ABSTRACT
The evolution of the Mayurakshi River Basin (MRB) is a complex process driven by the tectonic forces, climate change and the human interventions. In the era of Anthropocene, anthropogenic factors have emerged as the most intriguing factor of the recent evolutionary record of the MRB. The present chapter intends to relate the hydro-geomorphic changes due to the construction of dams and barrages, check dams, embankments, sand mining, stone quarrying, road stream crossing, brick fields and changes in land-use land cover. In the MRB, six dams and barrages (Massanjore, Tilpara, Deucha, Brahmani, Bakreshwar and Kopai) have been constructed under the Mayurakshi Reservoir Project which has drastically altered the fluvial regime from high-magnitude low-frequency flood event to low-magnitude high-frequency event. Moreover, the hydraulic sinuosity index has increased (1970: 6%, 2019: 28% in the upper reach, 1970: 9%, 2019: 25% in the middle reach; 1970: 0.8%, 2019: 1.8% in the lower reach) at the expense of topographic sinuosity due to changes in hydraulic regime. Channel bar formation in the upstream and bed scouring in the downstream of the Tilpara barrage is observed. Furthermore, about 1,625 check dams in the MRB also have small-scale impact on channel morphology (geometric shape) unlike dams. The embankment is found to narrow the channel and valley configuration downstream (e.g. upper reach: 795 m for valley width and 350 m channel width; lower reach: 183 m for valley width and 51 m channel width). Further, breaching of earthen embankment also increases sediment load of the river and sand plays. Intensive in-stream sand mining in the entire MRB especially in the middle and lower reaches has formed pit on bed and artificial ridge and furrow topography. Similarly, stone mining has formed deep stone quarry field while the bed deposition of materials from the stone crushing centres has reduced channel depth and cross-sectional area by about 5%–10% leading to channel abandonment. Besides, 12 bridges out of the 36 major road and rail bridges are found to have inadequate waterway due to channel constriction by about 5%–60%. The three-fold increase in the number of brick kiln in the past decades (2006: 61; 2019: 183) has also increased the rate of artificial movement of earth materials in the basin. Finally, the increase in the agricultural land, settlement area and mining area, and decrease in vegetation cover and inland water bodies have accelerated run-off and sediment flux. River channels used as agricultural beds in the post-monsoon period ceases to exist.
