The Jinan karst system is one of the typical karst systems in North China. The karst springs in Jinan are important historical heritage in China. However, in recent years, due to urbanization and the excessive exploitation of groundwater resources in Jinan City, the rate of spring flow has decreased tremendously. Preferential runoff belts are channels of karst aquifers where fractures and conduits are well-developed and serve as the main pathways for groundwater movement and solute transport. In view of this, a study was conducted in the Jinan Spring Basin to identify preferential runoff belts based on hydrological time-series correlation. Firstly, through cross wavelet transform and Pearson correlation coefficient, the time-lag and correlation of spring water level and precipitation were analyzed, the result show that the precipitation in the areas of Xinglong, Donghongmiao, Qiujiazhuang, Xiying, Yanzishan and Liubu stations has a greater impact on spring water level. In addition, combined with the hydrogeological conditions of the Jinan Spring Basin, the above stations meet the characteristics of the preferential runoff belt. In conclusion, the above stations are most likely to be located on the preferential runoff belt. The results of this study can serve as great reference points for building a correct hydrogeological conceptual model, and for the future planning of spring protection measures.

Freshwater resources on small coral islands mainly exist in the form of freshwater lenses. The freshwater lens is highly vulnerable to salinization due to natural recharge variations and urbanization construction. However, it is unclear how a freshwater lens evolves under the influence of urbanization construction and which factors control its evolution. Based on the hydrogeological data of a small coral island in China, a corresponding 3D numerical model was established by the Visual MODFLOW software to investigate the formation and evolution of freshwater lenses under natural conditions. Thereby, the island reclamation scenario and impermeable surface scenario were set up and the changes in morphology and volume of the freshwater lens were analyzed. The results show the following: (1) After island reclamation and island building, the freshwater lens would reach a stable state after 25 years and the freshwater lens would also appear in the newly added part of the island with a thickness of 9.5 m, while the volume of the total freshwater lens would increase to 1.22 times that of the original island. (2) When the impermeable surface is built at different positions of the island, the reduction in the volume of the freshwater lens, in the order from large to small, is Scenario B (northeast side), Scenario A (southwest side) and Scenario C (central); with the increase in the impermeable surface area, the volume of the freshwater lens would gradually decrease and the volume of the freshwater lens would decrease by more than 50% with the impermeable surface exceeding 30% of the island area. The study has important implications for the conservation and rational development of subsurface freshwater resources on islands.

The research of saltwater upconing is crucial for the development and utilization of island freshwater resources. In this paper, a laboratory physical experiment device was developed, and the saltwater upconing and recovery of island freshwater lenses were investigated using rainfall simulations and single-well and multi-well pumping tests with various pumping intensities. The results of the experiment revealed that: (1) The thickness of the freshwater lens increased continuously and linearly during the early stages of rainfall. As the rainfall continued, the upward trend slowed and eventually leveled off. (2) Under the same pumping duration, when the pumping intensity was less than the critical pumping intensity, the increasing height rate of the saltwater upconing increased linearly at a small gradient, and when the pumping intensity was greater than the critical value, the rising height rate of the saltwater upconing increased linearly at a large gradient. (3) Under the same pumping intensity conditions, the pumping duration of the multi-well was longer than that of the single-well pumping, and the pumping volume of the multi-well was also greater than that of the single-well pumping. The experiment results can provide support for the development and utilization of island freshwater lens.

Infiltration and anti-filtration recharge-pumping wells (hereinafter, referred to as IAF recharge-pumping wells) can enable rain-flood flowing in rivers or channel recharge to aquifers, in flood periods, and pump groundwater to be utilized in non-flood periods. In this study, a round IAF recharge-pumping well and a square IAF recharge-pumping well were developed, the structure and characteristic were introduced, the calculation equations of single-well recharge quantity of IAF recharge-pumping wells, in unconfined aquifers were deduced, and the steady-state flow recharge test was conducted in the laboratory. The conclusions were as follows. The theoretical equation of the single-well recharge quantity was reasonable. Compared to existing anti-filtration recharge wells, the new IAF recharge-pumping well had stronger anti-deposit and anti-scour abilities and the single-well recharge quantity increased by 400%. Compared to the square IAF recharge-pumping well, the round IAF recharge-pumping well had a better inlet flow pattern and a larger single-well recharge quantity. With an increase in the test times, the single-well recharge quantity gradually decreased and tended to be stable. The existence of the pumping pipe had a little influence on the single-well recharge quantity.

Karst water supplies freshwater to approximately a quarter of the global population and plays a crucial role in supporting the socioeconomic development of karst regions. As a key indicator for assessing and managing karst water resources, karstic water storage variation is influenced not only by the complex structure of karst aquifer media but also by the variability in natural precipitation infiltration. Based on the hydrogeological conditions of a typical karst aquifer system in northern China, this study developed a three-dimensional physical experimental setup and established a corresponding groundwater flow numerical model coupled with equivalent porous media and conduits. The factors affecting spring flow recession were investigated from a source–sink perspective. Precipitation events were categorized into two types: those with the same duration but different intensities and those with the same total volume but different intensities. The influence of varying precipitation events on the estimation of karstic water storage variation was quantitatively evaluated using the exponential fitting method, based on the analysis of spring flow recession curves. These findings could provide scientific guidance for the development, utilization, and protection of karst water resources.

A groundwater function evaluation systems and associated model was applied to Pingtan Island in China, to support future development, use and protection of groundwater. Groundwater function was assigned to resource, ecology and geological environmental functions, and then further sub-divided, based on hydrogeological conditions, development status, planning and Chine policy requirements. At the same time, it is the first time to try to apply the technical requirements for the division of groundwater resources in island areas. According to the planning and utilization of groundwater resources in Pingtan Island, established a second-level system of shallow groundwater function zoning. Then, by comparing the strong and weak relationships among the groundwater resource function, ecology function, and geological environment function, developed a scoring system of the shallow groundwater function zoning. The division of shallow groundwater function zones in Pingtan Island was finally carried out. The zoning result will play an essential role in the future development, utilization, and protection of groundwater in Pingtan Island. At the same time, it provides the first example for the application of groundwater function zoning in island areas and improves the theoretical results of groundwater function zoning.