A quantitative analysis for geomorphic indices of longitudinal river profile: a case study of the Choushui River, Central Taiwan

Due to the plate movement is considerably slow, the human history record is too short to register landscape change for such a long time scale. However, longitudinal river profile can display watershed landscape characteristics. Therefore, this paper applies a quantitative analysis of geomorphic indices coupled with some mathematical models for the Choushui River and its six tributaries, including the gradient index and slope–area relationship. The abnormally high SL and SL/k values indicated that a decreasing trend from lower- to mid-stream areas and south Lishan fault was higher than north Lishan fault on the upstream areas, and the result of slope–area relationship also indicated that the regression line of the upper and lower steam exhibit an obvious right-shift nearby Lishan fault, could be explained by geodynamic models of active deformation in Taiwan area. This study also found that the abnormally high values of SL/k were affected by river and fault intersecting to form a high angle or perpendicular and the abnormally low values of SL/k were affected by river along with a fault or form a low angle, but the channel of Junda River along with Lishan fault is opposite. Based on quantitative results of these geomorphology indices, this study suggests that the important factor influencing landscape of the Choushui River watershed is tectonic uplift.