| Summary: | 碩士 === 國立臺灣大學 === 森林環境暨資源學研究所 === 101 === The study investigate about the saturated hydraulic properties of soil in forest watershed. This study area was at Lienhuachih watershed No. 4 and No. 5, where we choose four transects respectively selected from ridge and hillslope. Each location comprised soil depths of 0 cm and 20 cm, where Double-ring infiltrometer was used to measure field infiltration rate, and calculate the hydraulic conductivities in each point. At the same time, use the 20 cm of diameter and 40 cm of length cylinder to dig the large-scale undisturb soil samples, in order to compare the difference measurement types (Constant-Head Permeability Test and Falling-Head Permeability Test ) whether the conclusions are differ or not. Besides, collect small undisturbed soil to do physical analysis so as to compared the field and lab infiltration results and illustrate the influence of soil texture, large macroporosity, coarse porosity to the penetrate rate. By the way, we compared the difference properties in Guelph infiltrometer, tension infiltrometer and double-ring infiltrometer.
The results of double ring infiltration test, the average saturated hydraulic conductivity in watershed No.5 are large than in No.4. The soil texture of No.5 is clay loam, and there is more sand; the texture of No.4 is silt clay, there is more clay. The clay water retention capacity is better than sand, so that the saturated hydraulic conductivity is watershed No.5 more large than No.4. In comparison with double ring infiltration, constant head permeability test and falling head permeability, the saturated hydraulic conductivity of double ring infiltration is all large than constant head permeability. The reason that constant head permeability’s water flow is through down to above, the soil at 30 cm is closely knit than 0~20 cm so that the saturated hydraulic conductivity is low. The saturated hydraulic conductivity of falling head permeability test is all large than double ring infiltration. The reason that falling head permeability test’s pressure head is large than double ring’s, and the falling head permeability test in good permeability soil may overestimate. Besides, we compare the hydraulic conductivity of Guelph infiltrometer, tension infiltrometer and double-ring infiltrometer. The saturated hydraulic conductivity of tension infiltrometer is lower than Guelph infiltrometer and double-ring infiltrometer, and the results of Guelph infiltrometer is closely by double-ring infiltrometer.
The lab simulated rainfall conclusion, use the Brooks and Corey method to get the unsaturated hydraulic conductivity properties with water pressure head. The soil pore size distribution parameter (η) of No. 5 watershed is more large than No. 4, show that the soil porosity structure in watershed No.5 was more heterogeneous. There are more abundant soil aggressive structure and loose properties. The critical capillary head of No.4 is large than No.5, appeared that soil texture in No.4 is silt clay and micropores content is relatively high, that’s the reason why there has the smller saturated hydraulic conductivity.
|
|---|
