Surface water and groundwater (SW-GW) are an inseparable whole, having a tightly coupled hydraulic relationship and frequent inter-transformation. As such, the quantitative calculation of water exchange between SW-GW is a difficult challenge. To address this issue, we propose the use of a physically based and distributed hydrological model, called WEP-L, in order to analyze the effects of the SW-GW interaction and its spatiotemporal variation characteristics in the Xiaoqing River basin. We demonstrate that the SW-GW interaction is significantly affected by season. The simulated annual average exchange volume of SW-GW above the control section of Huangtaiqiao Station from 1980 to 2020 is found to be 54.79 m³/s. The exchange volumes of SW-GW in the wet and dry season are 28.69 m³/s and 13.46 m³/s, respectively, accounting for 48.75% and 22.87% of the whole year. In addition, considering two types of climate change scenarios, the exchange capacity of SW-GW increases by 0.42m³/s when the rainfall increases by 5%, while the exchange capacity decreases by only 0.2 m³/s when the temperature increases by 0.2 °C. This study provides insights for the quantification of the SW-GW interaction at the regional scale, which will benefit our understanding of the water cycle and evolution of water resources in Xiaoqing River basin.

Saltwater intrusion is one of the most significant groundwater challenges in the southern Laizhou Bay. Previous studies have predominantly focused on regional scales, leaving the vertical saltwater intrusion pattern relatively underexplored. This knowledge gap hinders the effective prevention and control of saltwater intrusion. This study utilized hydrochemical and stable isotopic methods combined with hydrochemical facies evolution diagrams to investigate the groundwater evolution and the processes of saltwater intrusion in a typical profile and saline–fresh groundwater transition zones. The results showed that the groundwater types in the study area were complex and diverse, with fresh groundwater, saline groundwater, and brine. Stable isotope and hydrochemical analyses indicated that mixing and evaporation of seawater were the predominant processes governing the evolution and salinity of groundwater. In the south of the typical profile, carbonate dissolution played a significant role, and the silicate dissolution may represent the primary water–rock interaction in the saline–fresh groundwater transition zones. Groundwater samples from various locations within the study area exhibited different stages of hydrochemical facies evolution, and the majority of the typical profile samples were in the salinization phase during the mixing process. The saltwater intrusion in the saline–fresh groundwater transition zone primarily occurred between −20 and −30 m, exhibiting a wedge-shaped saltwater intrusion pattern. This study enhanced the understanding of vertical saltwater intrusion.

The two-phase displacement process occurring within the pores of a porous medium fundamentally represents the continuum-scale behavior of immiscible flow. Therefore, investigating pore-scale displacement patterns and flow morphologies provides deeper insight into the intrinsic mechanisms governing two-phase flow in geological formations. Unlike most previous studies, which mainly focused on single-factor effects, such as wettability or interfacial tension, this study develops a multi-parameter, coupled dynamic-capturing simulation framework that integrates the Navier–Stokes equations with the phase-field method. This framework systematically incorporates wettability, interfacial tension, pore-structure heterogeneity (disorder number λ), and surface roughness (root mean square) to elucidate their synergistic effects on immiscible displacement. Here, λ denotes a scalar heterogeneity index that sets the half-width of the uniform sphere-radius distribution in our model, i.e., r∈[(1−λ) r¯,(1+λ) r¯]; under this construction, the coefficient of variation satisfies COV = std(r)/r¯=λ/3, so larger λ monotonically increases geometric disorder [Blunt et al., “Detailed physics, predictive capabilities and macroscopic consequences for pore-network models of multiphase flow,” Adv. Water Resour. 25(8), 1069–1089 (2002) and R. Holtzman, “Effects of pore-scale disorder on fluid displacement in partially-wettable porous media,” Sci. Rep. 6(1), 36221 (2016)]. The simulations reveal the formation and evolution mechanisms of three residual oil forms: isolated oil droplets, oil columns, and clustered oil blobs, each arising from distinct structural configurations. This work provides a morphology-resolved, multi-parameter pore-scale analysis that integrates wettability, interfacial tension, quantified heterogeneity (λ), and surface roughness and highlights the dynamic fragmentation of clustered oil blobs. The findings provide a scientific basis for improving oil recovery in highly heterogeneous reservoirs.

Subsurface dams can effectively mitigate seawater intrusion while generating residual saltwater on their landward side, which has profound implications for the sustainable management in coastal aquifers. Therefore, identifying the dynamic behaviors and natural desalination processes of residual saltwater in post-dam aquifers is crucial, but research on this topic is still insufficient, especially under the combined action of geological anisotropy and hydraulic regulation. To solve this problem, a conceptual model of unconfined coastal aquifers was constructed and two indicators including the removal rate of residual salt mass (RRSM*) and the reduction rate of residual saltwater length (RRSL*) were selected to evaluate the desalination efficiency of residual saltwater behind subsurface dam. Then, this study conducted a series of numerical simulations, respectively, considering seasonal fluctuations in the groundwater level, hydraulic conductivity anisotropy as well as their combined effects to characterize the dynamic behavior of residual saltwater and capture their effects on the residual saltwater desalination processes. Furthermore, a sensitivity analysis for RRSM* and RRSL* was performed to investigate the primary factors controlling the residual saltwater desalination. The results show that the seasonal groundwater fluctuations and permeability anisotropy ratio (rk) can significantly influence the desalination efficiency of residual saltwater, exhibiting a synergistic effect on this process. In constant groundwater head scenario, an increasing rk can significantly diminish desalination efficiency, whereas in fluctuating groundwater head scenario, the desalination efficiency is influenced by the synergistic interaction of rk and horizontal hydraulic conductivity (Kx). And the peak desalination efficiency is observed during low groundwater level, exhibiting a distinct seasonal lag. The results are extremely important for the design and management of subsurface engineering in coastal aquifers under the combined influence of climate change and human activity.

The cause mechanism of collapse disasters is complex and there are many influencing factors. Convolutional Neural Network (CNN) has a strong feature extraction ability, which can better simulate the formation of collapse disasters and accurately predict them. Taihe town’s collapse threatens roads, buildings, and people. In this paper, road distance, water distance, normalized vegetation index, platform curvature, profile curvature, slope, slope direction, and geological data are used as input variables. This paper generates collapse susceptibility zoning maps based on the information value method (IV) and CNN, respectively. The results show that the accuracy of the susceptibility assessment of the IV method and the CNN method is 85.1% and 87.4%, and the accuracy of the susceptibility assessment based on the CNN method is higher. The research results can provide some reference for the formulation of disaster prevention and control strategies.