In this model, the landward boundary is chosen beyond the tidal limit, where the tidal motion has faded out entirely. The seaward boundary is chosen such that the river discharge does not influence the water level. Subtidal discharges are decomposed using the method of factor separation, to distinguish between the effects of tides, river discharge and river-tide interactions on the subtidal flow division. Results indicate that tides modify the river discharge distribution over distributary channels in the Yangtze River Delta, particularly in the dry season. A significant difference in the subtidal flow division during spring tide and neap tide shows that the tidally averaged flow division over the distributaries in the delta greatly depends on tidal amplitude. By varying the river discharge at the landward boundary and amplitudes and phases of the principal tidal constituents at the seaward boundary of the established model, the sensitivities of the subtidal flow division to the river discharge and tidal amplitude variation were investigated in detail. Generally, the tidal impacts on the subtidal flow division are around 12% to 22%, with river discharge varying from 30,000 m3s-1 to 20,000 m3s-1. This effect on the flow distribution can even overwhelm the effects induced by river discharge based on geometry only, when the flow discharge is lowest. Furthermore, the fortnightly tidal cycle plays an important role in enhancing the inequality of the subtidal flow division caused by the M2 tidal component solely at the tidal bifurcation in the Yangtze River Delta during low flow.

Due to strong abiotic forcing, dissolved oxygen (DO) in shallow tidal creeks often disobeys the conventional explanation of general aquatic DO cycling as biologically-regulated. In the present work, we seek to quantify the relative importance of abiotic (hydrologic and climatic), and biotic (primary productivity as represented by chlorophyll-a) descriptors of tidal creek DO. By fitting multiple linear regression models of DO to hourly chlorophyll-a, water quality, hydrology, and weather data collected in a tidal creek of a Chesapeake Bay marsh (Maryland, USA), temporal shifts (summer – early winter) in the relative importance of tidal creek DO descriptors were uncovered. Moreover, this analysis identified an alternative approach to evaluating tidal stage as a driver of DO by dividing stage into two DO-relevant variables: stage above and below bankfull depth. Within the hydrologic variable class, stage below bankfull depth dominated as an important descriptor, thus highlighting the role of pore water drainage and mixing as influential processes forcing tidal creek DO. Study findings suggest that tidal creek DO dynamics are explained by a balance of hydrologic, climatic, and biotic descriptors during warmer seasons due to many of these variables (i.e., chlorophyll-a, water temperature) acting as tracers of estuarine-marsh water mixing; conversely, in early winter months when estuarine and marsh waters differ less distinctly, hydrologic variables increase in relative importance as descriptors of tidal creek DO. These findings underline important distinctions in the underlying mechanisms dictating DO variability in shallow tidal marsh-creek environments relative to open water estuarine systems.

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

A tidal stream energy resource assessment can be achieved through direct measurements of tidal elevations or flow velocities, theoretical formulas, and numerical models. This paper first described the development of renewable energy in China. Then, the tidal stream energy resource in the Qiantang River Estuary was assessed. The present work established a 2D numerical model for calculating the power density in the estuary and validated it with in situ water level, tidal current, and suspended sediment concentration measurements. Three possible sites found near the Hangzhou Bay Bridge were selected for detailed resource assessment. The results indicated that if only 50 turbines are deployed to each site, the tidal stream energy output by all turbines would be 7.5 GWh/year. Finally, building a tidal stream power generation device into an existing bridge structure was proposed at the Qiantang River Estuary.

Recent studies suggest that tidal forcing can be as important as gravitational circulation in maintaining an estuarine turbidity maximum (ETM). It is further postulated that a long-term mass balance between the import and export of sediment in an estuary may require episodic large river discharges or ‘freshets’ to flush sediment out of the ETM towards the open sea. In this study, we use a 2-month data set from a mooring in a tidal river that drains into a large drowned-river-valley estuary (Kaipara Harbour, New Zealand) to investigate interactions between tidal-current asymmetry and gravitational circulation. During baseflow river discharge and on spring tides, suspended-sediment transport was directed up-channel (landwards), driven by tidal pumping due to tidal-current asymmetry. During neap tides, the suspended-sediment flux was approximately zero. The data suggest that the bed was not locally erodible and that bed sediments at the site were being supplied by an ETM. The ETM only migrated far enough down channel to be observed at the mooring site during spring tides when the tidal excursion was longer. Suspended sediments were effectively trapped and recycled within the ETM. During and after two freshets, high river discharge displaced saline water from the tidal river, water-column stratification strengthened and the surface and bed current speeds increased. As a result, the advective component of the down-channel directed suspended-sediment flux increased. This provided a transport pathway for sediment out of the otherwise tidally pumped, flood-dominant system. We conclude that largest export of sediments out of the tidal river would potentially occur when a large freshet coincides with an apogean spring tide.

Tides and river slope are fundamental characteristics of estuaries, but they are usually undersampled due to deficiencies in the spatial coverage of water level measurements. This study aims to address this issue by investigating the use of airborne lidar measurements to study tidal statistics and river slope in the Columbia River estuary. Eight plane transects over a 12-h period yield at least eight independent measurements of water level at 2.5-km increments over a 65-km stretch of the estuary. These data are fit to a sinusoidal curve and the results are compared to seven in situ gauges. In situ– and lidar-based tide curves agree to within a root-mean-square error of 0.21 m, and the lidar-based river slope estimate of 1.8 × 10−5 agrees well with the in situ–based estimate of 1.4 × 10−5 (4 mm km−1 difference). Lidar-based amplitude and phase estimates are within 10% and 8°, respectively, of their in situ counterparts throughout most of the estuary. Error analysis suggests that increased measurement accuracy and more transects are required to reduce the errors in estimates of tidal amplitude and phase. However, the results validate the use of airborne remote sensing to measure tides and suggest this approach can be used to systematically study water levels at a spatial density not possible with in situ gauges.

A tidal bore is a hydrodynamic shock, propagating upstream as the tidal flow turns to rising, with macro-tidal conditions in a funnel shaped system with shallow waters. The tidal bore of the Garonne River was extensively investigated in the Arcins channel between 2010 and 2013, typically over one to two days. In 2015, new field measurements were repeated systematically at the same site on 29 August-1 September 2015 and on 27 October 2015. The nature of the observations was comprehensive, encompassing hydrodynamics and turbulence, as well as sediment properties and transport. The tidal bore occurrence had a marked effect on the velocity and suspended sediment field, including a rapid flow deceleration and flow reversal during the bore passage, with very large suspended sediment concentrations (SSCs) during the passage of the tidal bore front and early flood tide, as well as very large suspended sediment flux during the very early flood tide. The suspended sediment concentration (SSC) data indicated a gradual increase in initial mean SSC estimate prior to the bore from 29 August to 1 September 2015. A comparison between suspended sediment flux data showed very significant suspended sediment flux on the first day of tidal bore occurrence, with a decreasing magnitude over the next three days. The data suggested a two-stage bed scour process: at each tidal bore event, surface erosion occurred initially, in the form of stripping; the first stage was followed by delayed mass erosion, occurring about 5–15 min after the tidal bore.

The paper considers tidal effects on the formation of the hydrological and hydrochemical characteristics of the mouth of the Northern Dvina River in the presence of ice cover were considered. The results of natural surveys at the river delta and near-mouth area in March 2014 were analyzed. No surveys as such were performed in winter formerly. It was found that short-term variations of flow rates during the winter low-water time might be traced at 85–95 km from the seaward border of the delta. The tidal effects upon the short-term variability of hydrochemical parameters appeared at 70 km from the delta seaward border. The tidal variations of all the considered parameters were most intense in the mixing zone of riverine and marine waters at the delta.

In arid regions, the construction of dams has led to an increase in irrigated agriculture, resulting in the desiccation of vulnerable lakes and wetlands. In many arid mountainous regions, such as in the Middle East, upstream dams typically feed rivers that flow into lowland terminal (closed) lakes or wetlands. The release of water for environmental purposes is a widely recognised option for reducing such impacts. The present study used monthly hydrological data from the Kor river in southern Iran, its main reservoirs and data above and below the Korbal irrigation system. The Kor river is a major source for feeding the Bakhtegan and Tashk lakes, which have recently started to disappear. An analysis of the water resource system before the dam construction (before 1973) showed that the monthly lake inflow depended on available water in river above the irrigation system (for eight months) and, during the irrigation season, water consumed for irrigation as well (for four months). However, in the post-development period (after 1997), the flow rate to the lake depended almost entirely on the Korbal irrigation system, except during some winter months when little irrigation was needed. Environment flow release has not been effective as it has led to greater water availability in the river, which results in more water being consumed for irrigation, as demonstrated here. To overcome this management mismatch, a new environmental flow release strategy (regime) was designed in which water is released from the upstream reservoirs during periods of low irrigation demand (e.g. winter months).

This study reports distribution of water quality parameters, i.e. salinity, nitrite, nitrate, and phosphate of the Kalibuntung estuary in the southeastern Surabaya coastal area. The study was conducted over 34 sampling points in the river channel, river mouth, and in the coastal water of the Kalibuntung estuary. The result shows that the minimum salinity of (2-4 ppt) reached 3,000 m far from the coastline to upper strem. The maximum salinity of 28.60 ppt found in the coastal water, about 1,000 m seaward from coastline. Based on the numerical modeling analyses, distribution of salinity followed the water movement of eeb-flood currents cycles due to tidal fluctuation. The result obviously revealed that during flood current, water mass from the sea moves to the upper river, on the other hand, during eeb current more volume of river water flows to the sea. It is indicated by salinity values in the river mouth, which reached 27 ppt during high tide and < 20 ppt during low tide. Concentration of ammonia ranging from 0.42 mg/l in the lower part close to the river mouth, up to 6.13 mg/l in the uppermost of the river. This indicated that the river is heavily polluted by organic waste. Concentration of phosphate range from 0.06 to 0.43 mg/l. Its concentration decrease seaward, it is distributed to a distance of 3,000 m fom the river mouth. The river water of Kalibuntung estuary is not permitted to be used as a drinking water, and also it is not feasible for coastal aquaculture. Only in the lower part of the study area where it close to the rivermouth, its water can be used as a source of the coastal aquaculture. This research also found that the river water of the study area has already heavily polluted by organic waste, which it might come from domestic waste, agriculture or fertilizer for fishpond, or industrial organic waste.

In coastal rivers, tidal pumping enhances the exchange of oxygen-rich river water across the sediment-water interface, controlling nitrogen cycling in riverbed sediment. We developed a one-dimensional, fluid flow and solute transport model that quantifies the influence of tidal pumping on nitrate removal and applied it to the tidal freshwater zone (TFZ) of White Clay Creek (Delaware, USA). In field observations and models, both oxygenated river water and anoxic groundwater deliver nitrate to carbon-rich riverbed sediment. A zone of nitrate removal forms beneath the aerobic interval, which expands and contracts over daily timescales due to tidal pumping. At high tide when oxygen-rich river water infiltrates into the bed, denitrification rates decrease by 25% relative to low tide. In the absence of tidal pumping, our model predicts that the aerobic zone would be thinner, and denitrification rates would increase by 10%. As tidal amplitude increases toward the coast, nitrate removal rates should decrease due to enhanced oxygen exchange across the sediment-water interface, based on sensitivity analysis. Denitrification hot spots in TFZs are more likely to occur in less permeable sediment under lower tidal ranges and higher rates of ambient groundwater discharge. Our models suggest that tidal pumping is not efficient at removing surface water nitrate but can remove up to 81% of nitrate from discharging groundwater in the TFZ of White Clay Creek. Given the high population densities of coastal watersheds, the reactive riverbeds of TFZs play a critical role in mitigating new nitrogen loads to coasts.

During a hurricane event, heavy rainfall can cause storm runoff and river flood. In tidal rivers, hurricane induced storm surge can increase the river downstream boundary water levels. The interactions of storm-induced rainfall runoff and storm surge in tidal rivers may cause more severe flood during hurricane events. In this study, hydrodynamic model simulations were conducted to characterize the interactions of rainfall runoff and storm surge in a tidal river in Rhode Island, USA. River floods under scenarios with and without storm surge were compared.

Large-scaled reclamation modifies the coastal environment dramatically while accelerating the disappearance of salt marshes, which causes the degradation of the coastal ecosystem and the biodiversity function. In this study, we explored the changes of tidal flat and salt marsh coverage in a small-scale tidal flat with an area of ~160 000 m2 in the plain coast of Jiangsu Province, China. Human activities (e.g., the construction of dikes) are a crucial contributor that benefits for the tidal flat accretions and the following changes of salt marsh coverage. Located in the front of the man-made “concave coastline”, the study area is suitable for sediment accretion after the dike construction in the end of 2006. On the basis of the annual tidal surface elevation survey from 2007 to 2012, the sedimentation rates in the human influenced tidal flat varied from a few centimeters per year to 23 cm/a. The study area experienced a rapid accretion in the tidal flat and the expansion of the salt marsh, with the formation of a longshore bar, and a subsequent decline of the salt marsh. Breaking waves during the flooding tide brought much sediment from the adjacent tidal flat to the study area, which caused burial and degeneration of the salt marsh. The vertical grain size changes within a 66 cm long core in the study area also demonstrated the above changes in the tidal environment. This study indicates that the responses of small-scale tidal flat changes to reclamation are significant, and the rational reclamation would benefit for the new salt marsh formation in front of the dikes. Further research about the evolution of small scale tidal flat as well as the spatial planning of the polder dike should be strengthened for the purpose to maintain a healthier coastal environment.

The finite volume community ocean model (FVCOM) has been applied to the Ganges-Brahmaputra-Meghna (GBM) delta in the northern part of the Bay of Bengal in order to simulate tidal hydrodynamics and freshwater flow in a complex river system. The delta region is data-poor in observations of both bathymetry and water level; making it a challenge for accurate hydrodynamic models be configured for and validated in this area. This is the first 3D baroclinic model covering the whole GBM delta from deep water beyond the shelf break to 250 km inland, the limit of tidal penetration. This paper examines what controls tidal penetration from the open coast into an intricate system of river channels. A modelling approach is used to improve understanding of the hydrodynamics of the GBM delta system. Tidal penetration is controlled by a combination of bathymetry, channel geometry, bottom friction, and river flow. The simulated tides must be validated before this delta model is used further to investigate baroclinic processes, river salinity and future change in this area. The performance of FVCOM tidal model configuration is evaluated at a range of sites in order to assess its ability to capture water levels which vary over both a tidal and seasonal cycle. FVCOM is seen to capture the leading tidal constituents well at coastal tide gauge stations, with small root-mean-squared errors of 10 cm on average. Inland, the model compares favourably with twice daily observed water levels at thirteen stations where it is able to capture both tidal and annual timescales in the estuarine system. When the river discharge is particularly strong, the tidal range can be reduced as the tide and river are in direct competition. The bathymetry is found to be the most influential control on water levels within the delta, though tidal penetration can be significantly affected by the model's bottom roughness, and the inclusion of large river discharge. We discuss the generic problem of implementing a model in a data-poor region and the challenge of validating a hydrodynamic model from the open coast to narrow river channels.

Lingding Bay in the Pearl River Estuary, located on the north coast of the South China Sea, experiences frequent storm surges caused by typhoons. The geomorphic features of the Pearl River Estuary have changed tremendously due to natural processes and human activities over the last century, and these changes have led to changes in the hydrodynamic environment, such as a reduced capacity for holding tides in the coastal zone. In this paper, the relation between geomorphic features and the capacity for holding tides is analyzed. In order to ascertain how historical landform change affects this capacity, we study the spatial morphology change of Lingding Bay in the Pearl River Estuary (since 1906) through the analysis of historical topographic maps and nautical charts. The shape index and fractal dimension were introduced as indicators to reflect coastline changes that have affected the tides. The tidal dissipation rate and tidal influx were found to describe a bay’s capacity to hold tides. The results show that, since 1906, the tidal influx and the tidal dissipation rate have decreased by about 14.11% and 23%, respectively, in the study area. We suppose that these changes could be attributed to geomorphic changes, primarily changes brought about by land reclamation projects.

Flood currents (tidal pumping) have led to the increase of transportation of sediments to the river’s upper estuary. In the tidal section of the Elbe River, more sediment is transported to the upper estuary with flood currents (tidal pumping) related to tidal asymmetry. This process contributes, amongst others, to dredging in order to obtain the water depth required for navigation safety. Cognizant of the above problems, construction of shallow water area is planned in order to reduce tidal asymmetry while improving ecological integrity at the tidal Elbe areas. The study on which this paper is based was conducted to assess ecological integrity and ecosystem services before and after the shallow water creation. Habitat identification and quality ranking were conducted for current habitat, while model habitats representing future state (after shallow water creation) were designed using HEC-RAS model simulation. The assessment matrix was used to assess ecological integrity and ecosystem services provisioning of the study area’s habitats before and after the shallow water creation, using potential indicators. Results indicate that there is increase in the ecological integrity after the project implementation. Based on the above explanation, it can be concluded that the measure will increase the flow of ecosystem services after its implementation.

Reservoir regulation is one of the effective ways to improve water quality. However, when water quality requirement is considered, reservoir operation is complicated due to tidal regimes in the tidal rivers. The study was carried out in the tidal river reach between Dongjiang Hydro-Project and Shilong in Dongjiang River. To evaluate the effect of reservoir regulation on water quality, a two-dimensional hydrodynamic model combined with water quality has been developed. Under the scenarios of differrent flood discharge from the Shima River and different release discharge of Dongjiang Hydro-Project, water quality is simulated using the two-dimensional model. NH3-N and COD concentrations are taken as the major indicators for water quality. Results indicate that (1) water quality is related to the tidal fluctuation, NH3-N and COD concentrations increase at flood tide and decrease at ebb tide; (2) There is no obvious over-limit of COD concentration, NH3-N concentration is found as the main pollution impacts water quality at water intake; (3) flood discharge from Shima River flows back to the upper reach of water intake during higher high tidal period, NH3-N concentration non-compliance occurs, flood tide is the main factor which impacts water quality; (4) reservoir regulation of Dongjiang Hydro-Project causes a significant improvement on water quality, release discharge of Dongjiang Hydro-Project is determined to insure the water supply safety, which keeps tidal-induced backwater always flowing to lower reach of the water intake. The study provides a hydrodynamic perspective on water quality improvement due to reservoir regulation in the tidal river.

Despite the growing interest in ecosystem services provided by intertidal wetlands, we lack suf-?cient understanding of the processes that determine the seaward extent of salt marsh vegetation on tidal?ats. With the present study, we aim to establish a globally valid demarcation between tidal ?ats and saltmarsh vegetation in relation to tidal range. By comparing results from a regional GIS study with a global lit-erature search on the salt marsh-tidal ?at border, we are able to de?ne the global critical elevation, abovewhich salt marsh plants can grow in the intertidal zone. Moreover, we calculate inundation characteristicsfrom global tide gauge records to determine inundation duration and frequency at this predicted saltmarsh-tidal ?at border depending on tidal range. Our study shows that the height difference between thelowest elevation of salt marsh pioneer vegetation and mean high water increases logarithmically with tidalrange when including macrotidal salt marshes. Hence, the potentially vegetated section of the tidal framebelow mean high water does not proportionally increase with tidal range. The data analysis suggests thatinundation frequency rather than duration de?nes the global lower elevational limit of vascular salt marshplants on tidal ?ats. This is critical information to better estimate sea level rise and coastal change effects onlateral marsh development

Tan, Y.; Yang, F.; Xie, D, H, 2016. The Change of Tidal Characteristics under the Influence of Human Activities in the Yangtze Estuary. In: Vila-Concejo, A.; Bruce, E.; Kennedy, D.M., and McCarroll, R.J. (eds.), Proceedings of the 14th International Coastal Symposium (Sydney, Australia). Journal of Coastal Research, Special Issue, No. 75, pp. 163–167. Coconut Creek (Florida), ISSN 0749-0208. The aim of this study is to understand the change of tidal wave characteristics in the Yangtze River Estuary by human activities. The harmonic analysis results based on measurement shows that the semidiurnal tides are dominant in Yangtze River Estuary. The shallow water constituents are significant. Tidal constituent Sa, which is one of main meteorological tides, is gradually increasing with the increase of upper stream river discharge. The amplitude of Sa is highly correlated to the maximum anomaly discharge value (maximum daily discharge differing from the long term mean). Due to human activities, the chang...

Field surveys covering a spring-neap tidal period were conducted to investigate the characteristics of tidal dynamics within a curved channel in the southern Hangzhou Bay, China. The channel has a maximum depth of more than 100 m with an average tidal range of 2.5 m, serving as the main tidal passage in the southern part of the Hangzhou Bay. Water salinity, temperature and velocity data were collected from the ship-based transects and mooring measurements. During flood tide, the tidal current intrudes into the Hangzhou Bay through the northern side of the channel with a maximum velocity of about 2 m/s, while retreats through the southern side during ebb tide with a maximum velocity of 1.8 m/s. Due to the pressure, density gradients, the Coriolis force and centrifugal effect, a lateral exchange flow is generated as the tidal current relaxes from flood to ebb. Salinity and temperature data show that the water in the channel is weakly stratified during both spring and neap tides in summer time. However, mixing in the middle region will be enhanced by the lateral circulation. Mooring data indicate that the temperature and salinity are varying at a frequency similar to tidal current but higher than sea level oscillation. Our results support the hypothesis that the high frequency salinity and temperature variations could be generated by combination of the tidal current and the lateral exchanging flow.

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.

Coastal lagoons are low-lying systems under permanent changes motivated by natural and anthropogenic factors. Ria de Aveiro is such an example with its margins currently threatened by the advance of the lagoonal waters recorded during the last decades. This work aims to study the tidal modifications found between 1987 and 2012 in this lagoon, motivated by the main channels deepening which induce higher inland tidal levels. Additionally it aims to study the impact that protective walls designed to protect the margins against flooding may have in those modifications under sea level rise predictions. The hydrodynamic model ELCIRC previously calibrated for Ria de Aveiro was used and tidal asymmetry, tidal ellipses and residual currents were analyzed for different scenarios, considering the mean sea level rise predicted for 2100 and the implementation of probable flood protection walls. Results evidenced that lagoon dominance remained unchanged between 1987 and 2012, but distortion decreased/increased in the deeper/shallower channels. The same trend was found under mean sea level rise conditions. Tidal currents increased over this period inducing an amplification of the water properties exchange within the lagoon, which will be stronger under mean sea level rise conditions. The deviations between scenarios with or without flood protection walls can achieve 60% for the tidal distortion and residual currents and 20% for the tidal currents, highlighting that tidal properties are extremely sensitive to the lagoon geometry. In summary, the development of numerical modelling applications dedicated to study the influence of mean sea level rise on coastal low-lying systems subjected to human influence should include structural measures designed for flood defence in order to accurately predict changes in the local tidal properties.

Yuan, R. and Zhu, J., 2015. The effects of dredging on tidal range and saltwater intrusion in the Pearl River estuary. A dredging project in the Pearl River estuary would influence the topography, water dynamics, and mass transport process. The effects of dredging in the channel of the Pearl River estuary on tidal range and saltwater intrusion were studied using a hydrodynamic model (finite volume coastal ocean model) and historical water depth data. The measured data showed that the tidal range decreased and saltwater intrusion increased in the North River. The tidal range increased and saltwater intrusion decreased in the West River in recent decades from the 1980s. The simulations in this study showed that after dredging (1) the upstream flow split ratio in the river changed (i.e. more freshwater flowed through the Sanshui station), whereas less freshwater flowed through the Makou station; (2) the tidal range increased in the West River network and decreased in the downstream reaches of the No...

Heavy metal distribution in soils is affected by soil aggregate fractionation. This study aimed to demons trate the aggregate-associated heavy metal concentrations and fractionations in “sandy,” “normal,” and “mud” soils from the restored brackish tidal marsh, oil exploitation zone, and tidal mudflat of the Yellow River Delta (YRD), China. Soil samples were sieved into the aggregates of >2, 0.25–2, 0.053–0.25, and 2 mm aggregates indicated contribution of carbonates to soil aggregation and metal adsorption in tidal mud flat. Soil type and aggregate distribution were important factors controlling heavy metal concentration and fractionation in YRD wetland soil. Compared with mud soil, normal soil contained increased concentrations of F5 and F3 of metals in the 0.053–0.25 mm aggregate, and sandy soil contained increased concentrations of bioavailable and total Cr, Ni, and Zn with great contribution of mass loadings in the

Tidal basin and delta morphodynamics have been broadly examined by numerical modeling efforts, but large scale estuarine morphodynamics under combined river and tidal forcing have been less examined. This study aims to explore morphodynamic development of a river- and tide-forced fluvio-deltaic system using a 2DH process-based numerical model (Delft3D). The model domain describes a 560 km long, convergent inner basin attached to a >50 km wide outer sea basin allowing for delta formation. Long-term (millennial) morphodynamic simulation is aided by a morphological factor approach which captures the feedback mechanisms between water motion, sediment movement, and morphology. The morphodynamic sensitivities to river discharge magnitude and its seasonal variations are systematically examined. Model results show that a fluvio-deltaic system develops with meandering channels and alternating sand bars in the estuarine part, and distributary channels with elongated sand bars in the delta. Sensitivity analysis shows that river discharge plays a profound role in the morphodynamic behavior by supplying sediment and enhancing ebb-directed residual transport. An intermediate river discharge can be defined which leads to a deeper estuarine basin. A river discharge smaller than the intermediate threshold limits ebb flow magnitude and erosive capacity. A river discharge larger than the threshold supplies much more sediment to the estuary so that the basin becomes shallower with larger meanders, more pronounced ebb tidal channels, and a larger delta. Based on our simulations we can differentiate tide-dominance from river-dominance in estuary classifications by ebb to flood ratios of flow and sediment fluxes. Overall, this modeling study extends understanding of morphodynamics of a comprehensive fluvio-deltaic system, thus allowing for a better management of estuaries and deltas.

Tidal channels are structurally and functionally prominent features in tidal marshes, so their restoration is central to tidal marsh habitat restoration. Consequently, an important question in tidal marsh restoration is how many tidal channels can a restoration site support, and thus, how many dike breaches should be made to restore tidal inundation and tidal channels, if the dike is not to be removed entirely. Allometric analysis of reference tidal marshes in Puget Sound river deltas and the lower Columbia River Estuary showed that channel outlet count scales with marsh area, and that completed and proposed tidal marsh restoration projects had 5-fold fewer channel outlets than reference marshes. This deficiency likely impacts fish access to the restoration sites. After addressing the question of tidal channel outlet count, or dike breach count, the next design questions are how should dike breaches be oriented in tidal marsh islands and how should they be spaced. GIS and statistical analysis of reference marsh islands indicated that outlets of the two largest tidal channels draining a marsh island are typically oriented downstream, in parallel with the nearest river channel. However, the outlets of smaller tidal channels are oriented randomly. Tidal channel outlet spacing is generally independent of site size and constant within a river delta. Geometric mean spacing ranged from 122 m in the Snohomish Delta to 280 m in the North Fork Skagit Delta. These results provide important guidance to improve tidal marsh restoration design, and illustrate a useful approach to restoration design evaluation.

Summary Understanding the way salinity distribution in an estuary reacts to external drivers (e.g., tide, fresh water discharge, dredging, etc.) is important for both water quality and water resources management in estuaries. The salinity distribution depends strongly on the geometry of an estuary, but also on the fresh water discharge that counteracts the salt intrusion. In estuaries it is notoriously hard to estimate this discharge and subsequently to predict the parameters that determine the mixing behaviour depending on it. Recently a method has been developed to predict the fresh water discharge on the basis of water level observations. In addition, predictive equations for tidal mixing have been updated and revised. In this paper, these two predictive methods are combined and subsequently applied to the Yangtze estuary under a wide variation of fresh water discharge. The predicted salt distribution appears to be in good agreement with observations. To provide insight into the optimum use of water resources (e.g., to determine the amount of fresh water discharge required to maintain a specific salt intrusion length), we further study the salt intrusion pattern under different tide and fresh water discharge conditions.

A hydro-dynamic model is established on basis of MIKE21FM to simulate the hydro-dynamic characteristics of Xinghua Bay and investigate the influence of reclamation project on the tidal elevation and tidal currents. Tidal elevation data was obtained at the six tide gauge stations around the Xinghua Bay, and another six current stations were established to observe the tidal current velocity and direction. Validation shows that the model-simulated tidal elevation and tidal currents agree well with observations made at different stations. Predictions are made according to the reclamation project proposed in the regional marine planning of Hanjiang Industrial Park around the port in Putian City. The variations of hydro-dynamic factors, such as tide, current velocity and direction and tidal influx are obtained, and the adverse effect of reclamation on marine environment is discussed. It is shown that the tidal level inside the Xinghua Bay during high tide decreases after the reclamation project is completed. The tidal currents during flooding tide generally decrease in the southeast of the reclamation region, with the maximum decreasing amplitude reaching 0.44 m s−1. On the other hand, the tidal currents during flooding tide increase around the southeast and southwest corners of the reclamation region. The tidal currents during ebb tide increase around the southeast and southwest corners of the reclamation region, with the maximum increasing amplitude attaining 0.18 m s−1. The results in this paper can give some guidance for the marine environment management and the effective utilization of land in Putian.

In coastal rivers, tides can propagate for tens to hundreds of kilometres inland beyond the saltwater line. Yet the influence of tides on river–aquifer connectivity and solute transport in tidal freshwater zones (TFZs) is largely unknown. We estimate that along the TFZ of White Clay Creek (Delaware, USA), 11% of river water exchanges through tidal bank storage zones. Additional hyporheic processes such as flow through bedforms likely contribute even more exchange. The turnover length associated with tidal bank storage is 150 km, on the order of turnover lengths for all hyporheic exchange processes in non-tidal rivers of similar size. Based on measurements at a transect of piezometers located 17 km from the coast, tides exchange 0.36 m3 of water across the banks and 0.86 m3 across the bed per unit river length. Exchange fluxes range from −1.66 to 2.26 m day−1 across the bank and −0.84 to 1.88 m day−1 across the bed. During rising tide, river water infiltrates into the riparian aquifer, and the downstream transport rate in the channel is low. During falling tide, stored groundwater is released to the river, and the downstream transport rate in the channel increases. Tidal bank storage zones may remove nutrients or other contaminants from river water and attenuate nutrient loads to coasts. Alternating expansion and contraction of aerobic zones in the riparian aquifer likely influence contaminant removal along flow paths. A clear need exists to understand contaminant removal and other ecosystem services in TFZs and adopt best management practices to promote these ecosystem services. Copyright © 2015 John Wiley & Sons, Ltd.

James, K.F.; Bourman, R.P., and Harvey, N., 2015. Rapid evolution of a flood tidal deltaic island in the River Murray estuary, South Australia: A canary in the cage of river management. Bird Island, at the oceanic outlet of Australia's largest exoreic river system, the Murray-Darling, did not exist before 1940. Originally, flood tidal sediments were moulded by tides, waves, wind, and river flows in the back-barrier lagoon, landward of the migrating River Murray Mouth. The estuary was fluvially dominated, and the terminal lakes were mainly fresh. Following more than a century of European settlement and freshwater abstraction, salinity levels increased, prompting the construction of barrages (completed in 1940) near the Murray Mouth to restore the former predominantly freshwater character of the estuary. Further reduced river flows, a restricted tidal prism, and management strategies produced irreversible changes in the dynamics of the River Murray Mouth. These are archived in the landforms and veg...

In many large estuaries there are significant variations in flow conditions due to the interaction between tide (with spring–neap changes) and river discharge (with wet–dry seasons), which is key to understanding the evolution of the morphology and the resultant equilibrium state. To explore whether there exists an equilibrium state, and what might control such a state in such a dynamic environment, both numerical and analytical methods have been used to investigate the relative importance of tide and river contributions to the work done locally and globally over a wide range of discharge conditions in the Yangtze estuary. In particular, we have quantified the contributions from the tidal flow, the river flow and the tide–river interaction in terms of energy and its dissipation under different river discharge conditions. Model results suggest that there is a state of minimum tidal work for the case representing the wet season, when river and tide are doing uniform work locally and minimum work globally, within the bi-directional tidal reach for tide and along the whole estuary for river. We also observe that the system is not optimized for other conditions (peak discharge and low flows during the dry season), but the system would tend to do the minimum work possible given the constraints on the system (e.g. imposed forcing conditions and available sediment supply). Results, therefore, are consistent with the use of these two energetic optimization principles, and the proposed method could be applicable to other alluvial estuaries.

Simultaneous field observations were made of time series of water level, current velocity, salinity and suspended sediment concentration at ten hydrological gauging stations along the North Passage in the Changjiang River estuary on 17 to 24 February (dry season) and 12 to 18 August 2012 (wet season), respectively. Quantitative analyses of those data are attempted to understand circulation and mixing along the Deepwater Navigational Channel in this estuary. Landward subtidal flow only appears during the neap tide. The maximum bottom landward velocity is in the order of 0.05–0.1 m·s − 1 in the dry season and 0.15–0.2 m·s − 1 in the wet season, respectively. In both dry and wet seasons, calculated mixing parameter ( M ), which is the ratio of the tidal timescale to the vertical mixing timescale, is below the critical value (1.0) on a neap tide but above it on a spring tide within the middle and lower reaches of the Channel. This suggests that tidal variation of mixing may be able to generate the tidal straining circulation during the periodic stratified spring tide. The interaction between significant river shear flow and longitudinal density gradient, a process termed “ river effect ” in this study, is revealed as the major reason for seasonal variation of stratification. The competition between tidal stirring, gravitational circulation and river effect could produce an increase in tidal mean value of the potential energy anomaly ( ϕ ) from neap to spring tides. Tidal mean value of the Simpson number ( Si ) over a neap tide surpasses the critical value (8.4 × 10 − 1 ) within the middle reach of the Channel, suggesting the occurrence of persistent stratification there. Tidal mean Si over a spring tide is in the order of 8.4 × 10 − 1 –8.8 × 10 − 2 within the middle reach, suggesting the occurrence of strain induced periodic stratification (SIPS). Shear prevails within the pycnocline in the middle and lower reaches of the Channel on a neap tide, with the value of squared shear ( S 2 ) exceeding 10 − 3 s − 2 . Calculated gradient Richardson number ( Ri ) is small at the salt–fresh water interface, indicating the occurrence of Kelvin–Helmholtz instability there.

Tidal rivers are intrinsically complex because tidal propagation is influenced by river discharge. This study aims to examine the seasonal variation of tidal prism and energy variance in the tidal river of the Changjiang (Yangtze) River estuary in China. In order to quantify the behaviour of river and tide, we use numerical modelling that has been validated using measured data. We conduct our analysis by quantifying the discharge and energy variance in separate components for both the river and the tide, during wet and dry seasons. We note various definitions of tidal prism and explore the difference between tidal discharge on the flood and ebb and tidal storage volume. The results show that the river discharge attenuates the tidal motion and reduces the tidal flood discharge but the tidal storage volume is approximately constant with different riverine discharge since part of the fresh water discharge is intercepted and captured in the estuary due to the backwater effect. It appears that the tidal discharge adjusts according to the variation of river discharge to keep a constant tidal storage volume. An analysis of the hydraulics shows that the transition from tidal dominance (at the mouth) to river dominance (upstream) depends on the location of tidal current reversal which varies from wet season to dry season. Duringthe wet season, the Changjiang River estuary is totally dominated by energy from fresh water discharge.

Tidal wetlands are affected by sea level rise. In the tidal freshwater stretches of estuaries in the temperate zone, willows (Salix spp.) form tidal freshwater forests above the mean high water level. Willows tolerance to prolonged periodic flooding in riverine systems is well documented, whereas effects of tidal flooding on willows are largely unknown. Flooding stress may play a major role in regeneration failure of willows in tidal forest stands along estuarine shores, and juvenile willows might be specifically affected by partial or total submergence. To assess the tolerance of juvenile willows to tidal flooding, we conducted a mesocosm experiment with cuttings from Salix alba and Salix viminalis, which are both characteristic species for tidal freshwater forests in Europe. Cuttings originating from either fresh or brackish tidal forest stands were grown under four tidal treatments with up to a tidal flooding of 60 cm. A general tolerance to a tidal flooding of 60 cm was observed in chlorophyll fluorescence, growth rates, and biomass production in both willow species. Overall, S. alba showed higher leaf and shoot growth, whereas S. viminalis produced more biomass. S. alba with brackish origin performed worst with increasing tidal flooding, suggesting a possible pre-weakening due to stressful site conditions in tidal wetlands at the estuarine brackish stretch. This study demonstrates that juvenile willows of S. alba and S. viminalis tolerate tidal flooding of up to 60 cm. It is concluded that tidal inundation acts as a stress by causing submergence and soil anaerobiosis, but may also act as a subsidy by reestablishing aerobic conditions and thus maintaining willows performance. Therefore, we suggest investigations on Salix tidal flooding tolerance and possible effects of willows on tidal wetland accretion under estuarine field conditions.