Streambed variation and channel stability evaluation of the Chungliao creek at Liukuei experimental forest of southern Taiwan

The rainfall amount and intensity of typhoon were rather different every year. The moving gravel size and scouring energy of streambed by annual maximum stream flow were also varied. Therefore, the characteristics of streambed variation and channel stability were not easy understood. Measuring characteristics of cross section variations with levelling and evaluating conditions of channel stability with procedure original from Forest Service of United States for streambeds of three reaches along Chungliao creek were carried out in this study. The scouring-deposition depths on streambeds of three reaches along Chungliao creek were between -19.0 cm and 94.3 cm from 2005 to 2007 years. The scores of channel stability indicators were between 81 and 123 and their ranks were from fair to good during three years from 2005 to 2007 year. The variations of scouring-deposition and channel stability indicators on three reaches for three years were affected by landslide areas along streamside as well as rainfall amount and intensity being carried by typhoon. The absolute values of scouring-deposition depths were positively responding with the variation of channel stability indicators. The absolute values of scouring-deposition depths increased as channel stability indicators increased and channel stability coditions become worse. The major seven factors in channel stability indicators affecting the absolute values of scouring-depsotion depths were as follows: mass wasting, debris jam potential, cutting, deposition, scouring, obstruction, and particle packing.