Journal of Korean Society of Agricultural Engineers ISSN:1738-3692(Print) 2093-7709(Online) 한국농공학회논문집

Climate change has intensified the frequency and magnitude of extreme rainfall events, underscoring the need to revise the design flood criteria for agricultural fill dams to ensure adequate hydrological safety. Although the current KDS 67 10 20 standard applies a 200-year return period with a 1.20 weighting factor (20% increase of the design flood discharge), recent hydrological responses suggest that this criterion may not fully reflect actual hazard levels. In this study, design flood discharges were estimated using frequency-based rainfall and probable maximum precipitation (PMP), implementing the SCS–CN method, Clark unit hydrograph, and simple lag routing within the K-HAS module. Using these estimates, the applicability of the current standard was assessed, and the resulting changes in return period under different weighting factors were quantified. Applying a weighting factor of 1.20 increased the effective return period from 200 years to approximately 650–850 years, while the same factor applied to the 500-year frequency increased it to 2,000–2,400 years, revealing a strong nonlinear amplification effect. The magnitude of this amplification varied substantially with watershed characteristics: smaller catchments and shorter times of concentration exhibited higher sensitivity, whereas total storage capacity had minimal influence. These findings indicate that a uniform weighting factor does not adequately account for the hydrologic and geometric diversity of agricultural reservoirs. The results highlight the need for flexible, site-specific design-frequency criteria that incorporate key watershed characteristics to better ensure hydrological stability under future climate conditions.