Min-Ho Koo

Radial collector well (RCW) intake is governed by complex interactions among aquifer properties, river–aquifer connectivity, clogging processes, and hydraulic losses within collector laterals. This study investigates these controls using a coupled aquifer–lateral flow formulation implemented in MODFLOW, in which laterals are represented as Drain cells with iteratively updated heads and conductance to account for near-lateral resistance and internal frictional and momentum losses. A conceptual model was used to examine aquifer hydraulic conductivity and anisotropy, aquitard properties, river-to-caisson distance, filter-pack and riverbed clogging, caisson operational head, and lateral design parameters. Intake increased with aquifer hydraulic conductivity, although the response became nonlinear as lateral head losses intensified. Vertical hydraulic resistance caused by anisotropy or aquitards reduced intake and, under some conditions, produced a finite optimal river-to-caisson distance. Well clogging exerted a much stronger influence than riverbed clogging, and severe reductions in filter-pack hydraulic conductivity reduced intake to near-zero levels. Among the lateral design variables, lateral diameter had the strongest effect, particularly in high-conductivity aquifers. Longer laterals were more effective in low-conductivity aquifers, whereas adding laterals was more beneficial in high-conductivity aquifers, where groundwater could be supplied from multiple directions. These results show that RCW performance depends on the location and magnitude of the dominant hydraulic resistance within the coupled river–aquifer–well system. The findings provide a process-based framework for RCW design, performance interpretation, and clogging management under site-specific hydrogeological conditions.

This study presents a physically based numerical framework for accurately simulating the intake performance of radial collector wells (RCWs) by explicitly accounting for internal flow dynamics and all major head loss mechanisms. Unlike conventional models that often simplify RCW hydraulics, the proposed approach integrates aquifer, filter, slot, frictional, momentum, and caisson head losses into a fully coupled formulation of lateral head and conductance. A Python–MODFLOW 6 coupling scheme, implemented using the FloPy library, iteratively updates lateral head and inflow until convergence, capturing the coupled interaction between the lateral and the surrounding aquifer. Simulation results show that lateral head variation becomes critical under high‐intake conditions, leading to nonlinear intake behavior and asymmetric aquifer drawdown. Neglecting key head loss components, especially the caisson and momentum losses, can result in substantial overestimation of intake. In addition to reproducing the head variation within the laterals, the model incorporates the Forchheimer term to account for nonlinear head losses in the aquifer and a slot‐loss component to represent structural resistance near screen openings. Although the influence of these factors increases slightly with higher flow rates, their overall impact on total intake remains negligible under the tested conditions. The proposed framework improves the predictive accuracy of RCW modeling and provides a practical tool for design evaluation, performance assessment, and long‐term planning of RCW systems.

During the cold dry season, a large amount of groundwater is pumped for water-curtain cultivation in agricultural fields mostly located near the four major rivers of South Korea. Several weirs, installed previously to secure sufficient water resources from these rivers, were opened in 2017 for restoring the riverine environment. Weir-controlled river level fluctuations have altered stream–aquifer interactions, leading to groundwater drawdown. In this study, changes in stream–aquifer interaction caused by seasonal pumping and weir opening were investigated, using Visual MODFLOW. Two indexes that considered the pump type and aquifer characteristics—the pumping available thickness (PAT) and aquifer productivity index (API)—were used to analyze the effects of weir opening on seasonal groundwater use. Our simulations indicated that weir opening had a large impact on seasonal groundwater use due to groundwater drawdown, especially with respect to centrifugal pumps located in low transmissivity areas where the API decreased after the weir was opened. The resulting decrease in groundwater pumping rates would lower the thermal effect of the water-curtain greenhouse process. This indicates that water supply alternatives are needed so that the weirs can be operated efficiently and field requirements can be met, while the deleterious effects on groundwater are avoided.

The Juksan weir, installed in the Yeongsan river in South Korea from 2010 to 2012, has secured sustainable water resources and helped control flooding. However, low river flow velocities due to the weir have deteriorated the quality of the river water. For natural river restoration, the water gate was opened in 2017. In this study, the three-dimensional finite difference model Visual MODFLOW was used to analyze the effects of gate opening on stream–aquifer interactions. A conceptual model was developed to simulate the stream–aquifer dynamics caused by the operation of the water gate at the Juksan weir. Groundwater data were also analyzed to determine the impacts of weir operations on groundwater quality. Our results indicate that a lower river level due to the weir opening changed the groundwater flow, which then affected the water balance. The change in groundwater flow increased the variability of the groundwater quality which had homogenized because of induced recharge after the construction of the weir. This could affect groundwater use in agricultural areas near the weir. Therefore, further groundwater monitoring and hydrodynamic analyses are required to anticipate and address any potential issues.

Hydraulic structures have a significant impact on riverine environment, leading to changes in stream–aquifer interactions. In South Korea, 16 weirs were constructed in four major rivers, in 2012, to secure sufficient water resources, and some weirs operated periodically for natural ecosystem recovery from 2017. The changed groundwater flow system due to weir operation affected the groundwater level and quality, which also affected groundwater use. In this study, we analyzed the changes in the groundwater flow system near the Geum River during the Baekje weir operation using Visual MODFLOW Classic. Groundwater data from 34 observational wells were evaluated to analyze the impact of weir operation on stream–aquifer interactions. Accordingly, the groundwater discharge rates increased from 0.23 to 0.45 cm/day following the decrease in river levels owing to weir opening, while the hydrological condition changed from gaining to losing streams following weir closure. The variation in groundwater flow affected the groundwater quality during weir operation, changing the groundwater temperature and electrical conductivity (EC). Our results suggest that stream–aquifer interactions are significantly affected by weir operation, consequently, these repeated phenomena could influence the groundwater quality and groundwater use.

In South Korea, a significant amount of groundwater is used for the heating of water‐curtain insulated greenhouses during the winter dry season, which had led to problems of groundwater depletion. A managed aquifer recharge (MAR) project is currently underway with the goal of preventing such groundwater depletion in a typical cultivation area, located on an alluvial aquifer near the Nam River. In the present study, FEFLOW, a three‐dimensional finite element model, was used to evaluate different strategies for MAR of the cultivation areas. A conceptual model was developed to simulate the stream‐aquifer dynamics under the influence of seasonal groundwater pumping and MAR. The optimal rates and duration of MAR were assessed by analyzing the recovery of the groundwater levels and the change in the groundwater temperature. The simulation results indicate that a MAR rate of 8,000 m³/d effectively restores the groundwater level when the injection wells are located inside the groundwater depletion area. It is also demonstrated that starting the MAR before the beginning of the seasonal pumping is more effective. Riverbank filtration is preferable for securing the injection water owing to plentiful source of induced recharge from the river. Locating the pumping wells adjacent to the river where there are thick permeable layers could be a good strategy for minimizing decreases in the groundwater level and temperature.

Large agricultural fields in South Korea are located mostly on alluvial plains, where a significant amount of groundwater is used for heating of water‐curtain insulated greenhouses. Such greenhouses are commonly used for crop cultivation during the winter dry season from November to March. After use the groundwater is discharged directly into streams, causing groundwater depletion. A hydrogeological study was carried out in a typical agricultural area of this type, located on an alluvial aquifer near the Nakdong River. Groundwater levels, chemical characteristics, and temperatures from 68 observation wells were analyzed to determine the impacts of seasonal groundwater pumping on the groundwater system and stream‐aquifer interactions. Our results show that the groundwater system has not yet reached a state of dynamic equilibrium. Decades of excessive seasonal pumping have caused a gradual decline of groundwater levels, leading to groundwater depletion, especially in areas further from the river. Seasonal pumping has also significantly affected groundwater quality in the aquifer near the river. Groundwater temperature is decreasing (in this case a disadvantage), and saline groundwater is being diluted by induced recharge. The results of this study provide a basic outline for effective integrated water management that is widely applicable in South Korea.

The “Four Major Rivers Restoration Project” was conducted to secure sufficient water resources, introduce comprehensive flood control measures, improve water quality, and restore river ecosystems in Korea. As a part of the project, 16 sites were dredged and weirs were installed in the Han, Geum, Yeongsan, and Nakdong Rivers from late 2010 to early 2012. Groundwater data were obtained from 213 groundwater monitoring wells near the four major rivers to analyze the impacts of weir construction on the nearby groundwater flow system. The groundwater level and chemical characteristics were analyzed to investigate how the groundwater flow system and water quality changed following weir construction. Our results show that the groundwater level immediately increased with increased river levels following weir construction. In addition, the hydrologic condition of some rivers upstream of the weirs was changed from gaining to losing streams. Consequently, the direction of groundwater flow changed from perpendicular to parallel to the river, and groundwater downstream of the weir became recharged from the area upstream of the weir. This should affect groundwater quality, which should become similar to the river water; however, this change has not yet been observed. Therefore, both further monitoring of the groundwater quality and further hydrogeochemical analysis are required for quantitative evaluation of the effects of weir construction in the study area.