| dc.description.abstract | Due to changes in the social environment and fast increasing population in Taiwan, the industry and domestic water demand is growing at a fast pace. In addition, the concepts of environment and ecology protection are more and more popular. Consequently the existing water resources become limited. How to quantify the functions from paddy rice field and to utilize efficiently return flow in the farm so as to reduce irrigation demand are the current major tasks. This study is to use field and sandbox model experiments to investigate and quantify the mechanisms of groundwater recharge and infiltration rates in paddy rice field. Furthermore, this study constructs a water balance model with optimization scheme for paddy field irrigation, in which irrigation water depth, drainage when the field is drying, and horizontal infiltration are taken into account.
The field investigation was conducted in the irrigation area of Taoyuan main canal for Taoyuan Irrigation Association (TIA), which consists of recession field, hardpan broken field and common field. The results show that at the first 40 days the groundwater recharge rate in common field with flooding is 3.8mm/day, and 13.6mm/day for hardpan broken field. These indicate that after hardpan is broken, the infiltration rate can be raised to increase groundwater recharge. However, after twice field preparation and plant growing periods, the infiltration rate will be reduced and the hardpan function can be fully recovered in the following cultivation.
With the climatologic data at TIA 11-2 rotational area at the first cultivation term in 2000, the water balance model with optimization scheme gives the following results. Based on the fact that the fourth and fifth strips collect the return flow from the third strip upstream, the fourth strip needs only 247.6mm of irrigation water, which originally needs 539.2mm without any consideration of return flow. The fifth strip needs 324.4mm instead of 539.2mm. With return flow utilization, the irrigation demand for the whole rotational area drops from 250,990m3 to 197,644m3. It is concluded that this model could be applied to estimate return flow in upstream area and to provide optimum irrigation demand and schedule to conserve water and increase the benefits. | en_US |