Weirs or small dams were often built across rivers to elevate river water table for providing public water supply in Taiwan. Most of the river beds in western foothills of Taiwan are composed soft sedimentary rocks. Due to low rock strength and the head difference caused by the weirs, rapid scour downstream of weirs is often observed. This type of scour may induce weir instability and accelerate river-bed incision. The project aims at investigating the erosion/scouring problems associated with weirs built on soft rock. The scope of this project includes the following: (1) collection of relevant data for eight weirs built on soft rock; (2) study of erosion mechanism and erodibility of soft rock ahead of weirs; (3) applicability evaluation of the available approaches for estimating local scouring in front of a weir built on soft rock; and (4) study on the strategies for weir-front erosion control.