Enhancement of River Bank Stability by Hibiscus tiliaceus Root Reinforcement: A Nature-based Solution

Abstract

Riverbank protection is becoming a significant environmental challenge in Sri Lanka. Although structural solutions have been commonly applied for slope stabilisation, many approaches using Nature-based Solutions (NbS) have been employed by humans for a long time to enhance riverbank stability as sustainable and ecologically practicable solutions. As an NbS, this research investigates the mechanical stabilisation potential of Hibiscus tiliaceus through field assessments and numerical modelling. Hibiscus tiliaceus is a native species that has been traditionally used in Sri Lanka. Field observations along the Kelani River (Hanwella to Kaduwela) showed that sections with Hibiscus tiliaceus displayed enhanced stability compared to non-vegetated areas. Numerical analysis was conducted using SLOPE/W software, simulating three slope geometries (1V:1H, 1V:1.5H, 1V:2H) under four hydraulic conditions: low flow, mid flow, full flow, and rapid drawdown in the river. The root reinforcement was modelled by incorporating depth-varying apparent cohesion based on literature-derived parameters. Results showed that vegetated slopes have consistently higher Factors of Safety (FoS), particularly on steep slopes under rapid drawdown. The findings highlight the importance of Hibiscus tiliaceus as a sustainable, cost-effective NbS for riverbank protection and offer a pathway for integrating tree vegetation into riverbank failure control strategies in Sri Lanka.