River Bank Protection at Paka  Narayanpur 

Location

North West Region of Bangladesh

Type of Project

Protection Works

Period of Study

2001

Client

Bangladesh Water development Board (BWDB)

Panka -Narayanpur Bank Protection Project Area

Description

The Panka-Narayanpur project is located in the Northwest region of Bangladesh under Shibganj and Nawabganj upzila in Nawabganj district on the left bank of the Ganges River.

Mathematical morphological model of the Ganges River at Panka Narayanpur has been carried out to provide the hydraulic design of bank protection work and the subsequent impact on the hydraulics and morphology of the river in the adjoining area.Bangladesh Water Development Board (BWDB) is the client of this project.

Infrastructure and valuable agricultural lands have been lost due to river erosion at the left bank of the Ganges at Panka-Narayanpur in the recent years. The rate of erosion is high and during the last monsoon (2000) the main river joined the Pagla river at the left bank. This may amplify the erosion problem in the Mohananda river and may threaten the Nawabganj town itself. SWMC carried out the hydraulic Mathematical Modelling Study through a close interaction with the Design Circle-VI, BWDB. The two-dimensional mathematical modelling system, Mike21C, was used in this study as the modelling tool that operates on curvilinear computational grid.

Altogether 9 options were tested in the model corresponding to 1 in 25 year return period design flood. Each option has 8 no. of spurs, but the spacing (or length) between the spurs being different in every option. Option no. 9 was approved by the BWDB Design Directorate VI. In this option, the proposed spurs do not encroach the river, and thus make the construction work easier and more cost effective. In this option, the accumulated bank erosion in 5 years time would be a maximum of 136 m (between spur no. 6 and 7), which is within the permissible limit of embayment between the river bank and the proposed embankment. The velocity between the spurs has reduced the erodible limit of 1.0 m/s; after 5 year, the velocities are almost down to 0.5 m/s between the spurs. Most importantly, the proposed spurs do not create any impact on bank erosion in the downstream of the proposed protection area. Accumulated 5 years bank erosion downstream of spur no. 8 is only 30 m; while in the existing condition (i.e., no project cndition) and in the other options, it is more than 300 m.