A STUDY OF WATER MOVEMENT IN UNSATURATED ZONE

• Main Authors: Jr-Chuan Huang, 黃誌川
• Other Authors: Mei-Ling Hsu
• Format: Others
• Language: zh-TW
• Published: 1999
• Online Access: http://ndltd.ncl.edu.tw/handle/36102848058812495034

碩士 === 國立臺灣大學 === 地理學研究所 === 87 === 　Water movement in the unsaturated zone deeply affects irrigation, hydrograph, landslide and recharge of groundwater. However, the difficulty of the development of the field are the representation of soil samples and the variation of space and scale. The research of the water movement in unsaturated zone should recognize soil hydraulic parameters in order to know the characteristics of the soil and understand the relationship between the parameters each other. Then analyze Richards equation to understand the change of water movement in soil. Last, set a station in a small terrace in upper Lan-yang River with 2 rainfall gauges, 12 piezometers and 12 tensiometers to observe the behavior of water movement. 　No matter in laboratory or in field, the saturation hydraulic conductivity in gravel layer decreases much with soil depth. The hydraulic conductivity of deep soil samples(75~100 cm) is three times than the one of surface soil samples(0~25 cm). The hydraulic conductivity of the surface layer is affected by root and clay content. In the deep soil layer, it is affected by clay and silt content. No matter in surface or in deep soil layer , gravel content affects hydraulic conductivity in some degree. The water retention curve of the surface soil samples more matches Gardner equation than that of the deep soil samples. The water retention curve of deep soil samples has a tendency of straight line. The hysterisis of the surface layer is very demonstrable and has 10 % change in water content. The hysterisis of the deep soil samples has 0.2 % change in water content , so the hysterisis effect in the deep soil samples is very faint. 　In the field observation, the rainfall events in the bamboo forest usually delay 30 minutes than ones outside. Interception effect is very complex. In the conditoin of rainfall intensity less than 4.85 mm/hr and rainfall less than 21mm , the water content in the soil is unchanged below 60 cm depth and the water content in upper soil (above 30 cm) change very clear in the segment before rainfall peak. Generally speaking , the simulation using the rainfall data outside the bamboo forest is much better than that inside the bamboo forest. Because the results of using data inside the bamboo forest occurs lag in the change of water content and usually overestimates water content.