Improving Water-Cycle Soundness Through LID in a Future Urbanizing Watershed: A Case Study of the Dawoon Watershed, Ulsan

Climate change and rapid urbanization are increasingly disrupting urban water cycles by intensifying runoff and reducing infiltration, particularly in watersheds designated for future development. However, most existing studies have focused on fully urbanized areas, with limited attention given to semi-rural or urban–rural transition watersheds at the planning stage. In this context, the Dawoon watershed in Ulsan, Republic of Korea, represents a critical case, as it is currently undeveloped but designated for large-scale urban expansion. This study evaluates the effectiveness of Low Impact Development (LID) strategies in restoring water-cycle soundness under anticipated urbanization conditions. A hydrological model of the Dawoon watershed was developed using the Storm Water Management Model (SWMM), and multiple land-use-specific LID scenarios were designed to reflect realistic planning-stage applications. Long-term simulations were conducted to assess changes in runoff, infiltration, evapotranspiration, and overall water-cycle performance. The results indicate that urban development substantially increases surface runoff while reducing infiltration and evapotranspiration. The integrated application of LID measures significantly mitigated these impacts, reducing total runoff by approximately 3% and improving the water cycle recovery rate to nearly 99%, restoring hydrological conditions close to the pre-development state. Among the evaluated scenarios, the combined implementation of vegetated swales, infiltration–storage basins, green roofs, and permeable pavements showed the highest effectiveness. These findings highlight the importance of incorporating LID strategies at the early stages of urban planning to enhance climate resilience and prevent long-term water cycle degradation. The proposed framework provides practical guidance for setting water-cycle management targets and selecting effective LID measures in developing or peri-urban watersheds.