Evaluation of measurement methods for assessing vertical velocity in groundwater systems: a case study from Osongji (Osong Pond), Jeonju-si, South Korea

The interaction between groundwater and surface water plays a crucial role in determining water quality and ecological health, highlighting the need for a comprehensive understanding to ensure effective water resource management. In this study, multiple methods—seepage meters, piezometers, and the type-curve fitting method using temperature profile data—were employed to estimate fluxes at the groundwater-surface water interface of a small pond (Osong Pond) in South Korea. Measurements were conducted and compared during the wet season of 2020 (July–August 2020). Additionally, temperature data were collected during the dry seasons of 2021 and 2022 (November 2021–March 2022) to assess the applicability of the type-curve fitting method for long-term monitoring. The average vertical velocity measured by seepage meters was the highest (2.67 × 10⁻⁸ m/s), while the type-curve fitting method estimated the lowest average velocity (2.58 × 10⁻¹⁰ m/s). During the dry seasons of 2021–2022, the type-curve fitting method yielded an average flow velocity of 7.11 × 10⁻¹⁰ m/s, comparable to the dry season values of 2020. Although the lakebed temperature-based method underestimated vertical velocities in this study area, it can be effective for long-term monitoring. We recommend combining multiple measurement techniques tailored to the geological characteristics (e.g., topography and sediment composition) and climatic conditions of study sites. This integrated approach facilitates a more accurate evaluation of groundwater-surface water interactions and enhances understanding of the broader flow system.