Shallow Water Bodies Research Articles

Numerical Realization of Shallow Water Bodies’ Hydrodynamics Grid Equations using Tridiagonal Preconditioner in Areas of Complex Shape

Introduction. Mathematical modeling of hydrodynamic processes in shallow reservoirs of complex geometry in the presence of coastal engineering systems requires an integrated approach in the development of algorithms for constructing computational grids and methods for solving grid equations. The work is devoted to the description of algorithms that allow to reduce the time for solving SLAE by using an algorithm for processing overlapping geometry segments and organizing parallel pipeline calculations. The aim of the work is to compare the acceleration of parallel algorithms for the methods of Seidel, Jacobi, modified alternately triangular method and the method of solving grid equations with tridiagonal preconditioner depending on the number of computational nodes.Materials and Methods. The numerical implementation of the modified alternating-triangular iterative method for solving grid equations (MATM) of high dimension is based on parallel algorithms based on a conveyor computing process. The decomposition of the computational domain for the organization of the pipeline calculation process has been performed. A graph model is introduced that allows to fix the connections between neighboring fragments of the computational grid. To describe the complex geometry of a reservoir, including coastal structures, an algorithm for overlapping geometry segments is proposed.Results. It was found that the efficiency of implementing one step of the MATM on the GPU depends only on the number of threads along the Oz axis, and the step execution time is inversely proportional to the number of nodes of the computational grid along the Oz axis. Therefore, it is recommended to decompose the computational domain into parallelepipeds in such a way that the size along the Oz axis is maximum, and the size along the Ox axis is minimal. Thanks to the algorithm for combining geometry segments, it was possible to speed up the calculation by 14–27 %.Discussion and Conclusions. An algorithm has been developed and numerically implemented for solving a system of large-dimensional grid equations arising during the discretization of the shallow water bodies’ hydrodynamics problem by MATM, adapted for heterogeneous computing systems. The graph model of a parallel-pipeline computing process is proposed. The connection of water body’s geometry segments allowed to reduce the number of computational operations and increase the speed of calculations. The efficiency of parallel algorithms for the methods of Seidel, Jacobi, modified alternately triangular method and the method of solving grid equations for problems of hydrodynamics in flat areas, depending on the number of computational nodes, is compared.

Deoxygenation and stratification dynamics in a coastal marine lake

Rogoznica Lake (RL; “Zmajevo oko”) is a shallow marine body of water that exhibits the physical characteristics of lakes (layer overturn and morphology), estuaries (distinct halocline), and seas (tidal regime). This study addresses the physicochemical stratification of the RL and its evolution over 27 years since the beginning of continuous RL research, in the context of regional climate variability. Stratification dynamics were evaluated from several aspects. First, reduced sulphur species accumulation was noted, which was associated with the anoxic water expansion from the bottom of the lake. Second, the connection of the lake with the sea and its attenuation was observed. These results are supported by the negative correlation between annual precipitation and water column salinity, which shows that the role of atmospheric variability in controlling the stability of the lake has increased. A change in the surface layer warming rate was noted, possibly related to unresolved quasi-decadal climate variability. At the same time, the enhancement of the chemocline is in favour of the reported stagnation of the bottom layer. All results suggest that there is a positive feedback mechanism leading to rapid ecosystem degradation.

Parallelization of numerical solutions of shallow water equations by the finite volume method for implementation on multiprocessor systems and graphics processors

An overview of approaches to parallelization of grid-based numerical methods for solving shallow water equations for multiprocessor systems and graphics processors is presented. A multithreaded approach for shared-memory computing systems implemented on the basis of the OpenMP programming interface and a geometric decomposition approach with message-passing using the MPI library for distributed-memory computers are described. Multithreading for programming GPUs based on the OpenACC software interface is considered. For the COASTOX-UN system of two-dimensional modeling of hydrodynamics, sediment and radionuclide transport in river systems and coastal areas of the seas, the parallelization of its hydrodynamic model COASTOX-HD was carried out. In the developed numerical model, the shallow water equations are solved by finite-volume numerical methods on unstructured computational grids with triangular cells of variable size. The parallelization is implemented using a hybrid MPI+OpenACC approach targeting multiprocessor systems and GPUs. For multiprocessor computers, geometric decomposition and MPI-based messaging are used, and for GPUs, multithreading is implemented using OpenACC directives. The performance of the developed parallel hydrodynamic model was evaluated during the calculation of typical problems of hydrodynamics of shallow water bodies, river flood, and tsunami wave run-up on the coast on a Dell Precision Workstation 7920 multi-core workstation with two 20-core Intel Xeon Gold 6230 processors and NVIDIA Quadro RTX 5000 and NVIDIA GeForce RTX 3080 graphics cards. It is shown that the developed model has significantly accelerated the simulation on the considered multiprocessor system and the considered GPUs. The acceleration on GPUs depends on the size of the computational grid, increasing to saturation with an increase in the number of grid cells. It is established that for the developed parallel model, whose numerical schemes are related to algorithms with low computational intensity, the memory bandwidth of the NVIDIA architecture GPUs is a more important limiting factor of acceleration than their performance.

KELLICOTTIA BOSTONIENSIS (ROUSSELET, 1908) AND K. LONGISPINA (KELLICOTT, 1879) (ROTIFERA: BRACHIONIDAE): THE PATTERN OF THE OCCURRENCE AND SPREAD IN THE LAKES IN THE UPPER AND MIDDLE VOLGA

In lakes of the Upper Volga (Yaroslavl district) and in the lower course of the Sura River (Middle Volga), closely related rotifers - common for both studied regions native K. longispina and alien K. bostoniensis - were found. Both species occur all year round and more frequently in spring or autumn, when they are the most abundant. Alien rotifer K. bostoniensis occurred not only simultaneously with indigenous species, but also separately, in more shallow waterbodies. Alien species is more tolerate to bathymetry, basin form, transparency and the trophy state of the waterbody. This likely facilitates wider distribution of the K. bostoniensis in the Sura basin waterbodies compared to indigenous species. Alien species K. bostoniensis spread relatively quickly in the Sura basin without any harm to closely related indigenous species, to which it is not a competitor.

About the sexual dimorphism of the crucian carp Carassius carassius (Cyprinidae)

The Crucian carp Carassius carassius (Linnaeus, 1758) is widely distributed in the Northern Eurasia. This is a medium-sized schooling fish, mainly its habitat is shallow water bodies overgrown of aquatic plants and slow flowing rivers. The Crucian carp is resistant to hypoxiaand fluctuations of water temperature. It is euryphage. In recent decades, there has been a widespread reduction in its range and a decline in numbers both in Western Europe and in Russia. In Western Siberia, Crucian carp was previously relatively numerous. Since the end of the 20th century, this species has a decrease reduces the number or complete extinction in some water bodies of the region. This provokes an increased interest to the peculiarities of the biology of this fish species, including the variability of its morphological characteristics in different types of water bodies and the environmental characteristics that determine them. We have revealed sexual dimorphism of C. carassius in 47% of the studied plastic characters: females have a longer head length, anteventral and antepectral distances, and males have ventroanal, ventrocaudal, anal-caudal and dorso-caudal distances. In addition, males have larger fins: the height of the dorsal and anal fins, the length of the pectoral, ventral, and lower lobe of the caudal fins are statistically significantly greater. There are differences in head morphology: males have the height of the head through the middle of the eye and diameter of eye are statistically significantly greater. There are no sexual dimorphism of C. carassius in countable morphological characters. The our data obtained make it necessary to take into account the sex composition of the samples when analyzing the features of the variability of the morphological features of the Crucian carp C. carassius.

The CryoGrid community model (version 1.0) – a multi-physics toolbox for climate-driven simulations in the terrestrial cryosphere

Abstract. The CryoGrid community model is a flexible toolbox for simulating the ground thermal regime and the ice–water balance for permafrost and glaciers, extending a well-established suite of permafrost models (CryoGrid 1, 2, and 3). The CryoGrid community model can accommodate a wide variety of application scenarios, which is achieved by fully modular structures through object-oriented programming. Different model components, characterized by their process representations and parameterizations, are realized as classes (i.e., objects) in CryoGrid. Standardized communication protocols between these classes ensure that they can be stacked vertically. For example, the CryoGrid community model features several classes with different complexity for the seasonal snow cover, which can be flexibly combined with a range of classes representing subsurface materials, each with their own set of process representations (e.g., soil with and without water balance, glacier ice). We present the CryoGrid architecture as well as the model physics and defining equations for the different model classes, focusing on one-dimensional model configurations which can also interact with external heat and water reservoirs. We illustrate the wide variety of simulation capabilities for a site on Svalbard, with point-scale permafrost simulations using, e.g., different soil freezing characteristics, drainage regimes, and snow representations, as well as simulations for glacier mass balance and a shallow water body. The CryoGrid community model is not intended as a static model framework but aims to provide developers with a flexible platform for efficient model development. In this study, we document both basic and advanced model functionalities to provide a baseline for the future development of novel cryosphere models.

Characteristics and genesis of reef-bank complexes in deep shelf facies: A case study of the Middle-Late Jurassic in the northern Amu Darya Basin, Central Asia

A large-rimmed carbonate platform was developed in the Amu Darya Basin during the Middle-Late Jurassic Callovian-Oxfordian period. What distinguishes it from typical carbonate platforms is that a series of reef-bank complexes had extensively developed in the deep shelf depositional zone of the basin. However, only a few studies have reported on the classification, characteristics, and genesis of these reef-bank complexes in relatively deep water, greatly limiting the development of deep-water carbonate sedimentology. To address this issue, the types and the genesis of reef-bank complexes in the deep shelf environment have been clarified based on the systematic petrography, seismic sedimentology, and geomorphology study of the Callovian-Oxfordian carbonate rocks in the northern Amu Darya Basin during the Middle-Late Jurassic period. The results find that the reef-bank complexes are widely distributed in the deep shelf environment in the study area with laminar, reticulated, and zonal distributions. The reef-bank complexes include barrier-bonding reef-bank complexes, lime-mud mounds (LMMs), and granular shoals (GSs). The deep shelf environment can be further divided into an inner shelf, shelf margin, and shelf slope. The inner shelf and shelf margin have a relatively shallow water body and a strong sedimentary hydrodynamic force, mainly developing reticulated reef-bank complexes and laminar GSs, whereas the shelf slope mostly develops zonal LMM deposits in strips. The scale of the reef-bank complexes is mainly controlled by basement paleogeomorphology and water energy. Relatively high-energy reef-bank complex bodies are developed on the seaward side of the paleouplift limb with relatively turbulent hydrodynamic conditions, whereas low-energy LMMs are mostly developed on the high position of paleouplift and landward side. The obtained findings can deepen our understanding of relatively deep-water carbonate sedimentation and enrich the carbonate sedimentation theory.

Analysis of Terrain Modelling Methods in the Coastal Zone

Geospatial data are increasingly used to model the terrain in the coastal zone, in particular in shallow waterbodies (with a depth of up to 1 m). In order to generate a terrain relief, it is important to choose a method for its modelling that will allow it to be accurately projected. Therefore, the aim of this publication is to analyze the terrain modelling methods in the coastal zone. For the purposes of the research, five most popular methods for terrain modelling were described: Inverse Distance Weighted (IDW), Modified Shepard's Method (MSM), Natural Neighbor Interpolation (NNI), kriging and spline. Each of the methods has been described in a uniform way in terms of: the essence of its operation, mathematical expression and application examples. The advantages and disadvantages of each of the methods for terrain modelling are also discussed. It should be stated that the choice of the method for the terrain modelling of a shallow waterbody is not unambiguous, as it depends on the type of data recorded during bathymetric and photogrammetric measurements.

Chironomidae in shallow water bodies of a protected lowland freshwater floodplain ecosystem.

Lowland floodplains are complex ecosystems comprised of standing and flowing waters interacting with terrestrial habitats, and the main force creating, shaping and influencing, both habitats and biotic communities, is a hydrological regime and water supply from the parent river. In areas not much altered by anthropogenic influence, the Danube creates such floodplain areas, and temporary shallow water bodies within represent biodiversity important habitats. In the Kopački Rit Nature Park floodplain in Croatia, diversity based on Chironomidae (Diptera) in both benthic and epiphytic communities was studied in eight ponds (temporary shallow water body) and at two channel locations (permanent shallow water body). At each location samples of sediment and macrophytes were taken at three sites. The benthic chironomid community was comprised of 29 taxa, most abundant being representatives of the Chironomus genus and Tanypus kraatzi in ponds, and Polypedilum nubeculosum and Cladotanytarsus sp. in channel samples. Cricotopus gr. sylvestris, Paratanytarsus sp. and Endochironomus tendens were dominant epiphytic chironomids (18 taxa). Non-metric multidimensional scaling and analysis of similarity analyses showed there was a clear grouping of sampling locations based on their position in the park and the distance from each other, more evident in the case of benthic chironomid communities. Furthermore, when the water bodies were compared based on the community structure from different locations and substrates, there was also a statistically significant separation. Community composition indicates high productivity and organic matter production of studied water bodies, but moreover, the differences in substrate preferences evident in 16 common out of 31 recorded chironomid taxa, indicate the importance of habitat complexity preservation in a floodplain.

The peroxidase response of Alternanthera philoxeroides (Alligator Weed) and Nasturtium officinale (Watercress) to heavy metal exposure.

We examined the effects of copper and lead on the antioxidant enzyme response of Alternanthera philoxeroides and Nasturtium officinale using a benchtop luminometer. Alternanthera philoxeroides is a nonnative invasive plant species that has spread throughout the wetland ecosystem in the southern part of the USA. Its invasion is facilitated by its ability to thrive in a wide range of abiotic conditions. Nasturtium officinale is an aquatic plant that is sensitive to relatively low amounts of pollution and is most commonly found in springs and shallow bodies of water. While A. philoxeroides tolerates organic pollution and heavy metals, N. officinale exhibits stress at low levels of pollution. Alternanthera philoxeroides antioxidant enzyme production was unaffected by increasing concentrations of both copper and lead. The antioxidant enzyme response of N. officinale showed a significant increase when plants were exposed to 10 and 25ppm lead. Endogenous peroxidase concentrations of the control plants were also compared showing that A. philoxeroides possessed a significantly higher concentration of peroxidases than N. officinale. We hypothesize that a higher endogenous peroxidase concentration may be a mechanism that hyperaccumulator plants use to tolerate inhospitable concentrations of copper and lead.

Ecosystem responses of shallow thermokarst lakes to climate-driven hydrological change: Insights from long-term monitoring of periphytic diatom community composition at Old Crow Flats (Yukon, Canada).

Shallow waterbodies are abundant in Arctic and subarctic landscapes where they provide productive wildlife habitat and hold cultural and socioeconomic importance for Indigenous communities. Their vulnerability to climate-driven hydrological and limnological changes enhances a need for long-term monitoring data capable of tracking aquatic ecosystem responses. Here, we evaluate biological and inferred physicochemical responses associated with a rise in rainfall-generated runoff and increasingly positive lake water balances in Old Crow Flats (OCF), a 5600 km2 thermokarst landscape in northern Yukon. This is achieved by analyzing periphytic diatom community composition in biofilms accrued on artificial-substrate samplers at 14 lakes collected mostly annually during 2008-2019 CE. Results reveal that diatom communities at 10 of the 14 lakes converged toward a composition typical of lakes with rainfall-dominated input waters. These include six of nine lakes that were not initially dominated by rainfall input. The shifts in diatom community composition infer rise of lake-water pH and ionic content, and they reveal that northern shallow lake ecosystems are responsive to climate-driven increases in rainfall. Based on data generated during the 12 -year-long monitoring period, we conclude that lakes located centrally within OCF are most vulnerable to rapid climate-driven hydroecological change due to flat terrain, larger lake surface area, and sparse terrestrial vegetation, which provide less resistance to lake expansion, shoreline erosion, and sudden drainage. This information assists the local Indigenous community and natural resource stewardship agencies to anticipate changes to traditional food sources and inform adaptation options.

Development of a 60-year high-resolution water body evaporation dataset in China

Evaporation from water bodies (Ew) is a critical component of the global water cycle. However, existing evaporation products that include Ew often suffer from drawbacks such as coarse resolution, short time span, and high uncertainty. This study developed a 60-year (1960–2019) high-resolution (0.05º×0.05º) evaporation dataset for small shallow water bodies in China based on the Penman model. Two key factors affecting the accuracy of the Penman model were considered: the uncertainty of the empirical wind function and changes in heat storage in the water body. Specifically, we used large-size (20 or 100 m2) pan evaporation (Epan) observations from 21 sites as a benchmark to correct the wind function of the Penman model. A data-driven model was then developed to map the spatial distribution of the wind function coefficients across China. The corrected wind function significantly improved the accuracy of Epan estimates compared to the original wind function, with the Kling-Gupta efficiency (KGE) increased by 0.05∼0.10. To model the effect of heat storage changes on evaporation, an equilibrium temperature method was used. We also introduced an area-dependent scaling factor into the wind function to account for the effect of water body's size on Ew estimation. The reliability of the Ew algorithm was tested on two lakes using eddy-covariance flux observations, and simulations showed good agreement with observations. The Epan (20 m2 pan) dataset and its two components calculated from the radiative and aerodynamic terms of the Penman model can be accessed at https://osf.io/qd28m/. Users can utilize the two Epan components and the area-dependent scaling factor to estimate evaporation for water bodies of varying sizes. However, caution is needed when applying this dataset to deep water bodies, as it is designed for shallow water bodies.

Original article Spatial-three-dimensional wave processes’ modeling in shallow water bodies taking into account the vertical turbulent exchange features

Introduction. Reliable prediction of indicators of turbulent flows is a very difficult task, which is explained by the exceptional physical complexity of turbulence, in particular its probabilistic nature, a wide space-time spectrum and a fundamentally three-dimensional non-stationary nature. Despite conducting a wide range of studies focused on the problem under consideration, they did not fully reflect the totality of various factors and processes affecting the structure and parameters of vertical turbulent mixing. This indicates the need for a systematic analysis of the problem and modeling of such complex formalized systems. The aim of the work is to construct a scenario of changes in hydrodynamic wave processes of the coastal zone, based on an improved mathematical model of wave processes.Materials and methods. The article is devoted to the study of spatial-three-dimensional wave processes in shallow water bodies, taking into account the features of turbulent exchange depending on the source and localization in the column of liquid, as well as the study of the influence of regular wave processes on turbulent exchange and vertically using a mathematical model of wave processes based on the system of Navier-Stokes equations, including three equations of motion in the with dynamically changing geometry of the computational domain.The results of the study. Based on the developed software package, a scenario of changes in hydrodynamic wave processes of the coastal zone is constructed, the formation of vortex structures is predicted. Discussion and conclusions. The separation of the wave flow into a near-surface macroturbulent layer caused by wave motion and a lower layer with background hydrodynamic turbulence is proved, the strength and intensity of turbulence changed synchronously with wave oscillations, demonstrating a pronounced asymmetry of turbulence generation throughout the water column.

An Advanced Spatiotemporal Fusion Model for Suspended Particulate Matter Monitoring in an Intermontane Lake

Ebinur Lake is the largest brackish-water lake in Xinjiang, China. Strong winds constantly have an impact on this shallow water body, causing high variability in turbidity of water. Therefore, it is crucial to continuously monitor suspended particulate matter (SPM) for water quality management. This research aims to develop an advanced spatiotemporal fusion model based on the inversion technique that enables time-continuous and detailed monitoring of SPM over an intermontane lake. The findings shows that: (1) the enhanced spatial and temporal adaptive reflectance fusion model (ESTARFM) fusion in blue, green, red, and near infrared (NIR) bands was better than the flexible spatiotemporal data fusion (FSDAF) model in extracting SPM information; (2) the inversion model constructed by random forest (RF) outperformed the support vector machine (SVM) and partial least squares (PLS) algorithms; and (3) the SPM concentrations acquired from the fused images of Landsat 8 OLI and ESTARFM matched with the actual data of Ebinur Lake based on the visual perspective and accuracy assessment.

Carbon dioxide emission and its impacting factor from goldenrod (Solidago canadensis) and bulrush (Typha angustifolia) decomposition during the winter period

Leaf litter decomposition in solution is an important part of the carbon cycle. When leaf litter is deposited in water, the decomposition process takes place, releasing carbon dioxide into the atmosphere. In Hungary, the goldenrod and bulrush are spreading over increasing areas along lakes and rivers, including the shores of Lake Balaton. The primary role of the Kis-Balaton wetland is to retain inorganic nutrients, thereby improving the water quality of Lake Balaton. As the water movement in this area is not very intensive and the water retention time is long, carbon dioxide emissions of parts of decomposing plants can be higher in this area. We set up a microcosm experiment in a climate chamber to determine the carbon dioxide emissions from the decomposition of goldenrod and bulrush leaves and stems in winter when information about the process is limited. Due to short investigation time, the difference in the impact of temperatures on decomposition of the studied plants was restricted to leaves only. In the study, significant difference was obtained for the plant species and the plant parts. The carbon dioxide increments ranged from 46.7 (p<0.001) to 54.5% (p<0.001) in every plant treatment related to control one. Changes in water temperature are reflected in carbon dioxide release with a minor time delay. The results showed that the decomposition of plant parts in water during winter contributes to the increase of carbon dioxide emissions from shallow water bodies, such as the Kis-Balaton wetland.

Investigating Environmental Matrices for Use in Avian Influenza Virus Surveillance-Surface Water, Sediments, and Avian Fecal Samples.

Surveillance of avian influenza viruses (AIV) in wild water bird populations is important for early warning to protect poultry from incursions of high-pathogenicity (HP) AIV. Access to individual water birds is difficult and restricted and limits sampling depth. Here, we focused on environmental samples such as surface water, sediments, and environmentally deposited fresh avian feces as matrices for AIV detection. Enrichment of viral particles by ultrafiltration of 10-L surface water samples using Rexeed-25-A devices was validated using a bacteriophage ϕ6 internal control system, and AIV detection was attempted using real-time RT-PCR and virus isolation. While validation runs suggested an average enrichment of about 60-fold, lower values of 10 to 15 were observed for field water samples. In total 25/36 (60%) of water samples and 18/36 (50%) of corresponding sediment samples tested AIV positive. Samples were obtained from shallow water bodies in habitats with large numbers of waterfowl during an HPAIV epizootic. Although AIV RNA was detected in a substantial percentage of samples virus isolation failed. Virus loads in samples often were too low to allow further sub- and pathotyping. Similar results were obtained with environmentally deposited avian feces. Moreover, the spectrum of viruses detected by these active surveillance methods did not fully mirror an ongoing HPAIV epizootic among waterfowl as detected by passive surveillance, which, in terms of sensitivity, remains unsurpassed. IMPORTANCE Avian influenza viruses (AIV) have a wide host range in the avian metapopulation and, occasionally, transmission to humans also occurs. Surface water plays a particularly important role in the epidemiology of AIV, as the natural virus reservoir is found in aquatic wild birds. Environmental matrices comprising surface water, sediments, and avian fecal matter deposited in the environment were examined for their usefulness in AIV surveillance. Despite virus enrichment efforts, environmental samples regularly revealed very low virus loads, which hampered further sub- and pathotyping. Passive surveillance based on oral and cloacal swabs of diseased and dead wild birds remained unsurpassed with respect to sensitivity.

Distribution, chemical speciation and human health risk assessment of metals in soil particle size fractions from an industrial area

The problem associated with metal contamination in the soil is intensified in the vicinity of industrial areas as they are more susceptible to discharges from medium to small scale industries. However, limited studies are available that consider soil size fractions along with their speciation due to multi metal contamination. This information is essential to apprehend their individual and competitive mobility, bioavailability and possible de-contamination strategies. In the present study, soil samples (n = 10) were collected from Ranipet industrial area, India and analysed for total metal concentrations (Al, Cd, Cr, Cu, Fe, Mn, Pb, and Zn). The ecological risk assessment indicated substantial anthropogenic enrichment of chromium along with moderate enrichment of copper, manganese and zinc. Further, the samples were fractionized into 300–150, 150–50, 50–22 and < 22 µm; the finer fraction concentrations were used to assess human health risks. The Hazard Index (HI) values reached 2.37 for children and 0.30 in adults from non-carcinogenic risk; indicated children are at higher risk. The soil exposure risk assessment study in three different scenarios were considered; results indicated possible non-carcinogenic risk to the non-residents working in study area. The Cancer risk (CR) values followed the order CR (ingestion) > CR (dermal contact) > CR (inhalation). The speciation study performed in bulk and size fractions indicated the bioavailable forms dominated residual fractions irrespective of sizes but varied with metals. This study can be considered as a framework for risk identification and assessment from multi metal contamination in industrial area having small and shallow waterbodies.

Groundwater sustainability in African Metropolises: Case study from Calabar, Nigeria

Study regionCalabar, Cross River State, Nigeria Study focusUrban groundwater is a strategic water resource in Africa that offers a buffer against climate variability. Increasing population, extensive pollution, and climate change threaten the contribution of urban groundwater in compensating increasing freshwater demand. Modern urban areas are often established on productive alluvial aquifers because of the proximity between shallow water bodies and historical settlements. Groundwater dynamics in urban aquifers are complex. Impervious surfaces impede water infiltration, and leakage from water infrastructure contributes to groundwater recharge. In this study, groundwater dynamics of an African metropolis are assessed, and insights into aquifer protection are provided through detailed hydrogeological analysis and numerical models. New hydrogeological insights for the regionThe Calabar metropolis (area of 166 km2 and 570,000 inhabitants) is characterized by a tropical climate, with annual rainfall of over 3000 mm/y and large groundwater resources enabling supply for 69% of the population. A simplified three-dimensional hydrogeological model of the metropolis was proposed using USGS-MODFLOW to assess groundwater resources and recharge rates. Recharge decreased to 46% from water-rich rural areas to disadvantaged and highly urbanized communities. Aquifer recharge driven by huge rainfall dilutes the nitrogen content and pathogens, contributing to an acceptable drinking water quality during the prolonged wet season.

Predictive modeling of wave hydrodynamics and relief formation in the presence of multi-scale turbulent exchange

Introduction. Reliable prediction of indicators of turbulent flows is a very difficult task, which is explained by the exceptional physical complexity of turbulence, in particular its probabilistic nature, a wide space-time spectrum and a fundamentally three-dimensional non-stationary nature. Despite conducting a wide range of studies focused on the problem under consideration, they did not fully reflect the totality of various factors and processes affecting the structure and parameters of vertical turbulent mixing. Materials and methods. The article is devoted to the study of spatial- three-dimensional wave processes in shallow water bodies, taking into account the features of turbulent exchange depending on the source and localization in the column of liquid, as well as the study of the influence of regular wave processes on turbulent exchange and vertically using a mathematical model of wave processes based on the system of Navier-Stokes equations, including three equations of motion in the with dynamically changing geometry of the computational domain. Results. Based on the developed software package, a scenario of changes in hydrodynamic wave processes of the coastal zone is constructed. Discussions and conclusions. The separation of the wave flow into a near-surface macroturbulent layer caused by wave motion and a lower layer with background hydrodynamic turbulence is proved, the strength and intensity of turbulence changed synchronously with wave oscillations, demonstrating a pronounced asymmetry of turbulence generation throughout the water column.

Improved parametrization of the vertical turbulent exchange coefficient, taking into account the shallow water bodies specifics

The article is devoted to the problem of improving the parameterization of the coefficient of turbulent exchange in shallow water bodies with significant depth differences and intensive vertical mixing. The article presents the basic equations of the model of taking into account the wave effect on the inhomogeneous vertical coefficient of turbulent exchange. This model is integrated into the system of Navier-Stokes equations taking into account the variable density, temperature and salinity, which describes the movement of a liquid under the influence of various forces, including pressure and viscosity, as well as forces caused by the action of waves. The article presents the discretization of the Navier-Stokes equations and the transfer equations by the finite difference method in three measurement directions. The additional term describing the wave effect on the vertical velocity in a shallow-water reservoir depends on the characteristics of the wave field: amplitude, angular frequency, wave number and coordinates. Using a model that takes into account the wave effect in three measuring directions and inhomogeneous turbulent exchange in the vertical direction, detailed information about the dynamics of waves in the simulated section of a shallow reservoir was obtained. The forecast of changes in hydrodynamic wave processes of the coastal zone is constructed. Inhomogeneous vertical turbulent exchange can vary significantly in different parts of a shallow reservoir and affect wave activity. Taking into account these changes makes the model more accurate and relevant to real conditions.