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To acquire knowledge of the surface storage effects in the flow separation zone of a T-shaped open-channel confluence, independent Large Eddy Simulations are performed of the flushing with fresh water of a downstream branch which is initially uniformly contaminated by a passive scalar. Based on the ensemble averaged concentration, the spatial distributions of the local flushing lag and the local flushing time are determined. The flushing lag is much smaller than the flushing time, except in the maximum velocity zone, where both timescales are of the same small magnitude. For the local flushing time, the separation zone shear layer forms a transition between the high values in the flow separation zone and the low values in the maximum velocity zone. Inside the separation zone, the highest flushing times occur in a small zone near the downstream junction corner. Delineations in the time-averaged velocity field of the separation zone or its proxies, the recirculation zone and the reverse flow zone, are also assessed as pragmatic means to find the zone with the highest local flushing times. Finally, a regional flushing time and a residence time distribution were also determined on the basis of performed simulations.

The freshwater–saltwater interface position in groundwater at coastal aquifers is determined by the location of the coastline. Anthropogenic-driven changes as modification of the land uses in catchments or the engineering construction in rivers can alter the transport of sediments to the coastal areas affecting to the coastline shape in detrital systems. This is the case of the Motril-Salobreña aquifer where the rapid coastline progradation over the last 500 years generated new land previously covered by the sea at a fast rate, 3 m year−1 during hundreds of years. The effect of these changes in the salinity of the aquifer and the flushing time by freshwater has been examined with a paleo-hydrogeological model simulating the transient evolution of the groundwater salinity for the last 500 years with SEAWAT. The results of the model indicate a differentiated flushing time depending on the hydraulic properties in the region ranging from 50 years in the western sector to up to more than 200 years in the central sector for the shallower parts of the aquifer. In the deeper layers, the time can be highly increased but the uncertainties in the hydraulic properties generate different scenarios both in flushing time and water circulation in the aquifer. The sectors in the aquifer where changes took place at a faster rate are also the most sensitive to the effect of global changes, especially those associated to human activity as they occur at shorter time periods.

Hydrodynamic processes are a major driver for marine systems, linking marine organisms with their environment. However, a lack of hydrodynamic data at an ecologically relevant spatial resolution has stymied our understanding of reef function, as exemplified by Lizard Island on the Great Barrier Reef. To address this gap, 23 to 27 Marotte HS current meters were deployed over three periods, collecting 15 months of current velocity data. Combining these data with wind and tide datasets, we provide a preliminary description of the circulation in the Lizard Island lagoon, examining wind and tide influence, and flushing time. During south-easterly trade winds, flood tides flow through the Lagoon Entrance, while wind-induced waves cross the Bird-South crest, driving a north-westerly flow through Loomis Channel and across the western lagoon. Ebb tides flow east–south-east through the Lagoon Entrance and south-west through the Palfrey-South channel. Tides contribute a mean of 20.4% to the overall current speed, particularly in deeper sites with less reef interference, while shallow sites were more influenced by wind. Lizard Island lagoon flushing times ranged from a few hours to 10 days; longer during periods with low wind speeds. Hindcast flushing times during the 2016 coral bleaching event (following 8 Degree Heating Weeks) were approximately 22 h, suggesting that flushing time likely had minimal influence on bleaching. Our analyses provide initial insights into the circulation of the Lizard Island system and aid understanding of the potential relationships between reef organisms and their physical environment, bridging the gap between ecology and hydrodynamics.

Simple flushing time calculations for estuarine systems can be used as proxies for eutrophication susceptibility. However, more complex methods are required to better understand entire systems. Understanding of the hydrodynamics driving circulation and flushing times in small, eutrophic, temperate estuaries is less advanced than larger counterparts due to lack of data and difficulties in accurately modelling small-scale systems. This paper uses the microtidal Christchurch Harbour estuary in Southern UK as a case study to elucidate the physical controls on eutrophication susceptibility in small shallow basins. A depth-averaged hydrodynamic model has been configured of the estuary to investigate the physical processes driving circulation with particular emphasis on understanding the impact of riverine inputs to this system. Results indicate circulation control changes from tidally to fluvially driven as riverine inputs increase. Flushing times, calculated using a particle tracking method, indicate that the system can take as long as 132 h to flush when river flow is low, or as short as 12 h when riverine input is exceptionally high. When total river flow into the estuary is less than 30 m³ s⁻¹, tidal flux is the dominant hydrodynamic control, which results in high flushing times during neap tides. Conversely, when riverine input is greater than 30 m³ s⁻¹, the dominant hydrodynamic control is fluvial flux, and flushing times during spring tides are longer than at neaps. The methodology presented here shows that modelling at small spatial scales is possible but highlights the importance of particle tracking methods to determine flushing time variability across a system.

Effects of islands and shoals on coastal water temperature and salinity, flushing time, and dispersion were quantified for a study area within the Western Long Island Sound, inshore of the Norwalk Islands. Analysis focused on a summer warming period in July 2015. Observations were used to force a realistic high-resolution hydrodynamic model nested within a larger domain model. Island and shoal effects were isolated through intercomparison of three model runs with islands and shoals (the natural configuration), without the islands, and without islands and shoals. With islands, there was cooler and saltier water along a band immediately inshore of the islands. With shoals, water was warmer and fresher between the coast and islands. The shoals influence occupied a larger area with higher magnitude water property differences than the island influence. The islands influence tidal residual currents by intensifying eddies and creating across-shore exchange through island passes. Islands reduce flushing time and shoals increase flushing time. The retention effect of the shoals dominates over the dispersive influence of the islands for 2 days after dye tracer release, but the effects offset each other for later times.

【Background and objective】 Emitter clogging is a problem facing drip irrigation and drip-line flushing is an effective anti-clogging technology. The aim of this paper is to study how key structural parameters of automatic flushing valve at the end of drip-line impact its hydraulic performance as well as the underlying mechanisms. 【Method】 Three structural parameters were examined: dentition length (L) and width (W), as well as the height of the bonnet (Z) in the valve. Overall, there were seven flushing valves with different structural parameters, which were made by a 3D printer. For each valve we tested how its hydraulic performance changed with the applied water pressure (H2), flushing time (T), flushing volumetric rate (Q) and flushing velocity (V). 【Result】 When H2 was in 0.038~0.096 MPa, T varied from 7.5 to 32.1 s, Q from 2 220 to 5 725 mL, and V from 0.87 to 1.53 m/s, depending on the valves. When H2≤0.058 MPa, T and Q were negatively correlated with H2, while when H2>0.058 MPa, H2 only negatively affected T and did not result in a noticeable change to Q. Both T and Q were positively correlated with L, W and Z; the minimum flow area in the labyrinth channel depended on L and W. The amount of water entering the upper cavity of the valve was affected by Z, and as a result, it impacted T and Q as well. The impact of the three structural parameters on T and Q was ranked in the order of W>L>Z. V was affected by H2 more than by the structural parameters. 【Conclusion】 T and Q are closely related to the velocity, the amount of water flowing into the upper cavity, and the distance between the elastomer and the water outlet. The air in the upper cavity within the valve is a key factor impacting on T and Q; V is affected predominantly by H2.

The Atlantic inventory of anthropogenic carbon (Cant) and its changes between 1990 and 2020 are investigated by applying the transit time distribution (TTD) method to anthropogenic tracer data. In contrast to previous TTD applications, here we take into account the admixture of old waters free of anthropogenic tracers. The greatest difference from other methods based on direct carbon observations is the higher Cant storage in the deep ocean. Estimations of the decadal Cant increase based on direct carbon observations yield in general a smaller share of Cant storage in the North Atlantic and a larger share in the South Atlantic compared to our results. Changes in oceanic circulation and/or ventilation have significant impacts on the Cant inventory on the regional scale. The enhanced upwelling of older water in the Southern Ocean and the variability in the convection depth in the Labrador Sea lead to deviations in the inferred Cant increase between 1990 and 2020 from the rate equivalent to a steady-state ocean. For the total Atlantic Cant inventory, however, decadal ventilation variability of individual water masses partially compensates for each other. In addition, its impact on the Cant storage is small due to the much higher flushing time for the whole Atlantic of the order of hundreds of years. The total Cant inventory increases from 43.0 ± 7.3 Pg C in 1990 to 68.2 ± 10.8  Pg C in 2020, almost in unison with the rising CO2 in the atmosphere. So far, ventilation changes have impacted the Cant concentrations only on the regional scale, especially in the subpolar North Atlantic and the Southern Ocean.

Oil-based drilling fluid has many advantages, such as stable performance, strong anti-pollution ability, and strong inhibition, and it has been widely used in the world. However, at present, there is no unified evaluation standard for the effect of flushing fluid under this condition, and most of them are based on the flushing effect evaluation of water-based drilling fluid. However, there are few studies on wetting reversal phenomenon, reasonable dosage, and flushing time between oil-based drilling fluid and flushing fluid on the two-phase interface. Therefore, it is necessary to establish a comprehensive evaluation method for the effect of flushing fluid under oil-based drilling fluid, and explore the relationship between the amount of flushing fluid and flushing efficiency, so as to determine the reasonable range of flushing fluid consumption. In this paper, using the existing experimental instruments, a type A oil-based flushing fluid commonly used in oil fields was selected for the experiment, and on the basis of the high-temperature and high-pressure filtration meter, a flushing fluid evaluation device was developed. Based on the principle of equal shear rate, the flushing displacement and flushing time were determined, and then the flushing effect was evaluated. In order to comprehensively consider the influencing factors of the well wall flushing effect, five experimental factors, including different core, flushing displacement, flushing time, flushing fluid type, and surfactant concentration, were selected to formulate the flushing experiment scheme. The contrast method was used to test the cementation strength of core and cement slurry under different conditions, and the microscopic morphology of the interface was observed and analyzed to explore the reasons for the change of cementation strength between core and cement slurry due to the existence of oil-based drilling fluid. The conclusion obtained has very important practical significance to guide the field practice.

In this article, we describe the use of diagnostic timescales as simple tools for illuminating how aquatic ecosystems work, with a focus on coastal systems such as estuaries, lagoons, tidal rivers, reefs, deltas, gulfs, and continental shelves. Intending this as a tutorial as well as a review, we discuss relevant fundamental concepts (e.g., Lagrangian and Eulerian perspectives and methods, parcels, particles, and tracers), and describe many of the most commonly used diagnostic timescales and definitions. Citing field-based, model-based, and simple algebraic methods, we describe how physical timescales (e.g., residence time, flushing time, age, transit time) and biogeochemical timescales (e.g., for growth, decay, uptake, turnover, or consumption) are estimated and implemented (sometimes together) to illuminate coupled physical-biogeochemical systems. Multiple application examples are then provided to demonstrate how timescales have proven useful in simplifying, understanding, and modeling complex coastal aquatic systems. We discuss timescales from the perspective of “holism”, the degree of process richness incorporated into them, and the value of clarity in defining timescales used and in describing how they were estimated. Our objective is to provide context, new applications and methodological ideas and, for those new to timescale methods, a starting place for implementing them in their own work.

A numerical hydrodynamic modelling study has been implemented based on the seasonal salinity variations in a networked system (comprising creek and an estuary), which is the first of its kind attempted for the Indian subcontinent. Salinity variations in the estuaries and creeks exhibited unique characteristics caused by the combined effects of various external forces such as tidal flow, freshwater runoff, wind and geometric effects. Precise understanding of dynamical conditions in estuaries and creeks is necessary to address pertinent issues related to oceanography, water quality and ecosystem dynamics. In a broader perspective, it is noted that due to the influence of winds during monsoon, the salinity fields in the estuarine environment are not in a steady state. However, in creeks, tidal flow plays a major role in altering the salinity structure apart from runoff. The results from this study decipher the fact that the networked system was vertically homogenous during all seasons. However, a horizontal salinity gradient was observed in the system depending on the river runoff. The flushing time for the Ulhas estuary was about 1.5 and 2.57 days during the monsoon and non-monsoon seasons, respectively. Similarly, for the Thane creek, tide-driven flushing time was about 3.68 days. The low flushing time during the wet season provides a suitable dynamic environment for effluent discharge in the mid and upstream reaches of the estuary, wherein the freshwater influx is higher. On the contrary, during the dry season over this region, the low runoff and the highest flushing times can increase the pollution or can support the growth of phytoplankton biomass accumulation.