Halda, one of the major tributaries of the mountainous river Karnaphuli, is well known as the country's only natural carp spawning ground. Naturally fertilized eggs of carps collected from Halda River are hatched in mud-made scoops on the river bank for aquaculture purposes. However, the river habitat is under constant threat due to human interventions like loop cutting, pollution from the paper mill and power plant, blocking natural water flow of larger tributaries by introducing sluice gates, embankments and rubber dam over the river at upstream, as well natural causes like siltation, erosion and climate change impacts. A study is conducted to address the issues of the ecosystem, sustainable management and the flow regulation impacts of dams in the Halda River, although the flow regulation assessments are conducted based on the macroinvertebrate, index-based framework, land-use effects on the hydrology, new indicators development, hydrologic impact assessment, hydrodynamics in dam regulated rivers, surface-water hydrodynamics and regimes of a small mountain stream and wide range of initiatives. In our case, we considered runoff flow, mountainous flow and dams in the rivers are primary parameters for assessment, so based on previous studies we decided to simulate a hydrologic and hydrodynamic model for the dam and without dam scenarios. Major difficulties and challenges for the environmental flow analysis of a river are continuous data availability. In this research, a hydrologic model ArcSWAT has been built to assess the contribution of rainfall on the river discharge to be used as output from the tributaries in the hydrodynamic model Delft3D. The research findings help us to perceive the effect of the dams on fish breeding condition in the river. In order to perform the environment flow analysis of the river, Tennant method has been followed in the study, which is a secure and reliable approach. The flow regulation impacts are assessed for fish habitat and spawning in the river area based on the simulations. Finally, the findings are further analyzed for velocity profiles for dams by building block method for the sustainable aquatic habitat in the Halda River.
This study presents the trends of channel flow against human interventions and proposes an adaptation plan through a public-private Partnership (PPP) model to overcome the existing deteriorating condition of the Halda River. Being the only natural carp breeding ground in Bangladesh, the Halda River is significant for the national economy. However, the river's destiny is now stricken with infrastructural obstructions, industrial and residual usage exploits, and shortsighted interventions, whereas the impacts of climate change are likely to worsen the scenarios with high salinity intrusion. The unplanned human interventions due to agricultural purposes are continuously obstructing the river flow and demolishing the carp habitats and spawning within the Halda River extremely. Most of the river bends are potential carp breeding grounds along the river stretch, and the low river flow during pre-monsoon is also impacting the sustainability of the aquatic ecosystem. To understand the issues behind the endangering Halda River, this study conducted a sustainability analysis through the river planform, stage trend, and frequency analyses. The planform analysis showed the encroachment of the river impacting the river bends, significant for aquaculture over the last three decades, whereas the stage trends showed the low availability water scenario in these four locations of the river stretch. Besides, the frequency analysis reviewed the threshold minimum flow for the survival of the aquatic habitat, showing that the flow during the pre-monsoon is unsuitable and unacceptable for the survival of the fish habitats using Gumbel distribution. Conservation of the Halda River is a national priority due to its unique ecological and commercial importance, and it is expected that the proposed PPP framework will ensure the long-term sustainability of the river ecosystem. This article is analysing the existing situation of the Halda River and proposing a joint effort from government and private organisation through the PPP model for sustainable ecosystem management as well as the economic benefits of the country. Working together, each of the stakeholders will find direct benefits and can be instrumental for the survival of the Halda River.
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