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

The purpose of this study was to quantitatively analyze variations in estimated inflow flood volumes caused by differences in rainfall frequency analysis methods and Clark unit hydrograph parameter estimation approaches, focusing on 26 small agricultural reservoirs with watershed areas under 10 km². It assessed the sensitivity of inflow estimates to these methods and identified trends according to watershed characteristics. Three methodological combinations were evaluated: (1) at-site frequency analysis with the Sabol and continuous Kraven formulas, (2) regional frequency analysis with the Sabol and continuous Kraven formulas, and (3) regional frequency analysis with the Seokyeong University formula. Regional frequency analysis generally yielded lower inflow volumes than at-site frequency analysis, with an average decrease of 13.2%. The largest decreases occurred in watersheds larger than 3 km², slopes over 35%, and stream lengths exceeding 3 km. In comparing Clark unit hydrograph parameter estimation methods, the Seokyeong University formula consistently resulted in lower inflow volumes, averaging an 18.6% decrease. The largest decreases occurred in watersheds of 1.5–3 km², slopes of 27–35%, and stream lengths exceeding 3 km. These differences were attributed to limited rainfall gauge coverage and to the larger times of concentration and storage coefficients produced by the Seokyeong University formula. The findings indicated that method selection significantly affected inflow estimation. This study provided baseline data for the design of small agricultural reservoir facilities and flood forecasting, and it highlighted the need for further research on regional distribution, high-resolution rainfall data, and additional hydrological factors.