BIMP2: Ashuganj Sylhet Tamabeel Road

Location

North East Region of Bangladesh

Type of Project

River Hydraulics

Period of Study

Jul to Sep, 1995

Client

Bridge Improvement and Maintenance Project, Phase-II

Description

The study involves hydrological and 1D hydrodynamic and morphological modelling and 2D hydrodynamic and sediment transport modelling. Out of the seven bridge sites the bridge at Sarighat has been studied by 2D modelling, due to complexity of the hydrodynamic conditions around the bridge site. It is located near a bend and drains a very large flashy catchment and the flow can be as high as 1500 m³/s.

The 1D hydrodynamic model for the North East Region (NERM) has been upgraded for the study of six bridges out of seven. Owing to scarcity of data at bridge sites, SWMC carried out the hydrometric data collection including water levels and discharges at the bridge sites and cross section measurements around the project area during November and December 1995. The layout of the bridge structures provided by the BIMP2 designers have been tested in the model.

The modelling activity yielded the results for alternative geometry of pier and abutment with location and orientation, which include: (a) design discharge and peak velocity at 50 years return period; (b) river bed and local scour depths; and (c) indications of required bank protection.

The model of the Sarighat bridge covers a length of 1.0 km of the Sarigowain river and 0.7 km of smaller tributary/distributary at the bridge site. The existing bridge is approximately at the middle to the model area with a ship mooring area immediately downstream of the bridge. A fine grid resolution of 10m has been used in a 2D curvilinear grid system. The modelling tool is MIKE21-C. The existing 1D model for the North East Region provides the design flood boundary conditions for the 2D model.

The outputs of the model results include: (a) distribution of flow within the model area; (b) potential erosion/deposition; (c) effect of smaller channel on the hydraulics of the main channel; (d) effect of the bridge pier on the flow; and (e) effect of ship mooring on the flow.