| Summary: | 碩士 === 國立中央大學 === 土木工程研究所 === 88 === Abstract
Water is limited on the earth. Recently, the growing population and the changing of the society in economy, industry and business result in the increasing demand on the water resources. In the consumption of water resources, agricultural water makes up of 87 %. Therefore, how to make good use of return flow in rice paddy irrigation is of emergency.
According to studies, the irrigation return flow accounts for 10 % to 74 % of the total irrigation water in flooded paddy fields. The range is so big that in order to proper estimate this quantity, the complication of flow mechanism on paddy field areas needs to be discussed.
This article about flow mechanism takes an example of a sand box, which is in mimicking of paddy filed areas. Through infiltration experiment and soil analysis, the soil preparation procedure of paddy field reduces infiltration during water ponding. The hardpan is formed mainly because of pudding. There is no hardpan under level. If the slope is fixed, the total flow increases with the higher depth, the water runs more deeply with increasing of total flow e.g the rate changes when the water depth changes from 4 cm to 6 cm, and 8 cm, the total flow changes from 1 to 1.55 and 1.94 respectively. However, the lateral seepage and vertical infiltration remain the same, as 1 to 4. By adjusting the slope of the sandbox with a fixed water depth, the total flow of water increases dramatically. In fact, when slope is 3.57%, 2% and 0%, the rate of lateral seepage to the vertical infiltration is 1 to 4, 1 to 6,1 to9,respectively. Hardpan affects lateral seepage dramatically with the change of slope.
The result of this research can explain what affects the flow in paddy field areas. The information of the change of the rate of lateral seepage to vertical infiltration can provides government agencies a scientific basis to promulgate policies concerning water resources management and serves as a demonstration to the research and to the investigation of water management problems in paddy field areas.
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