Arash Adib - Civil Engineering Department, Engineering Faculty, Shahid Chamran University, Ahvaz, Iran
Mahmood Shafai Bejestan - Hydraulic Structure Department, Water Science and Engineering Faculty, Shahid Chamran University, Ahvaz, Iran
Valiallah Shiri - Civil Engineering Department, Engineering faculty, Shahid Chamran University, Ahvaz, Iran

In this article a physical model is presented. A trapezoidal shape of channel with ۱.۴۵ m width, ۱ meter depth and banks slope of ۱H: ۱.۵V was applied. Circular piers (۶, ۸ and ۱۰cm diameter) were examined under three dissimilar flow discharges of ۵۰, ۶۵ and ۸۰ lit/s and three different median bed material sizes equal to ۰.۹۴, ۱.۳۱ and ۲.۱۲ mm. Seven different longitude distance to pier diameter ratios (۱, ۱.۵, ۲, ۲.۵, ۳, ۴ and ۵) were examined. Measurement of scour depth (upstream, around and downstream of pier) was accomplished in ۱۰, ۱۵, ۲۰, ۳۰, ۶۰, ۱۲۰, ۲۴۰ and ۳۶۰ minutes from the beginning of each examination. The results indicated that ۳۰%-۴۰%, up to ۶۵% and more than ۹۰% of local scour occurs at first two, ۱۰, ۱۲۰ and ۲۰۰ minutes from the beginning of test respectively. The effect of dissimilar parameter especially the distance between piers on scour depth at group piers in series was evaluated and the results were compared to other researchers. It was found that our results is best fitted with the general form of well known Sheppard et al. (۲۰۰۴)’s equation.

Local Scour, Group Piers, Physical Model, Sheppard et al. (۲۰۰۴)&#۰۳۹;s Equation, Sediment