Experimental study on hydraulic parameters and morphological behaviour of bank protection under oblique flow

Abstract

Braided river is one of the major river patterns of the alluvial river. It is a type of channel consisting of small branch channels with highgradient andsediment load separated by braid bars.This differentiation as well as further modificationof the channel originating oblique flow to the existing channel. This oblique flow has influenced to the flow hydraulics and morphological behavior of the affected braided channel. Discharge ratio and Obliqueangle between main and oblique flow channel have been observed asessentialparametersto investigate the dominant variables at the meeting point of these flow as well as downstream of combined channel. Time and flow dependent hydraulic parameters have been susceptible to erosion of bank protection works as well as the river bed itself. In the present study, a physical model has been carried out at River Research Institute (RRI), Faridpur, funded by Institute of Water Modelling (IWM), Dhaka to determine the hydraulic parameters and morphological behavior of bank protection work due to oblique flow. The basic variables such as discharge ratio and oblique flow angle have been considered in this research work.These two factors have influenced considerably to the hydraulic parameters as velocity distribution, scour depth and other related morphological parameters of the channel. There have been accomplishedtwenty-one (21) model run in this researchwork to fulfill the desired objectives.After a long trial and error process, the scale of the undistorted physical model has been selected as 1:50 but not to be done for bed material of the channel bed. In this study, there have been consideredthree oblique angles(200, 400,600).For each oblique angle, three different discharge ratios1.2,1.4,1.6 hasalso beentaken into account.For the design of bank protection works, stone boulders and geobag have been used at the right bank of the combined channel.It has been observed that velocity distribution and scouring pattern of the channel inclusive with the behavior of bank protective materialare beingclosely inter-related and influenced due to the presence of oblique flow.