| Summary: | 碩士 === 國立屏東科技大學 === 水土保持系 === 95 === Steep terrain and abundant precipitation make torrents in Taiwan highly vulnerable to scour. Hence, transverse structures like groundsills are common practices implemented to control channel gradient and prevent channel beds from scouring. However, installation of transverse structures often dissects channel into segments that causes discontinuity in flow, an in turns, seriously affects wildlife habits.
The objective of this research is to evaluate the effects of circular open-slit groundsills on flow hydraulics and channel bedform characteristics. Indoor hydraulic tests were conducted using scaled circular open-slit groundsill models with different numbers of slit openings. Resultant channel bedform elevations were analyzed and expressed in term of Shannon Diversity Index. PIV method was used in a set of experiments to quantify the surface velocities. Depth-weighted Darcy's friction factor representing each hydraulic condition was also calculated. Results from this research were then compared to those from Lin (2005) who investigated the same effects caused by open-slot groundsills with linear geometry.
Results of this research can be summarized as follows. Characteristics of the channel bedforms depend on flow rates, sediment sizes, channel slopes, number of openings as well as the geometry of the groundsill. A groundsill with less slit openings will create more diverse channel bedforms due to flow concentration. However, deep scour caused by concentrated flow plunging into the channel bed may generate threat to structures. The high friction zone caused by plunging flow can expand toward downstream direction as flow rate increases, and low friction zone therefore decreases. Results of this study also illustrates that open-slot groundsills with circular geometry create higher diversity in channel bed than linear ones.
|
|---|
