Abstract
Generally, hydraulic structures are installed along with rivers in Taiwan to prevent erosion. The groundsill is one of the most common structures to protect the underlying riverbed. However, the occurrence of bursting during the process of scouring can intensify the disturbance of sediment in the bed, sometimes even causing hydraulic structures to collapse. This paper aimed to study the mechanisms of bursting, the effects of bursting, and the scouring exceedance probability of sediment movement. To study this topic, a particle image velocimetry (PIV) was used to measure the hydraulic characteristics of a scour hole under different flow conditions. The results showed that, firstly, the bursting and the sediment entrainment rate increased with time at the beginning. Secondly, when bursting occurred at the beginning stage of scouring, the averaged velocity of main flow was reduced by about 30% and the thickness of the riverbed was deepened by about 20%. Moreover, when scouring time was 15 min, at the location of maximum scouring depth, all the experimental groups carried the proximity values of the scouring exceedance probability that stuck to a range from 35% to 53% at the bursting stage. Therefore, the scouring exceedance probability of the bursting of the maximum scouring depth can be further applied to designs and to protect the foundation of hydraulic structures.
Highlights
In Taiwan, the hydraulic structure of the groundsill is frequently used to prevent lateral scouring and to protect riverbeds
The results indicated that the particle image velocimetry (PIV)-measured profiles revealed good agreement with the curves presented by Nezu and Rodi [19], except that the region was very close to the water surface and had some noises
This study aimed to explore the physical characteristics of bursting
Summary
In Taiwan, the hydraulic structure of the groundsill is frequently used to prevent lateral scouring and to protect riverbeds. Liang et al [2] discussed the mechanisms of local scouring with the designed structure. They extensively reviewed the mechanisms, contributing factors, and equations in previous studies. They concluded that there were some limitations on investigating scouring in reality due to the complexity of the its process [2]. In order to obtain precise values during calculations, instantaneous velocities of near-bed and scouring variations of bed sediment can be measured by laser doppler anemometry. This study illustrated the interaction between the phenomenon of bursting and bed sediment transport [3]. The relation between spur and sediment scouring was worth discussing
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