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Mass transport in frozen ground is typically regarded slow. However, a highly permeable path can exist in frozen saline sand if the unfrozen water is interconnected at the pore scale. We therefore should consider when the unfrozen water is connected and how permeable can frozen saline sand be, yet there are few studies. This research utilizes in‐situ X‐ray CT to evaluate unfrozen water connectivity and permeability in frozen saline sand considering effects of initial salt content, temperature, freezing rate, and temperature gradient. Results show that higher initial salt content and/or temperature, both of which results in a higher unfrozen water content, easily maintains unfrozen water connectivity. Rapid freezing minimizes the brine expulsion and permits a higher unfrozen water content hence better connectivity. Permeability in frozen saline sand can be several orders higher than the typically reported value, highlighting the potential presence of rapid mass transport through the connected unfrozen water. Plain Language Summary Frozen aqueous sandy soils in nature often contain a lot of substances such as dissolved salts, gases, contaminants. Mass migration via unfrozen water is of vital importance to groundwater flow, greenhouse gas emission, even contaminated soil remediation. Permeability determination of unfrozen water is well‐studied in salt‐free soils. Our study shows there can be a highly conductive path in frozen saline sand when the unfrozen water is interconnected, even at a low unfrozen water saturation of 14%. The connectivity of unfrozen water remains at −20°C with an initial salt concentration similar to seawater. Rapid freezing causes better connectivity because less unfrozen water is squeezed out of the frozen sand during ice growth. Permeability in frozen saline sand can be several orders of magnitude higher than the typically reported value. These findings indicate that mass transport in frozen ground, via the connected unfrozen water, can be much more active than previously thought. Key Points Pore‐scale unfrozen water can be interconnected, enabling fast mass transport below 0°C when soil contains salt Rapid freezing enhances unfrozen water connectivity and permeability due to less and slower salt migration during freezing Permeability of frozen saline sand can be several orders of magnitude higher than that of salt‐free soil

The physical and mechanical characteristics of saline soil are significantly influenced by salt content, with macro- and mesoscopic mechanical properties closely correlated. This study investigates the strength and deformation behaviors of saturated saline sand through indoor triaxial shear testing under varying confining pressures and salt contents. The key innovation lies in developing a coupled finite element and discrete element analysis model to simulate the mesoscopic behavior of saline sand under triaxial shear stress state. Flexible boundary conditions were applied, and appropriate contact models for salt-sand interactions were selected. By adjusting mesoscopic parameters, stress-strain curves and variations in porosity, coordination number, particle displacement, and contact force chains were analyzed. The study further explores shear band development and shear failure mechanisms by examining relative particle displacement and the breaking of contact force chains. Additionally, the influence of salt particle size on the overall strength of the DEM model was assessed. The findings provide valuable insights into the internal structural changes of saline sand during shear deformation, contributing to a better understanding of its mechanical behavior in engineering applications.

Freezing construction in saline stratum under the action of groundwater is typical. To study the coupling effect of the groundwater velocity and salinity on the freezing in saline stratum, the freezing temperature of saline sand with different salinities was obtained through experiments. A controllable velocity double-pipe freezing physical model test system for saline sand was established. The temperature distribution in saturated saline sand under different salinities and velocities were studied. The test results showed that the temporal and spatial evolutions of the temperature field were affected by the velocity and salinity. Under the same boundary temperature, the higher the salinity, the lower the temperature at the measuring point on the main surface and interface. The overlapping time varies significantly. The analysis results showed that the larger velocity and the higher the salinity, the longer the overlapping time. The velocity and salinity inhibited the development of the frozen curtain. Under different test conditions, the development rate of the freezing curtain area was in the range of 3987–15,246 mm2/h.

The results of experimental studies of complex dielectric permeability of river sand and powders of granules of fused quartz with narrow distributions of particles in size at the frequencies from 10 kHz to 10 GHz are presented. The granule particles are spheres and the sand particles are irregularly shaped. The samples were moistened with distilled water and NaCl salt solution with conductivity of 0.1 and 0.77 S/m. It has been shown that the shape of the particles affects the complex dielectric permittivity (CDP) in the low frequency part of the range only when proportion of the solution is small and its concentration is weak. At full saturation of the samples with the solution and its high concentration, as well as in all cases at frequencies above 100 MHz, the influence of the particle shape is small. In the mid-frequency part of the range (from units to tens of megahertz) in a sample of quartz granules with small particles, there is a strong relaxation process, leading to a significant increase in the real part of the CDP. A similar, but slight increase is observed in samples of sand with larger particles. In the high-frequency range, the effect of the shape and particle sizes is very weak.

Vietnam Mekong Delta (VMD), the country’s most important food basket, is constantly threatened by drought-infused salinity intrusion (SI). The SI disaster of 2020 is recognized as the worst in recent decades, hence inspiring this perspective article. The authors’ viewpoints on the disaster’s impacts and causes are presented. The arguments presented are mainly drawn from (i) up-to-date publications that report on the recent SI intensification in the VMD and (ii) the power spectral analysis results using water level data. We verified the intensifying SI in the VMD both in its frequency and magnitude and remarked on four of the key SI drivers: (i) upstream hydropower dams, (ii) land subsidence, (iii) the relative sea-level rise, and (iv) riverbed sand mining. Also, a non-exhaustive yet list of recommendable management implications to mitigate the negative effects of the SI is contributed. The mitigation measures must be realized at multiple scales, ranging from pursuing transboundary water diplomacy efforts to managing internal pressures via developing early warnings, restricting illegal sand mining activities, alleviating pressures on groundwater resources, and diversifying agriculture.

Background Currently, using unconventional water sources in agriculture has become necessary to face overpopulation worldwide. Therefore, a pot experiment was carried out to evaluate the effects of irrigation with saline water in the presence of co-applied wood chips biochar (WCB) with chemical fertilizers on physicochemical properties and nutrient availability as well as growth parameters, and yield of red radish ( Raphanus sativus L.) grown in the saline sandy soil. Methods The WCB was added to the saline sandy soil at levels of 0 (control), 2.5, and 5% w/w. Then, this soil was cultivated by red radish plants and irrigated with saline water (5 dS m − 1 ). This experiment was performed in a randomized complete block design with three replicates. Results Compared with the control treatment, WCB treatments increased significantly soil water holding capacity by 34.8% and 73.2% for levels of 2.5 and 5%, respectively. Soil pH decreased significantly in all WCB treatments. The relative increase in the total available nitrogen over the control was 30.1 and 103.5% for 2.5 and 5% wood chips biochar, respectively. Compared to the control, applying WCB at 2.5% led to an increase in the fresh root weight of red radish plants by 142.7%, while 5% caused a decrease in the fresh root weight of red radish plants by 29.4%. Conclusion Recently, WCB represents an interesting approach to the rehabilitation of saline soils and the management of using saline water sources. It is recommended that combined application of WCB at a level of 2.5% with chemical fertilizers in order to improve red radish growth and nutrient retention in the saline sandy soil which preserves the ecosystem as well as increases productivity leading to the reduction of costs. Highlights Wood chips biochar applications into saline soil increased water holding capacity. Incorporated wood chips biochar with chemical fertilizers enhanced the availability of nitrogen and potassium in saline soil. Combining wood chips biochar at 2.5% with chemical fertilizers in saline soil improved yield parameters of red radish under saline water irrigation. Wood chips biochar at 2.5% incorporated with chemical fertilizers represents a promising strategy in saline agriculture.

To ensure the availability of freshwater resources in areas with limited water supply, it is crucial to enhance the efficiency of solar-powered desalination systems that are affordable, such as solar stills (SS). The parameters of basin water deepness and thermal storing beds were vital important parameters influencing the amount of yield from a SS. During rainy or cloudy days, the distiller does not operate in original conditions. This research purposes to raising the yield from salty water by a distiller operating with renewable energy sources. The study examined the impact of sands kinds (black and yellow) and sandy bed heights on TSS productivity, as well as the influence of internal reflectors on the TSS efficiency. The results of the experiment indicated that the production of TSS was enhanced by the presence of sandy layers. At 1 cm and black sands, the largest rise in cumulative output of sandy TSS with reflections was noted. When weighed against CSS, potable output under these circumstances increased by 105%.

The differentiation of saline water and fresh water interfaces is a key objective in ground water exploration and management. Bahawalpur is the twelfth biggest metropolitan area of Pakistan situated in south Punjab near the bank of River Sutlej and lies at 29°59’55” N latitude and 73°15’12” E longitude at an elevation of 521 ft AMSL in the Cholistan area close to the Thar abandon. The study area comprised of Lesser Cholistan experiencing acute shortage of water for inhabitants and livestock as well. The occurrence of fresh water is also challenging because of high salinity in groundwater. The present study is intended to identify hotspots of fresh groundwater zones. To achieve the goal, vertical electrical resistivity and borehole data are used to mark fresh and saline interfaces in groundwater. To achieve the results 230 vertical electric sounding were performed in the study area. A total of 3 to 5 geo-electric layers are identified with modeling along with the processing and interpretation of resistivity data. In the study area, resistivity values are classified as very high (>230 Ω-m), high (230–100 Ω-m), medium (100–40 Ω-m), low (40–20 Ω-m) and very low (<20 Ω-m). Borehole data is used to interpret subsurface lithologies and to calibrate the modeled resistivity curves. The electric resistivity data indicates that thick layers of Quaternary sediments is present in the subsurface that is primarily composed of clay, silt, sand, gravels and some kanker. Inversion technique is applied to generate 2D subsurface resistivity maps to delineate fresh and saline water zones. The generated 2D resistivity maps at variable depth above and below water table and formation resistivity maps are successfully utilized to differentiate fresh and saline water zones. The identification of a saline water aquifer within sediments rich in clay was made possible by the observation of very low resistivity measurements in the southern region. Conversely, the detection of relatively high resistivity values, coupled with the presence of sand and gravel deposits in the northern section of the lesser Cholistan area, provided compelling evidence of the existence of fresh groundwater. These findings have significant implications for the management of water resources in the region, as they provide valuable insights into the distribution and availability of groundwater resources for future use.

Human interventions at the river basin scale, such as sand mining and hydropower dam construction, have profoundly affected hydrological and hydraulic alteration regimes, sediment budgets, and morphological changes worldwide. Quantifying the consequences of unsustainable ongoing sand mining and hydropower is crucial for obtaining sediment load data and managing hydrogeomorphology. In this study, comprehensive long-term consecutive four-field monitoring, statistical methods, and hydrological models (SWAT) were applied to quantify the spatiotemporal changes in long-term discharge and sediment load from 1996 to 2020 for the tropical river of the Vu Gia Thu Bon (VGTB) in the central region of Vietnam. The SWAT model was calibrated from 1996 to 2010, validated from 2011 to 2020 and showed good performance for daily discharge and monthly sediment. The evolution of river bathymetric data (2010, 2015, 2018, and 2021) was analysed to clarify the upstream sediment supply trapped in the riverbed and how the sand mining volume was removed. The results showed that the mean annual sediment in the Vu Gia and Thu Bon Rivers decreased by 57.3% and 23.8%, respectively, in the postdam period compared with the predam period. The thalweg elevation decreased at the Ai Nghia and Giao Thuy stations from 2010 to 2021 by 1.8 m and 3.9 m, respectively. The water level decreased by 21.1% at Ai Nghia and 44.3% at Giao Thuy. Dam development, sand mining, and changes in land use are the main factors responsible for flow discharge and sediment morphodynamic alterations. Morphological change have increased the water transfer rate from the Vu Gia River to the Thu Bon River through the Quang Hue channel. Downstream of the Vu Gia River, water transfer and riverbed incision have decreased flow discharge and water level and increased saltwater intrusion in recent years. As a result, water shortages induced by saltwater intrusion during drought periods have emerged as a significant constraint in hindering the domestic water supply and agricultural production.

Deep geological repositories (DGRs) are considered the most promising technology for the long-term management of nuclear wastes. One of the major functions of the buffer or barrier material used in DGRs for nuclear waste is to prevent the release of high-level radioactive chemicals into the environment in the event of failure. To accomplish this, the buffer is typically designed to have very low hydraulic conductivity. The effects of mix-composition, swelling condition, temperature and groundwater chemistry on the hydraulic conductivity of compacted bentonite–sand barrier material were investigated in this study. Permeability tests were carried out using flexible wall permeameter after flooding the compacted samples in simulated groundwater. The obtained results showed that the saline groundwater prevailing in the Guelph region of Canada as well as high temperature have a negative impact on the swelling potentials of the buffer material, consequently increasing the hydraulic conductivity. The saline water reduces the thickness of the diffuse double-layer which is accompanied by a weak repulsion between the clay minerals. Similarly, elevated temperature decreases the basal spacing between the bentonite clay minerals which also results in less swelling. The combination of high temperature and salt concentration have an increased negative influence on the hydraulic conductivity. Furthermore, it was observed that restricting the swelling of the bentonite–sand mixture produces a well-packed material with a very low hydraulic conductivity compared to the free swelling. High confining pressure generates higher swelling stress from the hydration of clay minerals, which expand to fill the voids between the sand particles. It was also observed that increasing the percentage of bentonite and the initial dry density of the mix reduced the hydraulic conductivity by eliminating interparticle voids in the material. The research findings presented in this manuscript provide valuable information that will contribute to gain a deeper insight into the impact of field conditions (temperature, groundwater chemistry, confinement) and material characteristics (composition, dry density) on the permeability of bentonite–sand barrier, which is essential for a safe long-term management of radioactive wastes.