Estimation of the infiltration rate of a paddy field in Yun-Lin, Taiwan

Flooded paddy fields perform many functions, including not only rice production, but also ecological and environmental conservation, since the paddy field is periodically flooded and thus becomes a major source of ground water recharge. This work estimates the extent of infiltration in a paddy field in Yun-Lin, Taiwan by adopting a one-dimensional Darcy-based soil/water balance model SAWAH (Simulation Algorithm for Water Flow in Aquatic Habitats) and two sets of empirical equations used by the Taiwan Provincial Water Conservancy Bureau. A 7.5-cm thick plow sole layer with a hydraulic conductivity of 0.03-0.055 cm/day, coupled with the irrigation data obtained from the Ma-Yan station in Yun-Lin is selected to estimate the volumetric amount of annual infiltration in the study region. Simulation results from SAWAH indicate that the plow sole layer controls the movement of infiltrated water, with a rate ranging from 0.2167 to 0.2248 billion cubic meters annually. The infiltration rate estimated from empirical equations ranges from 0.337 to 0.3891 billion cubic meters per year, twice as high as that obtained from SAWAH. This finding suggests that the empirical equations designed to estimate the amount of irrigation water required for rice growth in the paddy may over-estimate infiltration rates. The simulated annual infiltration rate can be combined with the Geographical Information System to delineate the potential recharge zone for ground water management in Yun-Lin, Taiwan. (C) 2001 Elsevier Science Ltd. All rights reserved.