Figure 1. Research procedure.
2.1 Study Area
The study area was in the catchment area of the Chenyulan River (23°20’–23°35’ N, 120°47’–121°00’ E) (Figure 2), which is a tributary of the Zhuoshui River basin in central Taiwan; its catchment area is approximately 448 km² and the river’s length is approximately 42 km. Based on hydrological data, the annual average temperature in this area is 19–23°C and the annual average rainfall is 1600–2600 mm. Regarding the topography, the catchment area of the basin is narrow and elongated. The main stream flows northward and the tributaries flow into the main stream from the east and west. In terms of geology, the left bank of the river is mostly Middle Miocene sedimentary rock and the right bank is Paleogene slate. The topography of the main stream is a linear longitudinal valley (Lee, 1996).