Abstract

The sedimentation pattern of the lower reaches of Calabar River, on the south east coast of Nigeria was investigated with a view to evolving criteria for recognition of their ancient counterparts. Using grain size statistical parameters, the sediment-sediment relationships and flow structure of the river were examined from twenty-five georeferenced bottom samples. Results show that the tidal channel is uniformly impacted with eroded terrestrial sediments which have been delineated into A, B, and C distinct lateral facies. Facies A and B portrayed negatively skewed and near symmetric moderately sorted sands with a considerable upstream increase in kurtosis. But, Facie C depicted near symmetric, very leptokurtic well sorted sand, representing more of terrestrial-borne sediments inferring high rate of siltation/sediment accretion. Tidal flow measurements over-spring, mean and neap tidal cycles gave 0.59 m/s highest with maximum current velocity at neap tide flowing southerly. The mean near-bottom tidal velocity indicated a maximum of 0.40 m/s, predicting that bedforms such as ripples are likely to form based on empirical relationship between flow velocity and mean grain size distribution. The observed results are geared towards understanding the impact of flow regime on sediment mobility and the preservation potential of the environment.

Key words: Tidal channel, lateral facies, sediment accretion, tidal current velocities, Calabar River, Nigeria.