Experimental Study of The Effect of Vegetation on Flow Field in Prismatic Compound Channel with Inclined Floodplains

نوع: Type: thesis

مقطع: Segment: masters

عنوان: Title: Experimental Study of The Effect of Vegetation on Flow Field in Prismatic Compound Channel with Inclined Floodplains

ارائه دهنده: Provider: Saeed Derakhshandeh

اساتید راهنما: Supervisors: Dr. Bahram Rezaei

اساتید مشاور: Advisory Professors:

اساتید ممتحن یا داور: Examining professors or referees: Dr.Majid Fazli & Dr.Jalal Sadeghian

زمان و تاریخ ارائه: Time and date of presentation: 03-01-2023

مکان ارائه: Place of presentation: Department: Civil Engineering

چکیده: Abstract: When a flood occurs in the river, if the main section of the river is not able to transfer the flood, the flow exceeding the capacity of the main channel enters the flood plains. Floodplains are often home to a large number of plants. Vegetation generally increases the flow resistance and changes the velocity distribution and affects the discharge capacity and sediment transfer rate. In the present study, the effect of vegetation on the flow field in the mixed channel with sloping flood plains has been investigated experimentally. Experiments were performed for flow rates of ۲۷, ۳۰, ۳۵, ۴۰ and ۴۵ liters per second and for three conditions without vegetation, vegetation with zigzag arrangement and vegetation with parallel arrangement in flood plain. A ۳D acoustic Doppler velocimeter was used to measure the flow velocity. In order to model non-submerged vegetation in flood plains, hard compressed plastic rods with a diameter of ۱۰ mm and a length and width distance of ۱۰۰ mm were used. As a result, the ratio of the distance between the bars to their diameter was equal to ۱۰. The density of parallel vegetation is ۱۴.۲۸% higher than the density of zigzag vegetation. Using laboratory data, transverse distribution of flow velocity, boundary shear stress, flow rate distribution, secondary flows, water surface profile and flow resistance have been investigated. The results showed that the flow speed, average speed in depth, flow rate and boundary shear stress for the case with vegetation compared to the condition without vegetation in the main channel are always increasing and in the floodplains are always decreasing. The presence of vegetation causes the flow rate to decrease between ۳۰ and ۴۰% in the flood plain and the flow rate in the main channel to increase between ۱۰ and ۲۲%. The effect of the zigzag arrangement on the flow rate in the main channel is ۲ to ۳% higher than the parallel arrangement. With the presence of vegetation, compared to the condition without vegetation, the average velocity in the depth increases by ۱۰ to ۲۳% in the main channel and decreases by ۱۳ to ۱۹% in the flood plain. Also, in vegetation with a zigzag arrangement, more uniformity is observed in the transverse distribution of the average velocity in depth and the shear stress distribution in the Silabdasht area. The correction coefficient of kinetic energy along the vegetation cover and flow rate of ۲۷ L/s increases by ۱۰ to ۱۱.۵۰% and for flow rate of ۴۵ L/s by ۲۲ to ۲۴%. Larger numbers correspond to zigzag vegetation. Along the vegetation area of the channel, the overall flow resistance coefficients have the opposite relationship with the changes in the average flow speed. For example, at a flow rate of ۳۵ liters per second, a ۳۰% reduction in the Manning roughness coefficient and a ۵۰% reduction in the Darcy-Weissbach friction roughness coefficient can be observed

فایل: ّFile: Download فایل