TY - JOUR T1 - Experimental Study of the Effect of Ripple Bedforms with Fine and Coarse Sediments on Bed Shear Stress TT - مطالعه آزمایشگاهی اثر فرم‌های بستر شکنج با رسوبات ریزدانه و درشت‌دانه بر تنش برشی بستر JF - JSTNAR JO - JSTNAR VL - 26 IS - 2 UR - http://jstnar.iut.ac.ir/article-1-4200-en.html Y1 - 2022 SP - 283 EP - 297 KW - Ripple KW - Dune KW - Alluvial rivers KW - Bed shear stress N2 - Bed shear stress is one of the most important hydraulic parameters to determine the amount of bed and suspended load and the bed and bank scouring in rivers. Bed shear stress depends on bedforms (ripples, dunes, and anti-dunes) in alluvial rivers. In this study, the effect of artificial ripple bedforms on bed shear stress has been investigated. Two types of uniform granulation with average sizes (d50) of 0.51 and 2.18 mm were used to roughen the surface of the artificial ripples. The bedform length and height were 20 and 4 cm, respectively. The angles of its upstream and downstream to the horizon were selected equal to 16.4 and 32 degrees, respectively. Different flow rates (Q= 10, 15, 20, 25, and 30 l/s) and different bed slopes (S= 0, 0.0001, 0.0005, 0.001, and 0.0015) were examined. The results showed that by increasing the particle size on the bed surface, total shear stress (tb ), grain-related bed-shear stress (t¢b ), and form-related bed-shear stress ( t²b ) increase. The value of tb , t¢b , and t²b in bed form roughened by sediment size of 2.18 mm were, on average, 22.38, 30.86, and 22.3% more than the bed form roughened by sediment size of 0.51 mm, respectively. M3 10.47176/jwss.26.2.44911 ER -