Urbanisation and landslides: hazard drivers and better practices

Rapid unplanned urbanisation is driving increasing rainfall-triggered landslide risk in low-income communities in tropical developing countries. Conventional slope stabilisation techniques are often unaffordable and most disaster-risk-reduction funding is currently spent post-disaster. However, experience in the Caribbean has changed local engineering practice and World Bank policy, demonstrating that community-based surface water drainage is affordable and effective in mitigating urban landslides. New evidence presented in this paper identifies specific informal construction practices generating further landslide hazards and bioengineering schemes most effective for landslide mitigation. A dynamic hydrology-slope stability model is used to simulate the factor of safety response of nine slope classes (angle and soil strength) to progressive vegetation removal, slope cutting and loading, for six design storms. The effectiveness of 76 bioengineering schemes for improving stability is modelled. Key recommendations are that deforestation should be limited and slope cutting avoided as cutting is most detrimental to stability. Site-specific modelling is needed to identify where deep-rooting, lightweight trees might add stability, whereas grasses are beneficial in all locations.