Using a Combined Slope Hydrology/Stability Model to Identify Suitable Conditions for Landslide Prevention by Vegetation in the Humid Tropics

Abstract

The susceptibility of cut slopes to landsliding can be reduced in certain circumstances by the establishment of a vegetation cover. However, the hydrological implications of allowing a cover to develop may offset the mechanical benefits of soil reinforcement by roots. The balance between hydrological and mechanical effects is critical on slopes which are susceptible to the development of an infiltration-induced transitory perched water table, a common cause of landslides in deep, tropical residual soils. This balance is likely to change both between slopes of different types as well as temporally on any given slope. The net effect of a vegetation cover must be predicted either before natural vegetation covers are allowed to encroach on bare slopes, or if engineers are considering the use of trees as a protective measure. This paper presents a method of calculating the impact of a vegetation cover on slope stability. Simulations carried out on a wide range of slope types suggest that where failure is most likely to be triggered by infiltration rather than ground water rise, large-scale vegetation covers may contribute to instability. Whether vegetation had a positive or negative impact on slope stability was controlled by the permeability of the soil matrix, whilst the magnitude of impact was controlled by the soil strength and the slope height.

Risk-based models for potential large-scale landslide monitoring and management in Taiwan

“…In addition to road density, the exposure of constructed roads to internal forces should also be concerned for assessing the area with man-made vulnerability. For deriving the third vulnerability index, areas of vegetation deterioration are usually vulnerable to erosion and could cause slope failure (Collison and Anderson 1996;G€ okceoglu and Aksoy 1996). The index of green deterioration, which is calculated from satellite-based vegetation index, could be applied to show the degree of vulnerability.…”

Landslides in the Ethiopian highlands and the Rift margins

“…Particularly prone to the initiation of slope movements seems to be the first stage of vegetation regrowth after deforestation (Collison and Anderson, 1996;Nyssen et al, 2002). In case of heavy rain, the presence of woodcutting clearings and irrigation ditches on intensively cultivated slopes may increase the infiltration of rain water and the occurrence of landslides (Temesgen et al, 1999;Nyssen et al, 2002).…”

Development of the forSIM model to quantify positive and negative hydrological impacts of tropical reforestation

“…Fawcett et al (1997) went further with their DBM modelling by using rainfall to simulate soil moisture that was the used to estimate streamflow. Use of two DBM models in series, as in Fawcett et al (1997), allows the soil moisture dynamics to be first simulated for subsequent input in to models of: (i) soil moisture regulation of transpiration (Roberts et al, 2004;Tanaka et al, 2004), (ii) slope instability (Collison and Anderson, 1996;Burton and Bathurst, 1998) and (iii) soil-water quality and nutrient status (Geissen and Guzman, 2006).…”

“…2), have been collected in the tropics (Douglas et al, 1999;Sidle et al, 2006;Walsh et al, 2006), however, the hourly time-series data relate to natural forests not plantations. While we know of the effects root development and organic matter incorporation on slope instability (Sidle et al, 1985Collison and Anderson, 1996;Burton and Bathurst, 1998), those studies that relate these factors to the temporal delivery of sediments do so for temperate plantations or tropical natural forests, rather than tropical plantations.…”