Deforestation and its impact on sediment flux and channel morphodynamics of the Brahmani River Basin, India

Abstract Deforestation, sediment flux, and channel morphodynamics of rivers are intricately interrelated in the context of a drainage basin. The Brahmani River Basin (BRB), India covering an area of 39,033 km2 possesses a diverse portfolio of forests ranging from tropical deciduous to mangrove. The present study executed over 16 subbasins of the BRB from 1989 to 2019 shows that the forest cover recorded a fall from about 21,430 km2 in 1989 to 15,425 km2 in 1997 due to urbanization and industrial growth in the basin. However, forest cover again increased to 17,503 km2 in 2009 and 19,674 km2 in 2019. Similarly, the areas of the BRB having the normalized difference vegetation index above 0.2 (1989:59.23%, 1997:53.17%, 2009:59.18%, and 2019:53.59%) and advanced vegetation index in three upper classes using natural breaks (1989:60.34%, 1997:57.81%, 2009:65.10%, and 2019:64.13%) also depict this dynamism in the forest cover. This typical dynamics of forest cover has had great control over the sediment flux at the basin scale computed using the Soil and Water Assessment Tool in ArcGIS 10.4. The BRB portrays an increase in the sediment flux from about 1765 MT/h in 1989 to about 2447 MT/h in 1997 with a decrease of forest cover during this period. However, in tune with the increase in forest cover, the subsequent assessment periods (1997–2009) and (2009–19) depicted a decreasing trend of sediment flux of about 1524 and 1137 MT/h, respectively. The channel morphology also responded largely in tune with the changes in the forest cover and sediment flux. For example, there is a negative relationship between forest coverage and channel width. Besides, the channel shallowing, increasing braiding index, and lesser channel efficiency are the other common forms of channel adjustment to these stimuli.