بررسی آزمایشگاهی تاثیر آستانه، آبشکن و صفحات مستغرق بر کنترل رسوب و توپوگرافی بستر در آبگیرهای جانبی

Abstract: This paper presents the results of laboratory flume experiments, concerning the effect of sill, spur dike and submerged vanes on sediment control at lateral intakes and bed topography around them. Since a larger portion of the flow in the vicinity of bed, is diverted, the intake will receive a relatively large amount of bed load materials. So, appropriate and reliable methods are required to minimize the amount of diverted sediment material into the intake of a river. using submerged vanes, spur dike or sill, dividing stream-surface is contracted in the vicinity of bed and sediment transported into intake channel decreases Because either submerged vanes set up a tip vortex and thereupon a helical flow in downstream, or spur dike generates curved stream in the river resulting in helical flow. On the other hand, sill prevents direct movement of bed sediment into the lateral intake. For specifying the effect of mentioned structures, four sets of experiment were considered. In the first set, no structure was used to control sediment. In the second set, sill was placed at the intake entrance whose height is equal to one third of upstream uniform depth of main channel. In the third one, a single straight, non permeable and non submerged spur dike with the length equal to one fourth of main channel width, was placed at the opposite bank of intake besides sill at the intake entrance, and eventually, parallel submerged vanes was placed at the front of diversion entrance besides sill at the intake entrance and spur dike at the opposite bank of intake.

A recirculating sediment flume fitted with a 90 degree lateral diversion channel was used in all experiments. Three flow diversion ratios were used and studied some subjects including ratio of bed sediment transport into intake (G_r) , volume fraction of sediment deposited within the diversion, bed sectional profile, divided stream-surface and amount of scour in downstream of main channel beyond the intake. In this research discharge ratio (Q_r) and type of experiment set are independent parameters.

Results show that mentioned parameters depend maily on those independent parameters. In all sets, as Q_r increases, G_r goes up and dividing stream-surface extends in throughout depth. However, volume fraction of deposited sediment within the intake channel decreases. It can be seen that using the sill at the intake entrance make rate of diversion sediment to decrease up to 68 percent for lower values of Q_r, but the submerged vanes and the spur dike cause more significant effects on bed level in front of the intake entrance and dividing stream- surface, resulting high decrease in G_r . However,the spur dike mainly affects the sediment control and it causes G_r to decrease by 90 percent. the results also show that the sill generally has significant effects on scouring beyond the intake in downstream of main channel, while the spur dike and the submerged vanes have a more significant role. This paper also presents some relations to estimate rate of diversion sediment and dimensions of scouring beyond the intake in downstream of main channel.