Morphologic and hydraulic variability of small bedrock and alluvial channels in relation to lithological controls, Upper Ogun River Basin, Southwestern Nigeria

ABSTRACT

The influence of lithology on morphological variability across space presents a unique approach to understand how morphological variables and domain units respond to lithological variations. This study examines variation existing in channel morphological variables across domain units within a basement complex. Eighty-three reaches were surveyed across six third-order basins within the Upper Ogun River basin, Nigeria. Each of the six third-order basins is heterogeneously underlain by various lithological formations. Fourteen morphological variables (bankfull; depth, width, cross-sectional area, width-depth ratio, wetted perimeter, hydraulic radius, discharge, total stream power, specific stream power, shear stress, velocity, dimensionless stream power, Darcy-Weisbach friction factor and channel gradient) were measured and estimated across the 83 reaches. Analysis of Variance revealed that significant variation occurs in channel morphological properties between schist and granite and between granite and migmatite. Also, bankfull width showed exponent values of w_bf ~ Q^bf 0.21 for migmatite; w_bf ~ Q^bf 0.11 for granites; and w_bf ~ Q^bf 0.34 for schists. Channel unit sequence using Markov chain presents two transitions identified as bedrock to plane-bed and step-pools to plane-bed. The absence of transitions as observed is closely tied to the occurrence of non-cyclic patterns.

KEYWORDS:

• Lithology
• morphology
• alluvial-bedrock channels
• hydraulic Geometry
• markov chain

Disclosure statement

No potential conflict of interest was reported by the authors.