Analysis of flow modifications and stress in the Tangon river basin of the Barind tract

ABSTRACT

The Tangon river (267 km long), of India and Bangladesh, is highly affected by the construction of the dam (1989) at 10 km west of Boda in Panchgarh district, Bangladesh. The aim of the current work is to find out the impacts of flow change on hydrological and ecological components in the Tangon river and riparian wetlands using indicators of hydrologic alteration (IHA). Estimation of threshold flow, the magnitude of hydrological impacts, estimation of eco-deficit state, categorizing the indicators in natural and regulated flow condition are also to be exercised. Day-to-day flow data of the Bamongola river gauge station is used for calculating change and magnitude of the flow regime. The range of variability used for calculating the threshold discharge revealed that in the post-dam period, most of the years register flow below the threshold limit. Flow failure rate in different seasons ranges from 58% to 100% and it is a maximum during the pre-monsoon period. Eco-deficit and eco-surplus which provide the degree of alteration of a stream flow clearly exhibit that in the regulated flow condition most part of the years shows eco-deficit. The magnitude of flow alteration ranges from 0.451 to 0.582 for different flow regime component groups and it is a maximum in the case of frequency and duration of high- and low-flow pulses. Seasonal analysis of the same revealed that the river is highly impacted during pre-monsoon periods. In the regulated hydrological regime, heterogeneity among the components has reduced significantly. All these things clearly indicate that already this river is impacted hydro-ecologically due to the attenuation of flow and fluctuation and if such a condition continues the situation will highly be vulnerable. This ensuing situation is not expected because this river passes through a populous tract and a huge number of peoples are directly and indirectly engaged with this river for their lives and livelihood.

KEYWORDS:

• Tangon river
• construction of dam
• regulated flow condition
• IHA components
• hydro-ecological stress
• threshold flow
• flow failure
• magnitude of alteration and eco-deficit

Acknowledgements

We must acknowledge the North Bengal Planning division because this section has given lots of time series flow data free of cost. We are also thankful to the University of GourBanga for giving such space for doing research. We acknowledge to Swapan Talukdar for his help towards preparing flow exceeding graphs.

Disclosure statement

No potential conflict of interest was reported by the authors.