Short timescale riverbank erosion and bank stability of Sg. Bernam using Bank Stability and Toe Erosion Model (BSTEM)

Abstract

Riverbank erosion is significantly affected by the integration between hydraulic action of flowing water and geotechnical stability of the bank. This soil–water interaction is a complex process, requires in-depth understanding and integration between both factors that lead to fluvial erosion and geotechnical failures. This study was carried out to evaluate the short timescale riverbank stability using the Bank Stability and Toe Erosion Model (BSTEM) by integrating both factors. The model was applied to the selected reach susceptible to bank erosion along Sg. Bernam, between state of Selangor and Perak. Fieldwork measurements were conducted for two consecutive months at the selected sampling point, namely riverbank profile, soil sample, hydraulic parameters, and vegetation properties. Various scenarios applied to the model in quantifying the magnitude of erosion and the bank stability. The first scenario was on the effect on vegetative cover to the eroded bank, second scenario involved the effect of water table with the eroded bank under dry condition, partially saturated, and fully saturated comprising the effect of tension cracks. The bank stability analysis quantifies the Factor of Safety (FoS) of the bank based on three modes of stability, which is stable, conditionally stable, and unstable. Results showed that the FoS of both right and left banks improved with vegetative cover for the scenario without and with tension crack. On average, the right bank indicates unstable compared to left bank, with FoS ranging from 0.25 to 0.72, with lateral retreat between 28 to 77 cm. Although the left bank shows more stable in terms of the FoS, the erosion length ranging between 28 to 72 cm. Results from various scenarios indicated that BSTEM model successfully analyzed and quantified the short timescale riverbank toe erosion and the factor of safety of the eroded banks.