Curve Numbers for Rice Paddies with Different Water Management Practices in Korea

Abstract

The curve number (CN) method has been widely used to estimate the amount of direct runoff generated in agricultural watersheds around the world. However, its applicability to rice paddy fields has yet to be sufficiently tested to suggest the range of alternative CNs for irrigated and drained paddies. This study proposes CNs applicable to rice paddies that have different water management practices based on nine-year rainfall, irrigation, and drainage monitoring data. The results suggest that CNs should be adjusted to consider management practices characterized by rain-harvesting rates and drainage equipment, especially with a shallow ponding depth. When the soil water content was close to saturation and ponding depth was high due to irrigation and antecedent rainfall, CNs were less sensitive to drainage practices than they were under dry conditions. This study clearly demonstrated that irrigation and drainage practices implemented to manage rice paddies significantly affect the hydrological responses of the plots and subsequently impact CNs, suggesting the importance of careful CN determination for rice paddies. The proposed CNs are expected to be useful references in modeling hydrological processes in paddy rice areas and in developing agricultural watershed management plans using the CN method.