Mechanisms and evaluation of rockbed erosion after weir installation
Diversion weirs were often built across rivers to elevate river water table. Most of the river beds in western foothills of Taiwan are composed of soft sedimentary rocks, such as sandstone, siltstone, and mudstone. Due to the low rock strength and the head difference caused by the weirs, rapid scour downstream the weirs is often observed. This type of scour may induce weir instability and accelerate river-bed incision. This study aims to investigate the erosion/scouring problems associated with weirs built on soft rock. The scope of this project includes as follows: (1) collection of relevant data for eight weirs built on soft rock; (2) preliminary study of erosion mechanism and erodibility of soft rock; (3) applicability evaluation of the available approaches for estimating local scouring in front of a weir built on soft rock.
Illustration of the plucking type of scouring processes
Illustration of the uniform incision type of scouring process
Illustration of the cross section perpendicular to flow:
the Trenching incision type of scouring process
Scour hole in front of the Shih-Kang weir (Jan.5.2010)