Evaluation of sediment control due to notches of mountainous river

Upstream of notches in mountainous rivers reveal backwater effect and velocity decreasing characteristics. The sediment transport in the upstream of reach with notches is therefore affected by the plane morphological characteristics. The upstream reach could possibly play a role of sediment control section for temporary sediment trapping and mitigation similar like check dam. In this study, we used the DTM of difference (DoD) method to perform four multi-temporal high-resolution DTMs during 2009 to 2021 to obtain the quantitative terrain elevation variance of river channels in five notch regions. The research results show that during Typhoon Morakot, the sediment control in notch area no. 1 can reach more than 20%. From 2012 to 2018, the control effect of sediment in notch regions no. 1, 2 and 4 is more than 14%. Overall, the notches no. 1 and 2 are the main sediment control areas, and the area of notch number 3 is limited in the amount of sediment due to the small contraction ratio of notch; the area of the notch number 4 and 5 is the secondary sediment control area, because the notch area 5 both the area and the contraction degree of the notch are smaller than those in area 4, and the control effect of sediment is more significant in area 4. Therefore, if we can make good implementation of the natural morphological features combined with the engineering structures to improve the effect of sediment regulation and control, it can be used as a reference for formulating watershed management strategies.