Monitoring of riverbank stability and seepage undercutting mechanisms on the Iju (Atuwara) River, Southwest Nigeria

Abstract

Abstract This paper presents the results of a monitoring programme designed to investigate the inherent factors contributing to channel instability and riverbank erosion on the Iju River, Southwest Nigeria. Detailed reconnaissance surveys and in situ measurements were used to determine the geomorphometric characteristics of the riverbanks at more than 15 locations along the river channel. Laboratory tests in combination with the Bank Stability and Toe Erosion Model (BSTEM) and Bank Erosion Hazard Index (BEHI) were conducted to determine the shear strength characteristics and erosion potential of the riverbanks. The BSTEM results indicate that the factor of safety (FS) decreased from the initial values of 2.64 and 4.42 to 1.09 and 0.51, respectively. Further correlation of FS with root depth and depth of tension crack showed that FS was positively correlated with root depth but decreased with an increase in the depth of tension crack. The high BEHI values of 26 and 32 gave credence to the assumptions regarding the high erosion potential of the Iju riverbanks. These research findings are essential for the development of a watershed-scale natural disaster mitigation plan for the Southwest region of Nigeria.