Investigation of the effect of a sudden flood wave on the transition of bed loading in dry ducts and the effect of submerged plates on reducing bed load

Abstract
Background and Objectives: The prevailing rainfall in warm and dry areas is thunderstorm and cause the great floods. Destruction and sedimentation of the floods cause a lot of damage. considering that Iran is one of the hot and dry regions and the majority of rainfall is a thunderstorm, it is necessary to study the effects of floods caused by thunderstorm. In this study , the effect of flood waves on the bed load transfer in a laboratory slopble channel with unsteady flow was investigated.
Materials and Methods: In order to perform this study was used a channel that width, height and length were respectively equal to 0.3, 0.4 and 10 meters. The channel was sloppy that we used for of this study, two slopes of zero and 1.5% in the longitudinal. The walls of the canal are made of glass and it is possible to observe the passing flow. The sediments were of river sand in three types of uniform grains with a diameter of 0.85, 1 and 1.2 mm. We produced the triangular hydrograph with peak discharge of 20, 30 and 40 lit / s / m. It was also used to control the erosion of substrate materials and reduce the volume of transfer of the bed from the blade as a protective method against flow.
Results: In this research, experiments were conducted to investigate the factors affecting sediment transport in seasonal rivers. Peak discharge, symmetric flow rates, bed slope and bed particle size play a decisive role in sediment transport. The results showed that with increasing gradient from 0 to 0.015, the cavity length caused by erosion was 1.92. By examining the effect of sediment particle diameter on sediment transport, the experiments showed that by decreasing the diameter of non-sticky particles, the eroded cavity length increased by 1.84 times. Also doubling the peak discharge rate from 20 to 40 liters per second, the length of the eroded cavity was 2.2 times, and the maximum scour depth increased by 56 percent. To reduce the transfer of bed loading to the bottom of the blades, they were zigzag, diagonal and perpendicular. The results showed that using the blade, the sediment transport to the downstream decreases, in which case the perpendicular vertex of the substrate had the best performance and reduced the length and depth of the eroded cavity by the inputs, which in Ultimately, the amount of sediment transfer volume decreased by 89% relative to the non-blown state.
Conclusion: The results showed that the increase of peak water discharge in load transfer was effective, and also the bed sloping and reduction of the particle diameter average size caused a greater increase in bed loading. Based on the experiments, the most critical mode was selected and the blade effect on the erosion of the bed was investigated. The results of the surveys showed that the greatest reduction in erosion was due to the vertical placement of the blades, the crowns of the blades being flattened.