Physiological factors for watersheds of TFRI

Physiographic factors are the most important characteristics in establishing the hydrologic conditions of a watershed. They are crucial for experimental watersheds for model calibration and determining the effects of forest management practices on water yields. Originally those factors of Taiwan’s experimental watersheds were analyzed using topographic maps. The accuracy of values for factors obtained from maps and ground surveys has long been criticized due to the scale and man-made errors. With the development of geographical information system and digital photogrammetric techniques, it is increasingly common to determine basin characteristics from digital elevation models (DEMs). In this context, the physical characteristics of Taiwan Forestry Research Institute experimental watersheds including those at Fushan, Piluchi, Lienhuachih and Shanping were examined using by the WinGrid, computer software which combines techniques of GIS, remote sensing, the related theories, and models of soil and water conservation for topographic analysis of watersheds. The results indicated that there were significant differences of physiographic factors measured using topographic maps and DEM data for area and area-related factors such as the circumference of watershed, form factor, compactness, and average slope. Hopefully the adjusted measurements will be helpful in improving watershed and hydrologic studies in Taiwan.