35-years decadal changes in planform morphology of the Niger and Benue
Rivers confluence, West Africa
Abstract
In this study, time-lapse data covering 35 years record (1987-2022) of
publicly available Landsat imageries and shuttle radar topography
mission DEM are used to investigate the changes in planform morphology
at the confluence of River Niger and Benue in West Africa. The
confluence is flanked by high elevation areas, with the Niger, bordered
by ca. 400 m high plateaus and low-lying floodplains on its western
bank. Intra-channel and bank-attached bars are abundant in the Benue
compared to the Niger. The confluence is segmented, and its tip records
a net downstream migration of about 880 m in the last 35 years. With the
confluence angle significantly reduced from ca. 175° in 1987 to ca. 500
in 2006 and ca. 16° in 2022. The abrupt drop in confluence angle between
1987 and 2006 reflects a marked increase in river runoff in the study
area. Expansion along the banks of the Niger, Benue, and post-confluence
rivers is low and non-uniform, signifying resistance of the banks to
erosion due to the vegetated nature of the banks. These decadal changes
in confluence planform were triggered by dislodgment and erosion of
parts of the confluence, upstream erosion, and downstream migration of
bars. Decadal morphological changes observed at the confluence of the
River Niger and Benue are important for sustainable planning and for
understanding river confluence dynamics in and around major rivers
worldwide.