Abstract
This study intends to enhance a paddy's flood detention effect by adjusting the outlet mechanism to mitigate flooding. Since the paddy's detention effect is an additional function, this study focuses on figuring out a suitable design by comprehensively considering the inundation duration for rice, least peak discharge for flood detention and applicability for various ridge heights. This study establishes a water balance model by utilizing the outlet's discharge coefficients and loss intensity calibrated from the field test. The study adopts the shuffled complex evolution (SCE‐UA) method to optimize the peak discharge. Based on the dimensions of the paddy ridges around the test field and a 24‐h rainfall in a 50‐year return period, both the orifice type and the overflow type perform well, with peak discharge = 0.0105 m 3 s‾¹ and peak time = 960 min. Compared with the weir type, they function well in flood detention, with peak discharge reduction = 65.9% and detention time (time span between the peak time of the weir type and that of the others) = 200 min. Despite having the best performance in flood detention, the orifice type is the least applicable due to the limitation of ridge height. The overflow type has the advantages of both the weir and the orifice types. It is the most suitable design for paddies in Taiwan in terms of applicability and flood detention effect. © 2019 John Wiley & Sons, Ltd. © 2019 John Wiley & Sons, Ltd.