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River-tide dynamics remain poorly understood, in part because conventional harmonic analysis (HA) does not cope effectively with nonstationary signals. To explore nonstationary behavior of river tides and the modulation effects of river discharge, this work analyzes tidal signals in the Yangtze River estuary using both HA in a nonstationary mode and continuous wavelet transforms (CWT). The Yangtze is an excellent natural laboratory to analyze river tides because of its high and variable flow, its length, and the fact that there are do dams or reflecting barriers within the tidal part of the system. Analysis of tidal frequencies by CWT and analysis of subtidal water level and tidal ranges reveal a broad range of subtidal variations over fortnightly, monthly, semiannual, and annual frequencies driven by subtidal variations in friction and by variable river discharges. We employ HA in a nonstationary mode (NSHA) by segregating data within defined flow ranges into separate analyses. NSHA quantifies the decay of the principal tides and the modulation of M4 tide with increasing river discharges. M4 amplitudes decrease far upriver (landward portion of the estuary) and conversely increase close to the ocean as river discharge increases. The fortnightly frequencies reach an amplitude maximum upriver of that for over tide frequencies, due to the longer wavelength of the fortnightly constituents. These methods and findings should be applicable to large tidal rivers globally and have broad implications regarding management of navigation channels and ecosystems in tidal rivers.

Tidal flat, is a critical natural resource for coastal ecosystem and plays a tremendous role in coastal sustainable development. However, most tidal flats in the world are facing serious challenges from both natural change and anthropogenic activities. Based on the multi-year monitoring records of tidal flats in the Changjiang (Yangtze) Estuary, the temporal-spatial changes of tidal flats and possible driving factors were statistically examined. The results indicate that the increased rate of the majority of tidal flats in the Changjiang Estuary has become slow since 2000s. Tidal flats of both Hengsha and Jiuduan Shoal showed minor enlarged trends from 2004 to 2009. However, Tidal flat areas of Nanhui Shoal above 0 m had greatly decreased by 80.8% from 1958 to 2012. Even though estuarine hydraulic engineering structures can mitigate tidal flats decreased trends, the tidal flats of the Changjiang Estuary will still suffer significant losses due to the decreasing sediment flux from upstream, ground subsidence, sea level rise and recent intensive reclamation. Thereafter, the adaptive management strategies for sustainable tidal flat resources of the Changjiang Estuary are as follows: (1) Proceeding comprehensive adjustment involving watershed and estuary; (2) keeping balance between reclamation and rebirth of tidal flats; (3) coping with sea level rise; (4) scientifically promoting aggradation of tidal flats.

Irrigation is a significant human activity that affects surface water fluxes in the Tarim River Basin. To quantitatively assess the irrigation impact of this activity on surface water fluxes in the Tarim River, a land surface hydrologic model was coupled with a modified irrigation scheme and a reservoir module and applied to simulate these fluxes. Modeling results indicate that the combined effect of the irrigation process and reservoir operation is prominent in the study area, from which 70–75% of the surface water is extracted and used for irrigation. This scenario can primarily be attributed to the significant amount of water losses as a result of evaporation and the seepage of canals and aqueducts. The effective utilization coefficient of the extracted surface water is only approximately 0.40. The irrigation water withdrawals increased with the recent rapid expansion of cultivated land. Therefore, the water flowing into the main stem of the Tarim River still shows a downward trend, despite the significant increase in the total discharge of headwater basins since the 1960s.

Environmental impacts, including tidal regimes and sediment transport in the Minas Basin, caused by tidal power extraction in the Minas Passage have been investigated using a three-dimensional hydrodynamic model in which tidal power extraction is represented using an arbitrary method that adds a friction term to the standard momentum equations. Using the model results, changes in tidal processes and sediment transport in the Minas Basin are examined by comparing model results with and without power extraction. With the presence of power extraction, the tidal level decreases by 0.5–1.5% and the tidal phase increases by 1.2–1.8°. Tidal currents decrease by 15–35% at the western head of the Minas Basin and increase by a comparable magnitude at the Southern Bight. The presence of power extraction could move the location of the tidal residual gyre in the western head of the Minas Basin south by about 2 km. Model results also show that less sediment would move into the central area of the Minas Basin bu...

It is difficult to measure river discharge accurately in an estuary, and particularly, in the region where the tidal flow dominates over the river discharge. River discharge is important for the morphology and hydrodynamics of estuaries as it influences the salt intrusion process, tidal dynamics, freshwater supply (water resources management), and the occurrence of floods. Here we try to derive river regime characteristics from the seaward end: the estuary. It is found that there are empirical relationships that link the geometry of an estuary to its river regime, which can be used to estimate river discharge characteristics with the least of data available. The aims of this study are: (1) to derive empirical relations between geometrical characteristics of estuaries and the bankfull discharge; (2) to explore a physical explanation for this relation; and (3) to estimate the bankfull discharge in estuaries. The physical connection between an estuary and its river regime is found by combining estuary shape analysis, tidal dynamic analysis, and Lacey's hydraulic geometry theory. The relationships found between the estuary depth, width, and bankfull river discharge have been tested in 23 estuaries around the world (including seven recently surveyed estuaries). From the analysis, it shows that the depth of an estuary is a function of the bankfull flood discharge to the power of 1/3, which is in agreement with Lacey's formula. This finding not only provides a method to estimate estuary depth, it also allows estimating flood discharge characteristics from readily available estuary shape indicators.

Coastal wetlands, commonly inundated by periodic tides, have been recognized as important sources of greenhouse gases. However, little is known of tidal effects on in situ soil CO2 and CH4 emissions in a semi-lunar tidal cycle consisting of neap and spring tide periods (NTP and STP). A field study was conducted in the Yangtze River estuary to investigate temporal variations of soil CO2 and CH4 emissions along with the transition from NTP to STP in a semi-lunar tidal cycle. Soil moisture, salinity and sulfate were significantly greater in STP than in NTP, whereas soil redox potential had an opposite pattern because of frequent tidal inundation. Soil CO2 and CH4 effluxes decreased significantly in STP, being 29–34 and 28–35 %, respectively, compared with those in NTP. The decrease in soil CO2 effluxes was likely attributable to two causes, an anaerobic environment inhibiting CO2 production, and tidal inundation impeding CO2 diffusion from the soil into the atmosphere. The inhibition of methanogenesis by increased soil salinity and sulfate was likely the primary reason of the decrease in CH4 effluxes during STP. Our results suggest that the effects of semi-lunar tidal cycling significantly reduce soil carbon emissions, which may be one of the potential mechanisms underlying strong carbon accumulation in wetlands of the Yangtze River estuary.

Human activities, such as tidal sluice gate construction and reclamation, are prevalent along northern coastline of China and influence significantly sedimentary environments. The Sheyang River estuary is a small estuary situated on the Jiangsu coast. For the objective of storing fresh water, maintaining river channel depth and managing the land resource, a tidal sluice gate was constructed. At the same time, estuarine wetlands have been reclaimed extremely in recent decades. A numerical model based upon Delft3D was developed to quantify the impact of these human activities, and four simulation schemes were designed (a) tidal sluice gate present, but always closed; (b) tidal sluice gate not present; (c) tidal sluice gate present, but closed during flood and open during the ebb; and (d) intertidal area reclamation taking place in the estuary. A bathymetric survey confirmed the erosion and deposition results of the simulation. The rate of sediment deposition increased significantly after the gate was closed. However, during the third scheme, the sediment deposition rate reduced considerably; that was because the ebb current increased the scouring force when the gate was open, especially within the channel area close to the gate. Meanwhile, reclamation lessened erosion behind the gates and may have been enhanced by siltation. The coastline shifted seaward as the siltation area increased; it extended farther because of reclamation. Appropriate coastal management planning strategies must be developed to reduce negative effects of the channel siltation, resulting from the various forms of human activity. The results of this study can provide input to governmental recommendations on more effective tidal gate management strategies.

Evidence of decreasing sediment supply to estuaries and coastal oceans worldwide illustrates the need for accurate and updated estimates. In the San Francisco Estuary (Estuary), recent research suggests a decrease in supply from its largest tributaries, implying the increasing role of smaller, local tributaries in sediment supply to this estuary. Common techniques for estimating supply from tributaries are based on gages located above head of tide, which do not account for trapping processes within the tidal reach. We investigated the effect of a tidal reach on suspended-sediment discharge for Corte Madera Creek, a small tributary of the Estuary. Discharge of water (Q) and suspended-sediment (SSD) were observed for 3 years at two locations along the creek: upstream of tidal influence and at the mouth. Comparison of upstream and mouth gages showed nearly 50 % trapping of upstream SSD input within the tidal reach over this period. At the storm time scale, suspended-sediment trapping efficiency varied greatly (range −31 to 93 %); storms were classified as low- or high-yield based on upstream SSD. As upstream peak Q increased, high-yield storms exhibited significantly decreased trapping. Tidal conditions at the mouth—ebb duration and peak ebb velocity—during storms had a minor effect on sediment trapping, suggesting fluvial processes dominate. Comparison of characteristic fluvial and tidal discharges at the storm time scale demonstrated longitudinal differences in the regulating process for SSD. These results suggest that SSD from gages situated above head of tide overestimate sediment supply to the open waters beyond tributary mouths and thus trapping processes within the tidal reach should be considered.

A long-term data base (2000–2009) was used to evaluate tidal floodwater salinity and the resulting soil biogeochemical setting (methanogenic or sulfate reducing) at 54 substations, which included a variety of marsh and swamp community types along the freshwater/saltwater boundary of the Cape Fear River/Estuary, North Carolina. During this decade, a variety of extreme climatic events, i.e. floods and droughts, occurred, but overall data reflected long-term, natural conditions. At sites flooded by >1 ppt saline water more than 25 % of the time, wetlands consisted of varying types of tidal marsh. Temperate, tidal swamps were present at sites flooded by this level of saline water less than 12 % of high tides. Flooding >25 % of tides by >1 ppt seawater converted soils in those wetlands from methanogenic into sulfate reducing conditions >50 % of the time. The point along an estuarine gradient where adjacent wetlands are flooded by >1 ppt saline water less than 25 %, but more than 12 % is the zone of transition. The conversion of a tidal swamp to tidal marsh is not only caused by salt water itself, but by the sulfate constituent in seawater. Once a sufficient concentration of sulfate enters soils, sulfate reducing bacteria become active reducing the sulfate into hydrogen sulfide, which is toxic to any wetland plant species not adapted to this toxic substance. The incidence of flooding by high tides containing >1 ppt salinity is an accurate predictor of functional change in adjacent wetlands. Wetlands receiving intermediate levels of saline water, i.e. 12-25 % flooding with 1 ppt floodwater, were in some state of transition from swamp to marsh. Once trees in tidal swamps are killed, the wetland moves inevitably towards a tidal marsh dominated by species of herbaceous vascular plants with varying tolerance to saline water.

We investigate the morphodynamic equilibrium of tidally dominated alluvial estuaries, extending previous works concerning the purely tidal case and the combined tidal-fluvial case with a small tidal forcing. We relax the latter assumption and seek the equilibrium bed profile of the estuary, for a given planform configuration with various degrees of funneling, solving numerically the 1-D governing equation. The results show that with steady fluvial and tidal forcings, an equilibrium bed profile of estuaries exists. In the case of constant width estuaries, a concave down equilibrium profile develops through most of the estuary. Increasing the amplitude of the tidal oscillation, progressively higher bed slopes are experienced at the mouth while the river-dominated portion of the estuary experiences an increasing bed degradation. The fluvial-marine transition is identified by a “tidal length” that increases monotonically as the river discharge and the corresponding sediment supply are increased while the river attains a new morphological equilibrium configuration. Tidal length also increases if, for a fixed river discharge and tidal amplitude, the sediment flux is progressively reduced with respect to the transport capacity. In the case of funnel-shaped estuaries the tidal length strongly decreases, aggradation is triggered by channel widening, and tidal effects are such to enhance the slope at the inlet and the net degradation of the river bed. Finally, results suggest that alluvial estuaries in morphological equilibrium cannot experience any amplification of the tidal wave propagating landward. Hence, hypersynchronous alluvial estuaries cannot be in equilibrium.

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.

Over the past few decades, there has been large-scale land reclamation in Jiaozhou Bay, which inevitably has affected the hydrodynamics and sediment transport in the bay, and thus has consequences for its management. In this study we set up a three-dimensional barotropic hydrodynamic model based on the Finite Volume Coastal Ocean Model to investigate changes in tidal dynamic factors in Jiaozhou Bay from 1935 to 2008. According to the model, the M2 tide has experienced only minor changes over this period. Land reclamation on a large scale took place between 1935 and 1966, leading to significant hydrodynamic changes during this period. Again according to the model, the M4 tidal amplitude rose dramatically, by up to 80% at the northeastern part of Jiaozhou Bay, and this has caused a significant increase in the M2–M4 tidal-duration asymmetry. Concurrently, the M2 tidal-energy fluxes across the entrances to both the inner and outer bay were both reduced by more than 50%. From 1966 to 2008, land reclamation was conducted on a smaller scale. Over this period, the M2 tidal-energy flux continued to decrease but at a relatively smaller rate. Both the M4 tidal amplitude and M2–M4 tidal-duration asymmetry also experienced a gradual decrease during this period, probably due to the reduced M2 tidal energy, in contrast to the increase between 1935 and 1966. The changes in the M2–M4 tidal-duration asymmetry from 1935 to 2008 caused by the land reclamation were reproduced in the model by progressively removing tidal flats from the head of the bay to its mouth. However, the M2–M4 tidal-duration asymmetry showed a different variation when the tidal flats were removed progressively in the opposite direction, from the mouth to the head of the bay. Our study shows that the significant increase in the M2–M4 tidal-duration asymmetry between 1935 and 1966 was a consequence of the change in bottom friction when the tidal flats were land-filled; advection played only a secondary role.

At least 19 remarkable dikes and land reclamations have been constructed since 1970 along the west coast of Korea, which resulted in a reduction in tidal flat area of almost 50%. Both the reduction in tidal flats and the artificially simplified coastal line have distorted the spatio-temporal tidal hydrodynamics; to quantify this, we analyzed and evaluated tidal asymmetry by phase differences of the principal semi-diurnal lunar constituent M 2 and its first over-tide M 4 . Moreover, we applied the ADCIRC model to quantitatively investigate near- and far-field impacts on tidal variations using the gamma parameter, tidal energy flux, and dissipation rate. Through this study, we found that the tidal regime around the Incheon harbor area in Gyeonggi Bay has changed from ebb- to flood-dominant due to multiple nearby reclamations, in particular to the construction of the Siwha dike. The Saemangeum dike caused near-field de-amplification of M 2 but far-field amplification in the Shandong area of China. In addition to allowing a traditional asymmetry approach using phase difference, analyses based on the gamma parameter and tidal energy variations could distinctly improve spatial understanding of anthropogenic impacts on coastal tidal hydrodynamics.

Tidal flats constitute a unique and extensive depositional system encompassing the entire west coast of Korea. Tidal flats are classified into three types on the basis of morphologic setting, open-coast, embayment, and channel-margin. Macrotidal regime and highly indented coastlines favored tidal current-induced sedimentation, resulting in seaward coarsening sediment distribution. Tide-dominated sedimentary processes are complicated by the strong monsoonal climate, and associated seasonal wave activity and precipitation-induced discharge. Different exposure to wave activity leads to contrasting sedimentary processes, sedimentation and morphologic response among various types of tidal flats. Summertime heavy rainfalls accentuate runoff discharge-driven sedimentation in the tidal flats, irrespective of the presence of rivers. Tidal flats have been venue for government-driven mega reclamation projects such as Saemankeum, Sihwa, and Youngjong–Yongyou islands due to their geographic proximity to urban area and flat morphology. Massive destruction of tidal flats was justified by mandatory environmental impact assessments that failed to predict irreversible effects on coastal depositional system, triggering a nationwide controversy. Future reclamation projects must be supplemented by studies that can evaluate properly the complexity and dynamic behavior of tidal flats so as to minimize socio-economic cost as well as the loss of tidal flats.

The Aksu River is a principal headwater tributary of the Tarim River in northwest China providing 70–80 % of its water supply. This study aims to simulate the impact of potential future irrigation and cropping schemes on river discharge in the semi-arid and irrigation intensive part of the Aksu River basin. To achieve this goal, the eco-hydrological model SWIM (Soil and Water Integrated Model) was developed further by including an irrigation module and a river transmission losses module. The performance of the SWIM model in the region was then compared with that of another water management model, WEAP (Water Evaluation And Planning). The results show that both models are capable of reproducing the monthly discharge at the downstream gauge well using the local irrigation information and the observed upstream inflow discharges as inputs. Still, the SWIM model performs better than the WEAP model because it accounts for both hydrological processes and agricultural impacts. Therefore, SWIM was used for the scenario study. Different irrigation scenarios were developed based on the recent trends of agricultural practices. The study showed that the improvement of irrigation efficiency was the most effective measure for reducing irrigation water consumption and increasing river discharge downstream. The expansion of irrigation area in the basin leads to an increase in water consumption while the changes in crop structure (composition of crop types) on arable land do not have significant impact on the river discharge downstream.

The age of water (AW) concept is applied to investigate the water exchange process in a large and density stratified estuary, namely the Pearl River Estuary. A three-dimensional AW model has been built based on an existing hydrodynamic and solute transport model. The model is used to determine the AW distributions inside the Pearl River Estuary under various hydrodynamic conditions. The predicted mean AW values during the dry and wet seasons are approximately 25 and 10 days, respectively. In general, lower AW values are observed in the upper layers near the water surface, while higher values are observed in the lower layers near the bed. The difference becomes more pronounced during the wet season when the river discharge is very large. The tidal influence is relatively small. The variation of tidal forcing impacts mainly on the AW fluctuation range, but it has limited impact on the tidally averaged AW value. Moreover, the AW vertical difference is enhanced during neap tides. A comparison between the predictions using barotropic and baroclinic models indicates that the density-induced circulation has a significant impact on the water exchange rate.

Numerous research efforts have been devoted to understanding estuarine morphodynamics under tidal forcing. However, the impact of river discharge on estuarine morphodynamics is insufficiently examined. Inspired by the Yangtze Estuary, this work explores the morphodynamic impact of river discharge in a 560 km long tidal basin based on a 1-D model (Delft3D). The model considers total load sediment transport and employs a morphodynamic updating scheme to achieve long-term morphodynamic evolution. We analyze the role of Stokes drift, tidal asymmetry, and river discharge in generating tidal residual sediment transport. Model results suggest that morphodynamic equilibrium is approached within millennia by vanishing spatial gradients of tidal residual sediment transport. We find that the interaction between ebb-directed Stokes return flow/river flow with tides is an important mechanism that flushes river-supplied sediment seaward. Increasing river discharge does not induce continuously eroded or accreted equilibrium bed profiles because of the balance between riverine sediment supply and sediment flushing to the sea. An intermediate threshold river discharge can be defined which leads to a deepest equilibrium bed profile. As a result, the shape (concavity or convexity) of the equilibrium bed profiles will adapt with the magnitude of river discharge. Overall, this study reveals the significant role of river discharge in controlling estuarine morphodynamics by supplying sediment and reinforcing ebb-directed residual sediment transport.

The closed bay formed by a tidal power plant on the west coast of Korea has caused water quality to change due to nutrient increase and salinity alternation. The nutrients of the inner bay are often kept a balance with the aid of the outflow at the mouth of the bay. Hence it is necessary to minimize the environmental effects by forecasting the potential environmental changes caused by a tidal power construction. Seasonal observations of mass balance in the inner and outer Garolim Bay were performed. The low quality nutrients released from sediments, land and river were more dominant than the nutrients released from the outer bay in the study area. It was observed that the tidal power plant construction made water exchange ratio 57%.Various mitigation strategies such as water gates were studied so that the water exchange rate can be reduced. The change in the water exchange ratio is significantly reduced as the cross-section and the number of water gates is increased. The water exchange ratio was decreased by 8%, which increased nutrients in the inner bay. Results of numerical the nutrients decreased with the 7% increase in the inflow while the decrease in outflow discharges. However, it is considered only 0.2% increase in the entire mass balance of Garolim Bay relatively inadequate to mitigate the environmental impact.

The introduction of tidal stream turbines into water bodies can have an impact on the environment due to changes in the hydrodynamic flow fields resulting from the extraction of energy by the tidal turbines. Water levels, tidal currents and flushing characteristics could potentially be significantly altered with the introduction of tidal turbine farms, which could lead to possible loss of habitat and a change in the tidal regime. Therefore, planning of tidal turbines field deployments must take into account possible hydro-environmental impacts. This paper describes research undertaken by the authors in the Shannon Estuary to predict changes in the tidal regime and flushing characteristics, with the introduction of tidal turbine farms of different array configurations. The model was simulated using a 2D hydrodynamic model that was modified to incorporate the effects of tidal turbine fields. Water levels are shown to have been affected with the inclusion of turbines, especially in areas upstream of the turbine farm where inter-tidal zones could become predominately inundated resulting in loss of habitat in the estuary. Flushing parameters were also shown to be altered with the inclusion of turbines, with residence time shown to be increased, which could change pollutant transport in the region.

The revised Malaysian Urban Stormwater Management Manual (MSMA) eludes the importance of tidal backwater analysis in the engineering of lowland river drainage. Tidal gates and flood gates can only be adequately designed if a detailed investigation of the dynamic interactions of tidal high water and storm discharge be conducted. We propose a numerical and laboratory investigation of the lower Klang River in order to better understand the independent and joint effects of these factors to river flood stage.

Presented are the results of the study of the processes of interaction between the river and sea water in the estuary of the Keret’ River flowing into the White Sea. The studies were carried out using the georadar method which enables one to register the boundary between fresh and salt water with the high spatial and temporal resolution. The use of this method helped to determine the boundaries of the area of distribution of fresh water in the estuary during different phases of the tidal cycle and to reveal the typical fluctuations of the boundary between fresh and salt water manifested at different values of river runoff and weather conditions.

This paper examined the changes in flow patterns due to a blockage of tidal currents in the sea areas between Incheon North Port and Yeomha Channel when it would be influenced by the construction of the Incheon North Port Yeongjongdo dredged soil dumping ground and Incheon Bay tidal power plant. The numerical simulationwas performed for three cases: before and after constructing the Incheon North Port Yeongjongdo dredged soil dumping ground and after the construction of the sea-dyke on the east side of the Incheon Bay tidal power plant. The simulation results showed that the tidal directions and currents velocity were similar before and after the construction of the Yeongjongdo dredged soil dumping ground. After the construction of the East Sea-dyke of Incheontide power plant, however, the tidal currents patterns changed significantly due to flow blockage toward GyeonggiBay. The main flow was formed in the north-south direction, and the tidal currents velocity increased slightly on thedownstream areas (A,B,C) of Hodo, which is the entrance of the Ara Waterway. The tidal currents at the mouth(D)of Yeomha Channel decreased significantly. The tidal currents of the west side of Se-eodo and the east side of the sea- dyke were rotary currents. The results of this study will provide basic data for the environmental impact assessment and the operation of the Gyeongin Ara Waterway.

Water level records at two stations in the Guadalquivir Estuary (Spain), one near the estuary mouth (Bonanza) and one about 77 km upstream (Sevilla), have been analysed to study the amplification of the tide in the estuary. The tidal amplification factor shows interesting temporal variation, including a spring-neap variation, some extreme low values, and especially the anomalous behaviour that the amplification factor is larger during a number of periods. These variations are explained by data analysis combined with numerical and analytical modelling. The spring-neap variation is due to the quadratic relation between the bottom friction and the tidal flow velocity. The river flood events are the direct causes of the extreme low values of the amplification factor, and they trigger the non-linear interaction between the tidal flow and suspended sediment transport. The fluvial sediment input during a river flood causes high sediment concentration in the estuary, up to more than 10 g/l. This causes a reduction of the effective hydraulic drag, resulting in stronger tidal amplification in the estuary for a period after a river flood. After such an event the tidal amplification in the estuary does not always fall back to the same level as before the event, indicating that river flood events have significant influence on the long-term development of this estuary.

In the hypertidal Bay of Fundy, environmental impacts in response to commercial-scale tidal power development remain to be fully understood. The extraction of tidal energy may impact sediment dynamics in far-field environments, such as the intertidal zone, through potential alterations to tidal amplitude in the Minas Basin. Tidal conditions (e.g. current velocity, turbulence, suspended sediment concentration) were monitored in a sheltered salt marsh creek over 18 tidal cycles in various stages of the spring-neap cycle. Samples of deposited and suspended sediments were collected and analyzed for grain size using a Beckman Coulter Multisizer III. Results suggest that the flocculated component of both deposited and suspended sediment is consistently high over a wide range of tidal conditions. A routinely high incoming concentration of highly-flocculated material results in large amounts of sediment deposition in tidal creeks in response to individual tidal cycles. Resuspension and removal of newly deposited material is shown to vary with over-marsh, bankfull and channel-restricted tides. Disruption of the tidal regime due to a reduction in Minas Basin tidal amplitude may lessen the cumulative export capacity of tidal channels over time, potentially leading to gradual infilling of tidal creeks.

The Modaomen Waterway (MW), a major outlet of the Pearl River Estuary, is a crucial source of water supply for Macao and Zhuhai City in Southern China. This waterway is frequently affected by saltwater intrusion from the South Sea, which has caused serious water shortage in recent years. For the planning and management of water supply at this waterway it is necessary to understand the characteristics of saltwater intrusion particularly in the low flow period of the year. However, as a result of multiple impacts from tide, river discharge, wind, topography, channel bathometry, and some other factors, the saltwater intrusion into this waterway is highly non-linear. In order to account for the non-linear characteristics, the wavelet method was used to analyze the period characteristics of tidal range, river discharge, and salinity and the impact of tidal range and river discharge on the salinity. Results show that the tidal range at Sanzao station and the salinity at Pinggang station both exhibit a stable 14.8-day period and the salinity in the MW is largely impacted by the tidal range during low stream flow periods. River flows from upstream of the waterway don't show any stable period characteristic, it, however, is critical in mitigating the salinity for water supply during saltwater intrusion. A minimum total flow of 2 500 m 3 /s from upstream at Sanshui and Makou stations has been practiced as a threshold for safe water supply. This study has found that the percent time when salinity is below the maximum permissible salinity of 250 ml/g for water supply increases as the river discharge from upstream increases and up to 50–70% of the time the salinity at water supply pumping station is below 250 mg/l when the upstream flow is greater than 2 500 m 3 /s. Planning and management of water supply operation at the MW is politically, economically and mostly importantly technically challenging, findings from this study can provide some guidance for operation and further research. For example, the phase lag of average salinity to tidal range was quantified to be 3.4–3.8 days. This phase lag time would suggest that the pumping operation to store freshwater in the backup storages needs to be at least 4–5 days ahead of the spring tide so as to avoid serious impact from saltwater intrusion. Safer water supply strategies can be developed by scheduling reservoir operations to maintain the threshold stream flow and the pumping.

Pumping wells are common in coastal aquifers affected by tides. Here we present analytical solutions of groundwater table or head variations during a constant rate pumping from a single, fully-penetrating well in coastal aquifer systems comprising an unconfined aquifer, a confined aquifer and semi-permeable layer between them. The unconfined aquifer terminates at the coastline (or river bank) and the other two layers extend under tidal water (sea or tidal river) for a certain distance L. Analytical solutions are derived for 11 reasonable combinations of different situations of the L-value (zero, finite, and infinite), of the mid- dle layer's permeability (semi-permeable and impermeable), of the boundary condition at the aquifer's submarine terminal (Dirichlet describing direct connection with seawater and no-flow describing the existence of an impermeable capping), and of the tidal water body (sea and tidal river). Solutions are discussed with application examples in fitting field observations and parameter estimations.

This two-part paper provides comprehensive time and frequency domain analyses and models of along-channel water level variations in the 234-km-long Lower Columbia River and Estuary (LCRE) and documents the response of floodplain wetlands thereto. In Part I, power spectra, continuous wavelet transforms, and harmonic analyses are used to understand the influences of tides, river flow, upwelling and downwelling, and hydropower operations (“power-peaking”) on the water level regime. Estuarine water levels are influenced primarily by astronomical tides and coastal processes and secondarily by river flow. The importance of coastal and tidal influences decreases in the landward direction, and water levels are increasingly controlled by river flow variations at periods from ≤1 day to years. Water level records are only slightly nonstationary near the ocean, but become highly irregular upriver. Although astronomically forced tidal constituents decrease above the estuary, tidal fortnightly and overtide variations increase for 80–200 km landward, both relative to major tidal constituents and in absolute terms. Near the head of the tide at Bonneville Dam, strong diel and weekly fluctuations caused by power-peaking replace tidal daily (diurnal and semidiurnal) and fortnightly variations. Tides account for 60–70 %, river flow and seasonal processes 5–20 %, and weather 2–4 % of the total variance in the seaward 60 km of the system. In the landward 70 km of the LCRE, seasonal-fluvial variations account for 80–90 % of the variance, power-peaking 1–6 %, and tides

Tidal freshwater forested wetlands are dynamic, complex ecosystems that typically occur in large, floodplain river estuaries throughout the world. The estuarine portion of the Columbia River, in the Pacific Northwest region of North America, is exceptionally large and extends from the Pacific Ocean to the head of tide at Bonneville Dam, located at river kilometer (RKm) 233. Our study focused on the freshwater portion of the estuarine gradient (RKm 40 to RKm 233) of the Columbia River estuary and the corresponding continuum of hydrologic regimes and biotic communities. Several diverse forested wetland community types occurred along this freshwater estuarine gradient with major shifts in community composition corresponding to the transition from predominantly tidal to predominantly fluvial hydrologic regimes. We quantitatively characterized the floristic structure, species composition, and species richness of these tidal wetlands. Additionally, we documented variation in the avifaunal and insect assemblages associated with the floral structure. We found that freshwater tidal forested wetlands in the lower reaches of the estuary were characterized by high vegetation species richness and complex forest and scrub-shrub ecosystems, while tidal wetlands in the upper reaches of the estuary displayed a greater diversity of wetland ecosystems (forested, scrub-shrub, emergent, and aquatic bed) but comparatively lower species richness. A transitional area in the mid-estuary contained forested wetlands that exhibited some similarities to estuarine forested wetlands in both the upper and lower reaches. Likewise, avifauna and insect assemblage composition transitioned along the tidal freshwater estuarine gradient. Differences in geomorphological and hydrological regimes along the estuarine gradient appear to be the factors controlling the variation in tidal freshwater forested wetland characteristics and species composition. A thorough understanding of this complex and understudied system is necessary for predicting the potential impacts of hydrologic regime alterations and climate change and for guiding ongoing restoration efforts in the region.

The Meghna Estuary region of Bangladesh is a unique environment where the constant process of land formation and erosion takes place due to the complex interactions between large river discharge, enormous sediment load, strong tidal forces, wind actions, wave, salinity & cyclonic storm surge and estuarine circulation. These hydrodynamic factors and their interactions shape the morphology of the Meghna Estuary. During dry season upland fresh water flow into the Bay through the estuary is very much lower than that of monsoon season. Tidal action becomes stronger and dominates water flow pattern in the Meghna estuary. The distribution of flow and water level in the different channels of the Meghna estuary are governed by river discharge, the tide and the wind speed. Velocity is higher during ebb tide than that of flood tide due to combined effect of upstream flow and downward tidal current. Velocity in monsoon is much higher compare to dry period because upstream discharge is higher in monsoon. Most of the accretion and erosion mainly occurs during monsoon and post monsoon period. In pre-monsoon and post monsoon, wave height is less compared to monsoon as wind speed is less during these periods. Along the left Bank of this estuary, significant wave is considerable. As a result, tremendous whirl action due to tidal effects and whirl action due to enormous drainage flow during monsoon, wave action, tidal surge of the lower Meghna causes breaching of the major parts of the embankments of polder 59/2 and adjacent area. The main purpose of this research paper is to understand the hydrodynamic features of the Meghna estuary. The combined flow of the Ganges-Brahmaputra-Meghna (GBM) is drained through the Lower Meghna River into the Bay of Bengal via the estuary. Among the big rivers in the world, the combined flow of the Ganges-Brahmaputra-Meghna Rivers ranks third in terms of river flow and first in terms of total sediment discharge (1). There are distinct differences between Brahmaputra and Ganges river regimes (2). The Brahmaputra rises on average one month earlier than the Ganges, while flow recession in the Ganges river starts earlier that the Brahmaputra. The peak flow in the Brahmaputra occurs during July while in the Ganges River it is delayed until August. Discharge of river water into the Meghna estuary at different seasons is highly skewed. Some of the measurements done during the Meghna Estuary Study project suggest that in an extreme year, discharge through the estuary can be as much as fifteen times during the monsoon season compared to that during the dry season (3). It reported that in an average year the discharge through the estuary is about 20,000 m3/s during the dry season whereas it is 100,000 m3/s during the monsoon (4). In recent year IWM has measured discharge in the Lower Meghna under a project named as "Detailed Feasibility Study in Connection with Protection of Ramgati and Kamal Nagar Upazila and Adjacent Areas under Laxmipur District from the continuing Erosion of the Meghna River". The discharge through this river varies from about 10,000m3/s in dry season to 160,000m3/s in the wet season .In general, dry season (October -March) is the calm period in the estuary with weak wind from north and low river discharge. In contrast, monsoon season (June-September) is more vigorous with strong south-westerly wind and large river discharge and also higher mean water level (5). The interactions between the river discharge and tidal volume moving through the channels during the premonsoon and post-monsoon period in Lower Meghna Estuary, the estuary can be divided into 3 sub-units, the Tetulia and the west Shahbazpur channel can be termed as 'fluvial (in the sense that river outflow dominates over the tidal inflow)'; the east Shahbazpur and the west Hatiya channels can be termed as 'fluvio-tidal', and the east Hatiya and the Sandwip channels can be termed as 'tidal'. Monpura Island and Char Faizuddin divides the Shahbazpur channel into east and west. Char Nurul Islam divides the Hatiya channel into east and west (6).The 'fluvial' and the 'fluvio-tidal' sub-units as described above act as a tidal river with very high discharges in the

Tidal freshwater forested wetlands occupy a narrow ecological space determined by the balance between saltwater and freshwater inputs to the system. However, this balance is not well understood. In the Caribbean, tidal freshwater-forested wetlands dominated by Pterocarpus officinalis are vulnerable to changes in tidal influence and freshwater inputs. In this setting, the seasonal interactions of saltwater and freshwater inputs create less than ideal conditions for these forests to survive. Hence, it is crucial to have a better understanding of the hydrologic context of these and other tidal freshwater forested wetlands. We examined the extent of tidal forcing and saltwater influence in the largest Pterocarpus swamp of Puerto Rico by installing automated water level and conductivity recorders across a tidal creek transect at four different distances from the ocean, and by using water stable isotopes ratios (δD, δ18O) as natural tracers to determine the most important freshwater sources for tree transpiration. Records of water level and salinity revealed that the amount of rainfall was most influential on saltwater wedge migration in the creek for locations at the front and back of the tidal network, but that tidal dynamics were most influential at the middle section of the tidal network. Saltwater intrusion into the deepest parts of the tidal network was most prominent during sustained dry periods. Isotopic ratios of the surface water samples in the forest revealed that most of the water there was derived from freshwater runoff, but there was a seasonal change in its relative contribution to the forest hydrology. During the dry season, high δ values suggested the presence of runoff-derived water that had undergone evaporation, and saline influences were found in locations where past deforestation created preferential pathways for this water. During both seasons, δ 18O values of groundwater revealed the influence of saline water at depths 60 cm and greater near the adjacent tidal creek. Nonetheless, 18O-enriched stem water and low d-excess values suggested that Pterocarpus officinalis relies primarily on water accessed from unsaturated soil mounds that surround the tree and that are subject to evaporation, as opposed to groundwater at depth. This observation provides further insight to the adaptation mechanisms of Pterocarpus officinalis to survive in flooded ecosystems. In summary, our work demonstrates that for preventing saltwater intrusion, the amount of rainfall and freshwater inflow is more important than the sea level or the existence of an overland hydrological connection to the ocean.

With the global sea level rising, it is imperative to quantify how the dynamics of tidal estuaries and embayments will respond to increased depth and newly inundated perimeter regions. With increased depth comes a decrease in frictional effects in the basin interior and altered tidal amplification. Inundation due to higher sea level also causes an increase in planform area, tidal prism, and frictional effects in the newly inundated areas. To investigate the coupling between ocean forcing, tidal dynamics, and inundation, the authors employ a high-resolution hydrodynamic model of San Francisco Bay, California, comprising two basins with distinct tidal characteristics. Multiple shoreline scenarios are simulated, ranging from a leveed scenario, in which tidal flows are limited to present-day shorelines, to a simulation in which all topography is allowed to flood. Simulating increased mean sea level, while preserving original shorelines, produces additional tidal amplification. However, flooding of adjacent low-lying areas introduces frictional, intertidal regions that serve as energy sinks for the incident tidal wave. Net tidal amplification in most areas is predicted to be lower in the sea level rise scenarios. Tidal dynamics show a shift to a more progressive wave, dissipative environment with perimeter sloughs becoming major energy sinks. The standing wave southern reach of the bay couples more strongly back to the central portion of the bay, in contrast to the progressive wave northern reach of the bay. Generation of the M4 overtide is also found to vary between scenarios and is a nonnegligible contributor to net changes in high water elevation.

Groundwater is often overlooked as a source of nutrients to estuaries and most previous groundwater-surface water exchange studies did not consider the input of dissolved organic nutrients. Here, we hypothesize that groundwater is contributing to high dissolved inorganic and organic nutrient concentrations in an eutrophic subtropical tidal river and estuary (Caboolture River, Queensland, Australia). Several spatial radon (222Rn, a natural groundwater tracer) surveys indicated that the majority of groundwater discharge occurred in the tidal river just upstream of the estuary, and that the radon hotspot did not necessarily coincide with the nutrient hotspot. A radon mass balance revealed that groundwater discharge into the tidal river was equivalent to about 50% of the gauged river flow in February 2012. Groundwater discharge apparently contributed 85% of ammonium and 35% of phosphate entering the estuary. In spite of significant correlations between radon and nitrate and dissolved organic nitrogen (DON) during spatial surveys, groundwater could account for only 7% of nitrate and 9% of DON inputs due to low groundwater concentrations and other sources (i.e., apparently a sewage treatment plant for nitrate and floodplain tributaries for DON). Because total dissolved nitrogen (TDN) was dominated by DON (69%) and nitrate (23%), the groundwater ammonium inputs were a minor source to the TDN pool within the tidal river and estuary. This study demonstrated that correlations between a groundwater tracer and nutrient concentrations do not necessarily illustrate causation. To assess how groundwater drives nutrient dynamics in estuaries, it may be important to include the tidal river (not only the estuarine salinity gradient) in field investigations, consider DON (not only ammonium and nitrate), and perform detailed budgets that include minor tributaries.

Huangmaohai Estuary is a micro-tidal funnel-shaped estuary, located along the southwestern side of the Pearl River Delta complex. Variations of sediment transport patterns under different conditions of river discharge and tidal mixing are investigated by using field measurements and data analysis during both dry and wet seasons, respectively. The intratidal variation of sediment dynamics is largely controlled by the tidal asymmetry. The typical pattern of 25-hour mean sediment transport during the dry season is that the transport is landward in the channel and seaward on the shoals. A bifurcation pathway of sediment transport shows that sediments are imported from the East Opening and exported through the Middle Opening. However, this pattern can be altered by mixing processes and river discharge. Enhanced mixing or increased discharge can result in a predominantly seaward transport. Conversely, weak mixing can result in an emphatic landward transport. In general, the sediment transport is closely associated with the morphological evolution in the estuary.

Active deepening of tidal channels usually results in the alteration of the vertical and the horizontal tide. This may lead to concurrent significant increases in mean suspended matter concentrations (SPM) in coastal plain estuaries, the turbidity maximum (ETM) included. This is exemplified by an extensive analysis of the Ems estuary, a prototypical heavily stressed estuary in the Dutch-German border area. Measurements show that the SPM concentrations in the lower reaches of the estuary have increased an average of 2- to 3-fold between 1954 and 2005, with a 10-fold increase observed in the upper estuary (tidal river). Longitudinal profiles of surface SPM demonstrate that the ETM has moved upstream by up to 25 km and has broadened into a zone 30 km in length which extends into the freshwater tidal river. On an annual scale, variations in freshwater discharge significantly influence the formation and breakdown of the ETM: during low river discharge the ETM approaches equilibrium over 2–3 months, whilst elevated river discharges relocate the ETM downstream over several weeks. An exploratory, semi-analytical model is calibrated to simulate the equilibrium SPM distribution in the upper estuary during five time periods from 1965 to 2005, using archival bathymetric and tidal data. Results suggest that the deepening of tidal channels and a reduction in hydraulic drag have most likely resulted in a landward shift of the SPM trapping location. The measured increase in SPM concentrations and the development of fluid mud around the 1990s likely contributed to reduced mixing and bottom drag, creating a feedback loop that further altered tidal and SPM dynamics. It is argued that the removal of some non-erodible (consolidated) layers in the lower reaches of the estuary has created new internal sediment sources that may be responsible for feeding the observed high SPM concentrations, rather than increased sediment input from the boundaries. All findings are based on and supported by measured short-term seasonal fluctuations, as well as long-term developments of yearly averaged concentrations in the longitudinal SPM distribution.

In this study, we examined the influences of the differences in basin scale and river-crossing structures of 8 rivers of Ise Bay in Mie and Aichi Prefectures, Japan on the vegetation in the estuarine tidal flats of these rivers. The dominant plant communities of the estuarine tidal flats formed from rivers of large-scale river basins (exceeding 300 km2) were determined. In the Miya River, the dominant plant community was the Suaeda maritima and Artemisia fukudo community. In the Kushida River, the dominant plant community was composed of Phacelurus latifolius, Artemisia fukudo, Phragmites australis, and bamboo. In the Kumozu River, the dominant community was composed of the coastal plants Calystegia soldanella, Lathyrus japonicus, and Carex pumila and the exotic plant of Lolium multiflorum. The plant community of Suzuka River was dominated by the exotic plant of Eragrostis curvula. Among the estuarine tidal flats influenced by a small-scale river basin (50 km2 or less), the plant community of Shinbori River (Fukue tidal flat) was dominated by Suaeda maritima, and the plant communities of the Shio and Harai Rivers were dominated by Phragmites australis. The plant community of Tanaka River was dominated by Phragmites australis and coastal plants. Regarding the relationship between the vegetation and the river environment for each study site, we hypothesised that in a large basin area with few structures crossing the river, the river water catchment in the estuary after heavy rains caused large areas of disturbance and formed bare land, providing suitable habitat for an annual salt marsh plant community. In contrast, in cases with many structures crossing the river, a stable channel, an excavated riverbed and the suppression of runoff and the resulting disturbance of the estuary, flooding did not occur during high tide. Moreover, we hypothesised that in a small basin with many structures crossing the river, disturbance to the estuary was not likely, and the perennial salt marsh plant community of Phragmites australis would be widely distributed, except for a river type such as the Shinbori River, in which tide and river flow were managed by a final closure.

Here, the pelagic carbonate system and the δ13C signature of dissolved inorganic carbonate (DIC) were investigated in a tidal basin of the southern North Sea, the Jade Bay, with respect to tidal cycles and a transect towards the North Sea in winter time (January and November, 2010). Physical parameters, major and trace elements, and nutrient concentrations were considered, too. Primary production and pelagic organic matter respiration were negligible during winter time. Both, the compositional variations on the transects as well as during the tidal cycles indicate the mixing of North Sea with fresh water. The combined spatial co-variations of different parameters indicate an introduction of fresh water that was enriched in DI12C, metabolites (e.g., ammonia), protons, and dissolved redox-sensitive elements (e.g., Mn2 +). During the January campaign, the discharge via the flood gates was limited due to ice cover of the hinterland drainage ditches, allowing for an observation of tidal variations without significant mixing contributions from surface water discharges. Considering a binary mixing model with North Sea and fresh water as end-members, the extrapolated fresh water end-member composition for this campaign is estimated to contain about 3.8 mmol/kg DIC (δ13C ≈ − 10 ± 1‰ vs. VPDB), and enhanced concentrations of NH4+, Mn2 +, and protons compared to North Sea water. The fast temporal response of dissolved geochemical tracers on tidal variations in the Jade Bay indicates a continuous supply of a fresh water component. The measured composition of fresh waters entering the Jade Bay via flood gates (end of October, 2010) did not match the values estimated by the binary mixing model. Therefore, the overall fresh water component likely is a mixture between sources originating from flood gates and (in January) dominating submarine groundwater discharge entering the Jade Bay. This model is consistent with the results obtained during the November campaign, when a more important contribution from flood gates is expected and a more variable fresh water end-member is estimated. The co-variations of the concentrations and the stable carbon isotope composition of DIC are applied to evaluate possible superimposed sink-source-transformation processes in the coastal waters and a general co-variation scheme is suggested.

Land-ocean interactions in the coastal zone are severely influenced by tidal processes. In regions of high sediment discharge like the Mekong River Delta in southern Vietnam, these processes are even more significant. Three cruises in 2006, 2007 and 2008 were carried out to investigate the sediment suspension and their spatial distribution. Additionally, we investigated the influence of the tidal currents in relation to the suspended sediment. Therefore, all cruises took place during the inter-monsoon season between March and May where wave and wind influences are not dominant in contrast to the summer monsoon (May to early October) and winter monsoon season (November to early March). Suspended sediment concentrations (SSCs) in the particle-size range between 2.5 and 500 iim were measured with an LISST-instrument (Laser In Situ Scattering and Transmissiometry). Current velocities and directions were recorded with an Acoustic Doppler Current Profiler (ADCP). Additionally, data of different tidal gauge stations in the Mekong River Delta were correlated and compared to the mixed semidiurnal-diurnal tidal cycle. Our results show significant areas of SSCs greater than 25 mu l/l in the Mekong River branches and its subaqueous delta during the inter-monsoon season. 20% of all measured SSCs in the subaqueous Mekong Delta exceed 100 mu l/l. Highest concentrations occur close to the seabed. SSCs decrease at the transition to the open shelf. The shelf region contains only low suspension loads, especially on the south-eastern shelf (99% of all samples 25 close to the seabed in water depths of 20-25 m. Two surveys lasting 25 h each were performed on mooring stations in 12 m (Mooring 1) and 26 m (Mooring 2) water depth and located 3.2 km apart on the subaqueous delta slope. Similar patterns of SSC over time show that concentrations of suspension load correlate with the tidal current velocities. High tidal current velocities of up to 0.6 m/s near the sea bottom generate increasing SSCs of more than 25 gl in the water column. Additionally a significant trend of decreasing SSC from the near-seabed to the upper part of the water column can be observed. In terms of sediment transport the ebb phase dominates the tidal cycle by its higher tidal current velocities but the flood phase has the longer duration. The switch of the tidal current direction from ebb to flood phase occurs rapidly against which the change from flood to ebb phase requires up to 3 h. This leads to an asymmetry of the tidal ellipses and may cause a net-sediment transport from the shelf into the subaqueous Mekong Delta. In the subaqueous Mekong Delta and adjacent shelf, seven transects show similar patterns of SSCs dependent to the tidal phase. A hypopycnal sediment plume from the subaqueous Mekong Delta into the shelf region was not observed. Our results imply that resuspension by tidal currents dominates the sediment transport in the subaqueous Mekong Delta and adjacent shelf regions during the inter-monsoon season. (C) 2012 Elsevier Ltd. All rights reserved.

[1] The hydrologic processes by which tide affects river channel and riparian morphology within the tidal freshwater zone are poorly understood yet are fundamental to predicting the fate of coastal rivers and wetlands as sea level rises. We investigated patterns of sediment accretion in riparian wetlands along the nontidal through oligohaline portion of two coastal plain rivers in Maryland, U.S., and how flow velocity, water level, and suspended sediment concentration (SSC) in the channel may have contributed to those patterns. Sediment accretion was measured over a 1 year period using artificial marker horizons, channel hydrology was measured over a 1 month period using acoustic Doppler current profilers, and SSC was predicted from acoustic backscatter. Riparian sediment accretion was lowest at the nontidal sites (mean and standard deviation = 8 ± 8 mm yr−1), highest at the upstream tidal freshwater forested wetlands (TFFW) (33 ± 28 mm yr−1), low at the midstream TFFW (12 ± 9 mm yr−1), and high at the oligohaline (fresh-to-brackish) marshes (19 ± 8 mm yr−1). Channel maximum flood and ebb velocity was twofold faster at the oligohaline than tidal freshwater zone on both tidal rivers, corresponding with the differences in in-channel SSC: The oligohaline zone's SSC was more than double the tidal freshwater zone's and was greater than historical SSC at the nontidal gages. The tidal wave characteristics differed between rivers, leading to significantly greater in-channel SSC during floodplain inundation in the weakly convergent than the strongly convergent tidal river. High sediment accretion at the upstream TFFW was likely due to high river discharge following a hurricane.

By taking the Yong River for example in this paper, based on the multiple measured data during 1957 to 2009, the change process of runoff, tide feature, tidal wave, tidal influx and sediment transport are analyzed. Then a mathematical model is used to reveal the influence mechanism on hydrodynamic characteristics and sediment transport of the wading engineering groups such as a tide gate, a breakwater, reservoirs, bridges and wharves, which were built in different periods. The results showed the hydrodynamic characteristics and sediment transport of the Yong River changed obviously due to the wading engineering groups. The tide gate induced deformation of the tidal wave, obvious reduction of the tidal influx and weakness of the tidal dynamic, decrease of the sediment yield of flood and ebb tide and channel deposition. The breakwater blocked estuarine entrances, resulting in the change of the tidal current and the reduction of the tidal influx in the estuarine area. The large-scale reservoirs gradually made the decrease of the Yong River runoff. The bridge and wharf groups took up cross-section areas, the cumulative affection of which caused the increase of tidal level in the tidal river.

Comparisons of surface sediment distributions in summer 1997 and 2011 and elevations on the tidal flats in April 1998 and March 2013 had been used for understanding the long-term changes of sedimentary environments at southern Kanghwa tidal flat, west coast of Korea. The mud sediments dominated in the eastern part and sandy mud sediments dominated in the western part of the tidal flat in 1997. In 2011, the surface sediments were dominant mud and sandy mud at Sunduri and Tonggum in the eastern part, sandy mud at Tongmakri in the middle part, and sand and muddy sand at Yeochari and Changhwari tidal flats in the western part. The area of mud sediments had decreased, but that of sand-mud mixed sediments extended to eastward tidal flat for 14 years. The long-term topographic changes showed that deposition occurred at Tongmakri and Yeochari and erosion occurred at Changhwari tidal flat during 15 years. These changes should be effected the local hydrodynamic changes by several constructions near the tidal flat since the 1990s.

The Digital Elevation Model (DEM) based on the historical sea-charts and on-site hydrological records were used to examine the morphological change of the Elbe River estuary. The results show that siltation predominated in the tidal flat in the northern estuary, with a net siltation rate of 1.8 cm·a−1 during 1927–2006. In contrast, a continuous erosion prevailed in the main river channel, south of the estuary, with a net erosion rate of 2.5 cm·a−1 in the same time. In addition, a seaward shift of the estuarine island has happened with the old island coalescing to the northern tidal flat and new one emerging through siltation process. The tidal asymmetry via ebbing flow (maximum at 140 cm·s−1, and average at 76 cm·s−1) prevailed in the tidal flat, meaning continuous aggradation northwestward, while flooding flow (maximum at 100 cm ·s−1, and average at 67 cm·s−1) dominated in the main river channel with deepening thaweg at south, showing a landward sedimentation via the tidal pumping processes. This dextral extension of the estuarine morphology is due to the Coriolis force, leading to the inconsistent directions of in-out flows, which enables to facilitate the estuarine siltation. Human dredging prevailing in the estuary has dramatically altered the nature of the silted river channel to erosional since the last century. This is characterized by a net erosion rate of 3.2 cm·a−1 derived from the DEMs mapping, but only partially accounting for the dredging amount of 1994–2006, when the total dredging volume was 67 × 106 m3, equal to 5.9 cm·a−1.

Assessing submarine groundwater discharge (SGD) in mangroves can be challenging due to the complex, heterogeneous nature of sediments and temporally dynamic water flows. Here, we use natural tracers (i.e., radon and radium isotopes) to quantify groundwater–surface water exchange in a mangrove tidal creek at the ecosystem scale, and to assess whether SGD was a source of dissolved inorganic and organic nutrients to the nearby estuary. Hourly sampling for over 27 h in the winter and 30 h in the summer revealed clear tidal trends for 222Rn, 224Ra, 223Ra, 226Ra, dissolved oxygen, ammonium, and dissolved organic nitrogen (DON) in a mangrove tidal creek with no upstream freshwater inputs (Kangaroo Island, Southern Moreton Bay, Australia). Nitrate, phosphate and dissolved organic phosphorus (DOP) did not show a clear tidal trend. A mass balance revealed that 5–12% of the tidal prism volume infiltrated the sediments and drained back to the creek at low tide. Groundwater exchange accounted for nearly all the ammonium and about 30% of the DON exported by the creek. Crab burrows were a major factor influencing groundwater exchange in this tidal creek. A detectable 226Ra (half-life of 1600 years) enrichment in the creek at low tide could only be explained by the construction of new crab burrows during each tidal cycle exposing old sediments. Overall, the concentration of groundwater tracers and nutrients was higher in the summer most likely due to increased crab activity and organic matter degradation in the warmer months. Respiration of belowground organic matter apparently released nitrogen to groundwater seeping out from the creek bank at low tide and increased N:P ratios of surface water draining from mangroves. Therefore, we hypothesize that outwelling from mangroves with high SGD may influence the composition of downstream biological communities by altering estuarine N or P limitation conditions.

a b s t r a c t In arid lands, wetland loss is the result not only of the scarcity of water itself, but also of the management of water to maximize off-stream uses. In the Colorado River delta, Mexico, no in-stream flows are allocated for aqutic ecocystems, yet agricultural return flows and canal operational releases support 36,377 ha of valuable wetland and riparian habitat. We evaluated the relationships between water use in the Mexicali Irrigation District (DR014) and the water supply for the Colorado River delta wetlands. Mexicali farmers applied on average 1024 mm yr−1 to fields in 2008, less than half of what is applied to irrigated fields in a typical irrigation district in the U.S. portion of the river. Farm-level agricultural efficiency is high, as 90% of water applied to fields can be accounted for in evapotranspiration (ET), as estimated by a remote sensing technique and by a district water budget approach. By contrast, in a comparison U.S. irrigation district, ET accounts for only 60% of applied water and the rest emerges as irrigation return flows. Despite the apparent high on-farm irrigation efficiency in DR014, sufficient water is discharged to support valuable ecosystems. Seepage losses from canals are higher than in the comparison district in the U.S., and this water contributes to formation of a high, non-saline aquifer that supported riparian trees along the river. On the other hand, surface drainage water supports brackish wetland habitats south of the irrigation district. The goal of obtaining water for environmental uses by increasing agricultural efficiency in the irrigation districts would not by itself be an effective strategy for the delta aquatic habitats as the delta wetlands and riparian areas are currently dependent on canal seepage, return flows and waste spills from both the U.S. and Mexico.

Closed-off tidal basin reclamation represents a special type of reclamation. In several countries enclosing dams have been built to close off estuaries, shallow seas, or lagoons, and lands up to 5~6?m - MSL (below mean sea level) have been reclaimed in the former tidal basins. Although these areas were generally primarily reclaimed for agriculture, a second-stage development may have taken place where parts of these lands were transferred to urban and industrial use. The originally saline water in the created reservoirs was transformed to fresh water that may be used for irrigation, domestic and/or industrial water supply. In several of these reservoirs there are water quality problems, primarily due to pollution in upstream parts of the river basins. In 2007 the Enclosing Dam of the Zuiderzee Scheme in the Netherlands had existed for 75?years. This occasion was used to conduct a global inventory of closed-off tidal basin reclamation on which this paper is based. The study shows that closed-off tidal basin reclamation concerns 25 schemes with a total area of 738 000?ha, of which 337 000?ha have been reclaimed and 401 000?ha freshwater reservoirs have been created. This paper presents a summarized overview. Attention is paid to safety, land use and changes in it, development of water quality in the reservoirs, as well as to land subsidence and possible impacts of climate change, like rise in mean sea level. In time this may have implications for safety of the deep polders, the management of the reservoirs as well as for the sustainable development of tidal areas in the future. These items are presented for four major tidal reclamation schemes: the Zuiderzee Scheme in the Netherlands, the Saemangeum Scheme in South Korea, the Kuttanad Region in India and the Hachirogata Scheme in Japan

[1] Tidal rivers feature oscillatory and steady gradients in the water surface, controlled by interactions between river flow and tides. The river discharge attenuates the tidal motion, and tidal motion increases tidal-mean friction in the river, which may act as a barrier to the river discharge. Time series of tidal water level amplitudes at five gauge stations along the River Mahakam in Indonesia, and tidal flow velocity amplitudes at a discharge monitoring station were obtained applying wavelet analysis. Temporal variations in tidal damping coefficients for quaterdiurnal, semidiurnal, and diurnal tidal species were quantified from the observed amplitude profiles. The analysis shows that tidal damping during the rising limb of a discharge wave differs from damping during the falling limb. Wavelet cross-correlations between surface levels yielded empirical estimates of wave numbers. An empirical relation between tidal damping and river flow is derived to describe subtidal bottom friction along an idealized tidal river resembling the Mahakam. The subtidal friction is decomposed into contributions from the river flow only, from river-tide interaction, and from tidal asymmetry. Even for high river flow and low tidal velocity, river flow enhances friction attributed to river-tide interaction, causing subtidal water level setup. A simple multilinear regression model using subtidal bottom friction is employed to predict subtidal water levels at locations upstream, with a relatively good agreement between predictions and observations. The explicit expression shows the nonlinear dependence of subtidal friction on river flow velocity, explaining the complex behavior of tidal-mean surface level profiles.

A two-dimensional numerical model was set up to simulate the tidal current of the Yangtze River Estuary with MIKE21 FM. This model has been calibrated and validated with the observed tidal level. We simulated the change of flood and tidal stage in the Yangtze River Estuary after the sea level rising by 20~60cm. The simulate results indicate that: (1)With sea level rising, the extent of rise of the high tide is greater than that of rise of low tide. Under the same sea level rise, the closer to the lower reaches of the Yangtze River Estuary, the more obvious the increase in the low tide level is, the rise of the high tide does not change significantly. (2)For the changes of the tidal range increase, under the same sea level rise, the closer to the upper reaches of the Yangtze Estuary, the greater the tidal range increase is.

Types, factors, as well as the environmental and economic impacts of a dangerous hydrological phenomenon, i.e., intrusion of salt or brackish sea water into river mouths, are discussed. The main theoretical and empirical approaches used in studying this phenomenon are described. The experience in studying this problem in Russia and other countries is generalized. The case studies considered in the paper include the processes of seawater intrusion into river mouths of different types with regard to the tidal range.

The geomorphic configuration of hilly land (in the southern area), sea (in the northern area) and littoral plain (in the middle area) within the overall area of Cixi was formed about 2500 BP. The Cixi tidal flat belongs to the silting-up class of tidal flat. Eleven dykes have been constructed since the Song dynasty. The average outward migration rate of the coastline before the founding of the People’s Republic was 25 m/a, and it has been increased to 50-100 m/a since the founding. The influencing factors for the formation and evolution of the Cixi tidal flat mainly include landform restriction, river runoff and human activities. The influence of human activities has become even greater in modern times. The principle for the regulation of the tidal furrow during the process of tidal flat reclamation should guide action according to circumstances as well as to reclamation of the tidal flat accompanied by the regulation of the tidal furrow. The former part of this principle means that the strike of the river channel must be in accordance with the law of stream movement and transport of sediment. The latter part means that the regulation of the tidal furrow must be closely linked to alongshore reclamation of the tidal flat.