Abstract:
The Ganges and the Brahmaputra-Jamuna are the two major rivers in the Ganges-Brahmaputra-Meghna (GBM) river systems. The Ichamoti is a unique river in this system in the sense that it connects these two major rivers. Over nearly the past five decades, due to several incidences and anthropogenic activities, the Ichamoti River lost its hydraulic connectivity with the Ganges and Brahmaputra-Jamuna which ultimately caused the death of this system. By executing continuous numerical model simulations for 44 years from 1973 to 2017, the purpose of this study was to re-construct the history of this river system and find the root causes for the death of this system. Five major incidences and/or anthropogenic activities were considered in this period: Farakka Barrage, Phase-I of the PIRDP, Phase-II of the PIRDP, the 1998 flood event, and the 2017 flood event for the Ichamoti River. Hydro-morphological history for the 1970 condition was also simulated as a part of the reconstruction of the history of this river system.
Within the Delft3D modeling platform, a coarse resolution integrated modeling framework BDM, comprising the entire riverine, estuarine, and coastal systems of Bangladesh, and a fine resolution Domain Decomposition Model (DD-Ichamoti) covering the Ichamoti River system are applied as the numerical model.
The root causes identified from the re-construction of history with the continuous model simulations for 44 years are: (1) Implementation of Farakka Barrage initiated the process of sedimentation of the Bharara Channel which was once the main Ganges and with which the Ichamoti is connected. Sedimentation of the Bharara Channel disconnected this channel from the main Ganges, and also from the Ichamoti. This resulted the Ichamoti to be disconnected from the main Ganges flow (2) Phase-I of the PIRDP gradually decreased the conveyance capacity of the Ichamoti River (3) Phase-II of the PIRDP hydraulically disconnected the Ichamoti River from the Ganges and the Brahmaputra-Jamuna which ultimately made this system dead.
The 2017 flood of the Ichamoti River was the last event in 44 years of model simulations. It was found that even with this highly intervened condition, the Ichamoti can still be a flowing river if the flow from the Ganges can enter it with sufficient inertia force. This will convey the flow along the river up to the closure point.
The approach of re-construction of history and the methodology developed in this study can be replicated in the other dying rivers within and outside the GBM systems. This will make it possible to find a solution to resuscitate these river systems.
Keywords: Ichamoti River System, Anthropogenic Interventions, River Hydro-morphology, Numerical Modeling, History Re-construction, Resuscitation