Abstract:
The Turag River provides an important riverine link with the Dhaka Metropolitan City. Other peripheral rivers such as Balu, Lakhya and Tongikhal are also important in maintaining circular water route and natural environment of the city. Through the ages, these rivers have been silted up and offtakes from the main source with the Jamuna have been almost disconnected. During the dry season causing obstructions to navigation in the surrounding rivers of Dhaka due to reduced drafts. To address this issue, a mathematical model-supported study has been taken to develop strategies for maintaining the required draft of the Turag River and ensuring a continuous navigation route around the city.
The objective of this study is designed to assess the hydrodynamic parameters including water level, discharge and flow. For assessing the hydrodynamic condition, a 1D numerical model has been developed and simulated in HEC-RAS for the year 2017 and 2018. The model simulated stage hydrographs have been compared with observed stage hydrographs at station Mirpur SW302 of Turag river to calibrate and validate the model using Manning's roughness, n as the tuning parameter. Eventually, scenarios have been developed by dredging and checking the stability of dredged channel. The average percentage of lowering the existing bed level is 28.04%, and the average draft increased to 0.77 m. The model study indicates the necessity of lowering of existing bed by dredging about 67 Mm3. From dredged conditions, the longitudinal slope found 7 cm/km and the side slope for different cross-sections are approximately 1:2 to 1:3. To maintain the minimum draft at dry season for the BIWTA Class-III navigation route, some sections areas need to be dredged, and after that, BSTEM model analysis has been done for checking the stability of the dredged channel. It is hoped that the study will be helpful to assess hydrodynamic parameters and dredged Condition of the River for future Navigation of this route.