1. Introduction

In recent decades, global climate change has accelerated the variability and uncertainty of rainfall distribution, leading to frequent water crises and increased pressure on conventional water-supply systems. South Korea has experienced an increase in localized droughts, especially in inland and urban fringe regions, where rapid development has led to growing water demand.

Groundwater, once viewed as a supplemental water source, is now essential for ensuring water security in both rural and urban areas. Especially in locations near rivers, the use of groundwater has increased drastically because it is easy to obtain and is considered a reliable source when surface water is scarce.

However, these advantages have some limitations. Groundwater and surface water are hydrologically connected, which implies that water can move between rivers and underground formations called aquifers, depending on hydraulic gradients. Excessive pumping can therefore significantly reduce streamflow ^{(Chung et al., 2017b)}. This is especially critical during dry periods when groundwater is slowly released into rivers, maintaining their flow and supporting their aquatic ecosystems. Disruption of this balance not only harms ecosystems, leading to habitat loss and fish death, but also reduces the amount and quality of water available to people downstream.

Currently, water management approaches of South Korea tend to handle surface and groundwater as separate entities, with different agencies, regulations, and data systems overseeing each other ^{(KMGL 2015)}. This fragmented system makes it difficult to properly assess the combined impact of groundwater withdrawal on river systems, particularly in areas where legal boundaries do not align with the realities of water flow. Furthermore, public understanding of how water systems are connected is generally low and water management decisions often react to problems rather than anticipating them. Therefore, it is crucial that policymakers and stakeholders acknowledge the importance of developing integrated management strategies that consider the interconnected nature of water systems ^{(Lee et al., 2015)}. This should involve implementing technical tools to model the interactions between groundwater and surface water, improving the collaboration between agencies, and revising legal frameworks to enable shared oversight.

This study aimed to evaluate current practices in groundwater use near rivers, introduce scientific methods for assessing impacts, and propose a plan for implementing integrated water resource management in Korea. By combining what we have learned from local situations with insights from international case studies, this research seeks to promote water management practices that are more sustainable, equitable, and ecologically sound, while acknowledging the interconnected nature of water systems.

2. Necessity of Managing Groundwater Near Rivers

Extracting groundwater from areas adjacent to rivers can have a direct and notable effect on the volume of water present in the rivers and the change in water levels because of the typically close hydraulic connection between alluvial aquifers and the surface water bodies next to them. In South Korea, the development of groundwater resources near rivers has increased rapidly to meet the growing demands of agriculture, urbanization, and industry. However, the creation of effective regulatory frameworks to ensure that this use remains sustainable has not kept pace with growth.

Current laws state that groundwater extraction within 300 m of river boundaries requires consultation with the Ministry of the Environment; however, compliance with this rule is low ^{(Chung et al., 2017a)}. Several groundwater users either do not go through the consultation process or are unaware that they are supposed to, and enforcement is weak or inconsistent. A greater concern is the increasing number of unregistered wells, which do not require permits and are therefore not subject to meaningful oversight. These wells account for a large portion of groundwater use in areas near rivers, creating gaps in regulations that harm surface water management and contribute to the degradation of water resources.

Furthermore, the water laws of Korea—the Groundwater and River Acts—operate separately, leading to inconsistencies in policy, disputes over authority, and a lack of shared data. Consequently, the agencies responsible for overseeing groundwater often struggle to determine the total amount of water being extracted or where it is being taken from in relation to vulnerable river systems. This hinders efforts to manage the flow of groundwater into rivers and increases the risk of ecological damage. Without a comprehensive approach that considers the connection between groundwater and surface water, the country risks further depletion of its rivers, especially during dry periods when the flow of groundwater is essential for maintaining river health. Addressing these issues requires urgent changes in legal, technical, and administrative practices. This includes expanding the range of regulated facilities, setting limits on the volume of water that can be extracted, integrating databases between river and groundwater authorities, and raising public awareness on how water systems are linked. Only through these reforms can South Korea ensure that groundwater near rivers is managed in a manner that supports both human needs and environmental health.

3. Technical Approaches and Pilot studies

Managing groundwater use near rivers requires technical tools that can accurately describe and measure the interactions between underground aquifers and surface water systems at different locations and times. Analytical models, such as the Glover-Balmer ^{(Glover and Balmer, 1954)} and Hantush methods ^{(Hantush, 1965)} have been used to estimate the extent to which groundwater pumping reduces streamflow. However, these models rely on simplified conditions and assume that aquifer properties are uniform, making them inadequate for the complex hydrogeological conditions typically found in Korean watersheds.

To overcome these limitations, more comprehensive tools, such as the SWAT-MODFLOW integrated model ^{(Kim et al., 2008)} have been adopted. SWAT ^{(Arnold et al., 1998)} simulates surface processes, such as rainfall, runoff, evapotranspiration, and land use change, whereas MODFLOW ^{(McDonald and Harbaugh, 1988)} models groundwater flow using a finite-difference approach. Together, these tools enable the dynamic simulation of water movement within a watershed, capturing the interplay between rainfall, land cover, aquifer characteristics, and anthropogenic activities.

Pilot studies in watersheds, such as the Juksan Stream ^{(Lee et al., 2015)} and Hwangguji Stream ^{(Lee et al., 2017)} have demonstrated the practical application of these models in Korea. These studies involved detailed hydrogeological surveys, including aquifer pumping tests, hydraulic conductivity measurements, and groundwater level monitoring. The collected data were used to create maps of groundwater impact zones using geostatistical interpolation methods, providing visual representations of the spatial extent and degree of streamflow depletion. These maps serve not only as scientific references but also as tools for administrative screening and policy development. Importantly, a project is currently underway to integrate these outputs into the river water management system of the Han River Flood Control Office, including GIS-based consultation systems that enable stakeholders to evaluate potential risks before making decisions as shown in Fig. 1.

The success of these pilot projects highlights the need to implement these technical approaches nationwide. Establishing standardized protocols for data collection, model calibration, and map generation is essential to ensure the consistency, comparability, and credibility of future assessments. The integration of real-time monitoring data, automated evaluation systems, and feedback loops with stakeholders can further improve the transparency and effectiveness of groundwater management near rivers.

Fig. 1. The Stream Water Management System of the Han River Flood Control Office

4. Directions for Improving Governance in Groundwater Management

The effective governance of groundwater resources in areas adjacent to rivers requires institutional structures that acknowledge the integrated nature of water systems. Unfortunately, the current legal and administrative framework of South Korea is fragmented and outdated; therefore, it cannot adequately address the complexities of the interactions between groundwater and surface water. The Groundwater Act focuses narrowly on well construction, permits, and user reporting, whereas the River Act governs surface water use rights and user fees. This legal separation has led to inconsistent policies, regulatory overlaps, and ambiguities among those with authority.

For example, if groundwater pumping negatively affects a nearby river, it is unclear which agency has the power to require corrective action or deny further development. Furthermore, no standardized method exists for measuring streamflow depletion, which results in decisions being made on a case-by-case basis and creates legal uncertainty. These institutional shortcomings have contributed to the widespread underreporting of groundwater use, insufficient enforcement of consultation procedures, and failure to address the ecological consequences of extracting high volumes of water.

To address these issues, a major institutional overhaul is necessary, starting with bringing existing laws into harmony. This would involve revising both the Groundwater and River Acts to acknowledge that groundwater and surface water are interconnected resources that need to be jointly regulated. Second, a shared regulatory framework should be established to assess the impact on streamflow using scientifically sound criteria, such as percentage reductions in flow over specific timeframes. Third, administrative bodies must coordinate their efforts through shared databases, joint monitoring systems, and integrated platforms to issue permits. Fourth, initiatives to build capacity should be implemented to train local authorities and technical staff to apply hydrological models, interpret maps, and enforce regulations. Finally, public transparency must be improved through consultations with stakeholders, open access to data, and clear communication regarding the reasons for permitting decisions. Through these comprehensive reforms, Korea can develop a unified and adaptable groundwater management system that protects river ecosystems while meeting the needs of its population.

5. International Case Comparisons

Examining how other countries handle this issue provides a helpful perspective for evaluating groundwater management challenges of South Korea and identifying potential solutions. In countries with well-developed water governance systems, the hydrological connection between groundwater and surface water is a fundamental principle of regulation.

For instance, New Zealand has established regional frameworks that categorize aquifers based on how closely they are connected to surface water bodies ^{(Environment Canterbury, 2000)}. The Southland and Wellington regions use thresholds for streamflow depletion, such as the percentage of streamflow reduced over a 7-d pumping period, to inform their permitting decisions. Permits are contingent on these thresholds and stricter monitoring and mitigation measures are implemented in areas with greater connectivity. In some cases, pumping restrictions are imposed during periods of low flow to protect ecological flows.

Similarly, the United States has adopted conjunctive management systems in several Western U.S. states. In Arizona, for example, “safe yield” policies limit groundwater withdrawals to the amount that is naturally replenished. Oregon's water code requires the integration of groundwater and surface water rights in areas where they are hydrologically connected ^{(Barlow and Leake, 2012)}. These systems employ hydrological models and long-term monitoring to track water levels, predict the impacts of depletion, and adjust management strategies as required.

In Europe, countries, such as France and Germany include links between groundwater and surface water in their national water plans, with support from basin-level authorities that coordinate across administrative boundaries. They also involve stakeholders through participatory planning processes that increase both the legitimacy of decisions and the degree to which they are followed ^{(Closas and Moll, 2016)}.

These international examples share several common traits. They all use measurable criteria to assess the effects of water use, incorporate scientific data into their decision-making processes, have legal structures that acknowledge the interdependence of water sources, and establish governance systems that encourage collaboration across different sectors. By adopting similar approaches, Korea can close existing regulatory gaps and bring groundwater governance in line with leading global practices.

6. Conclusion

Groundwater resources near rivers are essential buffers against seasonal water shortages. They maintain the flow of rivers, support the ecosystems within them, and provide a dependent water supply for various uses. However, these benefits are increasingly jeopardized by groundwater extraction, which is either unregulated or poorly managed, particularly in areas where groundwater and surface water systems are closely connected.

This study examined the complex issues of groundwater management in areas adjacent to rivers from technical, institutional, and comparative viewpoints. These findings indicate that the current regulatory frameworks are not adequate for preventing accumulating effects on river flow. This is partly due to the fragmentation of legal responsibilities, weak enforcement of regulations, and lack of public awareness regarding the connections between water systems.

To address these shortcomings, this study proposes a plan for integrated groundwater and surface-water management. From a technical standpoint, the use of hydrological models, such as SWAT-MODFLOW, combined with mapping impact zones, offers a practical and scientifically sound method for quantifying risks and informing decisions about permits. These tools should be supported by nationwide efforts to collect data and by real-time monitoring and automated evaluation systems to ensure that they are consistently applied. Institutionally, Korea needs to pursue legal harmonization by revising the Groundwater and River Acts to reflect the interconnected nature of water systems. Regulatory agencies should adopt standardized methods for measuring streamflow depletion and coordination between administrative bodies must be improved through shared databases and joint consultation procedures.

In terms of policy, a total quantity control system must be introduced. This would allow the setting of limits on the volume of water that can be removed based on the combined usage of all water extraction points, including the registered wells. This should be accompanied by public education campaigns, forums to engage stakeholders, and incentives to encourage water conservation and compliance with regulations.

In summary, sustainable management of groundwater in areas near rivers requires a comprehensive and proactive strategy. This strategy should integrate scientific knowledge, institutional reforms, and community participation. By implementing the strategies outlined in this study, South Korea could build a resilient water governance system capable of safeguarding freshwater resources for future generations.