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Significant declines in Atlantic sturgeon (Acipenser oxyrhynchus oxyrhynchus) abundances along the US east coast have spurred major research efforts and management actions over the last 50 years, yet information on spawning stock abundances and habitat use is still lacking for many river systems, including in the Chesapeake Bay, USA. Here, we developed and tested a new quantitative PCR (qPCR) assay to detect Atlantic sturgeon environmental DNA (eDNA) in water samples with the goal of providing an alternative method to monitor presence and relative abundance. We also examined Atlantic sturgeon eDNA shedding rates in laboratory experiments. A qPCR‐probe assay targeting Cytochrome B was developed and showed no amplification of other related and co‐occurring fishes. Pond trials at a density of ~0.2 g/L sturgeon produced relatively strong eDNA detections (~1,000–25,000 copies/L) in all seven water samples assayed. Water samples taken from two river systems in the Chesapeake Bay produced zero eDNA detections in the summer, while fall sampling during sturgeon spawning produced positive eDNA detections in 26% of samples, though at much lower concentrations (400–1,800 copies/L) compared with the pond (mesocosm) detections. Acoustic detections of sturgeon near river sampling sites were positively associated with eDNA detections. However, the eDNA assay failed to detect the presence of sturgeon in some samples when abundances were very low or when fish were in deep water. Finally, Atlantic sturgeon eDNA shedding rates were estimated to be on the order of estimates for other fish species, which suggests that relatively weak detections in the field are not necessarily driven by low rates of eDNA shedding. Overall, eDNA analysis represents a promising new monitoring tool for Atlantic sturgeon. Applying these methods in other rivers along the US east coast is an important next step in documenting Atlantic sturgeon distribution for management and conservation purposes.

The present field study investigated hydraulic and sediment in tidal conditions. Measurements were made for two stations at neap tide and spring tide for 13-hour periods at no-dimensional depths of 0.2, 0.6 and 0.8 of the water level each time. In these measurements, the parameters of velocity, direction of flow, electrical conductivity, temperature and depth were measured directly, and to determine the amount of suspended sediments per hour, 3 samples of one litre from the mentioned depths were measured by the instantaneous vertical sampler and taken to a laboratory. An examination of the depth charts of the suspended sediments concentration for all stations, and in both the neap tide and the spring tide, showed that, in general the suspended sediments concentration increased with increasing depth. Moreover, the deep distribution of sediments concentration showed that the values obtained in the laboratory corresponded well with the values calculated from the Rouse equation, and as the depth increases, the sediments concentration usually increases.

Communities in London and along the tidal River Thames in the UK already benefit from world-class tidal defences, but climate change means flood risk continues to increase. In 2012, the Environment Agency published a plan for how 1.3 million people and £275 billion worth of property will continue to be protected from tidal flood risk until the year 2100. The first 10 years of the plan, which includes innovative asset management solutions on tidal flood defence systems, is being delivered through the £308 million Thames Estuary Asset Management 2100 (Team2100) programme. As described in this paper, the integrated delivery team is focusing on delivering value for public money through innovation, collaboration with the supply chain and a systems-level approach to asset and programme management.

The blue crab, Callinectes sapidus, has a broad geographic distribution encompassing coastal waters of the eastern USA and Gulf of Mexico, but intraspecific patterns of habitat use and quality are lacking at northern latitudes. This study examined the population structure of blue crabs in the Seekonk and Taunton Rivers (Rhode Island and Massachusetts, USA): two tidally influenced rivers contiguous with the Narragansett Bay Estuary and dominated by shallow-water, unvegetated habitats. Crabs were collected fortnightly from May through August (2012–2016), and abundance- and growth-based metrics were used to assess riverine habitat use and quality. These metrics were also analyzed with respect to crab life history traits and in situ abiotic conditions to elucidate patterns of habitat selection throughout ontogeny. Crabs measuring 8 to 185 mm carapace width (CW; n = 2577) were collected, and two distinct age classes occupied the rivers during the spring and summer (maximum abundance ~ 5 crabs/10 m2). The younger age-0+ cohort was numerically dominant (~ 88% of total catch) and comprised of male and juvenile female crabs (mean ± SD abundance = 0.28 ± 0.26 males/10 m2 and 0.14 ± 0.12 juvenile females/10 m2). Males accounted for the majority of age-1+ crabs (~ 83% of cohort), yet sexually mature females were also observed (9% of cohort; mean ± SD abundance = 0.04 ± 0.06 adult females/100 m2; size at 50% maturity ± 95 CI = 129.0 ± 0.2 mm CW). Crabs were spatially segregated along a salinity gradient with males and juvenile females prevalent in oligohaline waters (upper river salinity ~ 5 ppt) and adult females mainly concentrating in higher salinity areas (mid- and lower-river salinity ~ 11–21 ppt). Seasonal and interannual patterns in crab abundance also differed by sex and ontogeny. Peak catches of males and juvenile females occurred during the spring and mid-summer, and annual abundances were positively related to dissolved oxygen (DO) concentrations. In contrast, mature females were most abundant during August and years with elevated water temperatures. The absolute and relative growth rates of juvenile crabs equaled 0.9 ± 0.3 mm CW/day and 1.5 ± 0.6% CW/day, respectively, and were directly related to DO levels. A synoptic examination of crab abundance and growth across a broad geographic range indicated that shallow-water, unvegetated habitats presently serve as functional nurseries in southern New England tidal rivers.

Aim: Since decades, a major part of south-western coastal region of Bangladesh is being affected by water logging – a problem related to climate change along with some manmade activities. Therefore, the study was conducted to assess the causes and consequences of this problem and highlights the responses of affected people to attract policy planners’ intention for taking proper intervention. Place and Duration of Study: The study was conducted in the Laboratory of Plant Ecology, Department of Crop Botany, Bangladesh Agricultural University, Mymensingh, Bangladesh. Methodology: Qualitative and quantitative techniques have been applied to collect and analyze both the primary and secondary sources of data from various waterlogged areas of south west Bangladesh. Results: There is no single or a few factors are responsible for creating water-logging problem rather it is a combination of several factors and their cumulative effects over time. It is revealed from the analysis of primary and secondary sources of information that death of Mathavanga River in the 20th century, execution of Coastal Embankment Project since 1960’s, withdrawing water flow to the Padma River through operating the Farakka barrage after independent of Bangladesh, improper management of rivers, faulty land-use by influential people in the areas, monsoon downpour etc are major causes of the problem. The silted up river systems in area could not drain monsoon rain that occurred even for a couple of days. The consequences brought to inundate hundred thousand hectares of cultivable land unsuitable for crop production. More than one million people are directly affected in the areas and the number is gradually increasing over the years. Water stagnancy around the settlement areas remains 6 to 9 months in a year and many places became permanently waterlogged. The affected people have no other way out but to live with water. The congested water is polluted with salinity, chemical effluents with heavy metals, household debris’s and related other pollutants. Source of safe drinking water is destroyed. Therefore incidences of waterborne and skin diseases are increased. People are living with greatest inhumanity as food, shelter, sanitation, communications, educations and other prime needs are tremendously challenged. Many people lost their occupations and became destitute, some altered their livelihood to much lower grades, and many of them are forced to migrate to city areas. The marooned people demanded to the authority to declare their places as an affected area and sought the government intervention to bring an end to the crisis through operating the Tidal River Management plan and excavating or re-excavating of associated rivers, channels and rivulets. Conclusion: The authority need to pay keen attention to the issue and should take proper initiative to mitigate the water-logging problem permanently to save people living in the south western coastal region of Bangladesh.

Urbanized rivers flowing through polluted megacities receive substantial amount of carbon from domestic sewage and industrial effluents which can significantly alter the air-water CO2 flux rates. In this regard, we quantified the partial pressure of CO2 in the surface water (pCO2(water)), air-water CO2 fluxes, and associated biogeochemical parameters in the Hooghly River, India, flowing through two of the most polluted cities of the country, Kolkata and Howrah, over a complete annual cycle during spring tidal phase (SP) and neap tidal phase (NP). This urbanized part of Hooghly River was always supersaturated with CO2 having an annual mean pCO2(water) and air-water CO2 flux of ~ 3800 μatm and ~ 49 mol C m−2 year−1, respectively. Significant seasonal variability was observed for both pCO2(water) and air-water CO2 flux (pre-monsoon, 3038 ± 539 μatm and 5049 ± 964 μmol m−2 h−1; monsoon, 4609 ± 711 μatm and 7918 ± 1400 μmol m−2 h−1; post-monsoon, 2558 ± 258 μatm and 4048 ± 759 μmol m−2 h−1, respectively). Monthly mean pH and total alkalinity varied from 7.482 to 8.099 and from 2437 to 4136 μmol kg−1, respectively, over the annual cycle. pCO2(water) showed significant positive correlation with turbidity and negative correlation with electrical conductivity and gross primary productivity (GPP). High water discharge could have facilitated high turbidity, especially during the monsoon season, which led to depletion in GPP and enhancement in pCO2(water) which in turn led to very high CO2 effluxes. The CO2 efflux rate in this urbanized riverine stretch was substantially higher than that observed in previous studies carried out in the less urbanized estuarine stretch of Hooghly. This indicates that the presence of highly urbanized and polluted metropolis potentially enhanced the pCO2(water) and CO2 effluxes of this river. Similar observations were made recently in some Asian and Australian urban rivers.

Being the only tidal river where major Indian carps spawn naturally, Halda is a unique heritage of Bangladesh and the surroundings of this river undergo chronological changes because of rapid urbanization, anthropogenic and socioeconomic activities. In this study, an attempt has been made to analyze Land use/land cover change (LULCC) of Halda Watershed over the last 40 years using multispectral satellite data obtained from Landsat 2 MSS for April 15, 1978; Landsat 5 TM for February 26, 1999 and Landsat 8 OLI/TIRS for May 2, 2017. The watershed has been classified into five major land cover/use classes viz. Agriculture, Bare soil, Settlements, Vegetation and Water Body. Resultant LULC and overlay maps indicate a significant shift from Vegetation (35.1%) and Water class (85.47%) to Agriculture, Bare soil and Settlements. This study envisages to facilitate policy makers, planners and other associated development workers to adopt the best suitable land-use management option for Halda Watershed. Keywords: Halda river, Watershed delineation, Land use/land cover change (LULCC), Geographic Information System (GIS)

The Connecticut River plume interacts with the strong tidal currents of the ambient receiving waters in eastern Long Island Sound. The plume formed during ambient flood tides is studied as an example of tidal river plumes entering into energetic ambient tidal environments in estuaries or continental shelves. Conservative passive freshwater tracers within a high-resolution nested hydrodynamic model are applied to determine how source waters from different parts of the tidal cycle contribute to plume composition and interact with bounding plume fronts. The connection to source waters can be cut off only under low-discharge conditions, when tides reverse surface flow through the mouth after max ambient flood. Upstream plume extent is limited because ambient tidal currents arrest the opposing plume propagation, as the tidal internal Froude number exceeds one. The downstream extent of the tidal plume always is within 20 km from the mouth, which is less than twice the ambient tidal excursion. Freshwaters in the river during the preceding ambient ebb are the oldest found in the new flood plume. Connectivity with source waters and plume fronts exhibits a strong upstream-to-downstream asymmetry. The arrested upstream front has high connectivity, as all freshwaters exiting the mouth immediately interact with this boundary. The downstream plume front has the lowest overall connectivity, as interaction is limited to the oldest waters since younger interior waters do not overtake this front. The offshore front and inshore boundary exhibit a downstream progression from younger to older waters and decreasing overall connectivity with source waters. Plume-averaged freshwater tracer concentrations and variances both exhibit an initial growth period followed by a longer decay period for the remainder of the tidal period. The plume-averaged tracer variance is increased by mouth inputs, decreased by entrainment, and destroyed by internal mixing. Peak entrainment velocities for younger waters are higher than values for older waters, indicating stronger entrainment closer to the mouth. Entrainment and mixing time scales (1–4 h at max ambient flood) are both shorter than half a tidal period, indicating entrainment and mixing are vigorous enough to rapidly diminish tracer variance within the plume.

Study region South Korea (KR), Ulsan tidal river. Study focus Climate change and urbanization pose a serious threat to rising water levels and flooding in the estuary region. In particular, tidal river, which is located in the estuary area, is impacted by many hydrological factors such as tide, wave height, and rainfall. This paper develops a new rating curve that can predict the water level of the tidal river. It also assesses the accuracy of the developed rating curve through the verification event. New hydrological insights Tidal rivers show non-linear hydrological characteristics that are influenced by various hydrological factors. Thus, no rating curve has been developed for them. This study proposes a method to develop a rating curve that can estimate the water level by using the runoff from rainfall in a tidal river. To develop the rating curve, the water level at Ulsan station, Korea was decomposed into four components, which are tide, wave, noise and runoff component by using wavelet analysis, curve fitting, and a high pass filter. A distributed grid-based rainfall-runoff model (GRM) was applied to simulate the runoff. The simulated runoff and the water level components influenced by rainfall were used to develop a rating curve and estimate the water level from the simulated runoff. The results were then added to the other three components (tide, wave, noise) to calculate an integrated water level, which was compared with the observed water level at Ulsan station. With less than 10 % error during validation, the results are expected to contribute to the accurate prediction of water level of tidal river during flood season.

Halda is a unique resourceful tidal river of Bangladesh, where Indian major carps (Catla catla, Labeo rohita, Cirhinnus mrigala, and Labeo calbasu) spawn from April to June. Ecological conditions are auspicious from time immemorial which serves as a natural breeding ground in the world. The present study was conducted over the period of January-June 2017 to identify the main species of Zooplankton fauna and also fi nd out the dominancy of the highest plankton groups in the lower Halda River. A total of 3 major zooplankton groups-Copepoda, Rotifera and Cladocera were identifi ed during the six months period. A total of 35 species under 4 family showing the dominancy for the class Rotifera consisting of 7 genera were recorded from fi ve sampling sites. The lowest group was Cladocera consisting of 5 genera. The composition and dominance of the zooplankton community among fi ve different sites in the lower Halda River showed some close inter-relationships. The present study suggests for conducting further research to know the overall conditions and to make a complete list of available zooplankton fauna that exert impact on the water quality of the Halda River.

Limited evidence for spatial patterns of denitrification in tidal freshwater forested wetlands (TFFWs), seemingly due to high spatial variability in the process, is surprising considering the various spatial gradients of its biogeochemical and hydrogeomorphic controls in these ecosystems. Because certain physical environmental gradients may be useful for the prediction of denitrification in TFFWs, we measured denitrification and ecosystem attributes in hummock-hollow microtopography of TFFWs along longitudinal riverine positions (upper, middle, and lower tidal river sites, and nearby upstream nontidal forested floodplains) of the adjoining Pamunkey and Mattaponi Rivers, Virginia. We tested differences by river, site, and plot in denitrification enzyme activity (DEA) and substrate limitations of denitrification potential (DP). The Pamunkey River carries greater river nitrate concentrations, and we found less nitrate limitation of DP and greater soil nitrate in hollows of this river. DEA in tidal hummocks was positively correlated with soil organic matter, nitrogen, and carbon, with the highest rates in lower tidal sites. Hummocks also promoted greater oxygen-controlled substrate limitation of DP, whereby experimental aeration stimulated DP under subsequent inundation more in hummocks than hollows. Additionally, tidal sites had greater DEA than nontidal sites, inferred to be caused by a combination of higher moisture, organic, and nutrient content. Our results indicate that the increasing nitrogen concentrations in these rivers will increase denitrification more on the Mattaponi River by alleviating its greater nitrogen limitation compared to the Pamunkey River, and modification to sedimentation, inundation, or microtopography from sea level rise may alter denitrification gradients in TFFWs and upstream low-elevation nontidal floodplains.

This paper examines data from 18 USGS gauges in the lower Pee Dee Basin in an effort to explain the behavior of the flooding following Hurricane Florence (2018) in Georgetown County, South Carolina. Despite record or near-record flooding in all the tributaries to the Winyah Bay estuary, water levels near the city of Georgetown were well below predicted heights. Floodplain storage in the lower Great Pee Dee, Lynches, and Little Pee Dee River valleys stored over 1.2 million acre-feet of floodwaters, delaying peak stage near Bucksport for five days and reducing peak flow into the Winyah Bay tidal river/estuary system by nearly 50%. An unknown amount of flow from the Winyah Bay tidal river/estuary system flowed through the Atlantic Intracoastal Water Way to Little River rather than through Winyah Bay. The resulting freshwater flow to Winyah Bay only moved the point of tidal stagnation (where upstream tidal flow balances downstream freshwater flow) to near Georgetown. Since the city of Georgetown was near the point of stagnation, water level there was driven by ocean tidal height rather than river flood stage. The lack of discharge data from the tidal rivers in Georgetown County prevents evaluation of the importance of each of these factors and will limit efforts to make quantitative predictions of future flooding in the county.

Controlling floods and raising rice production in Bangladesh have been the centres of struggle for nearly a century - between North and South, and between engineering solutions and local knowledge. Decades of disastrous construction of dikes and polders led first to local protest, including cutting dikes, and then to a structured local solution known as tidal river management, which won the support of Bangladeshi scientists and academics. Suddenly, the global North has noticed and is rushing to catch up - asking what local farmers knew and hydraulic engineers did not, while trying to maintain the dominance of aid industry engineers and technicians in Bangladesh.

The Thames Tideway tunnel is a large sewer running up to 66 m below the tidal river Thames in London, UK. Its construction, started in 2016, was urgently needed to protect the tidal Thames from pollution due to the combined sewer overflows of untreated sewage that every year are spilled into the river. This paper reports on an exercise for evaluating the environmental impact associated with the construction process of the east section of the tunnel quantified by means of a life-cycle assessment, which not only primarily considered carbon dioxide emissions, but also took into account a wider series of impact categories. Operational and decommissioning impacts were not included. The results indicated the processes with the greatest effects on the environmental performance of the east sector construction and hence where alternatives on the design or materials used needed to be considered.

An inspection of a tidal river concrete bridge in the Mekong River Delta discovered a large number of map cracks in most piers within the tidal range. These map cracks distribute nearly vertically and horizontally with a distance of about 15 and 20 cm. Many of them have a width over 1 mm and a depth exceeding the thickness of the reinforcement protection concrete layer. Considering the location and the pattern of cracks, the most acceptable hypothesis on their cause was the strain gradient in concrete induced by the change of moisture content during tide rise and fall, i.e. by the effect of wet – dry action. To verify this hypothesis, experiments on the time dependent change of concrete moisture content and volume were conducted. Based on the results of these experiments, a computer simulation was performed. The simulated crack map and pattern agreed very well with the observed ones. With the obtained results, it is reasonable to conclude that strain gradient in pier concrete induced by the wet – dry action may one of main causes of cracks in such bridge piers

Coastal-water hypoxia is increasing globally due to global warming and urbanization, and the need to define management solutions to improve the water quality of coastal ecosystems has become important. The lower tidal Garonne River (TGR; southwestern France), characterized by the seasonal presence of a turbidity maximum zone (TMZ) and urban water discharge, is subject to episodic hypoxia events during low river flow periods in the summer. Future climatic conditions (higher temperature and summer droughts) and increasing urbanization could enhance hypoxia risks near the city of Bordeaux in the coming decades. A 3-D model of dissolved oxygen (DO) that couples hydrodynamics, sediment transport and biogeochemical processes was used to assess the efficiency of different management solutions for oxygenation of the TGR during summer low-discharge periods. We ran different scenarios of reductions in urban sewage overflows, displacement of urban discharges downstream from Bordeaux and/or temporary river flow support during the summer period. The model shows that each option mitigates hypoxia, but with variable efficiency over time and space. Sewage overflow reduction improves DO levels only locally near the city of Bordeaux. Downstream relocation of wastewater discharges allows for better oxygenation levels in the lower TGR. The support of low river flow limits the upstream TMZ propagation and dilutes the TGR water with well-oxygenated river water. Scenarios combining wastewater network management and low-water replenishment indicate an improvement in water quality over the entire TGR. These modelling outcomes constitute important tools for local water authorities to develop the most appropriate strategies to limit hypoxia in the TGR.Highlights. A 3-D model shows different efficiencies of management actions to limit hypoxia. Downstream relocation of wastewater discharge totally mitigates hypoxia. Sewage overflow reduction improves DO levels but only locally. Water replenishment improves DO in the upper estuary.

Increasing salinity levels in the tidal rivers are becoming a significant challenge to inland water quality. Salinization of the adjoining water resources and agricultural lands have prompted the water managers to optimize the solutions for mitigation of adverse effects. Keeping this in view, a hydrodynamic model coupled with a water quality model was used to analyze the propagation of tides from the Arabian Sea into the Indus River and their subsequent effect over longitudinal salinity distribution. Field observations of hydraulic parameters and salinity were used for validation of the model predictions in dry (no river flow) and wet (specific river flow) hydrological conditions. Results suggest that the tidal amplitude dissipates landward; salinity intrudes about 58 km (near Dandari) into the Indus River Estuary (IRE) at spring tide. Salinity in the proximity of Dandari point is sensitive to variations in fresh water supplies. A complete neap-spring tidal cycle was chosen for scenario-based evaluation of the impact of fresh water over the longitudinal salinity distribution. A daily river discharge 250 m3/s was found optimum for limiting the salinity interface (≤1) up to 31 km from the estuary mouth. In addition, tidal inlet modifications based on the theoretical framework of stable channel design combined with the optimum river discharge were tested. The cross-sectional modifications based on the regime/Lacey theory proven better and salinity interface was further pushed back up to 27 km. Thus, it is maintained that synergic impact of the optimized freshwater quantity and the estuary mouth modifications are considered as one of the pragmatic solutions for control of salinity intrusion and achieving the specific environmental conditions along the alluvial estuary.

This study constructs an analytical model to understand the phytoplankton dynamics in a one-dimensional system by integrating physical and biological processes. We present an analytical solution of phytoplankton distribution along the longitudinal direction of a tidal river. The solution has two components: water age and accumulative growth. The water age represents the overall effect of physical transport due to advection, while the accumulative growth represents the accumulation of phytoplankton biomass due to biological processes during the transport. In addition, an alternative solution with nonlinear reaction term is given to account for the feedback mechanism of nonlinear processes that affect phytoplankton growth rate. The nonlinear reaction term can be also used to approximate the effect of physical mixing on phytoplankton distribution. The analytical solutions can be further used to predict the temporal variation and spatial distribution of phytoplankton along the tidal river. They also serve as a mathematical tool to unite different field phytoplankton observations. We applied the model in the Tidal Freshwater Region (TFR) of James River under different dynamic conditions and the model results match well with the observations, which validates the theory on different time scales. Furthermore, an analysis is conducted for the Local Chlorophyll-a Maximum (LCM) in the TFR. It shows that the condition for LCM is biologically controlled, but its location is regulated by river flow and river geomorphology.

Watershed-scale stream temperature models are often one-dimensional because they require fewer data and are more computationally efficient than two- or three-dimensional models. However, one-dimensional models assume completely mixed reaches and ignore small-scale spatial temperature variability, which may create temperature barriers or refugia for cold-water aquatic species. Fine spatial- and temporal-resolution stream temperature monitoring provides information to identify river features with increased thermal variability. We used distributed temperature sensing (DTS) to observe small-scale stream temperature variability, measured as a temperature range through space and time, within two 400 m reaches in summer 2015 in Nevada's East Walker and main stem Walker rivers. Thermal infrared (TIR) aerial imagery collected in summer 2012 quantified the spatial temperature variability throughout the Walker Basin. We coupled both types of high-resolution measured data with simulated stream temperatures to corroborate model results and estimate the spatial distribution of thermal refugia for Lahontan cutthroat trout and other cold-water species. Temperature model estimates were within the DTS-measured temperature ranges 21 % and 70 % of the time for the East Walker River and main stem Walker River, respectively, and within TIR-measured temperatures 17 %, 5 %, and 5 % of the time for the East Walker, West Walker, and main stem Walker rivers, respectively. DTS, TIR, and modeled stream temperatures in the main stem Walker River nearly always exceeded the 21 ∘C optimal temperature threshold for adult trout, usually exceeded the 24 ∘C stress threshold, and could exceed the 28 ∘C lethal threshold for Lahontan cutthroat trout. Measured stream temperature ranges bracketed ambient river temperatures by −10.1 to +2.3 ∘C in agricultural return flows, −1.2 to +4 ∘C at diversions, −5.1 to +2 ∘C in beaver dams, and −4.2 to 0 ∘C at seeps. To better understand the role of these river features on thermal refugia during warm time periods, the respective temperature ranges were added to simulated stream temperatures at each of the identified river features. Based on this analysis, the average distance between thermal refugia in this system was 2.8 km. While simulated stream temperatures are often too warm to support Lahontan cutthroat trout and other cold-water species, thermal refugia may exist to improve habitat connectivity and facilitate trout movement between spawning and summer habitats. Overall, high-resolution DTS and TIR measurements quantify temperature ranges of refugia and augment process-based modeling.

A tidal river is a special zone where the basic hydrodynamic process is the interaction between riverine flow and tides. Existing studies focus mainly on the water level fluctuations, while the effort is limited regarding the flow regime between uni- and bi-directional currents. Along a tidal river, the current direction reverses where the landward flow meets with seaward flow. So far, the occurrence and movement of current reversal is not fully investigated, and the number and location of reversal points are not well understood. In this study, the water flow in the Yangtze tidal river was simulated using a hydrodynamic model, and the phenomenon of current reversals in the tidal river were investigated. It is found that in the dry season up to three reversal points may occur simultaneously, including two convergence points and one divergence point, separating the entire tidal river into two seaward-current reaches and two landward-current reaches. These multiple reversal points result from the co-existence of the preceding and present flood tidal waves. During a spring tide the peak landward flux of the preceding wave can reach up to 10,000 m3/s, about the same magnitude as the riverine discharge and the length of the landward-current occupation is as large as 120 km. It was also found that a current reversal point always coexists with a zero-gradient point of water level, and the location of this reversal is downstream of the zero-gradient point. The reversals shift landward from the river mouth consecutively, and could finally disappear farther at the upper reach of the tidal river. The bidirectional flow could extend up to 550 and 200 km upstream from the river mouth in the dry and wet seasons, respectively. The current reversals are influenced by the discharge regulation of the Three Gorges Dam. These movements of current reversals in the flow regime could furtherly have significant impact on local hydrodynamic process and material transportation.

The Ganges–Brahmaputra–Meghna delta in Bangladesh is one of the largest and most densely populated deltas in the world and is threatened by relative sea level rise (RSLR). Renewed sediment deposition through tidal river management (TRM), a controlled flooding with dike breach, inside the lowest parts of the delta polders (so-called beels) can potentially counterbalance the RSLR. The potential of TRM application in different beels across southwestern Bangladesh has been estimated previously but requires further exploration. Neither the seasonal and spatial variations in physical drivers nor the non-linear character of physical drivers and several sensitive parameters for sediment deposition have been taken into account so far. We used a 2D morphodynamic model to explore the physical controls of the following five parameters on the total sediment deposition inside the beels during TRM: river tidal range (TR), river suspended sediment concentration (SSC), inundation depth (ID), width of the inlet (IW), and surface area of the beel (BA). Our model results indicate that these five parameters and their interactions are significant for sediment deposition per day (SPD), where SSC and BA have a high impact, TR and ID have a moderate impact, and IW has a low impact on sediment deposition. Non-linear regression models (NLMs) were developed using the results of 2D models to quantify how sediment deposition inside the beels depends on these parameters. The NLMs have an average coefficient of determination of 0.74 to 0.77. Application of the NLMs to 234 beels in southwestern Bangladesh indicates that TRM operation in beels located closer to the sea will retain more sediment as a result of decreasing SSC further inland. Lower average land surface elevation is one of the reasons that the beels in the western part retain more sediment. Smaller beels have a higher potential to raise the land surface elevation due to the non-linear increase in sediment deposition per day (SPD) with beel area. Compartmentalization of larger beels may increase their potential to raise the land surface elevation. Thus, the length of time of the TRM application in a cyclic order will need to vary across the delta from 1 to multiple years to counterbalance RSLR, depending on the current beel land surface elevation and local TRM sediment accumulation rates. We found that operating TRM only during the monsoon season is sufficient to raise the land surface in 96 % and 80 % of all beels by more than 3 and 5 times the yearly RSLR, respectively. Applying TRM only seasonally offers huge advantages as to keeping the land available for agriculture during the rest of the year. The methodology presented here, applying regression models based on 2D morphodynamic modeling, may be used for the low-lying sinking deltas around the world to provide an a priori estimation of sediment deposition from controlled flooding to counterbalance RSLR.

Where rivers meet the sea, tides can exert a physical and chemical influence on the lower reaches of a river. How tidal dynamics in these tidal river reaches interact with upstream hydrological drivers such as storm rainfall, which ultimately determines the quantity and composition of material transferred from watersheds to estuaries, is currently unknown. We monitored a small freshwater tidal river in the Pacific Northwest, United States in high resolution over 1 year to evaluate the relative importance of tides vs. upstream hydrological flows (i.e., base flow and precipitation events) on basic physico-chemical parameters (pH, dissolved oxygen, turbidity, specific conductivity, and temperature), and how these interactions relate to the downstream estuary. Tidal variability and diurnal cycles (i.e., solar radiation) dominated water physico-chemical variability in the summer, but the influence of these drivers was overshadowed by storm-driven sharp pulses in river physico-chemistry during the remainder of the year. Within such events, we found incidences of counterclockwise hysteresis of pH, counterclockwise hysteresis of dissolved oxygen, and clockwise hysteresis of turbidity, although systematic trends were not observed across events. The dominance of storm rainfall in the river’s physico-chemistry dynamics, and similar pulses of decreased pH observed in adjacent estuarine waters, suggest that the linkage between tidal streams and the broader system is variable throughout the year. High-frequency monitoring of tidal river biogeochemistry is therefore crucial to enable the assessment of how the relative strength of these drivers may change with future sea level rise and altered precipitation patterns to modulate biogeochemical dynamics across the land-ocean-atmosphere continuum.

The downstream low-lying regions of the Kelani River, including some areas in the Districts of Colombo and Gampaha, Sri Lanka, frequently face severe inundations due to extreme rainfalls in the upper basin. In the present study, 1-D and 2-D hydrodynamic models in HEC-RAS have been used to examine the flood inundations in the tidal influenced Kelani River with ground observations and remote sensing. The HEC-RAS model has been used to produce a flood hazard map for hazard assessment in the lower Kelani River basin under different return periods. Furthermore, expected discharges for different return periods have been estimated using the hydrological model HEC–HMS with the updated intensity depth frequency curves for the Kelani River basin. Sentinel 1 imagery and field survey results are used to validate the simulated flood inundation extent; hydrodynamic model results validated against observed stage measurements; hydrological model validated against discharge measurements. Further, the validated hydrodynamic model showed the high capability to capture flow processes (Nash-Sutcliffe coefficient = 0.90 and Pearson coefficient of correlation = 0.95) along with inundation extent (Success Index = 0.90) of selected historical extreme events. Then the hydrological model is used to predict the flows of the Kelani River basin with a good agreement (Nash-Sutcliffe coefficient = 0.91 and the Pearson coefficient of correlation = 0.93). Finally, flood risk zoning for different return periods are developed based on the present model which would be a useful benchmark to design and implement flood control and mitigation measures for the river basin.

International audience; Climate and human pressures can influence the evolution of estuarine sediment dynamics concurrently, but the understanding and quantification of their cause–effect relationships are still challenging due to the occurrence of complex hydro-morpho-sedimentary feedbacks. The Garonne Tidal River (GTR, upper Gironde Estuary, France) is a clear example of a system stressed by both anthropogenic and climate change, as it has been subject to decreasing river discharges, natural morphological changes, and gravel extraction. To understand the relative effect of each hydrological and geomorphological pressure on the turbidity maximum zone (TMZ), the sediment dynamics in the GTR over the last six decades was evaluated using the width-averaged idealized iFlow model. Model results show a gradual increase in tidal amplitude and currents over the decades that has led to the upstream shift of the landward sediment-transport capacity components (external M4 tide, spatial settling lag, and tidal return flow). The upstream displacement of the TMZ between the 1950s and the 2010s was estimated to be at least 19 km, of which about three fourth was induced by geomorphological changes and one fourth by hydrological changes. Concerning the geomorphological changes, the natural evolution of the lower Gironde morphology was the main pressure inducing the displacement of the TMZ in the GTR. Anthropogenic and natural changes in morphology and bed roughness in the GTR itself also contributed to this evolution. The natural geomorphological changes were, in turn, probably promoted by the evolution of sediment dynamics, so this study reveals the closed circle that governs the intensification of the TMZ.

The spatiotemporal variation of phytoplankton and their relationship with environmental variables were analysed in the Saigon River – a tropical river in Southern Vietnam. Two longitudinal profiles were conducted during dry and rainy season at 18 sampling sites covering more than 60 km long in the river. Besides, a bi-weekly monitoring conducted upstream, urban area (Ho Chi Minh City - HCMC) and downstream of Saigon River was organized from December 2016 to November 2017. The major phytoplankton were diatoms (e.g. Cyclotella cf. meneghiniana, Leptocylindrus danicus, Aulacoseira granulata), cyanobacteria (Microcystis spp., Raphidiopsis raciborskii, Pseudanabaena sp) and euglenoids (Trachelomonas volvocina). Commonly freshwater phytoplankton species and sometimes brackish water species were dominant during the monitoring. Phytoplankton abundances in dry season were much higher than in rainy season (> 100 times) which was explained by a shorter riverine water residence time and higher flushing capacity during the dry season. There was a clear separation of phytoplankton abundance between the urban area and the remaining area of Saigon River because of polluted urban emissions of HCMC. Redundancy analysis shows that the environmental variables (TOC, Nitrogen, pH, salinity, Mo, Mn) were the driving factors related to the dominance of L. danicus and Cyclotella cf. meneghiniana in the upstream river and urban section of Saigon River. The dominance of cyanobacterium Microcystis spp in the downstream of Saigon River was related to higher salinity, Mg, Cu concentrations and lower concentrations of nutrients, Mn, Co, Mo. The dominance of potentially toxic cyanobacteria in Saigon River possess health risk to local residents especially upon the increasing temperature context and nutrient loading into the river in the next decades.

Southwestern Bangladesh has been seriously affected by perennial waterlogging over the last few decades. It is primarily due to excessive riverbed siltation outside the polders after the construction of embankments along both sides of the tidal rivers. These embankments de-linked the huge natural floodplains and restricted a gradual process of natural deposition inside the polders. An introduction of the tidal basin concept by temporary de-poldering (embankment cut) at some designated locations has substantially solved the issues. The current chapter looks at the historical practice of flood/sediment management, the evolution of embankments and their de-poldering, inclusion of Tidal River Management (TRM) in long term flood/sediment management, and discusses a technical aspect of flood/sediment dynamics across the tidal river system. The process of restoring beneficial tidal flooding by cutting embankment at certain locations, commonly known as TRM, is not a novel method. The TRM has started from age-old practice and proves technically one of the effective methods of sustainable flood/sediment management in the tide-dominated river system. It is an example of building with nature, where little human interventions are needed, and a resilient measure for waterlogging, drainage-congestion, and river-siltation.

Elevated phosphate (PO4) concentrations can harm the ecological status in water by eutrophication. In the majority of surface waters in lowland regions such as Flanders (Belgium), the local PO4 levels exceed the limits defined by environmental policy and fail to decrease, despite decreasing total phosphorus (P) emissions. In order to underpin the definition of currents limits, this study was set up to identify the pre-industrial background PO4 concentration in surface water of the Scheldt river, a tidal river in Flanders. We used the sedimentary records preserved in tidal marsh sediment cores as an archive for reconstructing historical changes in surface water PO4. For sediment samples at different depths below the sediment surface, we dated the time of sediment deposition and analysed the extractable sediment-P. The resulting time series of sediment-P was linked to time series of measured surface water PO4 concentrations (data 1967–present). By combining the sediment-P and water-PO4 data, the sorption characteristics of the sediment could be described. Those sorption characteristics allowed us to estimate a pre-industrial background surface water PO4 levels, based on deeper sediment-P that stabilised at concentrations smaller than the modern. In three out of the four cores, the sediment-P peaked around 1980, coinciding with the peak in surface water PO4. The estimated pre-industrial (~1800) background PO4-concentration in the Scheldt river water was 62 [57; 66 (95 %CI)] µg PO4-P/L. That concentration exceeds the previously estimated natural background values for lakes in Flanders (15–35 µg TP/L) and is about half of the prevailing limit in the Scheldt river (120 µg PO4-P/L). In the 1930s, river water concentrations were estimated at 140 [128; 148] µg PO4-P/L, already exceeding the current limit. The method developed here proved useful for reconstructing historical, background PO4 concentrations of a lowland tidal river. A similar approach can apply to other lowland tidal rivers to provide a scientific basis for local, catchment specific PO4 backgrounds.

The Ganges-Brahmaputra-Meghna (GBM) delta plain within Bangladesh is one of the most vulnerable to relative sea level rise (RSLR) in the world especially under current anthropogenically modified (i.e., embanked) conditions. Tidal river management (TRM) as practiced in coastal regions of Bangladesh may provide an opportunity to combat RSLR by raising the land level through controlled sedimentation inside beels (depression within embanked polders) with re-opening of polders. To date, TRM has been applied to tide-dominated coastal regions, but the potential applicability of TRM for the beels within the polders of river-dominated and mixed flow (MF) regimes remains to be assessed. We apply a calibrated 2D numerical hydromorphodynamic model to quantify sediment deposition in a beel flooded through breaching of the polder dike under conditions of river-dominated, tide-dominated and MF regimes for different seasons and applying different regulation schemes for the flow into the beel. Simulation results show considerable seasonality in sediment deposition with largest deposition during the monsoon season. The potential of controlled flooding is highest in the tide-dominated region, where sediment accumulation can be up to 28 times higher than in the river-dominated region. Regulating flow into a beel increases trapping efficiency, but results in slightly lower total deposition than without regulation. We conclude that re-establishing flooding of the beel within the polder without regulating the flow into the beel through breaching of the polder dike is a promising strategy for the mixed and tide-dominated flow regions in the delta as the sediment accumulation can raise the land surface at a higher rate than RSLR and effective SLR (ESLR). In the more upstream river-dominated section of the delta, accumulation rates would be much lower, but the pressure of sea level rise on these areas is lower as well. Owing to the abundant availability of sediment, application of controlled flooding like TRM therefore provides an opportunity to counteract the impact of RSLR and ESLR by means of land raising, particularly along the tidal river reaches in the GBM delta.

International audience; The hydrological dynamics of the Saigon River is ruled by a complex combination of factors, which need to be disentangled to prevent and limit risks of flooding and salt intrusion. In particular, the Saigon water discharge is highly influenced by tidal cycles with a relatively low net discharge. This study proposes a low-cost technique to estimate river discharge at high frequency (every 10 min in this study). It is based on a stage-fall-discharge (SFD) rating curve adapted from the general Manning Strickler law, and calibrated thanks to two ADCP campaigns. Two pressure sensors were placed at different locations of the river in September 2016: one at the centre of Ho Chi Minh City and one in Phu Cuong, 40 km upstream approximately. The instantaneous water discharge data were used to evaluate the net residual discharge and to highlight seasonal and inter-annual trends. Both water level and water discharge show a seasonal behaviour. Rainfall, including during the Usagi typhoon that hit the megalopolis in November 2018, has no clear and direct impact on water level and water discharge due to the delta flat morphology and complex response between main channel and side channel network and ground water in this estuarine system under tidal influence. However, we found some evidences of interactions between precipitation, groundwater, the river network and possibly coastal waters. This paper can be seen as a proof of concept to (1) present a low-cost discharge method that can be applied to other tidal rivers, and (2) demonstrate how the high-frequency discharge data obtained with this method can be used to evaluate discharge dynamics in tidal river systems.

Metals are mainly transported with suspended sediments in tidal rivers, and it is difficult to describe the transformation process of metals. Freely dissolved metals and suspended metals (including acid-soluble, reducible, oxidizable, and residual metals) were separately analyzed according to a sequential extraction scheme. The regression of the observed suspended metals and total suspended solids (TSS) concentrations allowed us to couple the two pollutant types. TSS is a highly dynamic parameter, and a model can be developed to simulate TSS transport. Thus, a method including the following five steps was proposed to estimate the loadings of metals entering the sea using TSS concentrations and water quality models: (1) collecting and observing basic information on the hydrological conditions, pollution sources, and water quality of the studied river; (2) obtaining a regression model between the suspended metals and TSS and analyzing the potential of establishing a suspended metal flux model; (3) introducing a model describing the fluxes of water-soluble metals into the sea; (4) establishing a calculation model to determine the fluxes of suspended metals into the sea; and (5) characterizing the fluxes of metals into the sea. The method was programmed, and metal concentrations and fluxes could be characterized quickly when the basic river data were sufficient. In addition, if regional development scenarios could be set, metal loadings in all scenarios could be predicted through the procedure developed herein, and some effective suggestions on regional sustainable development might be proposed for decision makers. Integr Environ Assess Manag 2022;18:198-208. © 2021 SETAC.

The tropical tanner grass, Urochloa arrecta, is one of the worst aquatic plant invaders in Brazilian freshwater ecosystems. This study aimed to compare beds of macrophytes dominated and without U. arrecta in the Guaraguaçu River, a subtropical tidal river in South Brazil, to analyze effects that this invasive grass has on the biodiversity of native macrophytes at two spatial scales. We compared macrophyte beds dominated by tanner grass to macrophyte beds without, considering species richness, composition, and beta diversity at two scales of variation: among-beds and within-beds. We expected that beds dominated by tanner grass would have lower biodiversity, thus promoting macrophyte biotic homogenization. Our results confirmed our hypotheses, highlighting the lower species richness in beds dominated by tanner grass. Species composition differed among beds. In general, nestedness among beds dominated by U. arrecta was more related to variation in species composition. Beds dominated by tanner grass had lower turnover and higher nestedness within beds. This study indicates a prominent sign of biotic homogenization promoted by U. arrecta, and highlights the degree of biotic homogenization among and within beds.

Ferrimagnetic greigite (Fe3S4) is widespread in the sedimentary environment. Despite abundant reports of greigite occurrence in marine and lacustrine deposits, its formation mechanisms in deltaic deposits remain poorly studied. Here we investigate greigite in Holocene Yangtze River delta deposits using granulometric, magnetic and geochemical methods. The studied cores consist of tidal river, estuary, shallow marine and delta facies in ascending order. The greigite‐bearing layers are found predominantly in the accreting tidal flat facies during the transgression stage and secondarily in the shallow marine facies during the regression stage of the delta's Holocene development. These sedimentary intervals have a higher total sulfur (TS) content and total sulfur to total organic carbon ratios (TS/TOC) suggesting the accumulation of iron sulfides, including greigite, under reducing estuarine and shallow marine conditions. The greigite‐bearing layers in the tidal flat facies have lower Sr/Ba ratios, in comparison to the shallow marine facies, indicating a lower salinity environment. Supported by the dating results, it is suggested that the higher sedimentation rate of the tidal flat facies, caused by rapid sea‐level rise during the early Holocene, favors the formation and preservation of greigite. Our results indicate that the magnetic detection of greigite provides a simple and useful tool for inferring salinity and sedimentation rate changes, and hence better a understanding of the heterogeneity of depositional processes in Holocene delta environments.

The study assessed the contamination level of seven heavy metals (Pb, Cd, Cr, Ni, Zn, As, and Cu) along with their potential ecological risks in sediments from the Halda river which is the largest natural carp breeding ground in South Asia. The concentration levels (mg/kg) of seven heavy metals from ten sampling sites were organized in the following descending order: Zn (71.89) > Cr (31.86) > Cu (31.85) > Ni (26.67) > Pb (20.46) > As (2.69) > Cd (0.05). Among the metals, Zn, Cr, Ni, and Cu exceeded some standard limits. Sediment quality guidelines (SQGs) suggested that the concentration of Pb, Cu, and Ni could occasionally cause an adverse effect on the ecosystem. However, the geo-accumulation index (Igeo), contamination factor (CF), and pollution load index (PLI) for heavy metals suggested that the contamination level was low. Moreover, the risk index (RI) and potential ecological risk index ( $$ {E}_r^i $$ ) confirmed the low ecological risk (as RI < 100 and $$ {E}_r^i $$ < 30) from heavy metals for the river ecosystem except for the Pb and Cu. High CF and $$ {E}_r^i $$ values for Pb in one site (S4) are deemed as combining elements of multiple metallic portions used in industrialization. The univariate and multivariate statistical analyses such as correlation matrix, principal component analysis, and cluster analysis of the metals for different sites signified that the metals were originated from similar anthropogenic activities like untreated industrial effluents and wastage disposal to the river system.

The estuary and tidal river of the Thames in south-eastern England were home to active commercial fisheries in the later middle ages. Despite conflicts over navigation, especially related to the use of fixed fish-weirs, the estuary supplied large quantities of fish to the London market. The importance of Thames fish to Londoners’ diet emerges from documentary and archaeological evidence. These fisheries remained important throughout the period 1250-1550 and were not destroyed by the rise of large-scale trade in preserved fish from more distant waters.

Big Soda Lake is a 63 m deep, 1.6 km2 maar lake in the Great Basin of Nevada, USA. Water level in the lake is controlled by groundwater inputs from the surrounding aquifer and the only surface water input is rainfall, which is negligible. A core taken in 2010 records an 8.75 m depositional history of the lake. A radiocarbon date on fossil pollen from 8.4 m below the sediment water interface (BSWI) of 14,740 (+1120/−825) cal yr BP suggests that the core may cover the latest Pleistocene and Holocene depositional history of the lake. Stable isotope values of oxygen and carbon (δ18O and δ13C) on authigenic calcite, diatom assemblages, and sedimentary structures all show consistent hydrological change from initially saline water at the bottom of the core to fresh/brackish water at about 6 m BWSI, back to saline water at 4.3 m. At 4.3 m depth, the bedding and color of the core change abruptly, and the stable- isotope and diatom assemblages indicate a consistently hypersaline lake until near the top of the core, when fresh water entered the lake due to irrigation and canal building in the twentieth century. The stable isotopes of the calcite abruptly change from inversely varying isotopic compositions below 4.3 m depth to covarying above. This break between relatively fresh and saline conditions in the lake occurs during the middle Holocene, although the exact timing of the transition is unknown due to variability in the 14C age determinations. The cause for such an abrupt change is difficult to explain through climate shifts, as evidence suggests climate in the Great Basin was different from what the Big Soda Lake record indicates in the Early Holocene. It is hypothesized that the Walker River flowed to the Carson River basin before 5600 cal yr BP, with water either flowing directly into the lake or raising the groundwater table sufficiently to freshen Big Soda Lake. The initial increase in salinity likely was caused by decreased flow of the Walker River due to Middle Holocene aridity. The lake level lowered slowly, and more saline conditions prevailed until 4.3 m depth when water from the Walker River stopped flowing into the Carson River basin. Above 4.3 m depth, diatom and isotopic evidence indicates that the lake became consistently saline. The isotopic and diatom assemblage transitions observed in Big Soda Lake sediment are not consistent with climate reconstructions and demonstrate that hydrologic shifts in a basin can be an important driver of change regardless of climatic conditions. However, climate shifts may also play a role in the hydrologic changes by supplying more or less water to river courses that may induce river avulsion.

Remotely sensed images document the occurrence of multiple packets of internal solitary waves (ISWs) in the Rhine River plume at the same time. We use a combination of field observations, and non-hydrostatic and hydrostatic modeling to understand the processes that lead to the generation and retention of multiple ISW packets within the Rhine plume. Previous numerical modeling shows that the tidal plume front is trapped in the mid-field plume for more than one tidal cycle due to tidal straining and recirculation within the plume, resulting in the presence of multiple fronts in the near-and mid-field plume regions. In this work, we show how variations in the strength of these fronts can lead to the release of ISW packets. We conclude that the retention of the fronts in the mid-field region of the plume and modulation in the strength of the fronts can explain the presence of multiple ISW packets. A frontal Froude number analysis shows that fronts generated during the previous ebb tide can release ISWs in addition to the newly released tidal plume front.

This paper describes the effects of anthropogenic deepening of tidal rivers in a conceptual way, with focus on tidal distortion and the residual transport of coarse sediment, driven by asymmetries in peak velocity. The rivers under consideration are fairly small, with small river discharge, and may have irregular hypsometry, with substantial intertidal area, or not. Residual sediment transport is driven by asymmetries in tidal velocity (horizontal tide), which is, however, difficult to establish in general. This paper discusses how and under which cases asymmetries in tidal elevations (vertical tide) can provide appropriate information on residual sediment transport. It is argued that deepening may induce a competition between an increase in tidal amplitude by amplification and a reduction in the asymmetry itself. Linear analysis shows that tidal asymmetry may show irregular behavior locally even for regular river configurations. It is therefore expected that these irregularities become larger in natural and engineered rivers. Analysis of local asymmetries may therefore be misleading in assessing the river's response to deepening with respect to the overall residual sediment transport and the river's morphology. Thus analysis of the overall morphodynamic response of a tidal river to tidal asymmetry, as affected by deepening, requires integration of the nonlinear effects along the entire river. It is argued that tidal asymmetry can be quantified by determining the difference in travel times of the high and low waters at any location within the river. This also implies that tidal water level variations and their asymmetries are governed by the entire tidal volume up-river of the cross section under consideration. River discharge further complicates the analyses by affecting residual water flows, effective hydraulic drag, tidal asymmetry, and mean water level. These effects reduce in response to deepening. However, salinity intrusion and gravitational circulation increase with deepening. We believe that assessing the (long-term) effects of deepening a fairway in a tidal river or estuary requires the use of process-based numerical models to account for all these nonlinear interactions, next to appropriate data collection. The current paper may help in analyzing and interpreting the numerical results.

Bangladesh, one of the countries most vulnerable to climate change, is threatened by sea level rise (SLR) and land subsidence. The tidal river management (TRM) practised in coastal regions of Bangladesh has the potential to raise the land by sedimentation, to counteract SLR and subsidence. TRM is an indigenous method in which dikes are breached to readmit sediment-rich water into a polder, which results in sediment being deposited in depressions in the polder called ‘beels’, while simultaneously preventing silting-up of the tidal rivers. However, after several years of continuous sedimentation from TRM, deposition has been uneven and less than expected. To study the effectiveness of TRM, this research analyses different scenarios to identify which operation schemes most effectively trap sediment to raise the land surface. The scenarios developed considered the number of inlets, flow regulation through the beel using open inlets or gated inlets with different operation schemes, and seasonality. The study area was Pakhimara Beel in southwest Bangladesh, where TRM is ongoing. To simulate the scenarios, a two-dimensional (2D) morphodynamic model with variable cell size was set up, calibrated and used. The simulation results were analysed for total sediment deposition, uniformity of spatial distribution of sediment deposition and trapping efficiency. Sediment deposition shows clear seasonal variability, with greatest deposition in the pre-monsoon period, less during monsoon and least in the dry season. Greatest deposition combined with high spatial uniformity was found for TRM that uses two inlets located at opposite sides connected to different watercourses. Regulated flow using successively opened gates resulted in highest sediment deposition in all seasons, about double that of the existing situation without gate. However, given the complexity and cost of gate operation, TRM with two inlets located at opposite sides of the beel without flow regulation may be considered more feasible, and still effective despite 20–30% less sediment deposition. To also increase acceptability by local affected stakeholders we propose to restrict this improved TRM to the monsoon period, to allow crops to be grown on the land in the dry and pre-monsoon periods, and ensure salinity is minimized. Such well-planned TRM has the potential to also counteract sea level rise in sinking deltas elsewhere in the world by enhancing sedimentation.

Abiotic filters that interact with wetland plant communities along tidal–fluvial gradients are highly dynamic, and understanding their quantitative thresholds and relationships to interspecific competition is important during an era of sea‐level rise and watershed hydrologic change. Yet, landscape‐scale studies of major coastal rivers from the river mouth to the head of tide, such as this study, remain rare. Here, we develop a new predictive framework for estuarine–tidal river research and management using a river‐specific low‐water datum and the wetland inundation indicator SEVg, the growing‐season sum exceedance value of hourly surface‐water depth. The distribution and variability of the wetland species pool (n = 203) on the 234 river kilometer (rkm) lower Columbia River and estuary floodplain are described for the first time. 4,940 quadrats at 50 marshes were surveyed (2005–2016). Throughout the estuarine–tidal river system, SEVg was well suited to describe the wetland inundation regime and its variability based on the combination of longitudinal river position and elevation. SEVg increased significantly landward. Two primary wetland inundation regimes were identified: the seaward‐tidal, usually greatest during the winter months, and landward‐fluvial, greatest during the growing season. Nearest the ocean, salinity is the abiotic factor limiting species richness and non‐native species. Farther upriver, the daily, seasonal, and interannual variability of the wetting and drying cycle encourage disturbance‐tolerant species and non‐natives and limit the number of hydrophytes and total vegetative cover. Hence, the average between‐year similarity of site‐scale areal cover significantly decreased landward. Hierarchical cluster analysis indicated five vegetative groups and five ecohydrologic zones between rkm 0 and 234 were discriminated with 76 significant species–zone associations. All zones had unique indicator species. Species with high indicator values were Carex lyngbyei throughout the estuarine zones, and Eleocharis palustris, Sagittaria latifolia, and the invasive non‐native Phalaris arundinacea in the upper estuarine and lower, middle, and upper tidal river zones (IV > 0.90). Competition from C. lyngbyei nearest the ocean and P. arundinacea in the tidal river was associated with reduced species richness when total cover was >65%. This framework of filters informs the design and prediction of future wetland plant communities on coastal river floodplains.

Sediment transfer from land to ocean begins in coastal settings and, for large rivers such as the Amazon, has dramatic impacts over thousands of kilometers covering diverse environmental conditions. In the relatively natural Amazon tidal river, combinations of fluvial and marine processes transition toward the ocean, affecting the transport and accumulation of sediment in floodplains and tributary mouths. The enormous discharge of Amazon fresh water causes estuarine processes to occur on the continental shelf, where much sediment accumulation creates a large clinoform structure and where additional sediment accumulates along its shoreward boundary in tidal flats and mangrove forests. Some remaining Amazon sediment is transported beyond the region near the river mouth, and fluvial forces on it diminish. Numerous perturbations to Amazon sediment transport and accumulation occur naturally, but human actions will likely dominate future change, and now is the time to document, understand, and mitigate their impacts.

Water chemistry of BRRS (Bhairab-Rupsha River System) is defining the water quality of BRRS, which is seasonally changed from premonsoon (March–May) to postmonsoon (June–August). The study identified the relation in changes of water chemistry and water pollution with riverbank land use patterns and regional climate through four analytical frameworks including—Hydrochemical framework; GIS and RS framework; Statistical framework; Climatic framework. Integration of these four frameworks defines the changes of water chemistry as in water quality and explores the relation in-between water chemistry, water quality, riverbank land use pattern, and regional climate. The concentration of ions is higher in premonsoon with low precipitation rate and high daily temperature. The spatial distribution of water chemistry of BRRS explored in upper reach (upstream), middle reach, and lower reach (downstream) according to the riverbank land use patterns. Highest EC is measured in upper reach and in middle reach with high Na+ at postmonsoon and in lower reach with high Cl− at premonsoon. TDS is highest in upper reach with high Mg2+ at postmonsoon and in lower reach with high K+, Ca2+, Mg2+, and Cl− in premonsoon. Water chemistry of BRRS is controlling by continental weathering in postmonsoon, and by high salt concentration in premonsoon. The combination of Piper plot and mixing diagrams explored precipitation-runoff dominates in postmonsoon and lacks ample discharge in the premonsoon press the tidal front downwards and consequently dominated by increasing salt concentration. The degree of pollution estimates % of pollution in BRRS which increases in premonsoon and decreases in postmonsoon. SAR, Na%, TDS, and EC explored that BRRS water is suitable for daily purposes and irrigation only in postmonsoon.

The late Holocene histories of Walker Lake and the Carson Sink were reconstructed by synthesizing existing data in both basins along with new age constraints from key sites, supplemented with paleohydrologic modeling. The repeated diversions of the Walker River to the Carson Sink and then back to Walker Lake caused Walker Lake–level fluctuations spanning ± 50 m. Low lake levels at about 1000, 750, and 300 cal yr BP are time correlative to the ages of fluvial deposits along the Walker River paleochannel, when flow was directed toward the Carson Sink. The timing and duration of large lakes in the Carson Sink were further refined using moisture-sensitive tree-ring chronologies. The largest lakes required a fourfold to fivefold increase in discharge spanning decades. Addition of Walker River flow to the Carson Sink by itself is inadequate to account for the required discharge. Instead, increases in the runoff coefficient and larger areas of the drainage basin contributing surface runoff may explain the enhanced discharge required to create these large lakes.

Exchange of groundwater is an important transfer mechanism for nutrients and pollutants between coastal aquifers and surface waters. Constraining such exchange in salt marshes - where biological productivity and biogeochemical cycling rates are among the highest of all coastal ecosystems – is vital for understanding ecosystem function and vulnerability. Here, we quantify groundwater discharge into the tidal Duplin River from the adjoining salt marsh near Sapelo Island, Georgia using high spatial and temporal resolution field measurements of radon-222. Field campaigns occurred for several weeks each summer during 2013, 2015, and 2016. Spatial surveys reveal a general increase in radon activity upstream through the Duplin River, which may result from either higher groundwater discharge or lower mixing rates in the headwaters. To distinguish between these possibilities, we use a radon mass balance model to determine groundwater input. We find that groundwater discharge (normalized to inundated marsh surface area) to the headwaters average 5.1–5.8 cm3/cm2 marsh/day across all three field campaigns, which are comparable to those to the main channel (averaging 6.0–6.5 cm3/cm2 marsh/day across all three field campaigns). Our work reveals a positive relationship between aerial extent of marsh inundation and groundwater discharge into the Duplin River. Discharge is generally maximal during falling tide, reflecting a hydraulic gradient driver, but also is significant prior to high tide, indicative of sediment compression as a driver of groundwater inputs. Constraining the relationship between marsh inundation and resulting groundwater dynamics is an integral aspect to assessing how salt marsh circulation processes may respond to intensifying inundation (from reduced sediment supply, subsidence, and/or rising sea levels).