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Effects of Barb Installation on River Bank Stability: a Numerical Simulation

S. A. A. M. Hossain
Department of Agricultural Engineering, Patuakhali Science and Technology University, Dumki, Patuakhali-8602, Bangladesh.

A. K. M. Adham
Department of Irrigation and Water Management, Bangladesh Agricultural University, Mymensingh-2202, Bangladesh.

M. J. Uddin
Department of Civil Engineering, Khulna University of Engineering & Technology, Khulna-9203, Bangladesh.

M. M. I. Chowdhury
Department of Agricultural Engineering, Patuakhali Science and Technology University, Dumki, Patuakhali-8602, Bangladesh.

Abstract/ Executive Summary:

The focus of this study is to observe the installation stream barb effects on river bank stability using iRIC-Nays2D, a multi-dimensional computational model for river flow and riverbed variation analysis solver package. The two-dimensional (2D) numerical simulation is represented the effects of stream barbs on the channel bank erosion prevention. The model was run by settings a single barb installed on sidewall of the river bank. The average flow depth, and discharge were used as 0.044 m and 0.028 m³/s, respectively. The numerical simulation reproduced the features of barbs with time at upward side and creates scour holes at the leeward side of the structure. The simulation results confirmed that the vicinity of the barb achieved a substantial reduction in scour, transverse velocity and sediment deposition. Sand bars were formed along the bank-line at the upstream portion of the structures. On the other hand, at the downstream side near the barb head scour occurs due to hydraulic jump and turbulence flow mixing.

Keywords: Effect, BARB installation, River bank stability, Numerical simulation

Location: Department of Agricultural Engineering, Patuakhali Science and Technology University, Dumki, Patuakhali-8602, Bangladesh

Start Date: 00-01-2013

End Date: 00-11-2013

Program Area: Resource Development and Management

Commodity: Watershed management

Objectives:

1. This paper reports two-dimensional numerical simulation to observe the effects of stream barb on river bank stability after single installation with erodible bed among a relatively high width-to-depth ratio.

Methodology:

A 13.3 m long and 0.8 m wide grid channel was generated by using iRIC-Nays2D, computation flow model, a multi-dimensional river flow and riverbed variation analysis solver package. Several numerical models have been developed to simulate the deformation of a relatively narrow, deep, straight channel with erodible, noncohesive banks in the laboratory. The channel shape was considered as rectangular flat movable bed with simple cross section. The slope of the channel was used as 0.005, as the model is designed by subcritical flow. Grid cells were generated along the longitudinal and lateral direction of hundred and ten numbers, respectively. It was estimated that the change of width of the grid channel in the direction of flow is constant. To evaluate the barbs hydraulic performance in case of bank stability, the model was run by settings a single barb installed on sidewall of the river bank. The barb structure is installed as an obstacle at one bank sidewall and it is 4.5 m apart from the upstream end of the channel. Before starting flow current through the channel provided small perturbation value at 5 selected grid nodes that are persuade the bars formation. The elevation set as zero along the whole channel alternately around 2.5 m equal distance. Flow approached into the channel to find the velocity vector, flow depth and the elevation of the bed topography, respectively.

Source of Information: Journal of Agricultural Engineering, The Institution of Engineers, Bangladesh, Vol. 41/AE Number 1, June, 2014

Article Link (Online Journal):

Funding Source:

Total Budget (Tk.) :

Achievement/Findings:

Using nearly uniform sand under controlled steady flow conditions the bars are formed at the upstream portion of the channel. In case of barb installation, due to the flow separation at barb head, return current developed at the upstream side, the zone of subcritical flow along the stream bank. It also influenced the flow at downstream side creating a mixing zone just behind the structure and along the near bank line. Potential energy increased in upstream zone due to backwaters effects. The upstream progression of subcritical reaches in the near bank region controls erosion and ultimately leads to deposition of sediments along the bank-line. At the downstream side of barb especially near the barb head scour occurs due to hydraulic jump and turbulence from flow mixing. As expected flow depth was present around the end of the barb and the water depth including scour hole varied between 2 cm to 12 cm.

Knowledge Management: Journal